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Über dieses Buch

Adhesives have been used for thousands of years, but until 100 years ago, the vast majority was from natural products such as bones, skins, fish, milk, and plants. Since about 1900, adhesives based on synthetic polymers have been introduced, and today, there are many industrial uses of adhesives and sealants. It is difficult to imagine a product—in the home, in industry, in transportation, or anywhere else for that matter—that does not use adhesives or sealants in some manner.

The Handbook of Adhesion Technology is intended to be the definitive reference in the field of adhesion. Essential information is provided for all those concerned with the adhesion phenomenon. Adhesion is a phenomenon of interest in diverse scientific disciplines and of importance in a wide range of technologies. Therefore, this handbook includes the background science (physics, chemistry and materials science), engineering aspects of adhesion and industry specific applications. It is arranged in a user-friendly format with ten main sections: theory of adhesion, surface treatments, adhesive and sealant materials, testing of adhesive properties, joint design, durability, manufacture, quality control, applications and emerging areas. Each section contains about five chapters written by internationally renowned authors who are authorities in their fields.

This book is intended to be a reference for people needing a quick, but authoritative, description of topics in the field of adhesion and the practical use of adhesives and sealants. Scientists and engineers of many different backgrounds who need to have an understanding of various aspects of adhesion technology will find it highly valuable. These will include those working in research or design, as well as others involved with marketing services. Graduate students in materials, processes and manufacturing will also want to consult it.

Inhaltsverzeichnis

Frontmatter

Introduction to Adhesive Bonding Technology

1. Introduction to Adhesive Bonding Technology

This introductory chapter gives a brief description of adhesive bonding and adhesion-related phenomena. The major definitions of the terms associated to this technology such as adhesion, cohesion, adhesives, sealants, and adherends are given so that there is uniformity of language throughout the handbook. The reasons that drove the editors to prepare this book are explained. Finally, the organization of the book is described.

Lucas F. M. da Silva, Andreas Öchsner, Robert D. Adams

Theory of Adhesion

2. Theories of Fundamental Adhesion

The historical development and current status of the four classical theories of adhesion are first reviewed. The adsorption theory emphasizes the point that once adhesive and substrate come into contact, forces of attraction will act between them. As long as the extent of wetting is good, these forces, whether primary bonds, such as covalent, or secondary van der Waals forces, are generally considered sufficient to give a high bond strength. Primary bonding may be necessary to achieve bond durability in a hostile environment.The mechanical theory focuses on interlocking between adhesive and a rough substrate surface. Again good wetting is required, or surface roughening is likely to lead to poor bond strength. It has been shown to apply to some surfaces rough on a macroscale as well as to microfibrous and microporous surfaces, such as anodized aluminum. The enhanced adhesion is associated with increasing plastic energy dissipation during fracture in the bulk adhesive.The electrostatic theory points to electrical phenomena such as sparking, which may be observed during the destruction of an adhesive bond, and consider the transfer of electrostatic charge between the adhesive and substrate. It regards the adhesive-substrate system as analogous to a parallel plate condenser. Estimates of the energy associated with this process are generally small compared with adhesion fracture energies, and the theory is much less vigorously supported than was the case some 50 years ago.The diffusion theory has attracted increasing interest since the development of reptation theory of polymer chain dynamics. It provides a model for polymer-to-polymer adhesion, and gives an explanation of the time and molecular weight dependence of adhesion to polymers of various compatibilities.The role of weak boundary layers is discussed with emphasis on the importance of careful investigation of the locus of failure of an adhesive bond.In conclusion, it is argued that the classical theories are best regarded as emphasizing a different aspect of a more comprehensive model, which, in principle, relates molecular dispositions in the region of the interface to macroscopic properties of an adhesive joint.

David E. Packham

3. Forces Involved in Adhesion

The establishment of interfacial bonds through forces at the interface causes materials to attract one another. Therefore, adhesion between materials and adhesive in assemblies are intimately related to the interatomic and intermolecular interactions at the interface of the two considered surfaces. Describing the mechanism responsible for adhesion in simple terms is difficult due to the complexity and evolving understanding of the subject. Nevertheless, when considering adhesion phenomena, it is important to consider both the bulk and surface mechanical properties of the materials in contact and the type of interfacial forces established at the interface. High adhesion can only be obtained if the interface can sustain sufficient stress to induce dissipative forms of deformation, such as flow, yield or crazing, in the polymer. Under most circumstances such dissipative processes can only be obtained when the interface is coupled with a sufficient density of bonds. This chapter focuses on the description of the main forces responsible for adhesion, from strong covalent bonds to weak van der Waals forces, also considering some more specific interactions such as acid–base (like hydrogen bonding) or capillary forces (that could, as an example, influence adhesion of nanoparticles). The second part of this chapter concerns recent developments in experimental scanning probe techniques that may give assess to direct adhesion forces determination at the nanoscale. A case study is presented.

Pr. Maurice Brogly

4. Wetting of Solids

The contact between a solid and a liquid involves the phenomenon of wetting. This is the intuitive, intimate contact between the two phases. We consider here thermodynamic aspects of wetting, which involves three phases in fact, since the environment must be taken into account. Methods for determining wetting characteristics are discussed.

Martin E. R. Shanahan, Wulff Possart

5. Spreading of Liquids on Substrates

A short overview of relevant processes and parameters in spreading of liquids on substrates is presented. In a simplified view, the dynamics of these processes can be understood as being controlled by the balance of driving forces and resistance due to dissipative processes. Analogies between spreading and dewetting are discussed.

Günter Reiter

6. Thermodynamics of Adhesion

Although practical adhesion depends on more than just interfacial bonds, clearly the latter are fundamental: the stronger the links, the higher the adhesion. In many cases, interfacial bonding is of a physical nature, and is closely akin to wetting, with the same types of physical phenomena occurring. These can be treated from a thermodynamic standpoint. Wetting data may be used to estimate the thermodynamic, or Dupré, energy of adhesion, provided certain assumptions are made and suitable models constructed for, in particular, interfacial tensions. Several models have been established with greater or lesser success. The main ones are reviewed here, underlining their essential assumptions.

Wulff Possart, Martin E. R. Shanahan

Surface Treatments

7. General Introduction to Surface Treatments

The use of surface treatments to optimize adhesion has been well established. In this chapter, the main treatment methods for metals and polymers will be considered in terms of how such processes are carried out and their influence on surface physical and chemical properties. Consideration has been given to a range of treatments from simple degrease options to the more highly complex multistage processes. An attempt has been made to relate the changes in physicochemical properties to adhesion performance, and, where relevant durability.

Gary Critchlow

8. Surface Treatments of Selected Materials

Proper treatment of an adherend surface is one of the most important factors in assuring high initial strength and extended durability of high-performance adhesive joints. There are several requirements for a good surface preparation: (1) The surface must be cleaned of any contamination or loosely bound material that would interfere with the adhesive bond. (2) The adhesive or primer must wet the adherend surface. (3) The surface preparation must enable and promote the formation of chemical and/or physical bonds across the adherend/primer–adhesive interface. (4) The interface/interphase must be stable under the service conditions for the lifetime of the bonded structure. (5) The surface formed by the treatment must be reproducible. In this chapter, high-performance surface treatments for several metals and other materials are discussed. Surface treatments of aluminum and other metals are used to illustrate how proper surface preparations meet these requirements.

Guy D. Davis

9. Surface Characterization and its Rôle in Adhesion Science and Technology

This chapter reviews a variety of methods of surface characterization that have been found to be useful in the study of adhesion. The methods considered can be conveniently classified in three groups: those that provide information regarding surface topography (scanning electron microscopy and atomic force microscopy [AFM]); those that probe the surface-free energy of a material (measurement of contact angles and inverse gas chromatography, in addition to simple test methods such as the water break test and dyne inks); and those that provide a surface-specific chemical analysis (X-ray photoelectron spectroscopy, Auger electron spectroscopy, and time-of-flight secondary ion mass spectrometry). All provide surface-specific information and this is essential for adhesion investigations as the forces responsible for adhesion operate over very short length scales and for any analysis to be meaningful the analysis technique must probe depths of a similar order of magnitude. These methods are used in all types of adhesion investigations, which, in general, can be considered in one of three areas of endeavor. The analysis of the unbonded surface and the relationship of surface characteristics to performance such as strength or durability, the forensic analysis of failed joints with a view to defining the exact locus of failure and any interfacial phenomena that may have exacerbated failure, fundamental studies of adhesion carried out with a view to gaining a fuller understanding of the interfacial chemistry of adhesion.

John F. Watts

10. Use of Surface Analysis Methods to Probe the Interfacial Chemistry of Adhesion

This chapter explores the manner in which the surface analysis methods of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) can be used to extract information regarding the interfacial chemistry of adhesion from polymer/metal systems such as adhesive joints. It will be shown that the analysis of a failure interface is an uncertain method to extracting interface chemistry but in certain situations, where a very thin layer of polymer remains on the metal oxide surface, this provides spectra characteristic of the interphase. In most situations, some form of chemical or mechanical sectioning is necessary, and microtomy and dissolution methods are described as ways in which chemical information at high depth resolution can be extracted from the interphase zone.An alternative manner in which interphase chemistry can be examined is by the use of model specimens consisting of thin layers of polymer deposited on the metal substrate. The construction of an adsorption isotherm from the liquid phase is a useful precursor to such studies as it provides an indication of the solution concentration at which monolayer coverage occurs. The shape of the isotherm can provide invaluable information regarding the adsorption of various components from a formulation on the substrate, indicating which component(s) has(have) the greatest affinity with the metal oxide. Specimens from the plateau region of the isotherm will have a monolayer of polymer deposited on them, and XPS and ToF-SIMS can be used to probe the interphase region through this very thin layer. This provides a powerful method for the elucidation of the specific interactions, such as covalent bonds, that are responsible for the forces of adhesion. Examples are given in this chapter of a range of systems featuring iron, zinc, aluminum, and ceramic substrates and polymeric systems as diverse as radiation-cured coatings and adhesives, through structural adhesives to an isocyanate-based systems turning finally to the fracture and analysis of a polyester-based nanocomposite.

John F. Watts

11. Organosilanes: Adhesion Promoters and Primers

Being amongst the most versatile molecules available to promote adhesion, organosilanes nonetheless remain a bit of a conundrum for some as one needs to know their chemistry thoroughly in order to utilize them in a useful fashion. In the first instance, this work starts with a short presentation of organosilanes defining this class of chemicals as well as explaining their genesis followed immediately by a section of this chapter dedicated to their chemistry which includes a few words of warning. Closely related are the necessary interactions that such molecules have to develop on materials in order to fulfill their main role as adhesion promoters, and this is described too but more particularly when considering metallic substrates and polymers. Reactions in a medium are also covered briefly as silanes are commonly included in a matrix which precludes a more comprehensive section of silanes behavior in formulations later on in this document. Is also covered other usages of silanes than as adhesion promoters together with principles to follow in order to chose a silane for a particular application. The following section is concerned with the use of silanes as primers particularly where the user aims to improve adhesion or protect from corrosion. To complete this work, a small section covers some other organic or nonorganic adhesion promoters.

Marie-Laure Abel

Adhesive and Sealant Materials

12. Classification of Adhesive and Sealant Materials

In this chapter, classification of adhesive and sealant materials is presented. For this purpose, various categories are considered depending on the polymer base (i.e., natural or synthetic), functionality in the polymer “backbone” (i.e., thermoplastic or thermoset), physical forms (i.e., one or multiple components, films), chemical families (i.e., epoxy, silicon), functional types (i.e., structural, hot melt, pressure sensitive, water-base, ultraviolet/electron beam cured, conductive, etc.), and methods of application. The classification covers high-temperature adhesives, sealants, conductive adhesives, nanocomposite adhesives, primers, solvent-activated adhesives, water-activated adhesives, and hybrid adhesives.

Erol Sancaktar

13. Composition of Adhesives

Adhesives and sealants are generally developed and prepared for many applications such as packaging, construction, automobile, electronic, etc. An adhesive formulation will depend on the base materials and requirements of a particular application. Development managers or formulators have to have a public knowledge about the chemical composition and role of many components for reducing trials and errors. This chapter focuses on the definition and function of adhesive composition such as primary resins, solvents, fillers, plasticizers, reinforcements, and various additives.

Hyun-Joong Kim, Dong-Hyuk Lim, Hyeon-Deuk Hwang, Byoung-Ho Lee

14. Adhesive Families

Adhesive bonding, which addresses applications in an ever-growing number of industrial, handicraft and service sectors, does not exist as a specific research activity in its own right. Every user of bonding technology – from surgeon and handyman to car manufacturer and aeronautical launch vehicle designer – has specific needs, especially in the area of adhesives. In order to answer to these needs, suppliers are diversifying and extending their product ranges in terms of conditioning and bonding processes. This results in some very difficult choices, making it necessary to have at one’s disposal “navigational tools” in an extremely complex network (Fabris and Knauss 1990; Pocius 2002). Because the basis of adhesive formulation is inevitably macromolecular in nature, polymer science is likely to shed valuable light in this area. By using our knowledge of the principles underlying these formulations, and also the basic physical chemistry rules that apply, we can establish a general classification system, allowing us to direct our decision-making processes toward those product “classes” best suited to each specific application. On this basis, adhesives can be presented according to the following main discussion:The basic rules to establish a classification system based on the process used to achieve the transformation of an adhesive into a bonded joint.The main characteristics of adhesives for which the transformation is based on a physical phenomena.The main characteristics of adhesives for which the transformation is based on a chemical process.The main properties of adhesives used as Pressure-Sensitive Adhesives.

Eric Papon

15. Pressure-Sensitive Adhesives (PSAs)

The basic concepts, formulations, and test methods of pressure-sensitive adhesives are presented. The importance of interfacial interactions, viscous loss, and extensibility are stressed. The common rheological tests are described and the equivalence of deformation rate and test temperature is emphasized. The much longer time scale for bond formation versus the rate of deformation upon debonding in peel or tack is exploited by the formulator to optimize properties. The formulation principles and common ingredients for preparing acrylic- and rubber-based adhesives are described, and the performance capabilities of these two types of pressure-sensitive adhesives are contrasted.

Charles W. Paul

16. Selection of Adhesives

Selection of the correct adhesive for an application can be a daunting task due to the many types commercially available ranging from different chemistries through different forms to an almost continuum of material properties. It is critical therefore to take a logical approach to this task and apply deselection criteria wherever possible. The needs of the final application are paramount and often a detailed review of the requirements can provide the engineer with some key selection needs or constraints which in turn may enable large groups of adhesives to be eliminated from consideration at an early stage of the process. In parallel to the needs of the final product, it is also important to appraise aspects related to manufacturing in terms of product volume, handling issues, curing equipment, dispensing equipment, etc., as an apparently perfect adhesive with the correct bond properties may not be able to be dispensed easily or it may require curing at temperatures above which the substrate cannot tolerate.Although the initial adhesive selection process is essentially a desktop exercise, the need to be smart and identify a small number of candidates with the greatest potential requires that this activity be given a high level of importance. Almost every application will require a bespoke approach to some extent and this will necessitate practical testing and trials to be carried out. Selection of unsuitable adhesives at the outset could be costly in the long run.

Ewen J. C. Kellar

Testing of Adhesive Properties

17. Physical Properties of Adhesives

A number of physical properties are relevant and important for characterizing adhesives, providing insights into the underlying behavior of the base polymer(s) as well as the effects that fillers, additives, and other factors may play in the liquid adhesive and bonded joints that may result. Characterizing these adhesive properties, interpreting the results, and interpreting the implications provides information that is vital assuring quality control, improving bond performance, assessing the relative merits of adhesive options for a given application, and understanding the polymer more completely. This chapter addresses several relevant physical properties of adhesives, including viscosity, density, and stress–strain behavior, quantities that are often thought to be intrinsic properties of a material. Methods of characterizing these properties are discussed, along with insights for interpreting these quantities and their implications for polymeric adhesive systems.

David A. Dillard

18. Thermal Properties of Adhesives

The thermal properties of adhesives affect the rate of cure, whether the latter is by evaporation, cooling, or chemical reaction. In the latter case cure may not go to completion in the sense that not all monomer is reacted, or may not be possible at all above a ceiling temperature. The heat of polymerization is a useful guide to what may happen.The glass transition temperature of a cured adhesive is of critical importance, in that although there are both sub-Tg and super-Tg adhesives, crossing Tg in service is not acceptable. Tg also has a role in latex-adhesives forming cohesive films.Adhesives exhibit a mixture of viscous and elastic properties and obey the WLF equation. This indicates that the fraction of free volume at the glass transition is 2.5%.Consideration is given to thermal conductivity and thermal expansion, and the thermal breakdown of adhesives.

John Comyn

19. Failure Strength Tests

Failure strength tests are used for quality control, for adhesive properties development, and for design purposes. Typically, manufacturers provide the average single lap joint (SLJ) shear strength and the peel strength. However, these are not intrinsic adhesive properties and are of limited use for design purposes. The prediction of the joint strength based on stress or strain limit criteria needs the adhesive stress–strain curve. In this chapter, the most important tests for the determination of the adhesive mechanical properties are described. Tests for the three basic loading modes – tension, compression, and shear – are discussed, indicating for each case the advantages and disadvantages. Reference is made to the corresponding standards according to the major standards-setting organizations such as the American Society for Testing and Materials (ASTM) and the International Standards Organization (ISO). Within each category (compression, tension, and shear), tests on bulk specimens and those on joints are compared. Recommendations to select the most suitable test are given, and it is shown that a reasonable relationship exists between adhesive properties measured in compression, tension, and shear.

Lucas F. M. da Silva

20. Fracture Tests

This chapter considers first the fracture in a bulk adhesive specimen under mode I, that is, tensile opening loading conditions. Then, the testing of adhesive joints using a linear-elastic fracture mechanics approach is considered. In these tests, the substrates are assumed to only deform in a linear-elastic manner, and any permanent deformation of the substrates is avoided. In adhesive joints, due to the directional constraint of the failure path that is often observed, it is common to encounter failures in the other loading modes, in addition to mode I. Thus, mode II (in-plane shear) and mixed-mode I/II testing of adhesive joints are also considered. There is often the need to measure the resistance to fracture in a joint with flexible substrates. In this case, the assumptions of linear elastic fracture mechanics may no longer be valid, and permanent deformation of the substrates may occur. One such test is the peel test and some variants of the peel test are considered in the present chapter, with a focus on the recent development of a geometry-independent peel test.

Bamber R. K. Blackman

21. Impact Tests

The mechanical properties of adhesives and the joints strength require specific tests. Indeed, since polymers are, in general, sensitive to the strain rate they undergo, different phenomena can be induced when a load is applied abruptly. Under such a condition, usually the adhesive tends to react to the deformation with higher stress and lesser ductility, which cause higher resisting loads but lower absorbed energy. This is why the common standard impact tests for adhesives, involving bonded blocks or strips, aim at measuring the energy required to break the bond.However, since this result is not sufficient to characterize an adhesive, other types of tests have been introduced to obtain a deeper insight. Different types of specimens (samples of bulk adhesive, lap joint, butt joint, double cantilever beam) and test rigs (pendulum, falling weight, hydraulic actuator) have been adopted in many works to measure the properties of interest. The fracture energy, typical of fracture mechanics, requires ad hoc tests and processing to be measured in dynamic conditions. The Split Hopkinson Pressure Bar, a special apparatus conceived to test materials at high strain rate, has been also applied with success to adhesives and joints. A special case is that of conductive adhesives, which are getting into use to replace soldering in electronic packaging: their capability to withstand the impact that a device can undergo in use must be assessed.This chapter, mainly relying on the results available from the technical literature, presents a survey of various test methods, focusing on the related problems and achievements.

Luca Goglio

22. Special Tests

This chapter gives a brief description of special mechanical tests for various types of materials and sample geometries, such as blister tests for membranes/adhesives/coatings, tensile tests and shear tests for sealants/foam adhesives, indentation and scratch tests for coatings, tack tests for pressure-sensitive adhesives (PSAs), and bimaterial curvature tests for characterizing residual stress, stress-free temperature (SFT), and coefficient of thermal expansion (CTE) of adhesives bonded to substrates of interest. In addition, some applications of these tests, including the nano-/micrometric scale, are also described in this chapter.

Tetsuo Yamaguchi, David A. Dillard

Joint Design

23. Constitutive Adhesive and Sealant Models

A complete approach to modeling adhesives and sealants needs to include considerations for: deformation theories and viscoelasticity with linearity and nonlinearity considerations, rubber elasticity, singularity methods, bulk adhesive as composite material, damage models, the effects of cure and processing conditions on the mechanical behavior, and the concept of the “interphase.”

Erol Sancaktar

24. Analytical Approach to Joint Design

This chapter presents analytical approach for determining stress and strength of adhesively bonded joints. Selected applications of adhesively bonded joints are discussed first, and then mathematical models for stress analysis of these joints are outlined. Various closed-form solutions for adhesive stresses and edge bending moment for balanced single lap joints are presented and compared. The method for finding analytical solutions for asymmetric and unbalanced adhesive joints is also discussed. Explicit expressions for mode I and mode II energy release rates for cohesive failure and interfacial debonding are presented for asymmetric joints with a semi-infinitive length subjected to general load combinations.

Liyong Tong, Quantian Luo

25. Numerical Approach: Finite Element Analysis

Finite element analysis (FEA) is a widely used computer-based method of numerically solving a range of boundary problems. In the method a continua is subdivided into a number of well-defined elements that are joined at nodes, a process known as discretization. A continuous field parameter, such as displacement or temperature, is now characterized by its value at the nodes, with the values between the nodes determined from polynomial interpolation. The nodal values are determined by the solution of an array of simultaneous equations using computational matrix methods and the accuracy of the results are dependent on the discretization, the accuracy of the assumed interpolation form, and the accuracy of the computation solution methods. The current popularity of the method is based on its ability to model many classes of problem regardless of geometry, boundary conditions, and loading. Modelling the behavior of adhesive joints is complicated by a number of factors, including the complex geometry, the complex material behavior, and the environmental sensitivity. FEA is currently the only technique that can comprehensively address the challenges of modelling bonded joints under realistic operating conditions. However, a reliable and robust method of using FEA to model failure in bonded joints is still to be developed.

Ian A. Ashcroft, Aamir Mubashar

26. Special Numerical Techniques to Joint Design

The aim of this chapter is to introduce special numerical techniques. The first part covers special finite element techniques which reduce the size of the computational models. In the case of the substructuring technique, internal nodes of parts of a finite element mesh can be condensed out so that they do not contribute to the size of the global stiffness matrix. A post computational step allows to determine the unknowns of the condensed nodes. In the case of the submodel technique, the results of a finite element computation based on a coarse mesh are used as input, i.e., boundary conditions, for a refined submodel. The second part of this chapters introduces alternative approximation methods to solve the partial differential equations which describe the problem. The boundary element method is characterized by the fact that the problem is shifted to the boundary of the domain and as a result, the dimensionality of the problem is reduced by one. In the case of the finite difference method, the differential equation and the boundary conditions are represented by finite difference equations. Both methods are introduced based on a simple one‐dimensional problem in order to demonstrate the major idea of each method. Furthermore, advantages and disadvantages of each alternative approximation methods are given in the light of the classical finite element simulation. Whenever possible, examples of application of the techniques in the context of adhesive joints are given.

Andreas Öchsner

27. Design Rules and Methods to Improve Joint Strength

One of the main reasons for the increasing use of adhesive bonding is the fact that the stress distribution is more uniform than with other conventional methods of joining which enables to reduce weight. However, even in adhesive joints the stress distribution is not perfectly uniform and this leaves room for improvements. The major enemy of adhesive joints is peel or cleavage stresses. These should be reduced if strong joints are to be designed. In this chapter, the main factors influencing the joint strength are first discussed. The focus is on lap joints because these are the most common. Methods are then proposed to improve the joint strength by using fillets, adherend profiling, and other geometric solutions. Hybrid joining is also a possibility to improve the strength of adhesive joints, and adhesives may be used in conjunction with rivet or bolts, for example. Joints may be damaged in some way and it is important to discuss also methods to guarantee an efficient repair design. Finally, configurations are recommended for several types of joints such as butt joints, strap joints, cylindrical joints, and T joints. The main rule for all cases is to spread the load over a large area and reduce the peel stresses.

Lucas F. M. da Silva

28. Design with Sealants

This chapter describes the many factors that go into the design of reliable sealant joints. Common causes of sealant joint failure are addressed. The various joint types are discussed and illustrated, and their critical dimensions and materials are described. Sealant properties critical to joint assembly, cure, function, reliability, and aging are discussed. These include chemical, physical, mechanical, and adhesion properties. Proper measurement of these properties is also presented. Finally, calculation of the differential movement of the substrates in a sealant joint, the accommodation of which is the primary mechanical requirement of a sealant joint, is discussed.

Gregory L. Anderson

29. Design for Impact Loads

Design methods of adhesively bonded joints subjected to impact loading are discussed in this chapter. Methodologies to treat the dynamic responses of structures are shown. In these cases, it is necessary to analyze the stress distribution considering stress wave propagation because inertia effects of the structures are more significant than those in quasi static conditions. Constitutive relations of materials are discussed. The relations are highly dependent to the stress and strain rates. Thus, the dependence should be considered for the dynamic analysis of materials. Some examples of stress analysis are shown, where closed-form approaches and dynamic finite element analyses are explained. In addition, an actual application, a crash problem of car structures, is explained because adhesively bonded joints have been recently introduced to car structures and the design of the joints subjected to impact loads has become very important.

Chiaki Sato

30. Vibration Damping of Adhesively Bonded Joints

A study into the vibration characteristics of adhesively bonded single lap joints has been carried out to investigate the effect of joint geometry and temperature variation on overall system damping. Concepts of vibration damping are introduced and it is shown how to determine the damping of a system. The methodology of calculating the damping of even a simple bonded element in the form of a lap joint from material and geometric parameters is shown to be complex. The vibration damping of bonded joints has been extended into an experimental program using four different adhesives. These were AV119, a one-part epoxy; 9245, a structural bonding tape; 3532, a two-part polyurethane; and Hysol XEA 9359.3, a two-part structural adhesive. High-strength steel adherends were used to manufacture single lap joints of varying overlap lengths. The specimens were vibrated flexurally and the damping values calculated using the free decay method. In this investigation, the damping of the adhesive layer dominates the damping of the specimens rather than the damping of the adherends. An optimum overlap ratio was found at approximately 0.25 in this study. The adhesives were tested under varying temperature conditions to illustrate the dominance of the glass transition temperature on the damping of the specimen.It has been shown that the damping of a structure is unlikely to be improved by using adhesive bonding as a joining method.

Robert D. Adams, Duncan G. A. Cooper, Stuart Pearson

Durability

31. Effect of Water and Mechanical Stress on Durability

Adhesive joints with structural adhesives are weakened significantly in air at high humidity, and the rate of decline is controlled by water diffusion into the adhesive. There appears, however, to be a critical relative humidity, and only if this is exceeded are joints significantly weakened; evidence is that this is about 65%. The most harmful effect of water is potentially at the interface between the adhesive and adherend; however, surface treatment of metallic adherends can greatly improve water durability. Accelerated aging using elevated temperatures and humidities can provide information on the environmental resistance of different systems but does not easily correlate to aging in natural conditions. The entry of water into the adhesive layer can conform to the simple Fickian model, which just depends on two parameters (diffusion coefficient and solubility coefficient), but in some cases it is non-Fickian. Current state-of-the-art environmental degradation modeling of bonded joints involves multi-physics finite element analysis combined with progressive damage modeling. Essentially, this involves three main steps. The first step is modeling moisture transport through the joint in order to determine the moisture concentration distribution in the joint as a function of time. The second step involves evaluation of the transient mechanical-hygro-thermal stress–strain state resulting from the combined effects of hygro-thermal effects and applied loads. The final step involves the incorporation of a damage or failure criterion in order to model the progressive failure of the joint and hence enable the residual strength or lifetime of a joint to be predicted.

Ian A. Ashcroft, John Comyn

32. Effect of Radiation and Vacuum

This chapter describes basic understanding of high-energy radiation as well as space vacuum and properties of high-performance polymers and adhesives when exposed to high-energy radiation in vacuum. Therefore, different radiation conditions are analyzed, and stability of different polymers under radiation and vacuum are described. As a case study, performance of space durable polymer such as polybenzimidazole (PBI) modified by low-pressure plasma and atmospheric-pressure plasma and fabrication of the polymer by ultrahigh temperature-resistant epoxy adhesive (DURALCO 4703) is reported. The service temperature of this particular adhesive ranges from −260°C to +350°C, and in addition this adhesive has excellent resistance to most acids, alkalis, solvents, corrosive agents, radiation, and fire, making it extremely useful when subject to space radiation. Prior to fabrication of PBI, the surface of PBI is ultrasonically cleaned by acetone followed by its modification through low-pressure plasma with 30, 60, 120, 240, and 480 s of exposure. Surface characterization of the unmodified and modified PBI sheets is carried out by contact-angle measurements by which surface energy is calculated. It is observed that polar component of surface energy leading to total surface energy of the polymer increases significantly when exposed to low-pressure plasma. X-ray Photoelectron Spectroscopy (XPS) reveals that the polymer surface becomes hydrophilic, resulting in increase in surface energy. High-energy radiation related to outer space is simulated with mixed-field radiation generated by SLOWPOKE-2 (safe low power critical experiment) nuclear reactor. Therefore, in order to see the performance of the adhesive joint of PBI under outer-space radiation, the joint is exposed to SLOWPOKE-2 nuclear reactor up to a dose of 444 kGy and critically analyzed.

Shantanu Bhowmik

33. Fatigue Load Conditions

Fatigue involves the failure of materials under cyclic loading, where the maximum load can be significantly lower than that required to cause static failure. Polymeric adhesives, like most materials, are susceptible to fatigue failure, and, hence, fatigue should be accounted for when designing bonded structures subjected to cyclic loading. Adhesive joints have potentially good fatigue resistance compared with other joining methods; however, they are also susceptible to accelerated fatigue failure due to the actions of environmental ageing or viscoelastic creep. In this chapter, the effect of the environment and various fatigue loading parameters on the fatigue behavior of adhesively bonded joints is discussed before describing the main methods of characterizing and predicting fatigue. Traditionally, fatigue behavior has been characterized through the use of experimentally derived stress-life plots, and fracture mechanics–based progressive crack growth methods have also been widely discussed. In more recent years, damage mechanics–based progressive modelling methods have been proposed that have the advantage of predicting both initiation and crack progression phases of fatigue and have also been shown to be readily adapted to the prediction of variable amplitude fatigue and combined fatigue-environmental ageing. The chapter finishes with descriptions of two special cases of fatigue: creep-fatigue and impact fatigue, which have been shown to be extremely detrimental to the fatigue life of bonded joints under certain conditions.

Ian A. Ashcroft

34. Creep Load Conditions

Polymer-based adhesives that have been especially designed to feature a high degree of toughness, flexibility, or, even deliberately, viscoelastic properties exhibit a pronounced time-dependent stress–strain behavior under static mechanical load conditions. Therefore, a suitable mechanical approach to describe and experimentally access phenomena related to creep in polymers and adhesives needs to consider elastic as well as viscous material properties. Creep occurs at load levels below the yield strength, and particularly, creep of viscoelastic materials by definition is assigned to reversible deformation being able to recover after unloading. In technical practice, the term creep is often being used to describe arbitrary time-dependent strain including viscous and elastic-viscous behavior. The concept of generating mechanical substitute models consisting of a combination of spring (elastic) and dashpot (viscous) elements dates back to the late eighteenth century with the Maxwell model, for example, representing a serial connection of both. Other viscoelastic models are discussed in terms of their creep (retardation) strain- and relaxation stress-response to a corresponding stress or strain input in the generalized form of a step-unit function. The resulting constitutive laws for stress–strain–time relationship under static stress or strain conditions can be applied in the limits of linear elasticity where the Boltzmann superposition principle and the correspondence principle are valid. The options for experimentally accessing creep and relaxation phenomena range from standardized procedures to advanced test methods, which are discussed in the context of experimental data. Applying the theoretical background of the standard models for viscoelasticity to the experimental results can improve the reliability of predictive methods intending to extrapolate results from short-term experiments to a long-term timescale.

Paul L. Geiss

35. Durability of Nonstructural Adhesives

In all bonded assemblies the durability of the adhesive or sealant joint is important to the integrity of the article concerned. The considerations of joint design, adhesive, sealant and substrate selection, surface preparation, and primer selection along with methods of application including mixing procedures, application techniques, and joint assembly are all reviewed. Methods of evaluation of durability and test regimes including exposure to elevated and reduced temperatures, UV radiation, moisture, saline solutions, stress, and fatigue, both individually and combined in cycles, are considered. The relevance and application of these test condition to specific situations are discussed, including the role of antioxidants and cross-linking additives to improve durability. Reference is made to the corresponding standards according to the major standard organizations such as the International Standards Organization (ISO), the European Committee for Standardization (CEN) and the British Standards Institute (BSI), and also to European Directives and Regulations, and National legislation.

James D. Palmer

Manufacture

36. Storage of Adhesives

A chapter on adhesive storage should be closely aligned with the current market practice. As such, a major part of this chapter focuses on the shelf life and the safety aspect of the adhesives. The adhesive shelf life is dependent on the adhesive system and the storage conditions, in particular, the temperature. For a stronger emphasis on the effect of temperature on adhesive shelf life, this chapter is subdivided into Room Temperature Storage and Low Temperature Storage.Due to the flammability and possible health hazards of solvent-based adhesives and majority of the chemically reactive adhesives, their storage usually requires special safety measures.Adhesive manufacturers are required to provide information on the shelf life and storage conditions in the product technical data sheet, as well as a description of the possible hazards in the safety data sheet (Material Safety Data Sheet, MSDS), e.g., in the event of a fire.Due to the wide range of adhesive systems available, it is not possible to devise a standard storage guideline applicable to all adhesives. In this chapter, adhesives are divided into four categories: solvent-based, water-based, hot-melt, and reactive adhesives. For some adhesives, their physical characteristics should also be considered (e.g., liquid or solid as powder, granules or film). Considering the variety of adhesive systems, it is necessary to provide a short introduction on the adhesive to indicate the type of packaging and storage conditions needed and its potential hazards.Similarly, in cases where the adhesive shelf life may be extended through storage at low temperatures, it should be indicated on the packaging, although this applies to fewer adhesive systems and applications. In order to explain the quantitative effect of low temperatures on adhesive storage, a brief sub-topic on activation energy and temperature-dependent chemical reaction (Arrhenius equation) is provided.

Hans K. Engeldinger, Cai R. Lim

37. Preparation for Bonding

Adhesives are used today with increasing volumes in many applications in different industries and are supplied to the end customers in various forms. Very common ones are liquid adhesives, pastes, mastics, as well as adhesive films or tapes. Less common ones are powder systems for coating purposes.Bonding with adhesives is not a simple operation and a lot of preparation work is necessary before the adhesive can be applied to the designated bonding area (Shields, Adhesives Handbook 1985). A chain of preparation processes is required. It starts with the mixing of the adhesive and its storage before the transfer to the customer. At the customer, the adhesives need to be transferred to the operation area. The substrates to which the adhesive will be applied have to be well prepared. The final process step includes the dispensing of the adhesive to the substrate and the joining of the parts which are intended to be bonded. Some adhesive formulations require an accurate metering of different components. Each of the steps is important and contributes equally to the quality of the final adhesive application. See below the summary of the different process preparation steps.1.Adhesive mixing at the supplier2.Packaging of the adhesive at the supplier3.Adhesive storage at the supplier or the customer4.Transferring the adhesive from the storage to the application area5.Substrate preparation6.Metering and dispensing the adhesive7.Quality controlDepending on for which application, in which industry, and by which end customers adhesives are used, different application techniques, dispensing, and metering devices are chosen.For smaller bonding operations like sealing work at construction sites, repair work at car garages, or to fix tiles to a floor, adhesives are typically manually applied out of smaller containers like cartridges. If adhesives are used in a larger scale, like at an automotive line, for example, for metal bonding reasons or to bond windows to the frame of a car, a robot application is used, which pumps the adhesive out of drums and transfers it to a dozer and a gun for the final application. The adhesive itself can be applied in different ways such as a simple bead, sprayed, extruded, or applied by air assistance, called swirling. Which technique is used depends on factors like the application, the rheological property of the adhesive, and the application temperature. Therefore, the rheological properties of the adhesive formulation need to be tailored to the application. Lower viscous adhesives can be applied by spraying or extrusion beside the simple bead application. Higher viscous adhesives are often limited to bead application or the application temperature needs to be significantly increased to be applicable by other methods.This chapter will discuss in further detail each item of the process chain: the storage of adhesives, the transfer to the application area, the different metering and dispensing technologies, the used mixing equipments, the substrate preparation, and the quality control. Proposals are made regarding people education and how to create a safe working environment.

Andreas Lutz

38. Equipment for Adhesive Bonding

This chapter describes the equipment required for manual adhesive bonding processes. For some readers, the comments about equipment may seem trivial, but they are important as nonobservance of these points can in practice lead to flawed bonded joints.The individual components which make up mixing and dosing systems have been described and their special features outlined in an attempt to quantify the hitherto qualitative descriptions that have prevailed in the literature.Thereafter, some basics of automation and robotics are outlined with a special excursion on the topic parameters affecting accuracy. Terminal opportunities of accelerated curing are explained using the examples of UV radiation and inductive heating.

Manfred Peschka

39. Environment and Safety

The handling of adhesives in a responsible way throughout their lifecycle, namely from their manufacture via the usage stage right through to recycling and disposal, is a generally recognized principle. The development and manufacture of adhesives is carried out following the principle of Responsible Care® and the subsequent rules for sustainable development defined by the International Council of Chemical Associations. This specifically means that health protection and environmental compatibility considerations are taken into account when developing and manufacturing new adhesives. This has consequences for the composition of the adhesives, the product design, the recommendations for application of adhesives, and the purpose of use and for the recycling of bonded products after they have been used. This chapter deals with the different aspects of consumer, work, and environmental protection, including health and safety information, related to the use of adhesives in industrial and private areas.

Ansgar van Halteren

Quality Control

40. Quality Control of Raw Materials

Since raw materials for adhesives influence the performance of final adhesive products, the selection, storage, handling, and testing of the raw materials are very important. In this chapter, types of raw materials including basic resins, hardeners, fillers, and functional additives for adhesives are firstly described. In addition, the roles of the materials are also shown. Practices for the quality control of the raw materials consisting of acceptance inspections and testing are also explained. Other tests conducted when adhesive products are shipped are explained too. These tests should be carried out following test standards. The standards for testing raw materials, and standards for materials are also mentioned in this chapter.

Kazutami Wakabayashi

41. Processing Quality Control

The processing quality control of adhesively bonded joints in actual production lines is discussed in this chapter. To improve the yield ratio of products, a scientific approach based on both probabilistic design and statistical treatment are indispensable. In addition, control of environmental conditions and materials is also very important. For the purpose, a realistic trial-and-error approach should be done to meet any demands or to solve problems occurring in the production. Investigation of reasons decreasing joint strength is another key point that should be done. The strength decrease occurs often due to mechanical or chemical mismatch of adherends and adhesives. The surface treatment of adherends is important too. Inspection, which can be carried out easily, is desirable in actual production lines.Process design should be done appropriately to improve the efficiency and the economy of the lines, and to increase the yield ratio of products. Parallel processes should be avoided if sequential processes can be adopted. Reduction of operator’s tasks is another important issue. The concept of foolproof should be introduced in the process design.Proper adhesive selection is vitally important, not only for good strength, but also for increasing operation efficiency. New types of adhesives have been available to meet the demands to control the process easily. The education and training of operators is also an essential issue. Operators should learn standard procedures to perform their work appropriately. The necessary information should be exchanged properly.

Kosuke Haraga

42. Nondestructive Testing

The objective of any system of nondestructively examining an adhesive joint is to obtain a direct correlation between the strength of the joint (howsoever defined) and some mechanical, physical, or chemical parameter which can readily be measured without causing damage to the joint. Faults may be defined as anything which could adversely affect the short- or long-term strength of a joint. There are two basic areas for examination in properly made joints, the cohesive strength of the polymeric adhesive, and the adhesive strength of the bond between the polymer and the substrate. In addition, voids, disbonds, and porosity create an additional issue for inspection.During the production phase, and also in service with critical structures, it is essential to use nondestructive tests to assess the quality and fitness for purpose of the product. The nondestructive test will not measure strength directly but will measure a parameter which can be correlated to strength. It is, therefore, essential that a suitable nondestructive test is chosen and that its results are correctly interpreted. Typical defects found in adhesive joints are described and an indication given of their significance. The limits and likely success of current physical nondestructive tests will be described, and future trends outlined.It is shown that a variety of techniques are available for disbond detection, ultrasonics, and different types of bond tester being the most commonly used. These techniques are very time consuming, especially if large bond areas are to be tested. Monitoring interfacial properties is much more difficult and there is currently no reliable test after the joint is made although there are some indications of a possible way forward using high-powered lasers.

Robert D. Adams

43. Techniques for Postfracture Analysis

Adhesives are used nowadays in an uncountable number of applications in everyday life, especially applications where a failure in service may lead to economic loss, injury, or death. In these cases, the ability to determine the causes of failure is essential. This chapter discusses the latest forensic engineering techniques used in the investigation of failed adhesive-bonded joints. An overview of the examination and analysis methodology is introduced in first place; the sequence of steps is important in order to guarantee that no vital information is lost along the way, avoiding cross contamination of fractured surfaces. Visual inspection, microscopy techniques – optic, electronic, and atomic probe microscopies – preparations methods for observation of the fractured surfaces – dissection, etching, coating – physical and chemical characterization methods – Raman microprobe, x-ray spectrometry, infrared analysis, thermal methods – are introduced as convenient tools for supporting the investigation on postfractured specimens. The fracture morphologies of adhesive joints are considered in relation to their locus of failure and directional stability of crack propagation. Mode of loading and strain rate influence on the failure morphologies of the surfaces are illustrated. Fatigue and creep failures imprint specific signatures on the fractured surfaces and are briefly introduced. Several case studies are shown to highlight some aspects of the general procedures and techniques that were previously described. Cases are grouped in three different categories: failures due to overload and design deficiencies, failures due to material and manufacturing defects, and failures due to in-service factors.

Juan C. Suárez

Applications

44. Adhesively Bonded Joints in Aircraft Structures

This chapter focuses on experience with adhesively bonded joints in aircraft structures. It covers their analysis (emphasizing the inherent nonuniformity of adhesive bond stresses), their design, some common pitfalls in past and current practices (the worst of which is the continued myth that adhesive bond load transfer is distributed uniformly over the bond area, so that all that is needed to make stronger joints is more bond area), the critical need for ensuring that the glue is stuck (not by after-the-fact monitoring, which is all but impossible and therefore unreliable, but by proper specifications and quality control during manufacture). It covers the load redistribution around defects and damage, showing that not all damage causes an immediate loss of strength (even though repairs may be necessary to protect against subsequent environmental degradation). It emphasizes a little-appreciated point that the adhesive bond, itself, must never be designed to be the weak link in the chain of strength, so that it cannot act as an instantly catastrophic fuse; the weak link must be in an adherend outside the joint for bonded designs to be reliable. The chapter also includes a discussion of the choice of appropriate bonding tool concept and the great benefits from sometimes using nontraditional tools. The key issue is shown to be that the governing tolerance is not that for the parts, or the tool, but for the thickness of the bond line. The real critical tolerance is on the order of 0.025 mm (0.001 in.), not ±0.4–0.8 mm (0.016–0.032 in.). This requires a far more thorough coordination between design of the parts and the bond tool than has customarily been applied in the past. It is made abundantly clear that tighter and tighter tolerances on the parts and tools is not the way to go. One must rely on a drape-to-fit manufacturing philosophy, the benefits from which are shown to be enormous. The issue of inspection is discussed because a failure to understand what can work and what needs to be checked has led to far reaching adverse consequences. Misplaced faith in after-the-fact inspections is shown to have replaced the proper emphasis on proper process control during manufacture. It is shown to be impossible to restore 100% of bonded joint strength after it has been manufactured incorrectly (or manufactured “correctly” in accordance with process specifications that simply do not work). And the futile search for the Holy Grail of being able to monitor degradation of bond strength during service has led to a ban on using this technology, in some instances, even when there is no other alternative approach that works. The chapter concludes with examples of the successful widespread application of adhesively bonded joints in aircraft primary structure.

L. John Hart-Smith

45. Aerospace Industry

This chapter aims to introduce some of the specific bonding-related issues that face those responsible for bonding operations in space applications: extremely high mechanical loads over a short time, with the launcher and its payloads subjected to gravity magnified by about 20, followed by exposure to extremely high temperatures over a very long period, with the observation and telecom satellites under zero gravity. To design for such oxymoronic specifications and to select materials, such as the adhesives, is just the first in a series of challenges. To perform tests on Earth reproducing space-like environments whilst subject to terrestrial gravity is the second, and not the least significant. This chapter is intended to be an introduction to the issues which have to be connected together in the case of spatial bonding from the bottom, on Earth, upward, to Space.

Christian Désagulier

46. Automotive Industry

Automotive industry is using increasingly structural bonding in a wider sense. This technology is already commonly used for hoods and doors and for windshield bonding. With the availability of a new generation of structural adhesives for the body shop, these adhesives contribute to build lighter car bodies with increased crash performance. The general requirements for adhesives in automotive production are outlined. The key properties of the various structural adhesives are described and the elements for the evaluation of adhesives with the right properties are mentioned. This chapter serves as a guideline for the evaluation of the right adhesive technology from an engineering point of view and will help to increase the use of this joining method to produce cars which cope with the future challenges for lightweight design.

Bernd Burchardt

47. Railway Industry

Adhesion is an indispensable joining technology for railway industries. Adhesives are used for the fabrication of almost all rolling stocks. In the steel main structure of conventional rolling stocks, adhesives are applied for bonding decorated aluminum sheets of wall and ceiling to frames, bonding of floor covering to floor plate, and fixing heat insulating material to the inside of carbody. A large amount of sealants are also used even in the conventional rolling stocks. Recent high-speed trains have modern lightweight structures consisting of aluminum hollow extrusions, sandwich panels, or carbon fiber reinforced plastics. For the structures, adhesion plays an important role as a structural joining method. Even for conventional rolling stocks, the use of adhesives is increasing. For instance, weldbonding is nowadays experimentally applied to the aluminum body structures. Moreover, adhesive is used to smooth the outsides of each carbody and between the outer surfaces of carbody and window. As a result, aerodynamic noises inside and outside the train and energy consumption are considerably reduced.Maglev trains will be increasingly use in the future, and the use of adhesives will expand due to the demand of reducing weight and energy consumption. In this chapter, the cases in Japan are mainly explained. Worldwide cases are shown in Sect. 47.4.

Yasuaki Suzuki

48. Marine Industry

This chapter describes the use of adhesive bonding to assemble structures in the marine industry. The marine environment is extremely aggressive, and this has resulted in widespread use of fiber reinforced composite materials. Adhesive bonding is a lightweight and corrosion resistant means of joining these materials. The main emphasis of this chapter will, therefore, be on the assembly of composites, though some examples of metal bonding will also be discussed. Three industrial applications are used to illustrate the use of adhesive bonding; small pleasure boats, high performance racing yachts, and bonded structures in the offshore industry. Each has specific design requirements, and there is no single marine adhesive suitable for all structures, but the requirement for long-term durability in a seawater environment is common to all these applications.

Peter Davies

49. Civil Construction

Bonding in the field of civil engineering has a long tradition. The history of adhesive bonding began in the pre-Christian Rome with the invention of mortar. Today, modern adhesive technology is an integral part of the civil construction, thus making important economic contributions to the stabilization of existing and creation of new jobs. Due to the wide range of construction materials used such as concrete, wood, steel, and combinations of materials in the form of hybrid structures, adhesive technology as a material-independent joining technology will play a significant role.In this chapter, adhesive bonding applications in the civil construction sector, specific requirements, and adherents are described. The execution of bonding and properties of adhesive-bonded civil constructions complete the theme.

Ilko Hartung, Stefan Boehm

50. Electrical Industry

Electrically conductive adhesives (ECAs) are used for the joining of electrical and electronic components in the electrical industry. ECAs are composites consisting of a polymeric matrix and electrically conductive fillers. The mechanical properties are provided by the polymeric matrix, while the electrical conductivity is supplied by the conductive fillers. Typically, there are three types of conductive adhesives, viz. isotropic, anisotropic, and nonconductive adhesives. These adhesives are classified according to their conductivity, which is controlled by the conductive filler content in the polymer matrix. For their application in the electrical industry, there are two main specific requirements for these adhesives, i.e., electrical conductivity and thermo-mechanical properties. In this chapter, the mechanism underlying the electrical conduction in adhesive joints is derived, while the thermal and mechanical parameters that should be measured are introduced. In terms of the evaluation of the reliability of adhesives in electronics, the basic test procedures, including several specific test methods and analysis techniques, are explained. Recommendations are also given to select a suitable test method.

Seung-Boo Jung, Jong-Woong Kim

51. Shoe Industry

This chapter constitutes one of the very few reviews in the existing literature on shoe bonding, and it gives an updated overview of the upper to sole bonding by means of adhesives. The surface preparation of rubber soles and both the formulations of polyurethane and polychloroprene adhesives are described in more detail. The preparation of adhesive joints and adhesion tests are also revised. Finally, the most recent development and technology in shoe bonding is described.

José M. Martín-Martínez

Emerging Areas

52. Molecular Dynamics Simulation and Molecular Orbital Method

Computer simulations have provided a powerful technique in understanding the fundamental physics and mechanics of adhesion. In this chapter, various simulation methods pertaining to adhesion technology are introduced, such as the molecular dynamics simulations, the quantum mechanics calculations, the molecular orbital method, the density functional theory and the molecular mechanics simulations. Besides, some combined methods such as the hybrid quantum mechanics/molecular mechanics simulations, ab initio molecular dynamics and the density-functional based tight-binding method are reviewed. General features and routines of these methods as well as the basic theory are described. The advantages and disadvantages of these methods are compared and discussed. Each method has the distinctive advantage and is suitable for specific condition. Some examples are proposed to give the direct perceive when investigating adhesion issues using various simulation methods. All these instances are expected to be helpful to readers when performing the corresponding simulations and analyzing of the results.

Ya-Pu Zhao, Feng-Chao Wang, Mei Chi

53. Bioadhesives

There is a pervading presence of adhesive joints in nature. Adhesive secretions are used by organisms for attachment, construction, obstruction, defense, and predation. Most natural materials are hybrid materials combining organic and inorganic building blocks. Bioadhesives are able to build durable interfaces between hard and soft materials, often of disparate scales, and exhibit a certain number of characteristics that make them differ greatly from synthetic adhesives. The title of this chapter (Bioadhesives) includes a broad variety of different concepts: natural adhesives, biological adhesives, biocompatible adhesives, and biomimetic and bioinspired adhesives. The term natural adhesive describes substances that are formulated from partially or totally bio-based raw materials, which are employed as adhesives in man-made technology, but are not substances used by biological systems as glues. The term biological adhesive refers specifically to adhesive secretions of natural organisms in marine and other wet environments, or those produced on land. A different concept refers to what is named as biocompatible adhesive, including any natural or synthetic adhesive that interfaces with living tissues and biological fluids, and is suitable for short-/long-term biomedical applications. Specific mechanisms of adhesion found in nature are discussed – interlocking, suction, friction, dry and wet adhesion, gluing – to get inspiration for the development of new synthetic adhesives. Biomimetic adhesives are synthetic adhesives design to closely mimic the molecular structure and mechanisms of adhesion found in nature. Bioinspired adhesives are synthetic adhesives whose design is inspired in biological concepts, mechanisms, functions, and design features. Also the promising technology of self-healing polymers is reviewed, as an effective method for controlling crack propagation and debonding.

Juan C. Suárez

54. Biological Fibrillar Adhesives: Functional Principles and Biomimetic Applications

Specific mechanisms of adhesion found in nature are discussed in the chapter Bioadhesives (Chap. 53). One of the most discussed biological systems in the last decade is the so-called fibrillar adhesive of insects, spiders, and geckos. These systems are adapted for dynamic adhesion of animals during locomotion and, therefore, have some extraordinary properties, such as (1) directionality, (2) preload by shear, (3) quick detachment by peeling, (4) low dependence on the substrate chemistry, (5) reduced ability for contamination and self-cleaning, and (6) absence or strong reduction of self-adhesion. In the present chapter, we review on functional principles of such biological systems in various animal groups with an emphasis on insects and discuss their biomimetic potential. Data on ultrastructure and mechanics of materials of adhesive pad materials, movements during making and breaking contact, and the role that the fluid plays in the contact between pad and substrate are presented here. The main goal was to demonstrate how a comparative, experimental approach in studying biological systems aids in developing novel adhesive materials and systems. The micro-structured adhesive systems, inspired by studies of biological systems of insects, spiders, and geckos, are also shortly reviewed.

Stanislav N. Gorb

55. Adhesives with Nanoparticles

The increased commercial availability and the reduced prices of nanoparticles are leading to their incorporation in polymers and structural adhesives. This chapter outlines the principal types of nanoparticles, and the methods that may be used to disperse the particles in a polymer matrix. It discusses how nanoparticles can alter the mechanical properties (e.g., stiffness), electrical properties (e.g., conductivity), functional properties (e.g., permeability, glass transition temperature), and fracture performance of thermoset polymers. The effect of nanoparticles on joint performance is also discussed.

Ambrose C. Taylor

56. Adhesive Dentistry

Adhesive techniques and materials are being used increasingly in clinical dentistry, and they are reviewed in the present chapter. Broadly speaking, there are two types of tooth-colored restorative material, the so-called composite resins and the glass-ionomer cements. There are, though, variations on these basic types, as explained in the chapter. In addition, there is the zinc polycarboxylate cement, which was the first adhesive dental restorative material to be developed, and it retains a niche in modern clinical practice.Composite resins are not themselves adhesive, but need to be used in conjunction with separate adhesive formulations known as bonding agents. Over recent years, this technology has developed rapidly, as described, and a wide variety of systems are currently available to the clinician. Bonding agents are often characterized by “generation,” and currently seventh generation bonding systems are available. These are applied to the tooth surface following cavity preparation, and may involve some sort of pretreatment to remove the layer of deranged dentin known as the “smear layer.” Modern bonding agents are frequently “self-etching,” so that smear layer removal or incorporation happens with the application of the bonding formulation, and the composite resin is then applied to this layer. High shear bond strengths are reported for these systems, even though they involve only a very thin layer between a hydrophilic substrate and a very hydrophobic repair material.Glass-ionomers, by contrast, are themselves hydrophilic and inherently adhesive to the tooth surface. It therefore requires only slight pretreatment, typically conditioning with 10% aqueous polyacrylic acid. Glass-ionomers rapidly form durable bonds to the tooth surface through the development of an ion-exchange layer at the interface. This ability to bond is exploited in both the Atraumatic Restorative Treatment (ART) technique and in bonding of orthodontic brackets, both of which are described in detail in the chapter.

John W. Nicholson

57. Adhesion in Medicine

Adhesives are increasingly being used in medicine for repairing cuts and tears in the body as an alternative to mechanical fixation such as sutures. There are very strict regulations controlling the application of adhesives within the body and this means that there are only a limited number of chemistries which are approved for clinical use. The principal internal adhesives in current use are those based on fibrin, gelatin, and poly(ethylene glycol) (PEG) hydrogels and function largely as sealants, though do bond to the tissue surfaces. Cyanoacrylates are approved, mostly only for application to the surface of the skin for wound closure, but are quite widely used in a range of other applications. There are many requirements of an adhesive for internal use and this has led to large number of further systems being proposed. A number of those currently being evaluated for internal indications are described. Some are based on synthetic chemistry, some from biological sources such as marine creatures, and some are akin to welding or soldering.Pressure-sensitive adhesives are widely used for securing dressings and devices to the skin surface. Most of these are now based on acrylic or silicone chemistries.

Robin A. Chivers

58. Recycling and Environmental Aspects

Recycling and environmental aspects of adhesion technology are discussed in this chapter. Adhesively bonded adherends should be often separated before they can be recycled. For this purpose, dismantlable adhesives, which can be separated with stimulations, have been developed recently. There are lots of technical processes to realize such adhesives. For example, softening of adhesive, expansion force due to blowing agents or thermally expandable microcapsules, chemical degradation, electrochemical reaction, and taking advantage of interfacial phenomena can be applied to dismantlable adhesives. These adhesives have many applications such as temporary joints of work materials, shoe making, integrated circuits (IC) chip fabrication, electronics, housing construction, car fabrication, and so on. The most used trigger to start the separation of these adhesives is heating. Many kinds of methods including infrared, induction, and microwave heating are recently available. In addition, novel dismantlable adhesives, which have anisotropy in strength or are triggered by electric currents, have been presented.

Chiaki Sato

59. Adhesion Technology Recap – Current and Emerging Areas

This chapter gives a brief description of the subjects and chapters that are included in this handbook. The handbook is organized in ten parts: theory of adhesion, surface treatment, adhesive and sealant materials, testing of adhesive properties, joint design, durability, manufacture, quality control, applications, and emerging areas. A total of 57 chapters are presented covering all aspects of adhesion and adhesives. In addition to the information contained in each chapter, an extensive list of references is given (approximately 4,000 references).

Lucas F. M. da Silva, Andreas Öchsner, Robert D. Adams

Backmatter

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