Mechanics of Composite and Multi-functional Materials, Volume 6

Composites made of reinforced scrap rubber are generating interest in transportation industries due to their unique combination of high strength, low density, and limitless availability. Whether the vehicle is an airplane, truck, car, or boat, weight reduction leads directly to reduced fuel consumption and operating costs. In the present study, different composite formulations are prepared by means of a low-cost production process. In this process, fresh scrap rubber is combined with varying amounts of boron and alumina, with the aim of optimizing strength through control of both composition and constituent bonding. Mechanical properties are evaluated by impact testing, bend testing, and nanoindentation. Microstructure is analyzed by scanning-electron microscopy (SEM).

Many industries, notably the automotive and aerospace industries, are now utilizing thermoplastic matrix composites (TPMCs) for their improved strength and stiffness properties compared to pure thermoplastic polymers, as well as their manufacturability compared to traditional thermoset matrix composites. The increase in the utilization of TPMCs ushers in the need for the development and characterization of joining methods for these materials. A widely used technique for joining thermoplastics is ultrasonic spot welding (USSW). During USSW, high frequency, low amplitude vibrations are applied through an ultrasonic horn resting on the polymer surface. The vibrations induce frictional heat, producing a solid state joint between polymer sheets. Advantages such as short weld cycle time, fewer moving components and reproducibility make this technique attractive for automation and industrial use. Prior work showed USSW as a feasible, repeatable joining method for a polycarbonate matrix filled with chopped glass fibers. The mechanical properties required for full characterization of the TPMC used in this work were not provided by the manufacturer. As such, the constitutive behavior of both as-received and USSW thermoplastic composite material (polypropylene matrix filled with 30 wt% chopped glass fibers) was characterized. The fiber orientation and distribution in TPMCs has a direct impact on constitutive behavior. To characterize these qualities, optical techniques such as scanning electron microscopy (SEM) and micro computed tomography (micro-CT) were employed. Digital image correlation (DIC) was used to acquire full field strain measurements from the composite material under different loading scenarios. Because the constitutive behavior of polymers is greatly dependent on temperature, temperature measurements during the USSW process and measurement of mechanical properties as a function of temperature will be conducted through infrared (IR) imaging and dynamic mechanical analysis (DMA), respectively. Following the calibration of the constitutive model for the polypropylene matrix TPMC, the mechanical and thermal properties will be used to develop a computational framework for the purpose of predicting the structural response of a composite joint under various loadings.

Laser beam machining (LBM) is widely used as thermal energy based non-contact type advance machining process which can be applied for almost whole range of materials. It is suitable for geometrically complex profile cutting in the metals used in manufacturing engineering.

In the present work, high-power laser cutting process of Titanium Aluminium (Ti-Al) based intermetallic composites designed through combined method of powder metallurgy and thixoforming were carried out. The thermal effects of laser cutting and effects of main operating parameters such as laser power, and cutting speed on the cutting edge and on the cutting surfaces were examined. The evolution of the microhardness underneath the cutting surface due to laser power is also examined. The composite used in this study was produced through combined method of powder metallurgical (P/M) and thixoforming. Microstructure of cutting edge and cutting surfaces are also investigated by scanning electron microscopy (SEM). Cutting surfaces have been analyzed with 3D optical surface roughness-meter (3D–SurfaScan).

Roughness evaluations of the cutting surface depending on the cutting speed and cutting power were taken as optimization criteria that have been carried out by Taguchi method. A simple and useful tool was proposed for using in real manufacturing environment. Results exposed that good quality cuts can be produced in this Ti-Al based composite, at a window of laser cutting speed variable between 0.35 and 0.6 m/min and at a minimum heat input variable between 1400 and 2000 W.

Epoxy rubber based structural composites (ERCs) are used in engineering applications mainly in the aeronautical area because they can meet the necessary requirements in new multifunctional systems. These composites exhibit good overall mechanical and thermal performance and they can potentially offer a large variety of functional properties. In order to realize an efficient engineering development process, the data for basic material parameters of these composites is essential. The present paper discusses the mechanical characterization of these composites. A combination of structural and energetic functions can be achieved by using different nanoparticle reinforcements in epoxy-rubber composites This type of material design gives an exigent task to the designers looking to integrate more functionality into the base material of their structure to achieve overall improved system performance. This paper is focused on the design of ERCs reinforced with nano powders in different ratios in a matrix of epoxy – fresh scrap rubber. It is expected this material would be attractive for industrial applications because of the readily available recycled materials that are utilized. The mechanical and some physical properties of these composite systems are studied in this research. Mechanical properties are evaluated by means of three-point bending tests, nano-indentation, drop weight tests and dynamic mechanical analysis. Scanning electron microscope is used to observe fracture surfaces and the microstructure.

The use of lightweight materials has accelerated recently due to the environmental restrictions and economic concerns. For this reason, in automotive and aerospace industries, designers and material manufacturers are in the search of durable materials in terms of their structural and energetic properties. Polymer matrix composites (PMCs) usually meet these expectations when proper reinforcements are used. Epoxy – rubber based composites reinforced with different materials are studied by several researchers. However, addition of scrap rubber to the matrix and graphene as reinforcement introduces a novelty in this area. Since, using of scrap rubber has favorable outcomes in economical and structural perspectives such as revaluation of scraps and compensating for the brittleness of epoxy. Also, due to its superior structural, thermal and physical characteristics, addition of graphene promises desired mechanical properties in case of a homogeneous distribution. This paper is focused on the design of PMCs reinforced with nano graphene in different ratios in a matrix of epoxy – fresh scrap rubber. The mechanical and some physical properties of these composite systems were studied in this research. Mechanical properties were evaluated by means of three-point bending tests, impact tests and nano indentation technics. Scanning electron microscope was used to observe fracture surfaces and the microstructure.

Recently, encouraged by the idea of sustainable development, the emissions of CO₂ have become a very prominent issue to be solved. As a consequence, in the automotive and aeronautic industries, the reduction of weight has become a major issue and needs to be addressed for all possible structures in the vehicle. Therefore, some metallic parts are being replaced by polymer based composites. For this to happen, the feasibility of using these composites has to be examined properly in terms of their mechanical and energetic properties. Epoxy – rubber based composites reinforced with ceramics are studied by several researchers. However, addition of scrap rubber to the matrix and alumina fibers (Al₂O₃) as a reinforcement introduces a novelty in this area. Since, using of scrap rubber has positive outcomes in economical and structural perspectives such as revaluation of scraps and compensating the brittleness of epoxy. Also, due to its favorable structural characteristics such as interlocking properties of fibers, addition of alumina fibers ensures desired mechanical properties in case of a homogeneous distribution. This paper is focused on the design of epoxy – fresh scrap rubber matrix reinforced with different ratios of alumina fibers. The mechanical and some physical properties of these composite systems were studied in this research. Mechanical properties were evaluated by means of drop weight tests, three-point bending tests and nanoindentation technics. Scanning electron microscope (SEM) was used to observe fracture surfaces and the microstructure. After all, UV degradation of the material was observed by electron microscopy.

Full-scale testing of large composite structures is time-consuming and very expensive. Scaled-down models can facilitate time- and cost-effective experimental evaluations of large structures. Due to the special characteristics of laminated composite structures, the design of a scaled-down model of a large composite structure can be challenging. Moreover, the similarity and correlation between the reduced-scaled model and the full-scale structure need to be demonstrated before the experimental data from testing of a scaled-down model can be used for predicting the behavior of the full-scale structure. In this study, laminated composite I-beam reduced-scale models in three different size scales are designed from the spar caps and the shear web geometry of a utility-scale wind turbine blade. The designed composite I-beams are manufactured and tested in a quasi-static four-point bending configuration, and the strain distributions of the loaded small, medium and large beams are measured using the digital image correlation technique. The strain fields of the three beams are compared and similarity of the strain distribution in the three scales is demonstrated.

Duplex stainless steels are preeminent materials that have been receiving special attention nowadays, due its considerable strength, toughness and exceptional corrosion resistance. This paper aims the production of a duplex stainless steel by powder metallurgy through cutting chips, X ray diffraction was used to identify the ferrite phase and austenite phase, also this paper compares the normal milling process to the addition of vanadium carbide to improve the milling action. To assure the significant changes by using the carbide and the change on time parameters, data was collected, and it was used statistical analysis by factorial design. Adding vanadium carbide at 0%–3%, the reduction in average particle size appeared to be significant, compared to the material without the carbide addition. The smallest particle size was obtained by the high energy milling that was performed in a planetary ball mill with ball to powder weight ratio 20:1, and mill speed of 350 rpm milled in argon atmosphere for 50 h, and adding 3% of vanadium carbide. Static data acknowledged that addition of carbides in the process is the most influential term, followed by the time of milling.

In this work, aluminium matrix composites (AMCs with scrap A356 powder given by French Aeronautical Society) were designed through combined method of powder metallurgy and thixoforming (sinter + Forging). Three different reinforcements (Magnetic iron oxide, Fe₃O₄ – Hybrid graphene nano-platelets, GNPs, Nickel, Ni) were used and preceded under the constant process parameters such as hot compaction, sinter-forging, sintering time, etc. Mechanical and physical properties of the composites were improved with the combined processing method of powder compacted specimens and reinforcement volume fractions. Static compression tests, Microhardness tests, surface scratch tests, measurement of magnetic permeability showed that the mechanical and physical properties of these composites can be improved with the optimization of process parameters. In the present work, an alternative and a low cost manufacturing process were proposed for these composites. The microstructure and damage analyses have been carried out by Scanning Electron Microscope (SEM).

In this work, a special copper aluminium matrix composite (ACMMCs) obtained from the fresh scrap – chips of AA7075 and- pure electrolytic copper were designed through combined method of powder metallurgy and sinter + Forging. First of all, Al-Cu matrix was doped with ZnO after the ball milling with two basic reinforcements (Nb₂Al– SiC, etc.) was carried out during the 4 h. A basic composition was prepared depending on the doping percentage of ZnO as 30 wt%. Mechanical and physical properties of this composite designed here can be improved with the doping process followed by combined method of powder compacted specimens and doping volume fractions. The surface scratch tests and micro-hardness results were compared according to the optimization conditions of the doping and the reinforcement. Static compression and impact-drop weight tests were carried out. The microstructure and damage analyses have been carried out by Scanning Electron Microscope (SEM).

The mechanical effects of dispersing solid particles within a continuous polymer matrix have been well studied for a variety of polymeric systems. These dispersions are of particular interest for electronically conducting polymer applications where the combined mechanical and electrical performance of the material is important, especially in the presence of large deformations. A key weakness of these systems, however, is apparent in soft polymer systems where the polymer is chosen for its elastic qualities, which are often negated by the presence of solid particulate fillers. To overcome this challenge liquid metal, in this work the eutectic Gallium-Indium-Tin (GalInStan), was dispersed in polydimethylsiloxane (PDMS), and the resulting composited material electromechanical properties were evaluated with respect to particle size and loading. Mechanical properties were compared to rigid Ni and soda-lime silica particles of similar sizes. Data presented will also illustrate the “fluid” dispersion viscosity behavior associated with GalInStan loading, and the effect of viscosity on dispersed liquid metal particle size, which is a key parameter in controlling material electronic performance. This work widens the potential scope of electronically conductive filled elastomers beyond the low-strain regime and promises to greatly increase the fatigue life of fabricated stretchable electronic devices based on conductive elastomers.

Laser cutting is commonly used for manufacturing of strong composites as an advance machining process. It is suitable for geometrically complex profile cutting in the metals used in manufacturing engineering. In the present work, laser cutting process of aluminium matrix composites obtained from scrap chips reinforced with hard ceramics (TiN + Al₂O₃) were carried out. They are being widely used in the aerospace and automobile industries such as aircraft structure, internal combustion engines, plain bearings, wheels, pistons, brake rotors for high speed trains, etc. In fact, TiN does not react with aluminium. It keeps its thermal stability up to 3000 °C and chemically inert to most of the common acids. It is industrially important due to its high hardness, good electrical and optical properties, etc. TiN is presently being used in cutting tools, solar-control films and other micro-electronic applications. For this reason, it was interesting to develop a new composite from scrap aluminium chips reinforced with TiN +Al₂O₃ ceramic powders and to examine its tailored beahviour of these composites. The thermal effects of laser cutting and effects of main operating parameters such as laser power, and cutting speed on the cutting edge and on the cutting surface were examined. The evolution of the microhardness underneath the cutting surface due to laser power is also examined. The composite used in this study was produced through combined method of powder metallurgical (P/M) and thixoforming (Semi solid). Microstructure of cutting edge and cutting surfaces are investigated in detail by scanning electron microscopy (SEM). Cutting surfaces have been analyzed with 3D optical surface roughness-meter (3D–SurfaScan).

Roughness evaluations were taken as optimization criteria as a function of the cutting surface and cutting parameters (power, speed, gas pressure etc.) that have been carried out by Taguchi method. A simple and useful tool was proposed for using in real manufacturing environment.

Tailored behaviour of scrap titanium based composites can be done reasonably by laser cutting at the optimum process parameter ranges. Laser cutting is frequently used for manufacturing of composites as an advance machining process. It is suitable for geometrically complex profile cutting in the metals used in manufacturing engineering. In the present work, laser cutting process of scrap titanium matrix composites obtained from scrap (Ti6242 + pure Ti) chips reinforced with aluminium, tin, zirconium, molybdenum were carried out. Actually these materials are being widely used in the aerospace such as aircraft structure. For this reason, it was interesting to develop a new composite from scrap (Ti6242 + Pure Ti) chips reinforced with certain elements and to examine its tailored beahviour of these composites for using in manufacturing engineering. Due to thermal effects of laser cutting process, it should be optimized main operating parameters such as laser power, and cutting speed, gas pressure, etc. on the cutting surface. The evolution of the microhardness underneath the cutting surface due to laser power was examined. The composite used in this study was produced through combined method of powder metallurgical (P/M) and thixoforming (Semi solid). Microstructure of cutting edge and cutting surfaces are investigated in detail by scanning electron microscopy (SEM). Cutting surfaces have been analyzed with 3D optical surface roughness-meter (3D–SurfaScan). Roughness evaluations were taken as optimization criteria as a function of the cutting surface and cutting parameters (power, cutting speed, gas pressure etc.) that have been carried out by Taguchi method. A simple and useful tool was proposed for using in real manufacturing environment.

In laser cutting process, the cut quality is of great importance. The Heat Affected Zone (HAZ), the kerf width (K_w) of laser cut and quality of the cut edges are affected by cutting parameters as well as the work-piece material. In this paper CO₂ laser cutting of 3 mm thick of Titanium alloy sheet grade 5 Ti-6Al-4 V is investigated. The main objectives of the present work are firstly focused on evaluating the effect of laser power (Pu), cutting speed (V) and gas pressure (p) on Heat Affected Zone and Kerf width quality. Secondly, the relationship between cutting parameters and laser process output variables are analyzed and optimized using the Taguchi method. Results indicate that the thickness of the Heat affected Zone increases with the evolution of laser power and decreases with the increase of cutting speed, and the optimum cutting condition was found to be 1 kW for the laser power, 2400 mm/min for the cutting speed and 2 bars for gas pressure. Also, it is underlined that the kerf width is mainly influenced by laser power and cutting speed.

The short-term failures of dental composites are a common limitation of these materials. Oral conditions apply fatigue load cycles in the form of chewing and thermal loads, and the damage due to fatigue loads plays a major role in restorative failures in the form of cracks. A lab-based fatigue test is a suitable technique to characterize the crack propagation in dental composites. In this paper, we investigate the ability of a self-healing material to repair or arrest propagating fatigue cracks. In-situ self-healing resin composites were prepared using 15 wt% of activator resin microcapsules and 5 wt% of initiator microcapsules, and equal amounts of 40 wt% each of dental filler and dental resin. Compact Tapered Double Cantilever Beam (cTDCB) specimens of self-healing dental resin composites were prepared by integrating two sets of microcapsules of diameter 45 ± 10 μm containing an acrylate monomer and a polymerization initiator (BPO). Samples were tested in a servo-hydraulic load frame in air at room temperature. Three specimen types are investigated, dental composite without microcapsules, dental composite with non-healing microcapsules, and dental composite with in-situ self-healing microcapsules. The results show that the in-situ self-healing dental composite successfully extended the life of the composite compared to the control samples.

Fiber reinforced polymer composites are frequently used in hybrid structures where they are co-cured or co-bonded to dissimilar materials. For autoclave cured composites, this interface typically forms at an elevated temperature that can be quite different from the part’s service temperature. As a result, matrix shrinkage and CTE mismatch can produce significant residual stresses at this bi-material interface. This study shows that the measured critical strain energy release rate, G_c, can be quite sensitive to the residual stress state of this interface. If designers do not properly account for the effect of these process induced stresses, there is danger of a nonconservative design. Tests including double cantilever beam (DCB) and end notched flexure (ENF) were conducted on a co-cured GFRP-CFRP composite panel across a wide range of temperatures. These results are compared to tests performed on monolithic GFRP and CFRP panels.

In this study, we estimated the effect of fiber constraint on the interphase region using 3D finite element model. Finite element based inverse analysis was employed to optimize the factors influencing fiber bias effect and to quantify the contribution of fiber constraint using an empirical model. We have also investigated the photocatalytic degradation on the interphase region of carbon fiber composites due to ultraviolet (UV) exposure using AFM indentation based force mapping. Samples were kept in ultraviolet (UV) chamber for 0, 0.5, 1, 2, 6, 12, and 24 h at 0.70 W/m² irradiance and 50 °C. Force mapping was done to generate “full-field” load-displacement indentation curves, which were then analyzed using the Oliver – Pharr model to determine elastic modulus map near fiber region. For neat CFRP sample, interphase region of thickness was found to be around 100–200 nm. It was observed that the interphase size reduce with the duration of UV exposure. The change in chemical cross--linking of the epoxy resin near interphase region by breaking of C-C bond of the carbon fiber, leads to the formation of new functional groups and chemical bonds. The effect of UV exposure on the carbon fiber was studied by X-ray photoelectron spectroscopy (XPS).

In the present study an attempt is made to determine the mechanical properties of sisal fiber reinforced polyester composites. Sisal fibers are the natural fibers obtained by processing the leaves of the sisal plants grown in nature. Sisal plant offers hard and strong strands of sisal fibers. The soft tissue of the sisal leaves is removed either physically or by using equipments. The fibers obtained are dried and brushed to remove the dirt left over to get the sisal fibers. In the present study, randomly oriented sisal fiber reinforced polyester matrix composite specimens of thicknesses 2 mm, 3 mm, 4 mm, 5 mm and 6 mm were fabricated by using hot compression moulding technique. 5% NaOH treated sisal fibers of length 10 mm is used as reinforcement for casting the composite specimens. A mixture of polyester resin, methyl ethyl ketone peroxide and cobalt naphthenate of ratio 50:1:1 is used as matrix for the fabrication of composite panels. Composite panels of fiber volume fraction 10%, 15%, 20%, 25% and 30% were casted and the test specimens were cut from the panels and tested for its tensile strength and flexural strength as per ASTM D-3039 and ASTM D-7264 respectively. From the experimental results it is observed that strength of tested specimens was found to show peak values at a fiber volume fraction of 20–25%.

The strain-rate-dependent matrix-dominated failure of multiple fiber-reinforced polymer matrix composite systems was evaluated over the range of quasi-static (10⁻⁴) to dynamic (10³ s⁻¹) strain rates using available experimental data from literature. The strain rate dependent parameter, m, was found to relate strain-rate dependent lamina behavior linearly to the logarithm of strain rate. The parameter was characterized for a class of laminates comprised of epoxy-based matrices and either carbon or glass fibers, and determined to be approximately 0.055 regardless of fiber type. The strain-rate-dependent Northwestern Failure Criteria were found to fit all data in superior agreement to classical approaches across all strain rates evaluated based on solely lamina-level properties. It was determined that using the determined m value with the Northwestern Failure Criteria provided an accurate prediction of material behavior regardless of fiber type for the identified material class, which significantly reduces the material characterization testing required for the typical building block approach used by industry for computational analysis validation.

The failure progression of a fiber-reinforced toughened-matrix composite (IM7/8552) was experimentally characterized at quasi-static (10⁻⁴ s⁻¹) strain rate using crossply and quasi-isotropic laminate specimens. A progressive failure framework was proposed to benchmark the initiation and progression of damage within composite laminates based on the matrix-dominated failure modes. The Northwestern Failure Theory (NU Theory) was used to provide a set of physics-based failure criteria for predicting the matrix-dominated failure of embedded plies using the lamina-based transverse tension, transverse compression, and shear failure strengths. The NU Theory was used to predict the first-ply-failure (FPF) of embedded plies in [0/90₄]_s and [0₂/45₂/−45₂/90₂]_s laminates for the embedded 90° and 45° plies. The Northwestern Criteria were found to provide superior prediction of the matrix-dominated embedded ply failure for all evaluated cases compared to the classical approaches. The results indicate the potential to use the Northwestern Criteria to provide the predictive baseline for damage propagation in composite laminates based on experimentally identified damage response on a length scale-relevant basis.

Low-cost unmanned aircraft that use affordable manufacturing and have limited service life can enable mission concepts in which there is a higher tolerance for aircraft loss, or attrition. Because of their higher risk tolerance, these low-cost attritable aircraft could also integrate emerging technology which may have previously been considered too risky for integration into expensive and long life aircraft. Light-weight multifunctional structural composites have the potential to integrate additional functions and enable mission agility without significantly adding weight or reducing payload capacity. However, design and development of these material systems are often difficult because of the traditional “building block” development approach used for traditional composites, the large option space available for structural and functional properties, and the potential complexity of the multiscale and multiphysics coupling. To realize integrated functionality, new multi-scales and multi-physical experimental mechanical characterization techniques should be merged with maturing integrated materials models. We discuss this need using examples of a reconfigurable liquid metal Structurally Embedded Vascular Antenna (SEVA), a plasmonic nanoparticle based method for measuring internal temperature gradients, and embedded micro-cantilever carbon-nanotube based sensors. The latter of these is also used to discuss the potential to accelerate development of multifunctional structural concepts by provide air flow measurement and structural feedback during testing of complex structures. This could, in turn, eliminate some testing of intermediate elements in the slow and expensive traditional “building block” approach.