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Über dieses Buch

This book contributes to the field of hybrid technology, describing the current state of knowledge concerning the hybrid material concept of laminated metallic and composite sheets for primary aeronautical structural applications. It is the only book to date on fatigue and fracture of fibre metal laminates (FMLs).

The first section of the book provides a general background of the FML technology, highlighting the major FML types developed and studied over the past decades in conjunction with an overview of industrial developments based on filed patents. In turn, the second section discusses the mechanical response to quasi-static loading, together with the fracture phenomena during quasi-static and cyclic loading. To consider the durability aspects related to strength justification and certification of primary aircraft structures, the third section discusses thermal aspects related to FMLs and their mechanical response to various environmental and acoustic conditions.



Chapter 1. Introduction

Historically, Fibre Metal Laminates were introduced as a laminated material concept to improve the fatigue and damage tolerance properties of metallic structures in aeronautics. However, the concept can be viewed from different perspectives. This chapter discusses that the FML concept can be seen either as reinforcement of metallic structures or as reinforcement of fibre-reinforced polymer composite structures. Cases are given to illustrate how the concept of damage tolerance can be exploited with FMLs, in particular if the concept is viewed as structural concept rather than a material concept.

René Alderliesten

Chapter 2. Laminate Concepts & Mechanical Properties

Inspired by the successful application of ARALL and GLARE on aeronautical structures, many researchers and scientists have pursued the development of FML concepts. The fact that the majority of these studies never reached maturity on structural applications may be explained by the observation that FML was mostly treated as a material concept. As a result, not enough consideration was given to the final structural applications. Nonetheless, many FML variants with their properties presented in the literature constitute valuable information for future developments. Therefore, an overview of all the FMLs and the most characteristic properties are given in this chapter.

René Alderliesten

Chapter 3. Patents and Intellectual Property

Along with the developments of hybrid laminated configurations comprising metallic and fibre-reinforced polymer constituents, patents have been filed to protect the intellectual properties associated with these developments. This chapter provides an overview of the patents filed worldwide over the past three decades to illustrate the various structural-, material-, and manufacturing concepts developed. These concepts are subsequently discussed with respect to their novelty and innovation.

René Alderliesten

Chapter 4. Stress and Strain

The in-plane mechanical properties of FMLs have been described with methods ranging from simple engineering methods to scientific laminated plate theories. This chapter describes the current understanding of stress and strain in FMLs, explaining the laminated plate theories adapted for the different thermal expansion properties of both metal and composites, and the plasticity induced by the metallic constituent. The application and limitations of the various methods are addressed.

René Alderliesten

Chapter 5. Blunt Notch Strength

The blunt notch strength of FMLs is discussed with respect to the deformation and failure phenomena of the individual constituents. The influence of metal plasticity, the splitting and delamination phenomena in the composite layers, and fibre failure are discussed. Various failure criteria and theories are presented to describe the blunt notch strength in the major material axes and under off-axis angles with respect to these axes.

René Alderliesten

Chapter 6. Bearing Strength

The bearing strength of FMLs is discussed with respect to the individual constituent phenomena. In particular the two main methods to experimentally obtain the bearing strength are discussed, addressing ply delamination buckling as an important phenomenon. The influence of the various characteristic specimen dimensions on the bearing strength is discussed, and theories are presented to predict the bearing strength of FMLs based on their constituent materials.

René Alderliesten

Chapter 7. Fatigue Initiation

This chapter explains how fatigue initiation in FMLs can be evaluated and predicted, assuming that the phenomenon primarily affects the fatigue property of the metal constituents. It is illustrated how definition of initiation in the theory enables the utilization of Wöhler failure life curves obtained for the monolithic metal, in combination with stress concentration factors and laminated plate theory. The accuracy of prediction is discussed in relation to the match between the conditions for the adopted Wöhler curves and the predicted conditions. In the end, the theory is related to the application of mechanically fastened joints, where a combination of tension and bending impose different fatigue initiation lives in each individual metal layer.

René Alderliesten

Chapter 8. Static and Fatigue Delamination

The delamination between metal and composite plies in FMLs is discussed for the two major crack opening modes and combinations thereof. The strain energy release rate is introduced as parameter to describe the static and fatigue behaviour, which is influenced by the interface geometry and fibre volume fraction of the composite plies. The relation between constant and variable amplitude loading is discussed. Furthermore it is explained how plasticity of the metal layers affects the quasi-static delamination fracture toughness. Some observations concerning delamination buckling and residual stress state are discussed.

René Alderliesten

Chapter 9. Fatigue Crack Propagation

This chapter explains the fatigue damage growth phenomena in FMLs, and provides theories to describe the growth of damage based on the individual fracture phenomena. The validity of various geometrical correction factors is discussed. The different crack geometries through-thickness and the crack paths, observed in FMLs, are explained for both in-axis and off-axis loading. Finally, the relation between variable amplitude and constant amplitude loading is covered.

René Alderliesten

Chapter 10. Residual Strength

The residual strength in FMLs can be described differently depending on the geometry of the initial damage. Theories and prediction models are presented for through-cut cracks and fatigue through cracks, based on R-curve and critical crack tip opening angle concepts. For part-through cracks, linear relations based on a damage ratio are presented, while for surface cracks a method is presented based on the through-thickness strain distribution, in combination with the corresponding stress concentration factor. In the end the damage tolerance after impact is discussed, explaining how the residual stress state in the plastically deformed dent improves the residual strength.

René Alderliesten

Chapter 11. Effect of Temperature

The influence of the environmental temperature is first discussed with respect to the residual stresses and thermal properties. The second part of the chapter explains how the temperature influences the mechanical and fatigue initiation properties, the delamination and crack growth resistance. It is illustrated how the relation between ambient temperature and constituent properties explains the FML behaviour.

René Alderliesten

Chapter 12. Effect of Environment

The advantageous properties of FMLs with respect to environmental conditions are explained based on the different diffusion characteristics compared to composites. The chapter illustrates how various environments influence the mechanical, fatigue and damage tolerance properties. In this context, the effect of test frequency on the fatigue performance is illustrated.

René Alderliesten

Chapter 13. Acoustic Fatigue

This chapter briefly addresses the typical damping characteristics of FMLs in context of the acoustic fatigue properties. Results of high frequency bending experiments are discussed to illustrate the excellent performance of FMLs with respect to this mode of excitation.

René Alderliesten


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