Transverse cracking and delamination in cross-ply glass-fiber and carbon-fiber reinforced plastic laminates: Static and fatigue loading

Understanding damage and failure of composite materials is critical for reliable and cost-effective engineering design. Bringing together materials mechanics and modeling, this book provides a complete guide to damage, fatigue and failure of composite materials. Early chapters focus on the underlying principles governing composite damage, reviewing basic equations and mechanics theory, before describing mechanisms of damage such as cracking, breakage and buckling. In subsequent chapters, the physical mechanisms underlying the formation and progression of damage under mechanical loads are described with ample experimental data, and micro- and macro-level damage models are combined. Finally, fatigue of composite materials is discussed using fatigue-life diagrams. While there is a special emphasis on polymer matrix composites, metal and ceramic matrix composites are also described. Outlining methods for more reliable design of composite structures, this is a valuable resource for engineers and materials scientists in industry and academia.

/pdf/damage-and-failure-of-composite-materials-2912ppxkug.pdf

Damage and Failure of Composite Materials

Analytical modeling of stiffness reduction in symmetric and balanced laminates due to cracks in 90° layers

Auxetics are a modern class of material fabricated by altering the material microstructure. Unlike conventional materials, auxetics exhibit a negative Poisson's ratio when subjected to tensile loading. These materials have gained popularity within the research community because of their enhanced properties, such as density, stiffness, fracture toughness and dampening. This paper provides a critical oversight of the auxetic field with particular emphasis to the auxetic foams, due to their low price, easy availability and desirable mechanical properties. Key areas discussed include the fabrication method, the effects played by different parameters (temperature, heating time, cell shape and size and volumetric compression ratio), microstructural models, mechanical properties and potential applications

A review of the manufacture, mechanical properties and potential applications of auxetic foams

Tensile fatigue of conventional and negative Poisson’s ratio open cell PU foams

The purpose of the paper is to investigate the transverse cracking of cross-ply laminates, subjected to uniaxial tensile loading. For quasi-static tests, most cracks, initiated in the 90° plies, instantaneously cross the entire test specimen width from edge to edge. In this case, the investigation of transverse cracking is reduced to a two-dimensional analysis. A finite element analysis has been implemented and the paper compares the results obtained by finite element analysis and analytical models. These comparisons show that a complete parabolic shear-lag analysis yields a fairly good approximation of the strain and stress distributions obtained by finite element analysis. The results deduced from this analytical model and from finite element analysis, for the longitudinal stiffness reduction as a function of the crack density, are in good agreement with the experimental results obtained for various cross-ply laminates. The complete parabolic shear-lag analysis is then used to develop a statistical damage accumulation process.

Transverse cracking of cross-ply laminates : Part 1. Analysis

Modelling the flexural behaviour of sandwich composite materials under cyclic fatigue

Within an experimental approach we describe the mechanical behavior of different resin-epoxy laminates reinforced with cross-ply Kevlar and glass fibers under conditions of static and cyclic three-point bending. In static tests, we consider the effect of stacking sequence, the thickness of 90°-oriented layers, reinforcement type on the mechanical behavior of laminates under loading and on realization of various damage modes leading to rupture. Cyclic loading studies have been performed in two steps. In the first stage, we inquire into the dependence of the behavior and durability of four glass fiber-reinforced laminate-types on the stacking sequence; the second stage is devoted to studying the dependence of cyclic strength and fatigue behavior of laminates on the reinforcement type. Fatigue tests are carried out in load-control regime for glass and hybrid (Kevlar + glass) fiber laminates. Fatigue curves are constructed in coordinates “stress – number of cycles until fracture” from the criteria corresponding to a drop in stiffness by 5 and 10%. Analysis of the results obtained permits evaluation of the effect of the stacking sequence and the reinforcement type on the behavior of cross-ply laminates in cyclic loading. The presence of Kevlar fibers accounts for nonlinear behavior of laminates in static tests and for low cyclic strength in fatigue tests under three-point bending.

Flexural Fatigue Behavior of Cross-Ply Laminates: An Experimental Approach

The analysis of stiffness and the identification of rupture mechanisms during and after static tests of sandwich panels and their components have been investigated. The sandwich panels, having cross-ply laminates skins made of glass fibre and epoxy resin were manufactured by vacuum moulding and subjected to three-point bending tests. Two polyvinyl chloride cores of similar type but with differing densities were investigated. The effect of core density and its thickness on the behavior and the damage was highlighted. In terms of stiffness and load at failure, the sandwich structure has better mechanical characteristics compared to its components.

/pdf/experimental-analysis-of-behavior-and-damage-of-sandwich-58jhlrmnxy.pdf

Experimental analysis of behavior and damage of sandwich composite materials in three-point bending. Part 1. Static tests and stiffness degradation at failure studies

A. El Mahi

Papers

Transverse cracking of cross-ply laminates : Part 1. Analysis

Modelling the flexural behaviour of sandwich composite materials under cyclic fatigue

Flexural Fatigue Behavior of Cross-Ply Laminates: An Experimental Approach

Experimental analysis of behavior and damage of sandwich composite materials in three-point bending. Part 1. Static tests and stiffness degradation at failure studies

Development of transverse cracking in cross-ply laminates during fatigue tests