Modes I and II interlaminar fracture toughness and fatigue delamination of CF/epoxy laminates with self-same epoxy interleaf

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Methods for the prediction of fatigue delamination growth in composites and adhesive bonds: A critical review

Mode I delamination fatigue properties of interlayer-toughened CF/epoxy laminates

Engineering structures are often subjected to the conditions of cyclic-loading, which onsets material fatigue, detrimentally affecting the service-life and damage tolerance of components and joints. Carbon fibre reinforced plastics (CFRP) are high-strength, low-weight composites that are gaining ubiquity in place of metals and glass fibre reinforced plastics (GFRP) not only due to their outstanding strength-to-weight properties, but also because carbon fibres are relatively inert to environmental degradation and thus show potential as corrosion resistant materials. The effects of cyclic loading on the fatigue of CFRP are detailed in several papers. As such, collating research on CFRP fatigue into a single document is a worthwhile exercise, as it will benefit the engineering-readership interested in designing fatigue resistant structures and components using CFRP. This review article aims to provide the most relevant and up-to-date information on the fatigue of CFRP. The review focuses in particular on defining fatigue and the mechanics of cyclically-loaded composites, elucidating the fatigue response and fatigue properties of CFRP in different forms, discussing the importance of environmental factors on the fatigue performance and service-life, and summarising the different approaches taken to modelling fatigue in CFRP.

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The fatigue of carbon fibre reinforced plastics - A review

The fatigue life behaviour and the underlying micromechanisms have been studied in two different Types of unidirectional carbon-fibre-reinforced plastics loaded in tension-tension along the fibre direction. The carbon fibres (AS4) were the same in the two composite systems. One thermoplastic matrix (polyetheretherketone, PEEK) and one thermosetting matrix (epoxy toughened with a thermoplastic additive) were used. The macroscopic fatigue behaviour was characterised by fatigue life diagrams. Surface replicas were taken intermittently during the course of the fatigue tests to monitor the active fatigue damage micromechanisms. The thermoset based composite showed a higher fatigue resistance with few microcracks initiated at distributed fibre breaks growing at a decelerating rate. The thermoplastic composite had a more pronounced fatigue degradation with a steeper fatigue life curve, which was caused by widespread propagating debonds and matrix cracks. The use of a tougher and more ductile matrix results in an inferior fatigue life performance, due to a more widely distributed accumulation of damage that propagates at a higher rate.

Fatigue damage mechanisms in unidirectional carbon-fibre-reinforced plastics

Effect of matrix resin on delamination fatigue crack growth in CFRP laminates

The influence of friction on the compliance and crack work release rate of an end notched flexure (ENF) specimen is investigated. The analysis includes asymmetric ENF configurations (i.e., when the crack is not on the specimen center line). The contact problem (i.e., the problem of determining the contact stress distribution between the cracked parts of the specimen) is solved using the assumption that Euler beam theory is applicable (i.e., transverse shear is not accounted for) and that friction is fully developed whenever acting. The numerical results from an analysis carried out on a realistic specimen geometry indicate that for this model the friction has a minor influence on both the compliance and the crack work rate.

The Influence of Friction on the Compliance and Crack Work Rate of an End Notched Flexure Specimen

The effect of the stress ratio on the near-threshold growth of delamination fatigue cracks was investigated with unidirectional laminates made from ICI APC-2 thermoplastic prepregs (AS4/PEEK). Tests were carried out under mode I opening loading by using double cantilever beam specimens. The crack growth rate under different stress ratios was a unique function of the equivalent stress intensity range proposed by the authors. The fatigue crack growth rate near the threshold was mainly controlled by the stress range rather than by the maximum stress. The resistance of CF/PEEK laminates against fatigue crack growth was much higher than that of conventional CF/epoxy laminates even near the threshold region. This increase of resistance, however, was smaller than that of fracture toughness. The difference in growth behavior between CF/PEEK and CF/epoxy laminates was discussed on the basis of the mechanism consideration.

Claes-Göran Gustafson

Papers

Effect of matrix resin on delamination fatigue crack growth in CFRP laminates

The Influence of Friction on the Compliance and Crack Work Rate of an End Notched Flexure Specimen

Propagation of delamination fatigue cracks in unidirectional cf/peek laminates