Several modelling approaches are available in the literature to predict longitudinal tensile failure of ibre-reinforced polymers. However, a systematic, blind and unbiased comparison between the predictions from the different models and against experimental data has never been performed. This paper presents a benchmarking exercise performed for three different models from the literature: (i) an analytical hierarchical scaling law for composite ibre bundles, (ii) direct numerical simulations of composite ibre bundles, and (iii) a multiscale inite-element simulation method. The results show that there are signi icant discrepancies between the predictions of the different modelling approaches for ibre-break density evolution, cluster formation and ultimate strength, and that each of the three models presents unique advantages over the others. Blind model predictions are also compared against detailed computed-tomography experiments, showing that our understanding of the micromechanics of longitudinal tensile failure of composites needs to be developed further.
A modeling approach is presented that recognizes that the residual properties of composite laminates after any form of loading depend on the damage state. Therefore, in the case of cyclic loading, it is necessary to first derive a damage growth law and then relate the residual properties to the accumulated damage.
The propagation of fatigue damage in notched laminates is investigated. A power law relationship between damage growth and the strain energy release rate is developed. The material constants used in the model have been determined in independent experiments and are invariant for all the layups investigated. The strain energy release rates are calculated using a simple finite element representation of the damaged specimen. The model is used to predict the effect of tension-tension cyclic loading on laminates of the T300/914C carbon-fiber epoxy system. The extent of damage propagation is successfully predicted in a number of cross-ply laminates of the form (90i/0j)ns and the quasi-isotropic laminate (90/+45/-45/0)s. The dependence of damage on load amplitude and specimen size is also well described.
Residual strength is calculated as a function of damage dimensions for (90/0)s specimens using a stress-based failure criterion in conjunction with a Weibull dependence of the 0° ply strength on the volume under stress.
The equivalence of quasi-static indentation and low-velocity impact loading regimes has been assessed for composite overwrapped pressure vessels. Test specimens were assessed in detail in terms of the force–displacement response, and micro-focus computed tomography was used for qualitative and quantitative assessment of the associated damage to the constituent materials/interfaces. The results show that the force–displacement response follows an essentially similar pattern between the two loading regimes (within 10% for all cases). Quantitative assessment of the projected composite damage area and permanent deformation of the aluminium substrate as a function of peak indentor displacement also showed a high degree of equivalence between the loading regimes. It is concluded that quasi-static indentation represents a usable analogue for mechanistic assessment of low-velocity impact damage in the tested composite overwrapped pressure vessels.
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