Mathematical modeling of the eddy current testing of delamination cracks in multilayer CFRP objects

We propose an approximate mathematical model making it possible to obtain estimates of the change in the eddy current signal under the influence of delamination in multilayer carbon fiber reinforced plastic (CFRP) objects. We give the dependences of the change in the eddy current signal on delamination in the CFRP objects for a new flaw detection method based on the comparison of eddy current signals from CFRP layers grouped by angular orientation.

Progressive failure analysis of CFRP composite laminates under uniaxial tension using a discrete element method

This study presents a 3D Discrete Element Method (DEM) model for the progressive failure analysis of Carbon Fiber Reinforced Polymer (CFRP) composite materials subjected to uniaxial tensile loading. Particles in the model are packed and bonded in regular patterns (hexagonal or square). The relationship between the bond stiffness and material properties is established based on the average strain energy method. The random distribution of bond strengths calibrated from experiments with a variation of 30% and 10% following a normal distribution law is assigned to the bonds in 0∘ and 90∘ plies to capture random cracks, respectively. Tsai-Hill failure criterion is utilized for the calibration of bond strength of [Formula: see text] plies to predict their failures in composite laminates. Quantitative and qualitative analyses were conducted for predicting the damage initiation and propagation of the cross-ply and Quasi-Isotropic (QI) composite laminates under tensile loading, respectively. Two interface stiffnesses were utilized in the failure prediction of cross-ply composite laminates, and it was found that the numerical results with the interface stiffness calculated from fracture energy are in good, quantitative agreements with the experiments. All the four stages of the failure process of QI composite laminates are well captured by the 3D DEM model, including isolated cracks, inner delamination cracks, outer delamination cracks and final failure.

The effects of voids in quasi-static indentation of resin-infused reinforced polymers

The focus of this study is the influence of voids on the damage behaviour in quasi-static loading of resin-infused carbon fibre-reinforced polymers. Experimental results are presented for quasi-static loading in combination with high-resolution tomographic imaging and statistical analysis (homology of pores or voids and induced cracks). Three distinct mechanisms were observed to control delamination growth in the presence of sharp and blunt voids. Delamination cracks interact with the supporting yarns, especially in combination with air pockets trapped in the resin in the form of long, sharp voids. This resulted in crack growth that coalesces with delamination cracks from neighbouring yarn-voids during increased out-of-plane load–displacement, with almost no presence of intralaminar transverse cracks. This highlights the benefits and drawbacks of the supporting yarn during out-of-plane loading.