Experimental and numerical investigation on fracture behavior of glass/carbon fiber hybrid composites using acoustic emission method and refined zigzag theory

In this study, damage evolution in glass/carbon fiber hybrid composites with various stacking sequences is investigated under pure bending and tensile loading conditions. Based on the experimental tests results, the hybrid effect and ratio is calculated for all laminates. Damage occurrence is recorded using acoustic emission method and then damage types are classified by means of K-means algorithm. Results show four clusters of acoustic data corresponding to four failure types, i.e., matrix cracking, interface failure, fiber pullout, and fiber breakage. Microscopic images together with the results of acoustic emission data point out that the stacking sequence of hybrid composites becomes a dominant factor for hybrid effect in comparison to volume fraction of carbon or glass fibers under flexural loading. Moreover, the presence of glass layers beneath surface carbon layers causes a level off in acoustic emission activity which is associated with a drop and increase in stress of the stress-strain curve of the flexural test. The experimental tests are numerically simulated through finite element method (FEM) based on refined zigzag theory (RZT). Deformation results of RZT-FEM analysis demonstrate the presence of considerable amount of out-of-plane displacements in the hybrid fiber laminates. This important fact is readily captured during the RZT-FEM simulation, which leads to the interlaminar delaminations observed in the samples under tensile loading. The RZT-FEM results are also validated against the experimental strain-stress results within the linear-elastic region. Finally, the comparison of experimentally and numerically calculated strain-stress curves shows that the onset of the damage inside the material is demarcated as the deviation of experiment results from numerical ones. Remarkably, at this deviation instant, the acoustic emission activity also initiates for both tensile and bending specimens, hence confirming major damage evolution inside the laminates.