Dynamic fracture behavior of model sandwich structures with functionally graded core: a feasibility study

Feasibility of introducing compositional gradients to the core of a sandwich structure and the resulting fracture behavior under impact loading conditions is the primary focus of the study. Model sandwich structures comprising of graded core with bilinear variation of volume fraction of hollow microballoons are considered for experimental and numerical simulations. Conventional sandwiches with homogeneous core are also developed for comparison. The crack tip in both configurations is positioned such that global as well as local material characteristics are matched in both models. Dynamic mode-I crack tip deformations are mapped experimentally using optical interferometry and high-speed photography. Measurement of fracture parameter histories is used to demonstrate equivalence between graded and conventional architectures. The fracture behavior in sandwich core is explained using independent experimental results obtained from monotonically graded foam sheets. The measurements up to crack initiation are also used to validate finite element models. The numerical models are subsequently used in a parametric study of different elastic impedance gradients in the core on mixed-mode fracture performance of graded sandwich structures having a crack at the face-sheet/core interface under stress-wave loading conditions. The results show significant reduction in stress intensification in the presence of compositional gradients when compared to conventional constructions.