Identification of Interlaminar Nonlinear Shear Properties for VARI-Manufactured Carbon Fabric Laminates

Abstract

This paper proposes an experimental approach based on the modified short-beam shear (SBS) test, combining digital image correlation (DIC) and finite element model updating (FEMU) to identify the nonlinear interlaminar shear constitutive parameters of carbon fabric/toughened epoxy composite laminates. Based on assumed initial material constitutive behavior, this method constructs an objective function using the variance between DIC-measured strains and FE-computed strains, and performs iterative updates within the finite element model to retrieve nonlinear interlaminar shear constitutive parameters upon convergence. Since the adopted loading configuration of specimens approximates a statically determinate structure, the stress distribution on the specimen surface exhibits weak dependence on the material constitutive relations and their parameters. The aforementioned iterative process is further transformed into identifying the trial interlaminar shear constitutive relations and corresponding parameters via least-squares regression between FE-calculated stresses and DIC-measured strains. The feasibility of the proposed identification method for characterizing nonlinear interlaminar shear properties is verified. Other constitutive parameters can be identified by flexibly selecting different high-strain regions. Accordingly, this method possesses the following merits: no explicit sensitivity matrix targeted at the identified parameters needs to be formulated during iteration, leading to high identification efficiency; the identification procedure is insensitive to the initial approximations of material constitutive parameters.