Scaling effects in the structural response of plain woven composite laminates

Abstract

Obtaining a clear understanding of scaling effects in the mechanical response of composites is an indispensable prerequisite for successful design of load-bearing composite structures. The aim of this research is to investigate scaling effects in the structural response of plain woven composites using a combined experimental and numerical approach, with an emphasis on scaling effects in the load-displacement response, damage mechanisms and energy absorption. In the experimental part of the study, scaled test models have been designed based on the similitude approach, and several sets of tests with different combinations of specimen geometrical shapes (i.e. rectangular beams and square panels) and loading conditions (i.e. low-velocity perforation, low-velocity bending, quasi-static perforation and quasi-static bending) have been conducted for a typical plain woven composite. An examination of the experimental results suggests that the load-displacement response of the composite specimens does not obey simple scaling laws, with the curve increasingly extended (or shrunken) with scale size under perforation (or flexural) loading at both quasi-static and low-velocity rates. Additionally, it has been highlighted that there was no obvious transition in the appearance of damage in all perforation cases, with fibre fracture being the primary failure mechanism and becoming more severe with scale size. Further, it has been analysed that scaling effects in the severity of damage are associated with the discrepancy between the scaling of input energy and that of the energy absorbed during the perforation event. In the numerical part, a multiscale model has been developed to predict the deformation and damage of plain woven composites under low-velocity loadings. The multiscale model includes a unit cell model that describes the geometrical architecture of the woven fabric analytically, aiming to account for the influence of the microscopic features on the macroscopic response. In addition, at the intra-ply scale, the nonlinearity and rate-dependence of polymer matrix are characterised based on a viscoplasticity based model, and the damage evolution of yarn material is evaluated by using a Weibull function based formulation. Further, at inter-ply scale, the initiation and evolution of interlaminar delamination are identified based on the bilinear damage model that has been built in the commercial finite element (FE) software ABAQUS. A user-defined material subroutine implementing the multiscale model has been incorporated into the FE solver ABAQUS/Explicit to simulate the low-velocity perforation and flexural tests. Based on these numerical examples, it has been demonstrated that the proposed model is capable of reasonably predicting scaling effects in the load-displacement response, impact damage and energy absorption of plain woven composites. The significance of this research includes quantitative identifications of scaling effects in the structure response of plain woven composite laminates, and the development of a multiscale model capable of replacing experimental routes for studying scaling effects in plain woven composites.