Prediction of interlaminar stress in composite sandwich joints

Abstract

Volvo Bus Corporation is one of the worlds largest bus manufacturers and has a long history of using traditional construction materials, such as steel and aluminium alloy. In efforts to meet the demands on reduced emissions andmaintained passenger capacity, the company has identified curved composite structures as candidates for weight reductions in future vehicles, where traditional materials today are used. To fully take advantage of the anisotropic properties of composite materials in these applications, new simulation methods able to capture the failure behaviour of these structures are needed. The current study addresses simulation methodologies for capturing the out¡of¡plane loading and failure behaviour of curved composite structures subjected to bending moments. Previously developed modelling strategies are discussed and a solid element simulation methodology is chosen. A benchmarking of available numerical software using a reference case is performed, where Abaqus is chosen as solver moving forward. Numerical models of curved composite beam structures are constructed, along with a physical testing protocol for verification of the numerical models. A set of failure criteria are presented and implemented in the numericalmodels. The methodology development shows that the first hand use solver MSC Nastran can not be used with the available pre and post processors for solid elementmodels where orthotropic material models are used. Results from the numerical simulations using Abaqus show that all beam models without a sandwich design, as well as one beam model with a sandwich design, fail in an out¡of¡plane matrix interface delamination mode. Two further sandwich beam models predict failure in an in¡plane matrix mode, subject to transverse tensile loading of 90° plies. The physical testing shows that failure is not initiated in the junction between the foam core and upper/lower laminate facings, and that the numerical models are somewhat accurate but too stiff. The results are discussed and future work based on the developed solid element simulation strategy is suggested.