Flexural behaviours and heterogeneous interface fracture in overmoulded multi-material thermoplastic composites

Abstract

The development of lightweight multi-material composites is imperative to meet the demands of the aerospace and automotive industries. Thermoplastic-based multi-material composites represent a novel approach, wherein two or more distinct composite materials are combined to create a hybrid material with enhanced performance characteristics. However, varying failure modes across multi-scale interfaces in the composites affect their mechanical performance in a complex manner. In this study, multi-material composites were manufactured through overmoulding of virgin polycarbonate (VP) and short-fibre reinforced polycarbonate (SFP) on continuous fibre-reinforced thermoplastic polycarbonate (CFRTP) laminate to assess behaviours of heterogeneous interfaces and structural performance under flexural loading. In the compression overmoulding process, the consolidation of thermoplastics creates interdiffusion of polymer chains across the multi-material interfaces. The multi-material composites successfully demonstrated enhanced flexural properties compared to single material constituent such as VP, SFP, and CFRTP. Benchmarking with CFRTP composite laminates, results revealed that overmoulding SFP on CFRTP results in 319 % higher flexural strength and 36 % higher of flexural modulus. VP/CFRTP composite offered 103 % more flexural strain and 175 % more specific energy absorption during fracture. Strategic optimization of the neutral axis (NA) and integration of high modulus materials in multi-material systems contributed to such performance enhancements. Failure analysis conducted using optical microscope and scanning electron microscopy (SEM) revealed progressive heterogeneous interface fracture and crack propagation in the CFRTP laminate layer. Results indicated that control of interface failure modes need to be considered in multi-material structure design to achieve desired flexural strength.