Predicting failure in injection-moulded short-fibre components through fracture mechanics and fractographic validation

• Full-sized components for automotive applications were tested and simulated. • Defects and asymmetries in the skin-core microstructure affected failure processes. • Conventional coupled FEA considering failure initiation only led to errors over 14% • Coupled FEA using cohesive zone modelling predicted failure load within a 0.6% error. • Weldline failure was accurately predicted by FEA using neat resin properties. Injection-moulded short-fibre composites are lightweight materials suitable for high-volume applications. When designing components, it is necessary to predict their ultimate load-bearing capability using Finite Element simulations. However, current methods (based on initiation failure criteria) to simulate components using these materials cannot yet accurately predict ultimate failure. This work applies a newly developed methodology – using a Cohesive Zone Modelling (CZM) to account for the material’s finite toughness – to predict failure of injection-moulded short-glass-fibre reinforced thermoplastic (IM-SFRP) components, based on experimentally measured properties at coupon level. An automotive component, selected from realistic applications in the automotive industry, was tested under quasi-static conditions, and fracture occurred either (i) around the loading area, or (ii) at a weldline. FE simulations of the components, coupled with fibre orientation fields predicted by an injection-moulding process simulation, combined with CZM, were conducted; this used properties measured using dogbone-coupon tensile tests and compact tension tests. These coupled simulations presented excellent agreement with the experimental results in terms of both (a) the peak load (within 2.3% error), and (b) the post-peak sequence of failure events (verified using fractographic analyses). The methodology used in this research can be used to confidently design safer and more efficient IM-SFRP components.