Modelling of interfacial morphology formation driven by thermal and hydrodynamic instabilities in injection overmoulding of fibre reinforced polymer composites

Composite injection overmoulding offers a cost-effective and repeatable method for manufacturing complex composite structures. However, accurately predicting the strength of the interface between subcomponents remains a significant challenge, particularly for load-bearing applications. This difficulty mainly arises from the multiscale nature of interface formation. This study presents a combined numerical and experimental investigation into the formation of a complex interface morphology at the microscale. A multiscale CFD framework was developed to simulate transient heat and momentum transfer in a two-component composite system, composed of polyetheretherketone (PEEK) overmoulded onto a carbon fabric reinforced polyphenylene sulfide (PPS) laminate. Two interface configurations, differentiated by surface resin depth, are examined. The simulations reproduce key morphological patterns observed at the microscale, which are shown to arise from hydrodynamic instabilities, including Kelvin–Helmholtz and Richtmyer–Meshkov. The numerical results are validated against scanning electron microscopy (SEM) observations, providing a link between interfacial transport phenomena and the resulting structural morphology. The study demonstrates how local thermal gradients and shear-induced effects contribute to resin penetration and surface patterning at the interface in addition to local temperature. As interface temperature is a critical factor in healing-based models of interface strength, these findings underscore the potential of microscale simulations to predict temperature profiles and explain the formation of weld-line features. These predictions ultimately inform the design of stronger, more reliable overmoulded composites and are also of interest for researchers working on thermal–fluid transport, multiphase polymer flows, and interface dynamics in advanced manufacturing contexts.<br/><br/>