Development of Novel Techniques to Characterize the Traction-Separation Responses of Delamination in Fibre-Reinforced Plastic Laminates

Abstract

Fibre-reinforced plastic (FRP) composite laminates are a compelling class of materials for crash-resistant automotive structures owing to their excellent specific energy absorption and damage tolerance characteristics. However, the widespread adoption of FRP laminates in load-bearing structures requires accurate modelling of progressive damage under mechanical loading, including interlaminar delamination. Current experimental techniques cannot fully parameterize numerical techniques such as cohesive zone modelling (CZM), which represents the delamination interface using traction-separation responses. This thesis aimed to develop experimental tests to measure the Mode I and Mode II/III traction-separation responses of delamination in a unidirectional E-glass/epoxy (UE400/REM) FRP laminate for use in CZM.

A novel composite rigid double cantilever beam (cRDCB) Mode I test specimen was developed to assess delamination response using metallic adherends co-cured to the FRP laminate. The cRDCB and analysis procedures developed in this work enabled direct assessment of the Mode I traction-separation response. The measured cRDCB traction-separation response was verified by accurately modelling the cRDCB test and validated by modelling the double cantilever beam test.

Two specimen geometries were developed to measure the Modes II and III traction-separation response under shear loading. The Mode II composite rigid shear (cRS) specimen demonstrated excellent sensitivity to damage onset and early damage propagation but was limited in assessing the unload response due to the high stiffness of the specimen. The Mode III composite rigid Mode III (cR3) specimen progressively loaded the delamination interface, providing a more reliable technique for assessing damage behaviour response. Traction-separation responses were extracted using a physics-informed inverse technique, providing a promising method to characterize delamination shear response.

The primary contribution of this work was new experimental specimens and associated analysis procedures that provided complete traction-separation curves for CZM, validated using computational models of contemporary test specimens. The properties measured with the proposed specimens have applicability in a range of current and future modelling techniques and can be used to inform the development of FRP laminate automotive structures.