The effect of compressive transverse stress on the mode II fracture toughness of composite joints used in structural batteries

Abstract

In the development of structural batteries, achieving optimal performance relies on the effective integration of different materials. Glass fiber Reinforced Polymer (GFRP) can be used as an insulator and structural shell in various types of structural batteries. However, the elastic mismatch with metallic current collectors can lead to interface cracks, compromising the mechanical and electrochemical functionality of the system. In this study, the modified transverse crack tension test is used to measure the mode II interlaminar fracture toughness of GFRP/current collector interfaces, with the current collectors being aluminum and copper. The dominance of mode II loading, using the modified transverse crack tension specimens is verified using the virtual crack closure technique. For the designed configurations, an analytical, closed-form solution to obtain the mode II interlaminar fracture toughness equation is derived, and verified numerically, considering residual thermal stresses and elastic mismatch. The effects of metal surface treatment and transverse pressure on mode II fracture toughness are assessed and compared with untreated samples and an All-GFRP configuration. Digital image correlation technique is employed to accurately identify the onset of crack propagation of each specimen. Additionally, scanning electron microscopy images of the surfaces of the current collectors are taken after debonding to analyze the failure mechanisms. The findings indicate that both compressive transverse stress and Sol–Gel surface treatment are effective techniques for enhancing the mode II interlaminar fracture toughness of hybrid joints in structural batteries.