How Pure Mode I Can Be Obtained in Bi-Material Bonded DCB Joints: A Longitudinal Strain-Based Criterion

Abstract

An essential question to predict the structural integrity of bi-material bonded joints is how to obtain their fracture properties under pure mode I. From open literature, it is found that the most commonly used design criterion to test mode I fracture is matching the flexural stiffnesses of the two adherents in a DCB coupon. However, the material asymmetry in such designed joints results in mode II fracture as well. In this paper, a new design criterion is proposed to obtain pure mode I fracture in adhesively bonded bi-material DCB joints by matching the longitudinal strain distributions of the two adherends at the bondline - longitudinal strain based criterion. A test program and Finite Element modelling have been carried out to verify the proposed design criterion using composite-metal bonded DCB joints. Both the experimental and numerical results show that pure mode I can be achieved in bi-material joints designed with the proposed criterion. GII/GI ratio is reduced by a factor of 5 when using the proposed longitudinal strain based criterion in comparison with the flexural stiffness based criterion.

Sofia Teixeira de Freitas

Principal Investigator

Sofia Teixeira de Freitas researches the structural integrity of bonded and layered materials to enable durable, sustainable structures. She is also an accredited group facilitator, committed to building academic environments grounded in cooperation and inclusion—key to overcoming technological limits and addressing the challenges of a truly sustainable society.