Determination of the mode I crack tip opening rate and the rate dependent cohesive properties for structural adhesive joints using digital image correlation

The present work addresses two key issues relating to the study of rate effects in adhesively bonded joints. Firstly, the accurate determination of the crack tip strain rate and secondly the accurate determination of cohesive zone length. The rate-dependent fracture behaviour of adhesive joints bonded with either a toughened epoxy or a ductile polyurethane adhesive was investigated under mode I loading rates ranging from 0.1 mm/min to 1.0 m/s with digital image correlation (DIC) analysis. The traction-separation laws (TSLs) were determined by measuring the J-integral values and the crack tip opening displacements simultaneously. An analytical method is proposed to correlate the crack tip opening velocity with the external loading rate. The lengths of the cohesive zones were measured, and the values were compared with results obtained from thickness-independent and -dependent models. The cohesive properties of the two adhesives exhibited very different rate dependences. The analytical tool developed using the DIC approach successfully determines the strain rates for the TSLs investigated. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study focuses on two key issues related to rate effects in adhesively bonded joints: the accurate determination of crack tip strain rate and cohesive zone length. Experimental results show that the cohesive properties of the two adhesives exhibit different rate dependences, while the DIC method developed successfully determines strain rates for the investigated TSLs.