Effects of substrate materials on fracture toughness measurement in adhesive joints

Abstract

To understand the eects of substrate materials on the fracture behavior of adhesive joints, experimental studies and 2nite element analyses have both been conducted for double-cantilever-beams (DCB) with aluminum andsteel substrates at dierent bondthickness (h). Numerical results show that the region dominatedby the crack singularity is much smaller than by the bondthickness. Very small plastic deformation may hence violate the requirements for small-scale yielding where the crack-tip 2eld can be characterizeduniquely by the stress intensity factor. Both critical strain energy release rate and J -integral for the joints with steel substrate are lower than those for the joints with aluminum substrate. Compared to the critical strain energy release rate, the critical J -integral is less sensitive to the substrate material if small plastic deformation occurs before cohesive failure takes place through the adhesive layer. For the joints with aluminum substrate, the fracture toughness initially increases andthen decreases with bond thickness. Elastic–plastic crack-tip analysis indicates that at the same level of loading, a higher opening stress is observedin the joint with a smaller bondthickness. A self-similar stress 2eldcan be obtained by the normalisedload ing parameter, J=h0. ? 2001 Elsevier Science Ltd. All rights reserved.