Rate effects for mixed-mode fracture of plastically-deforming, adhesively-bonded structures

Abstract

Mixed-mode fracture of an adhesively-bonded structure made from a commercial adhesive and a dual-phase steel has been studied under different rates. Since mixedmode fracture occurs along the interface between the steel and adhesive, the cohesiveparameters for the interface were required. The mode-II interfacial properties were deduced in earlier work. In this paper the mode-I interfacial toughness and the mode-I interfacial strength were determined at different rates. The mode-I interfacial strength was not affected by rate up to crack velocities at levels associated with impact conditions, and was essentially identical to the cohesive strength appropriate for crack growth within the adhesive layer. The mode-I toughness was reduced by about 40% when the crack propagated along the interface rather than within the adhesive. Furthermore, transitions to a brittle mode of failure occurred in a stochastic fashion, and were associated with a drop in interfacial toughness by a factor of about five. The mode-I interfacial parameters were combined with the previously-determined mode-II interfacial parameters within a cohesive-zone model to analyze the mixed-mode fracture of the joints which exhibited both quasi-static and unstable fracture. The mixed-mode model and the associated cohesive parameters for both quasi-static and unstable crack propagation provide bounds for predicting the behavior of the bonded joints under various rates of loading, up to the impact conditions that could be appropriate for automotive design. (August 15, 2008) 2

Modelling the fracture behaviour of adhesively-bonded joints as a function of test rate

“…Rate-dependent CZMs have been used extensively to model the fracture of ratedependent materials in general [e.g. [19][20][21][22][23][24][25][26][27][28][29].However, only a few authors have reported the use of rate-dependent CZMs to study the fracture of adhesive joints [15,[30][31][32][33][34][35]. For example, to capture the rate-dependency of failure in adhesive bonds of the double cantilever-beam test specimen, Xuet.…”

“…In both [15] and [35] the cohesive strength was assumed to be equal to the ultimate tensile strength of the adhesive, and its variation with rate was extracted from experimental stressstrain curves obtained at different rates. Sun et al [32][33][34] reported that the mode I properties of the adhesive were almost rate-independent, until the crack velocity increased such that a transition to a brittle fracture occurred. At this transient, the mode I fracture energy dropped almost by a factor of four (i.e.…”

“…15,[32][33][34][35][36]. In order to predict stick-slip behaviour using a FEA CZM approach, Sun et al [32,33] assumed an initial region ahead of the crack tip with a CZM toughness much higher than that in the rest of the specimen (i.e.…”

Assessments for impact of adhesive properties: modeling strength of metallic single lap joints

“…Xu and Y. Wei adhesives for joints [14,18]. The cohesive parameters utilized in the models were obtained from special tests.…”

“…The cohesive parameters utilized in the models were obtained from special tests. For example, the cohesive parameters of mode-I fracture were determined from double cantilever beam (DCB) tests [14,18,19]. Although in some numerical analyses of the SLJ, the adopted parameters of the mixed-mode CZ models were taken from related experimental measurements.…”