Mixed Mode I/II Fracture Analysis of Bi-Material Adhesive Bonded Joints Using a Novel Short Beam Specimen

Abstract

Until now, some test specimens with different shapes and loading mechanisms have been utilized for investigating the cracking behavior of adhesive bounded joints. In this research, using a novel test configuration called adhesive short bend beam specimen containing an inclined crack and loaded by three-point bending, mixed mode I/II fracture parameters of a crack initiated in the adhesive part is studied. Compared to other test methods, the specimen used in this research needs a lesser amount of material and the fracture test can be performed easily. A large number of finite element models of this specimen were analyzed using ABAQUS code to study the effect of adhesive and adherent type, and also the crack length and loading span distance on KI, KII, T-stress and fracture initiation direction under different mode mixities. The results showed that the fracture parameters (and in particular the shear mode component) are sensitive to the type and location of adherent in the bounded joint; however, the shape and size of fracture plastic zone is not affected noticeably by the type of adhesive-adherent materials. It was also shown that the complete mode mixities ranging from pure mode I to pure mode II can be introduced for adhesive bounded joints using the proposed test specimen and therefore the specimen is a good candidate test configuration for investigating the mixed mode I/II fracture behavior of adhesive bounded joints.

On the use of different diametral compression cracked disc shape specimens for introducing mode III deformation

“…In general, a positive T stress in a cracked specimen increases the mixed mode I/III fracture toughness and conversely negative sign of T stress decreases the mixed mode I/III fracture resistance 70 . However, compared to many other mixed mode fracture test specimens employed in several papers (that the absolute values of Biaxilaty ratio are higher than 1.5 65–67 ), the magnitude of Biaxiality ratio in the analyzed ENDC, DNDC, and UNDC specimens is not very significant demonstrating the lesser importance of nonsingular terms (such as T stress) relative to the effect of singular terms (SIFs). Therefore, by considering only the SIFs ( K I and K III ), the mixed mode I/III fracture behavior of the mentioned samples can be investigated and described with sufficient accuracy from the engineering viewpoint.…”

“…This parameter is dominantly negative in all three test specimens and its value varies between zero and −0.8 when moving from pure mode III towards pure mode I. According to the well‐known literature available for mixed mode fracture problems, 65–69 the influence of T stress in fracture process of cracked bodies becomes more important when the absolute magnitude of B i is large enough. In general, a positive T stress in a cracked specimen increases the mixed mode I/III fracture toughness and conversely negative sign of T stress decreases the mixed mode I/III fracture resistance 70 .…”