Due to the difficulties of applying torsional loads to introduce mode III effects, there are few studies for investigating mixed mode I/III fracture in brittle materials. In this paper using three novel single or double edge-cracked diametral compression disc shape specimens, complete ranges of mixed mode I/III are introduced. Fracture factors of the compressed disc specimens with different pre-notch shapes are determined numerically for a wide range of notch depth and notch inclination angles. The ability of specimens was studied using mixed mode I/III fracture experiments on gypsum. Different fracture envelopes were obtained for the gypsum demonstrating the influence of disc geometry and notch type on mixed mode I/III behavior. For all samples, mode III fracture toughness (K IIIc ) was approximately 1.2 to 1.8 times the corresponding value of K Ic . Depending on the crack front type, ligament shape and mode mixity, different fracture surfaces were observed. While the mode I fracture surface was smooth and flat in all samples, for mixed mode I/III and mode III, rotation and partially segmentation saw tooth shape wrinkles were observed.
K E Y W O R D Sbrittle geo-materials, fracture surface, fracture toughness testing, mixed mode I/III, numerical analyses, single and double edge-notched diametrically compressed discs
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.
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