An insight into mode II fracture toughness testing using SCB specimen

Abstract

The effect of friction forces between the test specimen and its bottom supports on the mode II fracture toughness values obtained using the semicircular bend (SCB) specimen is investigated. First, a number of experiments were conducted on SCB specimen in order to determine the mode II fracture toughness of polymethyl methacrylate (PMMA) according to the conventional approaches available in the literature. Three different types of supports that have been frequently employed by researchers in recent years were used to evaluate the effect of support type on the fracture loads. It was found that the friction forces between the supports and the SCB specimen have a significant effect on the value of mode II fracture toughness measured using the SCB samples. Then, the specimen was simulated using finite element method for more detailed investigation on the near crack tip stress field evolution when friction forces increase between the supports and the SCB specimen. The finite element results confirmed that the type of support affects not only the stress intensity factors KI and KII but also the T‐stress. The experimental and numerical results showed that the use of the crack tip parameters available in literature for frictionless contact between the supports and the SCB specimen can result in significant errors when the mode II experiments are performed by using the fixed or roller‐in‐grove types of supports.

KIcandKIIcmeasurement for hot mix asphalt mixtures at low temperature: Experimental and theoretical study using the semicircular bend specimen with different thicknesses

“…The predictions of these criteria lie also in the lower and upper band presented in Figure 9 for the tested HMA mixture with the SCB specimen. According to previous works available in the literature, the mode II over mode I fracture toughness ratio depends mainly on the geometry and loading type of the test samples, and this ratio may vary in a wide range typically between 0.4 and 3 (see previous studies [72][73][74][75][76][77][78] ). The main parameter affecting the reduction or enhancement of mode II fracture toughness relative to K Ic in different test specimens is attributed to the sign and magnitude of T stress.…”

Crack tip asymptotic field and K-dominant region for anisotropic semi-circular bend specimen

“…In order to apply mode I loading to the SCB specimen, a vertical precrack, that is collinear with the load, must be machined at the centre of the test sample. When the rock is isotropic, the roller supports are placed in symmetrical spans = S S 1 2 (refer to Bahrami et al [8,37] and Sedighi et al [38] for the necessity of the usage of free-rolling supports in the SCB tests). However, for SCB specimens made of anisotropic rocks that have anisotropy orientation forming an angle°°0 , 90 , asymmetrical support spans are required to enforce mode I loading [19] (see Fig.…”

Crack resistance of fiber‐reinforced asphalt mixtures: Effect of test specimen and test condition

“…Nowadays, several specimens with disc‐shaped geometries (with various loading setups) are used to investigate the fracture behavior of geomaterials subjected to pure mode I and pure mode II 28–30 . Some of these specimens are Brazilian disc (BD) specimen, 31–33 flattened BD specimen, 34 center cracked ring‐shaped specimen, 35,36 which are loaded using diametral compression, and the edge‐cracked semicircular bend disc (SCB), 22,37–40 edge‐cracked cylindrical specimen, 41 and edge‐notched disc bend (ENDB), 42–45 which are tested under three‐point bending load.…”