Rock Dynamic Fracture Toughness Tested with Holed-Cracked Flattened Brazilian Discs Diametrically Impacted by SHPB and its Size Effect

Abstract

Dynamic fracture initiation toughness of marble was tested using two types of the holed-cracked flattened Brazilian disc (HCFBD) specimens, which were diametrically impacted at the flat end of the disc by the split Hopkinson pressure bar (SHPB) of 100 mm diameter. One type of the discs is geometrically similar with different outside diameter of 42 mm, 80 mm, 122 mm and 155 mm respectively, and with crack length being half the diameter; another type of the discs has identical 80 mm diameter and different crack length. Issues associated with determination of the stress wave loading by the SHPB system and the crack initiation time in the disc specimen were resolved using strain gage technique. The stress waves recorded on the bars and the disc failure patterns are shown and explained. The tested dynamic fracture toughness increases obviously with increasing diameter for the geometrically similar HCFBD specimens. It changes moderately for the one-size specimens of identical diameter and different crack length. The size effect of rock dynamic fracture toughness is mainly caused by the fracture process zone length l and fracture incubation time τ, the latter being an additional influencing factor for the dynamic loading as compared with the counterpart static situation. Hence a method is proposed to determine a unique value for the dynamic fracture initiation toughness, the approach takes average of the local distribution and time history for dynamic stress intensity factor in the spatial-temporal domain, which is defined by l and τ jointly. In this way the dynamic size effect is minimized.

The effect of specimen shape and strain rate on uniaxial compressive behavior of rock material

“…30-35). However, only a limited number of studies were conducted to investigate the combined effects of specimen shape and strain rate on the mechanical properties of rock specimens (Bindiganavile and Banthia 2006;Wang et al 2010;Zhang and Zhao 2014). Zhang and Zhao (2014) reviewed the effects of shape on the mechanical properties of rock-like material under dynamic loading (see Table 10, p. 49 for details).…”

Investigation of proper specimen geometry for mode I fracture toughness testing with flattened Brazilian disc method

“…Among the short rod tests, comparing the average fracture toughness values of the smallest 50 mm diameter and the largest 74 mm diameter groups, K Ic value for 50 mm group was approximately 1.2 times lower than K Ic value for 74 mm group. Wang et al (2010) conducted dynamic fracture toughness tests on marble specimens of 42, 80, 122 and 155 mm, the largest size ratio being 3.7 = 155/42. Specimen type was the holed-cracked flattened Brazilian disc (HCFBD).…”

Dynamic Behaviors and Microstructure Evolution of Iron–Nickel Based Ultra-High Strength Steel by SHPB Testing

“…It is assumed that this is mainly caused by the difference in the sample size. The sample size is reduced from Φ4 mm × 4 mm for low strain rate range to Φ2 mm × 2 mm for high strain rate range, so called size effect works [20][21][22].…”

“…Metals 2020, 10, x FOR PEER REVIEW 5 of 14 difference in the sample size. The sample size is reduced from Φ4 mm × 4 mm for low strain rate range to Φ2 mm × 2 mm for high strain rate range, so called size effect works [20][21][22]. Metallographic analysis shows that the microstructure of the samples has no obvious change and remains lath martensites.…”