【企画講演／招待講演】 岩石や岩盤における変形・破壊の時間依存性

[3K0201-04-04] Strain-rate Dependent Dynamic Fractures in Rock Materials

○Sangho Cho¹、Gyeongjo Min¹、福田 大祐² (1. Jeonbuk National University(Republic of Korea)、2. 北海道大学)

司会：藤井義明（北海道大学）

キーワード：Dynamic rock fracture 、High strain rates、Loading rate effect 、3-D dynamic fracture process analysis(DFPA)、Fracture strength anisotropy

Rock fracture properties exhibit clear differences between the static and the dynamic loading conditions which leads to certain issues. The dynamic tensile strength of rock exceeds the static tensile strength by 6–10 times. In an attempt to explain this, the weakest part of rock may not have sufficient opportunity to be of concern in the fracturing process at high strain rates. The spalling test and the numerical method to investigate the strain rate dependency of the rock dynamic tensile strength. It was revealed that multiple small cracks were generated at the stress intense area under the dynamic loading state, while few large cracks were generated along the weak parts of the rock specimen under static loading. The strain rate dependency of tensile strength is closely connected to rock inhomogeneity. Recently, more studies have investigated the loading rate dependency with regard to rock anisotropy.
This study was performed to investigate the loading rate effect on fracture strength anisotropy with a focus on the fracture mechanism and to apply compression, spall tension, fracture toughness testing on a dynamic SHPB system. In addition, a three-dimensional dynamic fracture process analysis (3D-DFPA) method, based on the combined finite–discrete-element method (FDEM), was developed to reproduce the high strain-rate fracture behavior of a geomaterial subjected to impact loading. The 3D-DFPA method simulates the dynamic fracturing of a geomaterial by modeling the propagation of stress waves, crack initiation and propagation, and contact among fracture surfaces or fragments. The important issues for dynamic rock fracturing (such as the loading-rate dependency of anisotropic rock, fracture behavior of rock under impact loading, size effect of dynamic rock fracture in numerical analysis, and reinforcement element insertion code for simulating the collapse of a reinforced structure) are discussed with several examples to clarify the application of the developed numerical analysis method.