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• The influence of high temperature on the physical parameters of sandstone was investigated. • The effects of high temperature on the DIT and DPT of sandstone were explored. • The dynamic fracture mechanism of sandstone after high temperature treatment was discussed. High temperatures are a crucial factor in the drilling of rock and the extraction of geothermal resources, to investigate the change rules of the dynamic fracture mechanism and physical parameters of sandstone under high temperature environment, this study conducted a series of physical parameter measurements on the sandstone treated in a range of temperatures (room temperature to 700 °C) using large single cleavage semicircle compression (LSCSC) sample. According to the experimental results, it can be observed that 400 °C is the threshold for the variation of the physical parameters of sandstone. The mass, P-wave velocity, S-wave velocity, elastic modulus and Poisson' ratio have a significant downward trend with the temperature. The main mineral components of sandstone undergo thermochemical reactions and the variation of quartz is a fundamental cause for the deterioration of sandstone. The dynamic loading test was conducted using a drop hammer impact device and the fractured sample, the dynamic fracture test results indicate that the dynamic crack initiation time (CIT) of the samples is advanced with the temperature, but the crack speed and dynamic fracture toughness decreased with the temperature. Further discussions about SEM images and fractal box dimension of fracture surfaces can be found that with the temperature increases, the proportion of intergranular fractures of sandstone gradually increases, the effect of dynamic loads changes from destroying the grain structure of sandstone to orderly coalescing the micro-cracks in the sandstone. [ABSTRACT FROM AUTHOR]

• An Improved Single Cleavage Semicircle Compression specimen were proposed. • The whole process of crack propagation from macro and micro was analyzed. • The influence mechanism of interlaced holes on crack propagation was analyzed. • The holes affect the crack propagation by the re-release of deformation energy storage. Hole defects are common defects in natural materials, which obviously affect crack propagation. In this paper, an Improved Single Cleavage Semicircle Compression specimen made from polymethyl methacrylate with a pre-crack and two holes were used. In order to analyze the influence of the interlaced holes on crack propagation, a series of dynamic experiments were carried out utilizing the Split-Hopkinson pressure bar system with crack propagation gauges. In addition, the influence mechanism of interlaced holes on crack propagation was studied by numerical simulation. A good agreement was achieved between the simulation and experimental results. It was concluded that interlaced holes have a restraining and guiding effect on crack propagation. As the distance between two holes increases, the effect becomes weak. Under the action of stress waves, the two interlaced holes deform and form a pressure zone when the crack passes through the hole area. The phenomenon of crack arrest and crack deflection depends on the asymmetric distribution of the pressure zone. [ABSTRACT FROM AUTHOR]

• Crack parameter test meter was applied in crack propagation speed calculation. • A large specimen with tunnel was used to calculate rock dynamic fracture toughness. • The crack growth behavior outside the roadway under different impact loading directions was studied. • Stress wave and fracture mechanics theories were used to explain the interaction mechanism between cracks and tunnel. The backfilling of the tunnel is crucial for the stability of the goaf. To investigate the differences in crack propagation behavior before and after tunnel backfilling under different impact directions, a large rectangular plate LSCSC model was conducted. A crack parameter test meter was used to monitor the crack expansion behavior of pre-cracks under dynamic load in real time. Subsequently, the AUTODYN and ABAQUS software were used to simulate the crack propagation path and dynamic fracture toughness, and the following conclusions were obtained. The presence or absence of tunnel backfilling does not affect the crack propagation path, and the primary critical areas of the surrounding rock remain essentially the same. But have significant influences on crack propagation speed and fracture toughness. After backfilling, the crack propagation speed decreases significantly, and there is a noticeable crack-stopping phenomenon during the interconnection process. In addition, the influence of different wave impedance materials on the fracture behavior of cracks varies. In the selected filling material used in this paper, the initiation fracture toughness of the cracks increases by 45 %, and the average propagation toughness increases by 50 %. [ABSTRACT FROM AUTHOR]

A coupled material point model (MPM) based on the asymmetric generalized interpolation material point (aGIMP) and the tetrahedron convected particle domain interpolation (CPDI-Tet4) was established to simulate the dynamic splitting of a rock Brazilian disc under small deformation. Furthermore, a boundary-based contact algorithm was developed to accurately describe the contact force between the split bar's aGIMP particles and the rock's CPDI-Tet4 particles. The proposed aGIMP technology enabled particles to move on a non-uniform background grid by changing the original basis functions. A good simulation effect was achieved. It was concluded that the rock particle size plays an important role in the accuracy of the contact algorithm. Two shear failure bands were generated near the contact zones first after the rock specimen reached the force equilibrium state, and then the four arc fracture surfaces grew from the two sides of the shear failure bands and coalesced to a radial fracture surface on the mid-cross section of the specimen. In addition, the tensile strength calculated by the MPM model exhibited the typical rate effect of rock material and was slightly lower than the practical tensile strength of the particle on the radial fracture surface. [ABSTRACT FROM AUTHOR]

Although many mechanical responses of rock-like material subjected to dynamic loads can be simulated by commonly-used material models, it's still hard to accurately describe the interactive mechanism of tensile and shear damages caused by different kinds of loads. This paper presents a novel constitutive model with three smooth failure strength surfaces and three invariants. The new model can precisely and quantitatively capture the damage mechanisms of hydrostatic pressure based on test data and the interaction of the tensile and shear damages based on the Mohr-Coulomb criterion. Then, the new model is implemented into LS-DYNA, and a series of numerical validations, e.g. TXC, UUC, and UUT tests at single element, SHPB tests, rock blast test, and projectile penetration, are conducted. A satisfactory agreement between the numerical predictions and experimental data shows the suitability and accuracy of the present model for rock-like material under dynamic impact and blast loads. [ABSTRACT FROM AUTHOR]

• The influence mechanism of the circular hole on crack propagation behaviour was studied. • The cause for the turning point during crack propagation was analyzed using AUTODYN software. • The effect of the circular hole on the dynamic propagation toughness (DPT) was measured. • The dynamic fracture toughness versus crack speeds were analyzed. Hole defects and crack defects usually coexist in a real engineering rock masses, they together affect the structural security of rock masses. With the purpose of investigating the effect of circular hole on crack initiation and propagation process under dynamic loads, a circular opening specimen with straight crack cavity (COSSCC) model was proposed in this study and polymethyl methacrylate was chosen to make the specimens. A series of dynamic experiments were carried out utilizing a drop hammer impact test system (DHITS), crack speeds and crack initiation time were determined utilizing crack propagation gauge (CPG). The maximum principal stress field evolution in the crack evolution process was simulated using a modified finite element difference method software, and dynamic fracture toughness was calculated by a traditional finite element method software. Some significantly conclusions can be obtained: As the inclination angle θ of the circular hole is less than 10o, crack propagation trajectories will propagate to the surface of the circular hole; As the inclination angle θ of circular hole is 20o and 30o, crack propagation trajectories will turn in the direction of circular hole but not reach the circular hole; As circular hole inclination angle θ is 40o and 50o, the crack shows a pure mode I crack propagation. As crack propagates near the circular hole, crack propagation speeds increase significantly. The dynamic propagation toughness during crack propagation is not constant and is less than dynamic initiation toughness (DIT) and the dynamic propagate toughness (DPT) is inversely proportional to the crack speeds. [ABSTRACT FROM AUTHOR]