Experimental and numerical studies on dynamic crack growth in layered slate rock under wedge impact loads: part I—plane strain problem

Abstract

A B S T R A C TThe experimental and numerical investigations presented in this paper were carried out to determine the splitting forces and crack propagation scenarios of naturally bedded layered slate rock. Splitting loads were determined by impact splitting of regular-sized slate blocks under plane strain test loading conditions, using a hydraulic actuator with a wedge-shaped indenter. The mechanical properties of slate blocks required for numerical analyses were obtained from detailed experimental testing. The velocity of dynamic crack propagation in slate blocks under indenting wedge impact loading was determined using a series of strain gauge sensors. Numerical studies were carried out using ABAQUS, a general purpose, finite element analysis (FEA) program. Mode I dynamic crack propagation was simulated numerically by the gradual releasing of the restrained node on the symmetric plane of the specimens. Mode I stress intensity factors were computed for different crack lengths and the results were compared with the plane strain material fracture toughness obtained from earlier experiments/FEA. Very good agreement was obtained between analysis results and the measured fracture toughness value of slate, for the applied impact splitting load. Using the equation derived from a parametric study, of results obtained from the numerical analysis of different sizes of slate blocks, the maximum theoretical impact splitting force was determined using the plane strain fracture toughness value obtained from FEA. The difference between the loads obtained from the experimental studies and the derived empirical equation, varied between + 4.96% and −32.34%.Keywords Dynamic crack propagation-finite element analysis-fracture toughnessimpact splitting-slate-stress intensity factor-wedge-shaped indenter. I N T R O D U C T I O NIn order to quarry layered rocks such as slate, schist, sandstone, coal, etc., from a mine, blasting procedures using detonating materials have been used for a long time. Because blasting degrades a major portion of the virgin rock and makes the major portion of the resulting products unusable for high cost construction procedures, other mechanical procedures have also being recently used to get an efficient and economic form of excavation. 1-4 Mechanical procedures in rock extraction are advantageous over blasting for enhancing the continuity of operations, clean-cut excavation profile, safety and minimum wastage. A recent

Study of mode I crack dynamic propagation behaviour and rock dynamic fracture toughness by using SCT specimens

“…The study on crack dynamic propagations of rock has been performed by several researchers, and a large progress has been achieved by using SHPB test systems . Meanwhile, several new methods have been developed, such as experimental‐numerical method and the high‐speed photography method .…”

Experimental and numerical investigation of cracked chevron notched Brazilian disc specimen for fracture toughness testing of rock

“…For rock materials, crack propagation can be easily induced by mode I loading; thus, most studies of rock fracture toughness focus on mode I . Particularly, four different laboratory test methods have been successively recommended by the International Society for Rock Mechanics (ISRM) to quantify K Ic of rock, including chevron bend (CB) method, short rod (SR) method, cracked chevron notched Brazilian disc (CCNBD) method, and semicircular bend (SCB) method .…”

“…For rock materials, crack propagation can be easily induced by mode I loading; thus, most studies of rock fracture toughness focus on mode I. [1][2][3][4][5] Particularly, four different laboratory test methods have been successively recommended by the International Society for Rock Mechanics (ISRM) to quantify K Ic of rock, including chevron bend (CB) method, 6 short rod (SR) method, [6][7][8] cracked chevron notched Brazilian disc (CCNBD) method, [9][10][11][12][13][14][15] and semicircular bend (SCB) method. [16][17][18][19][20][21][22][23][24][25] Compared with the CB and SR methods, the CCNBD has simpler specimen preparation process, fewer restrictions on the testing apparatus, easier testing operations and no need of a special fixture.…”