Influence of bedding plane on the tensile properties and crack propagation of soft and hard laminated rock-like under Brazilian test

Abstract

To investigate the tensile properties and crack propagation of anisotropic rock-like specimens, soft and hard laminated rock-like specimens were made for the Brazilian splitting test. Five bedding plane inclination angles (θ = 0°, 30°, 45°, 60° and 90°) and three thickness ratios of soft and hard layers (1:1, 1:3 and 3:1) were taken into consideration for the rock-like concrete specimens. The effects of different θ and rock layer thickness ratios on the tensile strength, brittleness and energy characteristics were analyzed. The variation in tensile strain and crack opening displacement of tensile fracture were obtained by the digital image correlation (DIC) technique for the specimens. The crack initiation position and propagation path were determined. It was found that the fracture process zone appeared before the initiation of macroscopic cracks owing to the accumulation of tensile strain. The crack initiation position occurs near the two loading points regardless of the different angle θ. When θ = 0° and 90°, the crack propagates toward the center of the specimen along the loading direction. However, when θ = 30°, 45° and 60°, the cracks tend to propagate along the bedding plane. The influence of the crack propagation path on the final fracture pattern was analyzed. The results indicated that the angle θ has a strong influence on tensile crack initiation and propagation under the Brazilian test. The fracture process zone appears at the location of crack initiation and the expanding cracking path before the formation of macroscopic cracks. The absorbed energy increases with increasing tensile strength, and it decreases as θ increases. The brittleness index of the specimen increases gradually with increasing θ.