Mechanical and fractal characteristics of sandstone with Pre-existing fissures of different lengths under varying impact loads in SHPB tests

• Published in: Theoretical and applied fracture mechanics Vol. 125; p. 103884
• Main Authors: Du, Weihang, Zhang, Dongming, Yu, Beichen
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2023
• Subjects: Different heights slices; Fractal characteristics; Pre-existing fissures with different lengths; SHPB; SHPB; Fractal characteristics; Pre-existing fissures with different lengths; Different heights slices
• ISSN: 0167-8442; 1872-7638
• DOI: 10.1016/j.tafmec.2023.103884

•We have designed novel pre-existing fracture types and investigated the influence of pre-existing fissure length on the mechanical properties of sandstone after failure, and analyzed the detailed distribution of cracks after failure. The evolution of different types of cracks from the incident end to the transmitted end was found to be different under different launch pressures.•We quantitatively analyzed the influence of pre-existing fissure length and launch pressure on the fractal dimension of sandstone at different heights of slicing, and this method can more accurately characterize the overall failure of sandstone.•As the length of the pre-existing fissure increases, the failure mode of the rock changes, which is mainly caused by changes in the ability of the pre-existing fracture to store and release energy. However, the overall failure of the sandstone is dominated by splitting tensile failure, and local compression-shear failure occurs after the launch pressure increases. The Split Hopkinson Pressure Bar (SHPB) with a 100 mm diameter was used to investigate the impact of pre-existing fissure length on the mechanical properties of sandstone under different launch pressure (P = 0.3 MPa, P = 0.45 MPa, and P = 0.6 MPa). Subsequently, CT scanning was conducted on sandstone samples with pre-existing fissure after failure to examine the relationship between pre-existing fissure length (Lc) and fractal characteristics under different launch pressures. Our findings indicate that, compared to intact sandstone, the proportion of plastic deformation in the stress–strain curve of sandstone with pre-existing fissure increases. As Lc increases, the initial plastic deformation stress and secant modulus decrease. After CT scanning, sandstone failure was classified into three conditions for different Lc: (1) Axial-splitting-tensile failure is caused by the development of natural defects, and in this case, the degree of development of pre-existing fissure is low, (2) Radial-splitting -tensile-failure is caused by the development of pre-existing fissure, in which the degree of development of pre-existing fissure is high and dominates the macroscopic failure of sandstone, while the degree of development of natural defects is low, and; (3) Combined-splitting-tensile failure: The failure of sandstone includes both axial-splitting-tensile failure and radial –splitting-tensile failure. At this time, both the degree of development of natural defects and pre-existing fissure are high, which jointly dominate the macroscopic failure of sandstone. With increasing launch pressure (P) and Lc, the failure mode of sandstone transitions from axial splitting-tensile failure to radial splitting-tensile failure, and eventually to combined splitting-tensile failure. However, local compression-shear failure occurs with increased launch pressure. Moreover, Lc significantly affects the fractal characteristics of sandstone. Under 0.3 MPa launch pressure, the fractal dimension (DH) on different height (H) slices initially increases and then decreases with increased Lc. Under 0.45 MPa launch pressure, the DH on different H slices exhibits two changes with increasing Lc. For H = 70 mm and H = 100 mm, the variation of DH is decreasing-increasing–decreasing-increasing, while for H = 0 mm and H = 30 mm, the variation of DH is increasing–decreasing-increasing. Under 0.6 MPa launch pressure, the DH on different H slices increases first and decreases secondly with the increase of Lc, but Lc is different when DH reaches its maximum.