Rock Mechanics
Vahab Sarfarazi; Hadi Haeri; Jinwei Fu; Pejman Kalvandi; Mohammad Fatehi Marji; Alireza Shaker
Abstract
Determining the tensile strength of brittle, layered materials, including layered rocks and cracked concrete, is difficult when using commonly adopted indirect loading configurations that do not induce pure tensile conditions. Therefore, obtaining tensile strength through direct experimental quantification ...
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Determining the tensile strength of brittle, layered materials, including layered rocks and cracked concrete, is difficult when using commonly adopted indirect loading configurations that do not induce pure tensile conditions. Therefore, obtaining tensile strength through direct experimental quantification is crucial for such materials, particularly when examining crack onset and subsequent crack growth in the vicinity of crack tips. The present research proposes a novel direct tension-based testing framework designed to deliver more reliable strength characterization of layered quasi-brittle materials, while simultaneously enabling a detailed assessment of fracture initiation and propagation mechanisms. The testing apparatus consists of a steel beam with a load converter that serves as both the loading fixture and the load cell. A pre-holed layered sample is securely positioned at the center of the apparatus using a strong metal plate, while strain gauges on both sides capture critical data on the specimen's tensile behavior. Significantly, the apparatus can detect and quantify asymmetric failure within the specimen, offering a detailed understanding of crack formation and failure patterns. The design, calibration protocols, and empirical test results are thoroughly detailed and analyzed. Additionally, this study employs 3D PFC modeling to clarify the breakage mechanisms in various layer configurations, thereby enhancing the accuracy of tensile strength measurements. The numerical modeling results demonstrate that increasing the thickness of the hard layer leads to a nonlinear increase in the specimen's resistance. Furthermore, at a constant hard layer thickness, increasing the number of hard layers results in a decrease in the model's resistance.
