A simple method for determining independent fracture toughness and tensile strength of rock

Abstract

This paper develops a model that only requires two sets of small-size rock specimens with the ratio of the structural geometry parameter maximum to minimum ae,max:ae,min ≥ 3:1 to determine the rock fracture and strength parameters without size effect and predict the actual structural performance of rock. Regardless of three-point-bending, four-point-bending, or a combination of the above two specimen types, fracture toughness KIC and tensile strength ft of rock were determined using only two sets of specimens with ae,max:ae,min ≥ 3:1. The values KIC and ft were consistent with those determined using multiple sets of specimens. The full structural failure curve constructed by two sets of small-size specimens with ae,max:ae,min ≥ 3:1 can accurately predict large-size specimens fracture failure, and ±10% upper and lower limits of the curve can encompass the test results of large-size specimens. The peak load prediction curve was constructed by two sets of specimens with ae,max:ae,min ≥ 3:1, and ±15% upper and lower limits of the peak load prediction curve can cover the small-size specimen tests data. The model and method proposed in this paper require only two sets of small-size specimens, and their selection is unaffected by the specimen type, geometry, and initial crack length.

Keywords

• Rock
• Size effect
• Boundary effect
• Structural geometry parameter
• Fracture toughness
• Tensile strength