Testing Impact Load Cell Calculations of Material Fracture Toughness and Strength Using 3D-Printed Sandstone

Abstract

Short impact load cell (SILC) tests provide insight on the dynamic breakage behaviour of rocks. The measured impact force to first fracture of a rock specimen is used to calculate properties such as fracture toughness, tensile strength, and stiffness. To explore the repeatability and performance of the SILC test and verify the underlying assumptions for interpreting the test measurements, a comprehensive SILC testing program was conducted using additively manufactured (3D-printed) sandstone. 3D-printed sandstone specimens with known mechanical properties were used to indirectly determine the mechanical properties of specimens from SILC test measurements with respect to different sizes (from 5 to 12 mm diameter), shapes (sphere, flattened sphere, ellipsoid, and cylinder) and fabric orientations (i.e. angle variation of microstructures relative to the impact or loading direction). Unconfined compressive strength tests were also conducted on twin sets of various sized cylinder-shaped specimens to verify the estimation of compressive strength from the SILC test. Confidence in interpretation of SILC testing results is obtained by excluding the intrinsic material variability. Ultrahigh-speed digital camera was used to observe the fracture mechanism and to verify the force–time profiles against specimen physical response. Well-defined shaped specimens instead of irregular single-particles showed clear peaks corresponding to the force to first fracture on the force–time profiles. The study found that the minimum energy required to fracture the specimen, therefore the specimen strength, was strongly influenced by the shape effect.