Dynamic Fracture Strength of Oil Shale under Torsional Loading

摘要

A torsional split Hopkinson bar is used to investigate the fracture strength of a nominally lean grade of oil shale at strain rates between approx. 20/s and approx. 800/s. To achieve homogeneous stress and deformation states, the test samples are relatively small thin-walled tubes. The axes of these samples are both parallel and perpendicular to the material bedding planes. Under dynamic torsional loading, sample response is divided into two phases. An initial, essentially linear phase, ending at a shear stress level, Tau/sub y/; and a second phase characterized by a substantially reduced specimen stiffness. Analysis of the failure process has revealed that Tau/sub y/ is essentially the tensile fracture initiation stress level for the material, whereas sample response in the second phase cannot be simply correlated with material behavior. The test results establish that Tau/sub y/ is a strong function of strain rate, however no clear evidence of fracture strength depending on bedding plane orientation is revealed. (ERA citation 04:035816)