抄録
Tensile strength of bolt or screw is usually obtained directly by the tensile test. However, for bolt or screw with short length, tensile test is not always feasible. In such a case, torsional test specified in ISO898-7 is applied, in which the breaking torque calculated from the tensile strength and the strength ratio is evaluated. In this study, torsional rupture test on M8 bolts and FE analysis were done to find out the influence caused by free-threaded length and thread lead angle of bolt on the breaking torque. Discussion includes the equivalent diameter which used in the calculation for the polar modulus of section. It was clarified that the screw lead had a significant effect on the breaking torque, and it was advised that the equivalent diameter should be evaluated taking into account this effect.
