A method of finding the effective length of the specimen used in the hot torsion test and recommendations on geometry of the test specimen

The length of the specimen in the hot torsion test is an important geometrical parameter and affects all calculations based on the results of the hot torsion test. To lessen the error in the analysis of the specimen due to deformation outside the gage length, an effective length may be used. Improvement in the accuracy of analyses of the hot torsion test is also important to inverse numerical solutions because the initial guess needed to start an inverse numerical solution may be obtained using an analytical solution. Determination of the effective length of a specimen is explained and illustrated for two different constitutive relationships. Recommendations on the choice of the hot torsion test specimen are given. It is shown that neglect of deformation outside the gage section may result in the flow curve obtained by using the hot torsion test results being lower than the flow curve achieved by other tests.