Torsion testing for general constitutive relations: Gilles Canova's Master's Thesis

Abstract

Torsion testing is useful but cumbersome: useful as a technique to determine large-strain plastic behaviour in a plane-strain mode; cumbersome because the testing of a solid rod provides reliable data in only the simplest of circumstances, for example, when there is no strain hardening or rate sensitivity. The testing of short thin-walled tubes is widely regarded as the best current technique to determine general constitutive behaviour; a drawback is the requirement for large specimen blanks (say, 3 cm cube) and the complex machining procedure. Gilles Canova proposed an alternative - the testing of a series of solid rods of differing diameters, proving the principle by using 10 such rods for one test. We have undertaken a similar series of tests on just four rods plus one short tube for comparison. We found the results from the two types of torsion test in excellent agreement; however, it was not a critical test, inasmuch as the rate sensitivity of the pure copper used was too small. Had it been greater (as, for example, in aluminium and at higher temperature), the evaluation of perhaps six rods would have provided the constitutive response with regard to both hardening and rate sensitivity at the same time - which would require two short-tube tests (plus duplications). The main drawback of the multiple-rod test is that it requires considerable numerical effort in the evaluation. A closer integration with modelling of the constitutive behaviour would be helpful.