An Improved Experimental Method for Determining the Workability Diagram

The workability diagram is often used for ductile fracture predictions in metal forming processes. Its determination requires the measurement of the strain to fracture in several tests in which the triaxiality ratio is supposed to be known and fixed throughout the process of deformation. One of such tests is the uniaxial tension test. In practice, however, it is very difficult (or even impossible) to keep the triaxiality ratio fixed in this test because of necking. It is shown in the present paper that the uniaxial tension test can be replaced with the collar test for obtaining a point of the workability diagram when the fracture criterion based on an average value of the triaxiality ratio is adopted. It is also shown that the collar test provides a more accurate prediction of the strain to fracture. The test carries out at quasi-static strain rates.