Abstract
This paper aims to develop a method for determining the workability diagram by varying frictional conditions in the cylinder upsetting test. The method is based on a known theoretical relationship between the average stress triaxiality ratio and in-surface strains if the initiation of fracture occurs at a traction-free surface. This relationship is valid for any rigid/plastic strain hardening material obeying the Mises-type yield criterion and its associated flow rule, which shows the wide applicability of the method. The experimental input to the method is the strain path at the site of fracture initiation. Neither experimental nor numerical determination of stress components is required at this site, though the general ductile fracture criterion involves the linear and quadratic invariants of the stress tensor. The friction law’s formulation is neither required, though the friction stress is the agent for varying the state of stress and strain at the site of ductile fracture initiation. The upsetting tests are carried out on normalized medium-carbon steel C45E, for which the workability diagram is available from the literature. Comparison of the latter and the diagram found using the new method shows that the new method is reliable for determining a certain portion of the workability diagram.
Highlights
Empirical ductile fracture criteria have been successfully used to predict fracture initiation in metal forming processes for several decades.Usually, such criteria involve several constitutive parameters that should be identified using experimental or hybrid experimental-numerical approaches
An advantage of the fracture criterion based on the workability diagram and an average stress triaxiality ratio is that this criterion involves an arbitrary function rather than arbitrary parameters [8]
This function is determined in the course of ductile fracture testing
Summary
Empirical ductile fracture criteria have been successfully used to predict fracture initiation in metal forming processes for several decades (see [1,2,3,4,5] among many others) Such criteria involve several constitutive parameters that should be identified using experimental or hybrid experimental-numerical approaches. An advantage of the fracture criterion based on the workability diagram and an average stress triaxiality ratio is that this criterion involves an arbitrary function rather than arbitrary parameters [8]. This function is determined in the course of ductile fracture testing. To increase the accuracy of the criterion, one has to design experiments to cover a wide range of the stress triaxiality ratio at the site of fracture initiation
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