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Prediction of a Material Property Gradient near the Friction Surface in Axisymmetric Extrusion and Drawing

The present paper provides a theoretical prediction of the evolution of material properties near the friction surface in axisymmetric extrusion and drawing. The method employed is based on the strain rate intensity factor and uses empirical equations that connect the integrated strain rate intensity factor with the thickness of a narrow layer of intensive plastic deformation and the hardness of the surface layer. The material obeys Hosford’s yield criterion. Therefore, the empirical equations above are reformulated in terms of the work rate intensity factor. Since no numerical method is available, the strain rate and work rate intensity factors are determined from an approximate solution. The solution reveals the effect of process and material parameters on the thickness of a layer of intensive plastic deformation and the hardness of the surface layer. Since the solution is semi-analytical, it is straightforward to use its results to design the metal forming processes.