Orthotropic yield criterion for Ti-6Al-4V titanium alloy after friction stir processing (FSP)

Purpose: This works aims at applying friction stir processing (FSP) to Ti-6Al-4V titanium alloy. Derived from friction stir welding (FSW), it is a recent process developed in the 1990s for aluminum joining. Its application to other types of materials such as steel and high performance alloys, in particular titanium, has interested industry. Design/methodology/approach: The methodology applied to evaluate FSP in this work consisted in tensile testing Ti-6Al-4V sheets in mixed conditions. The workpieces were processed in a conventional CNC milling machine with special fixture devices. Findings: A contribution to the modeling of anisotropic materials yield stress is proposed based on an orthotropic yield criterion. Additional equations based on the mixed tests for tensile and shear loadings are proposed to modify the former Cazacu orthotropic model. Research limitations/implications: Although the application limit for the model appears to be small, sheet forming process similar to those used in this work, are predominantly in the region of this analysis. Practical implications: The purpose of the model is to indicate the conditions under which the material has reached its yield regime, and may be a basis for practical simulations in similar conditions. Originality/value: The purpose of this model is to indicate the conditions under which the material has reached its yield regime, and may be a basis for practical simulations in similar conditions.