Mathematical modelling and integration of micro-scale residual stresses into axisymmetric FE models of Ti6Al4V alloy in turning

Abstract

The selection of process parameters during machining has a significant impact on the in-service life of the parts. This is particularly relevant in industries such as aerospace with product lifecycles extending beyond 20 years. The paper presents a model for prediction of turning induced residual stresses of Ti6Al4V alloy. The finite element method (FEM) is used in the current study. Dynamic thermo-mechanical FE analysis using explicit integration is performed. The workpiece is modelled as an isotropic thermal–elastic–plastic model using the Johnson–Cook constitutive equation. The near-surface residual stresses are predicted and compared with experimentally measured results. Mathematical algorithms and formulations for integrating micro-scale residual stresses into axisymmetric FE models are developed and successfully implemented in the ABAQUS FE code by a user-defined subroutine. As an example, the micro-scale residual stresses are integrated into an axisymmetric FE model of a shaft subjected to turning. The models are experimentally validated using face turning and the residual stress profile of a Ti6Al4V workpiece is generated and measured at two cutting depths (100 and 500 μm). The feed rate is kept constant at 100 μm/rev. Two residual stress measurement methods (X-ray diffraction and hole-drilling) are utilised in the current study. The X-ray diffraction method is used to measure the residual stress profiles on the surface of the machined workpiece. Compressive near the surface residual stresses are measured. The experimentally measured and the FE predicted residual stresses are in good agreement.