Theoretical Aspects and Design of a Numerical Model for Friction Tapered Hydro-pillar Processing of Aisi4140 Steel

Abstract

This paper considers the theoretical aspects required for the development of a coupled two-dimensional axi-symmetrical computational fluid dynamics (CFD) and heat transfer model for the Friction Taper Hydro-Pillar Process (FTHPP). The model applies the plasticised material movement during welding as the laminar, viscous flow of a non-Newtonian fluid, while making use of a dynamic mesh to simulate the continuous deformation of plasticised material at the friction interface. The plastic material flows through a stationary discretized flow domain not requiring a moving mesh, resulting in the Eulerian CFD approach being effective - this CFD material flow model thus avoids the requirement for re-meshing. The material properties are entered via a viscosity function used to describe the flow stress, locally dependent on material strain rate and temperature. A non-linear multiphysics problem exists as the frictional and viscous heating act as heat sources. The simulation model applies an iterative approach for coupling the plastic deformation flow analysis with the thermal analysis. Strain rate and temperature distribution of the welding material mutually affect each other, as the flow stress is temperature-dependent and the plastic work (adiabatic shear) performed during the process generates heat, in addition to heat added by friction. Isotropic temperature-dependent thermo-physical properties are required and thus incorporated into the model. A successfully coupled simulation is presented with the thermal response analysis delivering the temperature distribution through the weld for which process temperature and subsequent hardness plots are drafted. Measurements obtained from experimental welds show favourable comparison, validating computed values. The presented work attempt to show how comprehensive numerical modelling, carried out through computer simulation, can assist in the analysis of the identified process characteristics during FTHPP