1-5. Introduction of materials modelling into processing simulation – the past, the present and the future

Zhanli Guo1, Nigel Saunders2 and Jean-Philippe Schillé1

1.Sente Software Ltd., The Surrey Research Park, Guildford GU2 7YG, UK 2.Thermotech Ltd., The Surrey Research Park, Guildford GU2 7YG, UK

Abstract: Computer-aided engineering (CAE) simulation tools are increasingly being used in metals industry to speed up processing and manufacturing, where material data have been an integral part ever since such simulations were made possible. Recent advancement in computing power drives the simulation capabilities forward, from only being able to deal with simple heat transfer in the early days to the current ability of incorporating a multitude of physical phenomena, including heat transfer (thermal field), deformation mechanics (stress/strain field) and phase transformations (microstructural field). The interactions and interdependencies of these phenomena are shown in Fig. 1. An accurate coupling of these phenomena is essential to achieve reliable simulation, which demands the availability of a wide range of material data, from physical and thermophysical properties to rheological properties as well as phase transformation kinetics. The traditional way of obtaining such data is through experimentation, which is expensive and time-consuming, and even impossible in cases where accurate simulation requires the property data of each phase involved rather than just that of the alloy. To provide reliable and cost-effective data for process simulation, computer-based models must be developed so that such properties can be readily calculated, which is the so-called materials modelling.

      Processing simulation essentially consists of two types of modelling. One is the materials modelling, i.e. modelling of composition-processing-microstructure-property relationships; the other is the CAE type simulation based on finite-element or finite-difference (FE/FD) analysis and alike. For historical reasons, the development of these two types of modelling techniques falls into two separate research areas, resulting in two types of computer software, each performing fairly well in its own field but no links exist between them. While the advanced computing power has made the integration of materials modelling into processing simulation possible, the demand for higher accuracy in simulation results has made it necessary.

Fig. 1. Interactions between three main physical phenomena in materials processing.

      Modelling materials properties and behaviour has been the focus of our research in the past two decades . It incorporates a spectrum of material models covering thermodynamics (the CALculation of PHAse Diagrams, or CALPHAD approach), phase transformation kinetics, and microstructure-property relationships. Most of the material data required for processing simulation can now be readily calculated and then easily transferred to many commercial CAE tools for the simulation of casting , welding, forming and heat treatment processes of various industrial alloys such as Fe-, Ni-, Ti-, Al- and Mg-based alloys. The first part of the paper reviews the development of material models over recent years, followed by some new case studies on the forming simulation of some industrial alloys.

       The common simulation practice at present leaves materials design outside the optimisation loop of product design and manufacturing, which reduces the potential design space and may result in suboptimal end products. This is because the necessity of material data for simulation means the alloy has to be physically prepared and have its properties measured before any simulation of its processing becomes possible. The case studies presented here therefore have demonstrated great potential, as most of the material data essential for processing simulation can now be reliably calculated for the first time. It is probably fair to say that merging materials design and processing optimisation into one complete design space has become a real possibility, and we are moving one-step closer towards true virtual design.

Keywords: Materials modelling; Processing simulation; Virtual design; CALPHAD.