Abstract
This paper describes the development of a computer model for the calculation of hightemperature flow stress curves of titanium alloys. Two competing mechanisms for deformation,either dominated by dislocation glide or dominated by dislocation climb, were considered in the calculation. Validation has been carried out for a variety of titanium alloys over a wide range of temperatures and strain rates. The flow stress data can be used as replacement to the constitutive equations in computer-aided-engineering simulation.
Introduction
Thermo-mechanical processing simulation requires critical material data such as strength and stress-strain curves (or flow stress curves). The traditional way of obtaining such data is through experimentation, which is expensive and time-consuming, because mechanical properties are temperature and strain rate dependent. It is therefore of no surprise that lack of material data has been a common problem for computer-aided-engineering (CAE) simulation tools.
CAE simulation packages normally provide a range of constitutive equations that describe stress as a function of temperature, strain and strain rate, e.g. the widely used Johnson-Cook model [1]. However, the choice of the equations used can significantly affect the simulation results [2,3,4], as each has its own limitations and can only work in a certain range [5]. Not only do users have to decide which equation to use, but they also have to determine the values of the material parameters used in the equation, where experimental flow stress data is a pre-requisite [4,6,7]. The present paper looks at material flow from the viewpoint of the actual mechanisms during deformation. Two competing mechanisms for deformation, i.e. either dominated by dislocation glide (DDG) or dominated by dislocation climb (DDC), were considered in the investigation. After a recapitulation of previous work on the calculation of high temperature strength, the paper focuses on calculating stress-strain curves in different temperature and strain rate regimes. The advantages of using such an analytical approach to replace subjectively selected constitutive equations are discussed.
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