Stress—Strain relationships of wax-based model materials

Model materials are often used when simulating metal-forming processes under laboratory conditions and, in particular, the laboratory testing of the effects of tool-profile variations on the metal flow is very useful. Here the strains and possible disturbances (non-homogeneities) in the material flow can be measured qualitatively under controlled conditions. Tool profiles can be varied easily, since the tools are made of wood, plastics etc., and in addition, problems caused by high temperatures and tool pressures can be avoided.

Successful simulation requires the flow properties of the model material to resemble those of the material being simulated. For many practical purposes a proper model material is found by comparing the flow pattern of a product to those of the model-material parts produced under laboratory conditions, when the flow properties of the model material do not necessarily have to be known. For a more quantitative analysis, where strains, deformation loads etc. are calculated, the stress—strain relationships have to be known and represented by a constitutive equation: this is especially important for the computer simulation of working processes.

In the present work, the flow properties of some wax-based model materials are measured experimentally by carrying out isothermal compression tests. On the basis of the resulting stress—strain curves, constitutive equations representing the flow stress as a function of strain, strain rate and temperature are derived for the limited ranges of strain, strain rate and temperature investigated. It is shown that the flow stress of the model materials examined is strongly dependent on strain rate and temperature: this has to be taken into account in interpreting the results of model-material simulation.