| Flow stress of a material, usually measured by compression test, is obtained for a strain rate and an environmental temperature. During the compression test, however, temperature of the material increases due to the deformation heat. Especially, the flow stresses of Inconel 718 and Ti-6Al-4V are quite sensitive to temperature, the deformation heat should be taken into account to obtain flow stresses of such materials. In the present study, a series of compression tests were performed for the two materials under various temperatures and strain rates, and temperature increases were calculated under the assumption that 90% of the deformation work was converted to heat. Using inter/extrapolation schemes, flow stresses at certain temperatures and strain rates were obtained and they were fitted into the Holloman equation of σ￣=Cε￣^m, where C and m varied with strain, strain rate and temperature. To show the influence of the deformation heat onto the estimation of flow stress, flow stresses of the materials when the deformation was considered were compared with those when it was not. It was worthwhile to note that the influence became more significant as the strain rate increased. |
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