NUMERICAL-ANALYSIS OF THE HOT TENSION TEST

Plastic flow during the round bar, uniaxial tension test has been anal yzed for conditions representative of the hot-working of metals. Two m ethods of analysis were employed: the finite element method and a simp ler finite-difference technique using a so-called ''direct equilibrium '' approach. Variables which were investigated included material prope rties (strain-hardening exponents of 0 or 0.1; strain-rate sensitivity exponents between 0.02 and 0.30) and sample geometry (gage length-to- diameter ratios between 4 and 15; samples with and without tapers from the fillet to the center of the gage section). Results were summarize d in terms of nominal (engineering) stress-strain curves, axial strain distributions after the onset of rapid flow localization, and total e longations. A comparison of the results from the two types of numerica l analyses were very similar. This similarity was interpreted to resul t from the similar degrees of stress triaxiality during neck formation which were predicted via the finite element method and assumed (based on the Bridgman analysis) for the direct equilibrium approach. Total elongation predictions from the numerical models were compared to meas urements and to a simple closed form analytical solution contained in the literature. The numerical results showed good agreement with the m easurements but differed greatly from the analytical solution, thereby quantifying the effect of the neglect of stress triaxiality in simple analytical models on predicted elongations.