Adiabatic heating of PolyAmide 11 under monotonic loading : effects of the initial stress triaxiality ratio

International audienceAssociated with the partial conversion of plastic work into dissipative heat [1], adiabatic heat build-up of polymers under mechanical loading may be exceptionally high so that it can locally reach the glass transition temperature Tg, even though the ambient testing temperature is lower than Tg. A significant modification of the local material response and damage mechanisms is then expected. However, the effects of the stress triaxiality ratio on the heat build-up are still unclear. In this study, the coupled thermomechanical response of a PolyAmide 11 (PA11) under quasi-static loading was investigated.A Gurson-Tvergaard-Needleman based thermo-mechanical model [2], integrating temperature-dependent coefficients, implemented in an in-house finite element code Zset [3], was enhanced to account for the plastic work converted to heat during deformation, and therefore the adiabatic heat build-up. By simultaneous infrared thermography measurements during experimental tests under quasi-static loading on gradually increasing stress triaxiality ratio samples, the model parameters were identified at several temperatures, for a given stress triaxiality ratio, and compared numerically with experimental data. Afterwards, a continuous dependence of the model parameters with temperature was deduced. The predictive capability of the proposed thermo-mechanical model to simulate the isothermal behaviour ofPA11 led to adiabatic simulations accounted for the temperature rise highlighted experimentally. Predicted evolutions given by the proposed model for other stress triaxiality ratios and geometries have been found to be in good agreement with experimental data.[1] W.S. Farren and G.I. Taylor. The heat developed during plastic extension of metals.Proceedings of the RoyalSociety of London. Series A, Containing Papers of a Mathematical and Physical Character, 107:422–451, (1925).[2] L. Laiarinandrasana, J. Besson, M. Lafarge, and G. Hochstetter. Temperature dependent mechanical behaviour ofpvdf: Experiments and numerical modelling.International Journal of Plasticity, 25:1301 – 1324, (2009).[3] J. Besson and R. Foerch. Large scale object-oriented finite element code design.Computer Methods in AppliedMechanics and Engineering, 142:165 – 187, (1997)