Influence of Twinning on the Constitutive Reponses of Zr : Experirnents and Modeling

The stress-strain response of Zr due to twinning is distinctly different from that due to slip as a function of temperature and strain rate. When the applied stress is lower than the transition stress, dislocation slip is the dominant deformation mechanism. The traditional MTS model is shown to adequately represent the constitutive behavior of Zr. Above the transition stress twinning becomes the dominant deformation mechanism where the flow stress increases linearly with strain. In this regime the rate-dependent strain hardening can be described by equations based on thermal activation theory that are very similar to the formula used in the MTS model. Rbsumb: Le maclage du zirconium induit une rtponse micanique, en fonction de la temptrature et de la vitesse dtformation, bien distincte de celle produite par glissement. Quand la contrainte appliquee est inftrieure h la contrainte de transition, le glissement est le micanisme de dtformation pripondirant. Le modkle MTS 'classique' dtcrit alors correctemenl le comportement viscoplastique du zirconium. Au dessus de la contrainte de transition, le maclage devient le mode de diformation dominant; la contrainte d'icoulement croit liniairement en fonction de la dtformation. Dans ce rtgime, le comportement peut stre dicrit par des tquations, fondies sur des lois d'activation thermique, similaires 5 celles utilisies dans le modkle MTS.