Experimental study of the mechanical behavior of materials under transient regimes of superplastic deforming

Transient regimes of deforming are always present in any technological process and can be taken into account and used more widely if properly studied. The behavior of the materials under such regimes is becoming even more interesting if initial microstructure is coarse grained and undergoes transformation in the process of deforming. One of the transient processes which happen in any Superplastic deformation is the initial stage of loading, before steady superplastic flow starts. Initial parts of stress-strain curves during superplastic deformation are not frequently studied experimentally but provide very important information about mechanical properties of material. They are also necessary for development and verification of the constitutive equations. The results of experimental analysis of the behaviour of titanium alloys under superplastic conditions at the initial stages of loading and also under unloading are presented here. Another type of transient regimes of deforming is represented by the strain rate jumps. In such kind of experiments if the amplitudes of the jumps are big enough, the shifts of the corresponding parts of the stress-strain curves about the basic ones (hardening or softening) can be observed depending on the amplitude of the jump and microstructure of the material. Some experimental results related to this effect are discussed in this paper. The applicability of some constitutive equations for description of the observed results is discussed. The necessity of involving visco-elastic properties of material for proper description of its behavior in some regimes of deforming is also mentioned.