A procedure for the computational investigation of stress-relaxation phenomena

The analysis of stress-relaxation tests in viscoelastic materials is discussed. Stress-relaxation tests are performed by means of a two-stage process, as a stretching stage up to an assumed strain level, according to a given strain rate, followed by a constant strain stage. Major attention is devoted to the influence of experimental variables, namely the strain level and the strain rate during stretching stage, on the subsequent relaxation phenomena. A constitutive analysis to interpret the behaviour shown by experimental tests is performed, accounting for the influence of the above mentioned experimental variables, to get an actual definition of time dependent behaviour of the material. This procedure is applied to investigate stress-relaxation phenomena in polymeric materials and soft biological tissues, as ligaments. The results confirm the necessity to analyse data from stress-relaxation tests taking into account the experimental variables that characterize the different stages, and evaluating the influence of the specific variables outlined.