Experimental methods for dynamic stress analysis in viscoelastic materials

This paper deals with experimental methods of dynamic stress analysis in viscoelastic materials. Plasticized polyvinyl chloride is used as the model material. Dynamic properties, both mechanical and optical, in the form of a complex modulus and a stress fringe value as functions of frequency are determined by means of sinusoidal oscillation tests. These are converted into a relaxation modulus and a stress fringe value as functions of time. Two approaches are discussed. In the first one, measured strains in the model and the material relaxation modulus are used for the computation of stresses by numerical integration of the integral constitutive relations of viscoelasticity. In the other approach, birefringent measurements in the model and the stress fringe value of the material are used for the computation of the principal stress difference by numerical integration of the integral stress-optic relation. The application of these methods is demonstrated in the cases of a strut and a plate subjected to the impact of a falling weight. Results obtained independently by the two methods are in satisfactory agreement.