Accession Number : AD0821620

Title :   ON THE DETERMINATION OF MATERIAL CHARACTERISTICS IN NONLINEAR VISCOELASTICITY.

Descriptive Note : Final rept. (Part 1), Oct 65-Feb 67,

Corporate Author : STANFORD UNIV CA DIV OF ENGINEERING MECHANICS

Personal Author(s) : Gleason, Robert F.

Report Date : JUL 1967

Pagination or Media Count : 109

Abstract : A method is presented for finding response characteristics for nonlinear viscoelastic materials from experimental data. No specific loading or deformation histories are required in the experiments. The general constitutive relation for simple, homogeneous, anisotropic, hereditary materials is approximated by a series of multiple integrals. The integrands consist of products of the material response functions and functions describing the deformation. It is these response functions that must be determined. While the method presented is applicable for any order of multiple integral approximation, the equations are developed for the second order expansion. The response functions are determined by using a least squares method to fit the multiple integral expansion to experimental results. The second order integral expansion for an isotropic material is developed. It is shown that biaxial tension tests, with deformations measured parallel to and normal to the directions of loading, are sufficient to determine all of the second order isotropic response functions. The equations needed to compute these functions, which are simultaneous linear integral equations of the first kind, are developed in detail. A technique for approximate numerical solution is presented. The first order isotropic response functions for polyethylene, computed from published data, are presented. (Author)

Descriptors :   (*VISCOELASTICITY, NONLINEAR SYSTEMS), (*DEFORMATION, MATHEMATICAL MODELS), EXPERIMENTAL DATA, CURVE FITTING, TENSOR ANALYSIS, INTEGRALS, APPROXIMATION(MATHEMATICS), EQUATIONS, SERIES(MATHEMATICS), ISOTROPISM, ANISOTROPY, POLYETHYLENE PLASTICS, STRESSES, TENSILE PROPERTIES, FUNCTIONS(MATHEMATICS), LEAST SQUARES METHOD, LOADS(FORCES), THESES.

Subject Categories : Statistics and Probability
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE