MULTIPLE INTEGRAL REPRESENTATION OF MECHANICAL BEHAVIOR OF POLYETHYLENE.
Technical rept. no. 10,
BROWN UNIV PROVIDENCE R I DIV OF APPLIED MATHEMATICS
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The response of viscoelastic solids to quasi-static loading, under conditions where non-linear theories have to be used, was investigated. Creep measurements of tension and of torsion in polyethylene specimens are described. Step loading was used and the deformations were measured optically by means of travelling microscopes for the tension experiments and by the reflection of light beams from mirrors for the torsion experiments. The deformations were too large for the theory of linear viscoelasticity to hold and the constitutive relations used were of multiple integral form some of the kernels involved were determined. It was found that for the loading range used, two kernels were sufficient for describing pure shear deformations and three kernels were required for tension. It was also shown that in this non-linear region, the relation between shear stress and shear strain depended on whether or not dilatational stresses were present. Author