ANISOTROPY OF CREEP BEHAVIOUR IN ORIENTED THERMOPLASTICS.

Creep studies on low-density PE, PMMA and PVC, are reported. All creep functions were measured. The anisotropy of time dependence and non-linearity of creep modulus (i. e. modulus is a function of stress) is reported. The results are presented in a formalism emanating from classical elasticity theory and it is shown that this is useful, although non-rigourus, in describing the complex and unexpected behavior observed. Comment is made on the engineering significance of anisotropy of stiffness and strength properties. Experimental results are presented in curves and discussed.