Orthotropic elastic constants for polyimide film

The orthotropic constants of polyimide film have been characterized using the theory of elasticity of an anisotropic material, Experimental techniques coupled with the mechanics of orthotropic materials are used to determine all 9 independent orthotropic elastic constants (3 tensile moduli, 3 sheer moduli, and 3 Poisson's ratios) and 3 coefficients of thermal expansion. Vibrational holographic interferometry is used to determine the orthotropic axes of symmetry. For this polyimide film, the two principal axes coincided with the machine and transverse directions, it is also used to evaluate the 2 in-place Poisson's ratios by measuring residual stresses in 2-D and 1-D square membranes. Using other instruments such as a high pressure gas dilatometry apparatus, a tensile tester, a pressure-volume-temperature apparatus, a thermomechanical analyzer, and a torsion pendulum, the 7 other orthotropic constants and the 3 coefficients of thermal expansion are determined.