Anisotropic mechanical properties and constitutive relations of PTFE coated glass fibers

This paper presents the anisotropic mechanical properties and constitutive relations of PTFE (Polytetrafluoroethylene) coated glass fibers. First, the monotonous and cyclic tests are carried out, in which the effects of stress amplitude and bias angle are considered. Then, the decomposition of material strain during the cyclic tests is studied and the predicted models are also discussed. Finally, an anisotropic constitutive relation is proposed to predict the off-axial creep behaviors. Results show that the tensile behaviors of PTFE coated glass fibers are anisotropic, which is mainly related with the crimp degree of woven structure. The material deformation can be divided into three parts, elastic deformation, recoverable viscous deformation and unrecoverable viscous deformation. The bias angle and stress amplitude have significant effects on the cyclic tensile behaviors. After unloading, the total residual strain has decreased about 90% in the first 3 days. The final unrecoverable strain of 45 specimen is the highest, about 30 times of that of warp specimen, or 8 times of that of weft specimens. Besides, the revised Burgers model can be used to describe the cyclic tensile behaviors. Finally, the proposed anisotropic constitutive relation can be used to predict the creep behaviors at any directions.