A Novel Real Time True Stress-True Strain Birefringence Measurement System for Biaxial Deformation of Polymers under Linear and Programmed Deformation Profiles (Paper No. 18A)

摘要

In processed semi crystalline polymers, birefringence carries combined information about the orientation and crystallinity. In case of single-phase polymers such as amorphous polymers it directly carries information on the orientation. Rapid determination of these parameters together with the "true" mechanical parameters " true stress and "true strain" allows an integrated monitoring of mechanical stimulus (strain) and response (stress) together with structural (birefringence) parameters. These "quantitative" relationships between the thermal-deformation history imposed by the manufacturing processes on the development of structure as manifested in optical anisotropy as the birefringence measure is essential in uncovering how the polymeric materials behave during various stages of their structural rearrangement. Of particular interest are the quantitative relationships between the process dynamics such as stress and strain and the structural parameter birefringence. Development of such constitutive relationships is essential for future predictive modeling efforts. The linear stress optical rule that couples the stress and birefringence has been known to deviate from linearity at high stress levels for amorphous and crystalline polymers. With the real time measurement system developed in this research, we investigated the fundamental characteristics of extension of this stress optical rule to these non-linear regions particularly for those materials that undergo stress induced crystallization. The ultimate goal obviously will be to capture these relationships in a quantitative framework that will be very useful in predictive modeling of these materials under a variety of processes In this paper the design and validation as well as example data obtained under biaxial conditions will be discussed.