ABSTRACT

Constitutive Modeling of the Mechanics Associated with Crystallizable Shape Memory Polymers

Speaker: Gautam Barot

Advisor: Dr I J Rao

Shape memory polymers are novel material that can be easily formed into complex shapes, retaining memory of their original shape even after undergoing large deformations. The temporary shape is stable and return to the original shape is triggered by a suitable mechanism such as heating. Crystallizable shape memory polymers are called crystallizable because the temporary shape is fixed by a crystalline phase, while return to the original shape is due to the melting of this crystalline phase. A set of constitutive equations has been developed to model the mechanical behavior of crystallizable shape memory polymers. The modeling is done using a framework that was developed recently for studying crystallization in polymers ([3], [1], [2], [4]) and is based on the theory of multiple natural configurations. Constitutive equations for the original amorphous phase and the semi-crystalline phase that is formed after the onset of crystallization are also developed. In addition, we model the melting of the crystalline phase to capture the return of the polymer to its original shape. The model has been used to simulate a typical uni-axial cycle of deformation, the results of this simulation compare very well with experimental data. In addition to this we also simulate circular shear of a hollow cylinder and present results for different cases in this geometry. On finite analysis software (ABAQUS) using computer programs (UMAT), developed based on the model, a cycle consisting of different process for three-dimensional geometry is simulated.

Work Sited:

[1]  I. J. Rao and K. R. Rajagopal, A study of strain induced crystallization in polymers. International    Journal of Solids and Structures, 38, (2001), 1149–1167.

[2]  I. J. Rao and K. R. Rajagopal, A thermodynamic framework for the study of crystallization in polymers. ZAMP, 53, (2002), 365–406.

[3]  I. J. Rao, Effect of the rate of deformation on the crystallization behavior of polymers.  International Journal of Non-Linear Mechanics 38 (2003), 663–676