A Comparative Finite Element Analysis of Hart-Smith Hyperelastic Model Under Uniaxial, Planar and Equi-Biaxial Tension

The classical phenomenological compressible Hart-Smith model expressed in exponential-logarithmic terms of stretch invariants is compared with substantial hyperelastic models available in Abaqus. It is implemented in Abaqus Explicit using a customized user subroutine. Compressible Hart-Smith model together with selected acclaimed models available in Abaqus are evaluated under uniaxial tension, equi-biaxial extension and planar tension modes of deformations. The required material constants are determined from a simple uniaxial tension test. In order to investigate mode-independent characteristics of considered models, predictive planar tension and biaxial extension simulations are performed using the material constants derived from a uniaxial tensile test. Obtained numerical results are validated with respect to classical experimental data for natural rubber reported by Treloar.

Influences of Process Conditions on Stretching Characteristics of Crystalline Polymer Film

Developing the interior structures of polymer films is essential for creating novel functions of such films. This study investigates the effects of extension parameters and processing procedures on the super-structure of a polypropylene (PP) film. An biaxial extension device is also designed and fabricated to analyze the effects of annealing, extension temperature, extension rate and other parameters on the super-structures of PP films. Based on super-structure analyses, the relationships between extension parameters and film structures are determined, and an extension process that involves a second time stretching procedure is suggested. Experimental results indicate that void structures can be generated by biaxial extension at the interface between the crystalline and amorphous regions in a film. The mechanical strength of the film is also affected by stretching and become highly oriented. Although a low extension temperature can increase the number of void structures generated at a low extension ratio, structure sizes are dispersed. Additionally, voids with uniform size can be obtained when the film is stretched at a high temperature; however, it needs a high extension ratio to promote the formation of void structures. As for annealing treatment, when the annealing temperature increased, the size and quantity of the spherulites that were formed in films by annealing also increased, but these films tend to have similar sizes and numbers of void structures. Based on the experimental results, this study also describes how parameters influence the void structures of a PP film created during the extension process. Analysis results further demonstrate how extension parameters and processing procedures can be adjusted to improve the fabrication of PP films.

Human Annulus Fibrosus Lamellae Generate Significant Multi-Axial Forces and Moments in Biaxial Extension

Low back pain is a widespread public health issue affecting about 75% of Americans in their lifetime [1]. In many individuals, the origin remains unknown in spite of decades of research. However, intervertebral disc (IVD) degeneration has been theorized as a major precursor to nonspecific low back pain [2,3].