Comparison of Constitutive Models for predicting the formability of SS 304 by tubular hydroforming process

Finite Element (FE) simulation of sheet/tube forming precision depends mainly on the accuracy of the constitutive modeling. The present paper aim is to compare the constitutive models to fit the stress-strain curves. The accurate deformation behavior of the SS 304 tubes depends on the constitutive modeling of hardening behavior. Deformation data of the tensile specimens cut from tubular sample were collected by conducting Uniaxial tensile tests (UTT) at three different rolling directions. Five constitutive relationships were then recognized by fitting the true stress and strain data with the constitutive models of Hollomon, Power, Krupowsky, Voce and Ghosh, and the fitting accuracy were analyzed and compared. Effects of hardening models on Forming Limit Curves (FLC), pressure loading and bulge height of the hydroformed tube were then studied. The obtained FLC from the simulations were compared with experimental FLC to predict the accuracy of the hardening models.

The Interventricular Septum Is Biomechanically Distinct from the Ventricular Free Walls

The interventricular septum contributes to the pumping function of both ventricles. However, unlike the ventricular wall, its mechanical behavior remains largely unknown. To fill the knowledge gap, this study aims to characterize the biaxial and transmural variation of the mechanical properties of the septum and compare it to the free walls of the left and right ventricles (LV/RV). Fresh hearts were obtained from healthy, adult sheep. The septal wall was sliced along the mid-line into two septal sides and compared to the epicardial layers of the LV- and RV-free walls. Biaxial tensile mechanical tests and constitutive modeling were performed to obtain the passive mechanical properties of the LV- and RV-side of the septum and ventricular walls. We found that both sides of the septum were significantly softer than the respective ventricular walls, and that the septum presented significantly less collagen than the ventricular walls. At low strains, we observed the symmetric distribution of the fiber orientations and a similar anisotropic behavior between the LV-side and RV-side of the septum, with a stiffer material property in the longitudinal direction, rather than the circumferential direction. At high strains, both sides showed isotropic behavior. Both septal sides had similar intrinsic elasticity, as evidenced by experimental data and constitutive modeling. These new findings offer important knowledge of the biomechanics of the septum wall, which may deepen the understanding of heart physiology.