Date of Award

6-2018

Document Type

Thesis

Publisher

Santa Clara : Santa Clara University, 2018.

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Michael Taylor

Abstract

Recent studies suggest that auxetic materials such as porous metals with orthogonal periodic void patterns have an increased fatigue life compared to non-auxetic materials. This study provides numerical solution to support the existing experiments with the use of contour J-integral as a parameter of stress intensity factor for computing the number of fatigue life cycle of the materials with auxetic structures. Representative volume elements (RVEs) were constructed to characterize the physical test specimens with void patterns such as ellipse, slot, and stop-hole. Extended finite element method (XFEM) was performed to verify the direction of crack propagation on auxetic materials. Sixty-five distinct RVEs were made for each void shape with increasing horizontal double notch to mimic the crack propagation. Using Abaqus, the contour J-integral was calculated automatically at the crack-tip region. Numerical computation showed that auxetics have lower rate of overall crack propagation compared to non-auxetics. Variation of geometric parameters were employed to the void patterns of the RVE which changed the porosity and the minimum hole distance of the auxetics. Computation on stress intensity factor for each crack increment showed that models with relatively larger negative Poisson’s ratio have faster crack initiation. XFEM and J-integral simulations were performed on aluminum plates with circular and stop-hole void patterns and compared with experimental data. Results were in good agreement to the experiment where stop-hole void model had lower rate of crack evolution compared to the circular void model.

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