Semester of Graduation

Fall 2024

Degree

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Document Type

Thesis

Abstract

This work features a new approach that is used to measure the rate of plastic work during a cyclic fatigue test, based on the first and second laws of thermodynamics. Using the one-dimensional Fourier heat equation coupled with the concept of fracture fatigue entropy, the rate of plastic work during fatigue can be measured without the need to interrupt a fatigue test, and the accumulated entropy to failure can be quantified. Experimental fatigue tests are conducted on Aluminum 6061-T6 specimens under cyclic axial loading and Carbon Steel 1018 specimens under fully reversed cyclic bending loading. The obtained results in addition to a thermal FEA model validate the framework and demonstrate the model’s ability to accurately quantify the plastic work rate and FFE in scenarios of very-low-cycle fatigue as well as mid-to-low-cycle fatigue. Results show that this method of calculating the plastic work rate is accurate, as its values agree with the values of other proven methods. The FFE’s of CS 1018 and Al 6061-T651 were found to be 21.4 ± 2.2 and 3.3 ±0.8 MJ/(m3K), testifying that Fracture Fatigue Entropy is a material property. With this developed model, the fatigue life is predicted for two cases and result in fatigue life predictions with errors both less than 4% of the experimental results. The TP-TG method is applied to three different irregular geometries with stress concentrations and a reduction in FFE is seen. The reduced values of FFE are explained via the concept of entropy capacity which is explained in detail.

Date

10-28-2024

Committee Chair

Khonsari, Michael M.

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Available for download on Tuesday, October 28, 2025

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