Detecting fatigue in aluminum alloys based on internal friction measurement using an electromechanical impedance method

TL;DR

This study introduces a method to monitor low-cycle fatigue in aluminum alloys by measuring internal friction via electromechanical impedance, providing a potential universal fatigue criterion for metallic materials.

Contribution

It presents a novel application of internal friction measurement using Q-EMI for fatigue detection in aluminum alloys, with a proposed general fatigue criterion based on IF.

Findings

IF increases steadily with fatigue cycles

IF reaches 2.5 to 3.4 times initial value before failure

Resonance frequency drops less than 2% before failure

Abstract

Detecting mechanical fatigue of metallic components is always a challenge in industries. In this work, we proposed to monitor the low-cycle fatigue of a 6061 aluminum alloy based on internal friction (IF) measurement, which is realized by a quantitative electromechanical impedance (Q-EMI) method using a small piezoelectric wafer bonded on the specimen. Large strain amplitude (3.3*10^-3) was employed thus the fatigue life can always be below 10^5 cycles. It was found that except for the initial testing stage, the IF always increases steadily with the increasing fatigue cycles. Before the fatigue failure, the IF can reach 2.5 to 3.4 times of the initial value, which is thought to be caused by the micro-cracks forming and growing. In comparison, the resonance frequency of the specimen just drops less than 2% compared with the initial value. Finally, a general fatigue criterion based on IF measurement is suggested for all the metallic materials.