Acoustic Entropy of the Materials in the Course of Degradation

Abstract

Abstract:We report experimental observations on the evolution of acoustic entropy in the course of cyclic loading as degradation occurs due to fatigue. The measured entropy is a result of the materials' microstructural changes that occur as degradation due to cyclic mechanical loading. Experimental results demonstrate that maximum acoustic entropy emanating from materials during the course of degradation remains similar. Experiments are shown for two different types of materials: Aluminum 6061 (a metallic alloy) and glass/epoxy (a composite laminate). The evolution of the acoustic entropy demonstrates a persistent trend over the course of degradation.

Characterisation of the damaging micromechanisms in a pearlitic ductile cast iron and damage assessment by acoustic emission testing

“…The results allowed to identify potential damage criteria associated with the AE entropy, similarly to other studies . In particular, two alternative criteria identifying the incipient failure are proposed accordingly: (a) a lower bound threshold limit for δ (log 10 ΣS E )/ δt and (b) an upper bound threshold limit for log 10 ΣS E,r .…”

“…The basic AE analysis produced weak correlations that are hardly implementable to damage assessment and health monitoring purposes. The evaluation of information entropy of the AE data allowed to establish more quantitative damage criteria, similarly to other studies . Both Shannon and Kullback‐Leibler entropy formulations were correlated to the damage evolution; ie, they identified the proceeding of the damage.…”

“…This aims at verifying whether the observed trends are related to the specific conditions of the current application, or they have a more holistic significance. Some studies already supported this latter hypothesis, such as the work by Kahirdeh and Khonsari that focussed on cyclic bending testing of aluminium and epoxy/glass specimens. In this study, the Shannon entropy trend over the course of degradation did not (significantly) depend on the material, as well as the failure value of the entropy.…”

“…A schematic application of the technique is shown in Figure A (by Mistras LTD). The evolution of the main features of the AEs (namely, AE features , Figure B) is potentially correlated to the damage, even though a more refined analysis typically allows a more robust assessment …”

“…The evolution of the main features of the AEs (namely, AE features, Figure 2B) is potentially correlated to the damage, even though a more refined analysis typically allows a more robust assessment. 17,26,27 Several studies 21,25,[27][28][29][30] used AE testing for the damage identification in various metals and alloys. However, very few studies applied AE testing for evaluation of damage in DCIs.…”