Probabilistic Improvement of Crack Propagation Monitoring by Using Acoustic Emission
In this work, acoustic emission (AE) is used as a measurement technique to detect and locate the crack tip and, to monitor its propagation in a wooden specimen subjected to mechanical stresses. Tensile tests were performed on DCB specimens to generate mod
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Probabilistic Improvement of Crack Propagation Monitoring by Using Acoustic Emission Malick Diakhate, Emilio Bastidas-Arteaga, Rostand Moutou Pitti, and Franck Schoefs Abstract In this work, acoustic emission (AE) is used as a measurement technique to detect and locate the crack tip and, to monitor its propagation in a wooden specimen subjected to mechanical stresses. Tensile tests were performed on DCB specimens to generate mode I cracking. Under these stresses, the material response results in a release of energy in the form of transient elastic waves that were recorded by AE sensors. By means of the AE technique, the monitoring of material damage lies in the ability to identify the most relevant descriptors of cracking mechanisms. The latter are identified by clustering the AE data. A K-means++ algorithm was used, and two AE features—peak frequency and number of counts— represent adequately the AE events clustering. This unsupervised classification allows the AE events that were generated by crack tip growth during the test to be identified. There are many parameters that can affect the accuracy of AE monitoring such as noise signals, geometry, wood species, etc. Consequently, in this study, probabilistic approaches (Probability of Detection) were used to both characterize uncertainties and improve AE experimental protocol. Keywords Acoustic emission • Crack tip monitoring • Cluster analysis • Probability of detection • Wood material
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Introduction
Due to the manufacturing process of building materials some defects are presents in civil engineering and mechanical structures. These manufacturing defects could propagate under environmental or mechanical loadings, and could induce the total collapse of the structure. It is a well known fact that timber elements exhibit micro-cracks [1] which can propagate under fatigue, overload, or creep loading, and can cause failure of the structure [2]. In addition, wood is a hygroscopic material whose mechanical behavior is very sensitive to climatic changes such as temperature and moisture content variations [3]. For example, drying process accelerates the crack growth, whereas humidification process lead to a delay in crack propagation [4]. In order to bring some responses to these scientific problems, the ANR JCJC2013 CLIMBOIS project [5] is dealing with the effects of climatic and mechanical variations on the durability of timber structures. As part of this research project devoted to both an identification of failure mechanisms in wood material and an evaluation of the crack length evolution during tests, the study carried out herein included both experimental tests in constant and variable environmental conditions and statistical and probabilistic analysis of the acoustic emission (AE) results. Recent years witnessed a dynamic development of the acoustic emission method. It finds a wider and wider application in many industrial fields, mainly to monitor the structural health of the structure components [6–8]. In fracture mechanics, some authors have applied the AE
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