Research On Acoustic Emission Characteristics Of Ductile Metal In Microscopic Damage Process

Acoustic emission technique is a mature nondestructive testing technology with simpleworking principle and high sensitivity, the weak stress wave signal coming from the innerregion of the material can be collected continuously in real time, it has been widely used inthe performance analysis of materials and structural integrity assessment. Ductile metal arewidely used engineering materials in people’s production and life, the microscopic damageresearch for ductile metal has been a major direction on damage mechanics and materialsscience currently, Based on this background and combined the Heilongjiang provincenatural science fund project “Study on the microscopic damage mechanism of metalcomponents under low-cycle fatigue and AE evaluation method”, this article carries out thecharacteristics research of AE signals that produced by the microscopic damage of ductilemetallic materials.In this paper, taking the rod notched specimens of20steel and Q345steel as theresearch objects to carry out tensile and acoustic emission experiments, and then obtain thedata of mechanical and acoustic emission signals. In addition, according to the GTN modelwhich commonly used on the study of micromechanical damage for ductile metallicmaterials, the numerical simulation analysis is used in the stretching process for two kindsof specimens by the ABAQUS finite element software, and the changes of micromechanicaldamage parameters are obtained in the cross section of specimens where withstand themaximum force. Basing on the above mentioned that the paper carry out many detailedanalysis. Main contents as follow:In the first chapter, the paper introduces the purpose and significance of the thesis topic,and outlines the history and development of the damage mechanics research, then itintroduces the history and basic principles of the acoustic emission techniques as well astwo novel signals processing methods, furthermore the chapter describes the contents androutes for this study. In the second chapter, the paper details the mechanism of acousticemission in the process of ductile metallic materials damage, the wave propagation andsignals acquisition as well as the methods of acoustic emission signals analysis. In the thirdchapter, the paper introduces the tensile and acoustic emission experiments for rod notchedspecimens, describes the whole process of the testing and analyzes some data preliminarily.In the fourth chapter, the continuous wavelet transform and the higher order spectra are used on the feature recognition of AE signals during specimens stretching, and get thetime-frequency and high-order spectral features of signals for different injury behaviors atdifferent damage stages. In the fifth chapter, the GTN model is introduced into thenumerical simulation for specimens of ductile metallic materials to obtain the law ofparameters variation for describing the microscopic damage. In addition, the chapterstatistics the change of acoustic emission signals parameters, and analyzes the relationshipbetween the cumulative parameters of microscopic damage and the cumulativecharacteristic parameters of acoustic emission signals, and establishes the assessmentformula based on the energy for the microscopic damage.