| Metal materials under certain conditions with a variety of unique and excellent performance,are the widely used materials in the dustry.Metal fatigue is very common.Therefore,the study of damage and fracture of metal materials has been the subject in modern materials science.As a new non-destructive testing technology,AE technology provides a useful tool for the study of damage and fracture of metal materials.This article mainly studies acoustic emission characteristics of deformation and damage fracture of aluminum alloy material under uniaxial and three-point bending loading.The AE mechanism of metal materials at different stages of deformation was discussed.The variation law of AE characteristic parameters was achieved.The main contents and achievements of this paper are as follows.(1)The stress-strain curves of aluminum alloy under uniaxial tensile loading show typical elastic,plastic,and deformation to fracture failure.Combined with the microstructure characteristics,the mechanical mechanism of PLC effect in plastic deformation of aluminum alloy is analyzed,and the critical strain of the PLC effect is achieved.(2)AE characteristics of aluminum alloy under uniaxial tensile loading and three-point bending loading were investigated by using advanced acoustic emission testing system.The variation of acoustic emission parameters such as events,amplitude,energy,and counts reflects the deformation characteristics of the microstructure.Plastic deformation such as shear band slip and dislocation generated a large number of AE signals.The AE signals are mainly generated by crack propagation during fracture.Compared with the non-notched specimen,the pre-fabricated notched specimen the three-point bending loading produced a large number of high-amplitude AE events in the elastic phase and the fracture stage,because of stress concentration at the notch leading to plastic deformation and crack formation and spread.(3)AE signals in two typical loading methods by Wavelet decomposition and wavelet packet decomposition were analyzed.Time-frequency diagram and energy distribution results show that the AE signals in the elastic,plastic and fracture phases have different timefrequency characteristics.With the increase of deformation,the high frequency part of the AE signals generated in the aluminum alloy material increases and the low frequency part decreases(4)The internal damage of aluminum alloy specimens was characterized by acoustic emission cumulative counting.The correspondence between the characteristic parameters of acoustic emission and damage variables was established.The evolution equation of damage parameters of aluminum alloy specimen under three-point bending loading at a constant rate was presented. |
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