Analysis Of Characteristic Signal Of Acoustic Emission During Compression Of Aluminum Foam Based On VMD Algorithm

The closed-cell aluminum foams is a lightweight,porous material with cell structure.It has been widely used in the automotive,aerospace and high-speed rail industries due to its physical properties and the good energy absorption properties.In this paper,for the mechanical properties of closed-cell aluminum foam,the acoustic emission(AE)signals and CCD images of the aluminum foams compression process at different rates were collected by acoustic emission and high-speed camera,and the acoustic emission signals were resolved by variational mode decomposition(VMD).The deformation mechanism and mechanical properties of aluminum foams were studied by acoustic emission signals and CCD images.The main research contents of this paper are as follows:(1)Using VMD to analyze foam aluminum from the microscopic level,the acoustic emission signal is decomposed into four mode acoustic emission signals to study the mechanics and energy mechanism of aluminum foam.According to the sparsity of the mode acoustic emission signal of the VMD,the stochastic process of acoustic emission and the orthogonal coefficient method are given.The K value of the orthogonal coefficient is more accurate than the correlation coefficient,and it can more directly reflect the energy relationship between the mode acoustic emissions.(2)The relationship between mechanical properties and acoustic emission parameters of closed-cell aluminum foams during compression was investigated by quasi-static compression experiments.The results show that the count of the acoustic emission in the linear elastic stage has a linear relation with the amplitude;the energy count has an exponential relation with the amplitude.The higher the count,energy count and amplitude distribution under the higher compression rate.The acoustic emission count curve has a high similarity with the stress-strain curve.The dense strain has a good eorrespondence with the acoustic emission energy eount.The acoustic emission energy-strain curve has the same trend as the energy absorption efficiency of aluminum foams and has a good correspondence with compact strain.(3)VMD method was used to decompose the AE signal,then produced the mode AE signal which was correlated with stress-strain curve and CCD images to analyze the microscopic deformation mechanism of aluminum foams.Besides,the mode Shannon entropy would be proposed and analyzed.The results show that during the static compression elastic stage,the hardened plastic buckling and plastic hinge,the AE signals are mainly IMF2(with a central frequency of 0.15 MHZ);the AE signals are mainly IMF1(with a central frequency of 0.8 MHZ)in the stage of large-area shear damage of the stress platform;dislocation friction signals are mainly high frequency IMF3/4 signals;the higher the loading rate is,the larger the AE entropy would be.After entering the stress platform,the larger the amplitude and energy are,the larger the AE entropy would be.