Analysis Of Tensile Acoustic Emission And Natural Frequency Characteristics Of 2D-C/SiC Ceramic Matrix Composites

With the development of modern science and technology,ceramic matrix composites(CMCs)is one of the emerging new materials in recent years.Compared with other metal materials,ceramic matrix composites have excellent properties such as high specific strength,high specific modulus,corrosion resistance,oxidation resistance,high temperature resistance,wear resistance and low coefficient of expansion resistance.Therefore,it has a large application space in aviation and aerospace.With the increasing application of ceramic matrix composites in aero-engines,the performance of ceramic matrix composites decreases in the face of internal damage.So this paper mainly focuses on the detection and analysis of internal damage and natural frequency of ceramic matrix composites.In this paper,the damage identification principle of acoustic emission technology is introduced,and the parameters of acoustic emission signal are explained.In the process of damage identification by acoustic emission technology,the principles of signal preprocessing such as noise elimination in unsupervised mode,feature parameter selection and parameter standardization of acoustic emission signals are analyzed successively,then the clustering algorithm and the principle of effectiveness analysis of clustering results are explained,and finally the spectrum analysis principle of acoustic emission signals is introduced.Secondly,a two-dimensional braided C/Si C composite sample was subjected to monotonic tensile and cyclic tensile loading and unloading tests at room temperature.Firstly,the acoustic emission signal is preprocessed,and then damage pattern recognition is carried out by hierarchical clustering analysis.It is concluded that there are four damage modes of 2d-c /Si C composites under tensile load: matrix cracking,interfacial debonding,fiber fracture and fiber bundle fracture.The fast Fourier transform(FFT)method is used to analyze the spectrum of the collected sound signals.According to the analysis,the 2d-c /Si C composite material mainly has damage signals of 39,52,147 and 182 k Hz at four frequencies under the action of tensile load,which respectively correspond to the fracture damage of matrix,interface delination-slip damage,fiber fracture damage and fiber bundle fracture damage.Combined with the acoustic emission signal during monotone tensile test,the acoustic signal under cyclic loading is analyzed.In addition,by comparing the CT scan results of ceramic matrix composites before and after the test,the damage distribution and the maximum stress position of the structure before and after the test can be obtained.The differential equation of vibration mode of the beam material are introduced in detail,and the natural frequency of the ceramic matrix composites is tested after each loading and unloading test,and the damage degree and natural frequency of the composites are analyzed and studied.According to the analysis of a total of 15 tests of the sample,the internal damage can be divided into four stages: test no.1～4 is the first stage,and the main damage is crack formation;Test no.5-9 is the second stage,the main damage is fiber fracture and a few fiber bundle fracture;Test no.10 is the third stage,the main damage is fiber bundle fracture and a few fiber fracture;Test no.11～15is the fourth stage,and the main damage is the disbonding and sliding of the interface.The results provide a basis for damage evolution and natural frequency variation of 2d-c /Si C composites.The relationship between the acoustic emission signal and the natural frequency of the ceramic matrix composite and the damage signal is found.It is concluded that the damage degree of the samples in cyclic tensile test can be divided into four types: the loading stress of 0～72MPa is the first stage of damage of ceramic matrix composites,and the main damage mode is matrix cracking;the loading stress of 72～126MPa is the second stage of damage of ceramic matrix composites;the loading stress of 126～168MPa is the third stage of damage of ceramic matrix composites;the loading stress of test number is 168～197MPa,which is the fourth stage of damage of ceramic matrix composites..Finally,the acoustic emission and natural frequency of a two-dimensional braille C/Si C composite sample during monotonic tensile and cyclic tensile loading and unloading tests at room temperature are summarized.Based on the environment,testing process and damage analysis method,the future research contents of this field are prospected and discussed.