Research On Damage Pattern Recognition Method Of Carbon Fiber Composites

With the continuous progress of science and technology,higher requirements are placed on the performance of materials.Carbon fiber composite materials have broad application prospects in the fields of aerospace,pressure vessels,wind power generation,and ships due to their advantages such as high specific strength and high specific rigidity.However,the failure mechanism of composite materials is involved,including fiber fracture,matrix cracking,interface debonding,and delamination failure.In particular,the multiple damage failures in in-service containers and equipment mix and overlap with each other,which makes it very difficult to identify the damage type and characterize the evolution process.Acoustic emission technology is often used to detect the damage of carbon fiber composites.However,the damage pattern recognition rate of the conventional acoustic emission analysis method cannot guarantee the accuracy of damage identification.Therefore,it is of considerable significance to study the relationship between the physical damage mechanism and the acoustic emission source,to extract the characteristics of the damage mode waveform from the transient waveform of the sound source,and to master the modal variation law of different damage types,to realize the dynamic characterization of the damage acoustic emission of composite materials.Then it is of considerable significance to realize the online monitoring and intelligent evaluation of the damage state of the composite containers and equipment in service.In this paper,based on the Lamb wave theory,a multi-excitation mode acoustic emission signal experiment system is constructed.The modal separation of acoustic emission waveforms is realized by employing empirical mode decomposition and continuous wavelet energy spectrum.The fast Fourier transform is used to transform the separated modal components in the frequency domain to obtain the peak frequency range of different models.Furthermore,the frequency characteristic attenuation test under different propagation distances is carried out for the separated modes,and the peak frequency and the center frequency range are selected as the judgment indicators to obtain the frequency characteristic changes under different distances and different excitations.Based on the damage mechanism of carbon fiber composite materials,for the two typical damage types of fiber fracture and matrix cracking,the acoustic emission monitoring experiments of fiber bundle breakage and epoxy resin breakage was designed.The two types of damage acoustic emission were obtained by correlation analysis through characteristic parameters.The distribution range of time-domain parameters,in which the matrix cracking damage is divided into macro cracking failure and microcracking.The combination of empirical mode decomposition and continuous wavelet transform is used to extract the peak frequency and energy distribution of the two types of acoustic emission signals.Secondly,the modal acoustic emission characteristics of the two types of damage are analyzed to obtain the modal waveform characteristics of fiber breakage damage and matrix cracking.Two modal characteristic parameters TWA and TWE,are constructed.The modal characteristic value is extracted,and the time experience is analyzed by a time window function,the numerical variation rules under different loads are analyzed.The in-plane bending damage model of carbon fiber composite laminates is established,and the in-plane bending numerical simulation of carbon fiber composite laminates is carried out by using H-P failure criterion.Based on the numerical simulation results,the in-plane bending damage acoustic emission monitoring experiment is designed.The modal characteristics of composite layered damage AE signals are also obtained.On this basis,based on three-dimensional Hashin,the stress-strain distribution and stress concentration of the cylinder under three different loading conditions are obtained,and the matrix cracking and fiber fracture damage evolution law of the filament wound layer are obtained.The experimental system of acoustic emission monitoring of the composite cylinder was built,and the changing trend and numerical range of typical damage parameters of the filament winding layer were obtained by time-domain parameter load correlation analysis.Based on TWA parameters,the algorithm of the modal characteristic criterion of gas cylinder damage signal is put forward to realize the practical separation of different modal types.The evolution trend of different damage types is accurately characterized by the accumulated counting rate of the separated modal parameters with the load.K-means clustering algorithm is applied to pre-classify the damaged acoustic emission signals,then the model characteristic parameters such as modal rise time,peak amplitude,peak frequency,duration,etc.were designed as damage pattern recognition Enter the sample.The primary component analysis method is used to reduce the dimensionality of the multi-dimensional input data.Based on the correlation vector machine algorithm,a composite gas cylinder damage signal modal recognition algorithm is constructed.According to the algorithm,cross-recognition of different source signals is effectively implemented Identify.The damage mode TWE and the load of the separated cylinders were analyzed,and the time-domain distribution of the damage modes was obtained.The least-square method was used to fit the TWE time cumulative counting curve,and the TWE_b value was extracted as the evaluation parameter of different damage stages.The results showed that the TWE_b value was sensitive to the damage process,and the trend change was simple,which could realize the practical evaluation of gas cylinder damage.