Study On Acoustic Emission Testing And Evaluation Technology Of Carbon Fiber Reinforced Plastics Gas Cylinder Low Velocity Impact Used In Vehicle

Carbon fiber reinforced plastics(CFRP)gas cylinders are widely used in aerospace,transportation,petrochemical and medical industries due to their advantages of light weight,good rigidity,high strength,good fatigue resistance and long service life.In recent years,with the rapid development of LNG,CNG and hydrogen energy vehicles,the ownership of CFRP gas cylinders is increasing,and accidents caused by damage to the winding layer of composite gas cylinders occur from time to time,and the safety of such cylinders needs to be solved.The winding layer of CFRP cylinder is the main load-bearing part of the cylinder,which is woven with carbon fiber and bonded with resin,and it is a typical structure that is resistant to internal pressure but not to impact.The winding layer containing the impact damage will have a reduced load carrying capacity due to the expansion of the damage under the working pressure.Since the damage process occurs mostly in the internal and each anisotropic non-metallic material,it is difficult to implement effective detection by conventional non-destructive testing methods.Therefore,this paper selects the acoustic emission detection method which is sensitive to the dynamic expansion of damage,and conducts the impact test for CFRP gas cylinder,and investigates the damage expansion behavior of the cylinder after impact,which has certain theoretical significance and significant engineering application value.Firstly,the strain-based failure criterion and damage evolution criterion are adopted to numerically analyze the damage evolution process of carbon fiber plywood fiber stretching and compression,matrix stretching and compression under impact loading with different weaving methods,and numerically analyze the material damage evolution process under different impact energies of dropping hammers with the same weaving method,to determine the minimum impact energy that leads to delamination and fiber fracture damage of the specimen.Threshold value.Secondly,based on the numerical analysis of the impact damage of carbon fiber plywood,combined with the power index cohesion model of mixed mode,the mechanical behavior of fiberwound containers with metal liner under impact with and without internal pressure is investigated to obtain the impact damage distribution.By analyzing the simulation results of damage distribution under different impact loads,the relationship between impact energy and damage degree is obtained.On the basis of the above analysis,a low-speed impact test rig is designed and constructed to perform ball impact test and acoustic emission monitoring on laminates with different weaving methods.The nonlinear ultrasonic damage quantification and extraction results are fitted to the collected damage acoustic emission characteristics,and the change rule of acoustic emission characterization parameter is obtained under different degrees of damage.Carry out in-face bending acoustic emission monitoring test on carbon fiber composite laminate after impact damage,use empirical mode decomposition,principal component analysis and support vector machine to extract features and identify patterns of acoustic emission signals in bending test,and obtain the damage evolution law of carbon fiber composite material after low-speed impact.Finally,in order to characterize the damage evolution of gas cylinder after impact,a carbon fiber gas cylinder impact damage test bed is designed and constructed,and acoustic emission monitoring is carried out for the impact damage process of the gas cylinder based on the optimal transducer selected from the attenuation test.Using the wavelet packet decomposition results,based on the convex vector optimization method to obtain the best acoustic feature quantity to characterize the degree of impact damage of the cylinder as the wavelet packet energy,and to obtain the corresponding relationship between matrix cracking,delamination,fiber fracture and wavelet packet energy.The hydrostatic test and acoustic emission monitoring were carried out on the carbon fiber-wound composite cylinders after impact damage.Ultrasonic C-scan was used to extract the acoustic characterization of cylinders with different damage levels and statistically analyzed,and the results were in good agreement with the results of the acoustic emission analysis of the impact damage of the laminate.Based on the test results,the Felicity ratio,which does not take into account the Felicity effect of the cylinder itself,is determined as the evaluation index of cylinder safety,and the damage reliability assessment method for carbon fiber composite cylinders is established.