Tearing Test And Numerical Simulation Of Airship Envelope Material

The stratospheric airship has the advantages of fixed-point flight,long idle time,wide detection range and strong load capacity,and the highperformance envelope material is one of the key technologies of the stratospheric airship.With the development of a new generation of composite material,the world’s major military powers have once again set off a research boom in stratospheric airship.Generally,airship envelope material need to have high strength,light weight,low leakage,low temperature resistance and tear resistance.However,in engineering practice,it is found that the envelope material is prone to have internal defect or tear damage during manufacturing or installing,and the lighter case may cause slight air leakage,the severer case may destroy the overall structure of the airship,thereby affecting the safety of the airship and life.Therefore,it is of great significance for the study of the tear properties of the envelope material.In this paper,a new type of airship envelope material is studied.Based on the one-side slitting tear test,the central slit tear test and the extended finite element numerical simulation,the tear properties of the membrane are systematically studied.Firstly,the side slit tearing test was carried out in different test piece width and slit length,which not only studied the tearing process of the test piece,but also analyzed that the length of the side slit and the width of the test piece were how to effect the critical tearing stress of envelope material.The results show that the tearing process can be roughly divided into four stages,namely the initial stage,the slit opening stage,the slit expansion stage,and the tear failure stage;when the width of the test piece is the same,the critical tearing stress of the envelope material decreases nonlinearly with the increase of the length of the slit;when the length of the slit is fixed,the critical tearing stress of the envelope material increases nonlinearly with the increase of the width of the test piece.At the same time,the central tearing test was carried out with fixed test piece width but different slit length to compare the similarities and differences between side slit tearing damage and central slit tearing damage.The results show that the extended failure process of the central slit is consistent with the side slit,and because the test piece with the central slit has other yarn constraint on both sides of the slit,there is no obvious warpage near the tip of the slit in the initial stage of load loading,but there is obvious warpage near the tip of the slit in the initial stage of load loading for the test piece with the side slit because of the lacking of other excess yarn constraint;the value of critical tearing stress of the specimen with central slit(width of 50 yarns)is approximately equal to that of the specimen with side slit(width of 25 yarns).Secondly,by using the extended finite element method to simulate the tear propagation characteristics of the envelope material,compare the extended finite element simulation results of the side slit tearing failure and the uniaxial side slit tearing test data,deep study the distribution of stress near the tip of the slit,study the influence of the width of the test piece on the critical tearing stress of the envelope material,and compare tearing performance of the uniaxial side slit and the simulation results of the tearing performance of the symmetric center slit to analyze the similarities and differences of critical tearing stress.The results show that the extended finite element numerical simulation method can effectively simulate the tearing process of the new membrane specimens with the initial slit;the stress of the yarn is nonlinearly reduced with the distance from the cutting tip and the stress of the yarn farther from the tip of the slit is approximately evenly distributed;when the length of the slit is fixed,the critical tearing stress of the membrane increases with the increase of the width of the piece,but the extent of the increase will gradually decrease,as the width of the test piece is gradually increased,the critical tear stress value of the membrane will tend to be stable;the value of critical tearing stress of the specimen with central slit is approximately equal to that of the corresponding specimen with side slit(The width of the side slit test piece and the length of the slit are respectively half of the width of the center slit test piece and the length of the center slit.).Finally,from the micromechanical point of the tearing damage of envelope material,the theoretical formula of the critical tearing stress equivalent stress transfer factor is obtained.And the theoretical values of the critical tearing stresse,experimental values and simulated values of the side slit are also compared.The results show that the critical tearing stress value calculated by the theoretical formula is in good agreement with the experimental and simulated values.