Study On Tearing Properties Of Envelope Material For Airships Based On Tearing Test And Theoretical Analysis

With the development of science and technology,the gradual accumulation and improvement of airship technology and theory has greatly enhanced and ensured the safety of airship.The airship rekindled its vitality with its huge military and civilian value and unique advantages.Now the development trend is mainly concentrated in military airships,supplemented by the civilian ones.In recent years,the position of the stratospheric airship in the military development has become even stronger.It has been unanimously favored by the world's major military powers.The United States,the European Union and Japan have all formulated plans for the study and implementation of the stratospheric airship to seize the dominant position.Develop large stratospheric airship became the strategic needs of our country.At present,there is still no airships that can be stably flown for a long time in the stratosphere.The development of stratospheric airships still faces many key technical problems and challenges,such as the development of the high performance and light-weight airship skins and controlling its failure of tearing propagation.Airship skin,as the main structure of the airship is key to establish a stratospheric platform.If the initial slit or tearing in the airship skin propagates,the entire airship will face the risk of failure.In this paper,via experimental research and theoretical analysis,the tearing properties of a stratospheric airship envelope material was studied,compared with the fabric with part of the functional layer of this airship skin material.And factors influencing the tearing performance of the skin membrane are further studied by finite element analysis.First,the tensile strength of the two materials was measured by uniaxial tensile test,the uniaxial single edge notched tearing test was carried out to study the relationship between the critical tearing stress with different slit length,specimen width and cutting ratio.The propagation process of the two materials was analyzed and compared and the mechanism and reason of the difference were also analyzed and given.The results show that the critical tearing stress decreases with slit length and increases with specimen width,and is related to the cutting ratio of specimen with a finite width.In addition,when the yarns are not closely adhered,the tear expansion is not obvious,the stress concentration at the slit tip is small and the tear strength is thus increased.However,the stratospheric airship skin material which has more densely weaving contexture,good adhesion,shows a gradual slit expansion process,but the tear strength decreased compared with the other material tested;So qualitatively,the interaction of yarns,the adhesive layer and yarn weaving density can all affect the tearing performance.Secondly,three types of crack propagation failure theories were used to analyze the test results.These three theories are respectively the stress intensity factor theory,the exponential stress field theory of the equivalent stress transfer factor theory obtained from the simplified physical model.The theoretical calculation and comparative analysis shows that the theory of inherent flaw theory,exponential stress field theory considering the size effect,and the equivalent stress transfer factor theory can be used to study the tear strength of flexible fabric material.Of which the inherent flaw theory is the best one.The inherent crack length calculated by this theory can be used as a reference index to measure the defect performance of the membrane material itself.However,the theory of exponential stress field and the theory of equivalent stress transfer factor are intrinsically linked.The parameters in these two theory can be transformed thus these two theories can be treated equivalent.In addition,based on the modified exponential stress field theory?,the allowable slit length of the stratospheric airship skin material is obtained under the allowable working stress.Finally,based on the finite element simulation software ABAQUS,the analytical model of the membrane layer was established.The uniaxial tensile test of the yarn was carried out.The effect of different contact and weaving density between warp and weft yarns on the tearing performance was studied.The results show that the yarns' breaking stress is related to the weaving density.The binding contact between warp and weft yarns leads to significant stress concentration at the cutting tip,resulting in the tear strength being significantly lower than the frictional contact.With the same areal density,the lower weaving density with the coarse yarn that has better tear resistance.