Research On Airship Envelope Material Of Tensile And Tearing Properties

It is believed that the stratospheric airship has many advantages.Such as capable of floating in a fixed area,staying long time in the air,detecting capacious acreages and transmitting comprehensive information message,etc.Therefore,study on the stratospheric airship has been set as national strategy in our country.The mechanical properties of envelope fabric play a pivotal role in the stable analysis of an airship structure.But in real engineering applications,initial small crack-induced rapture is the common failure form for envelope fabric of airships,which is prone to be punctured by internal load or external sharp objects.If the crack on the envelope fabric begin to propagate,the airship could be destroyed in the end.However,researchers in domestic and overseas rarely systematically study the tearing properties of airship materials.This paper studied a new airship envelope membrane.The tensile properties and the tearing properties of the new airship envelope fabric based on the uniaxial and biaxial tensile tests and theoretical analysis were researched.Firstly,a new reinforcement scheme on the clamped region of the specimen was settled after series of attempts.Then,according to the uniaxial tensile tests on the fabric,the yarns and the coated materials,and the crimping properties of the material during weaving,the mechanical response properties of the new material were figured out.Meanwhile,the constitutive equation of the material was analyzed from the point of the strain energy.Then,the variation and distribution properties of the elastic model of such material were analyzed in the uniaxial cyclic loads.Then,the uniaxial central tearing tests and the biaxial central tearing tests were performed.The loading speed,the initial crack length,the crack orientation and the proportional loading between the warp and the weft direction were studied.The validity of the equivalent crack length was proved after comparing the uniaxial and biaxial experimental data.The difference of tearing mechanical properties of such material in the uniaxial and biaxial tensile loading conditions were contrasted.Then,a computing method was presented which can predict the allowing bearing load and the allowing crack length of an airship envelope.Thirdly,the equivalence of the tearing mechanical response properties of such material with central crack and single edged notched crack was verified.Then,the specimen width influence on the tearing mechanical properties of such material was analyzed.It is concluded that the specimen width has significant influence on such material.Meanwhile,the testing results showed that the crack length ratio is not an appropriate factor to judge the tearing mechanical properties of membrane material.To reinforce the tearing membrane,the welding performance of the material was studied.The tensile mechanical properties of such material with and without welding zone were compared.Fourthly,based on the plain weave fabric property of such envelope fabric material,the finite element modeling(FEM)and the extended finite element modeling(XFEM)were applied to study the tearing propagation and the distribution of the stress fields near the crack tip.The numerical analysis results showed that the distribution of the stress fields near the crack tip manifest nonlinear reduction.The chapter summary offered some foundation for the coming theoretical research.Additionally,according to the stress field theory,a new mechanical model was proposed for modeling and simulation of tearing mechanical properties on airship envelope fabric.In such model,the author focused on the increasing stresses between the stretching yarns.The geometric progression was assumed to calculate the stress distribution of the crack tip.Then,the tearing propagation in the infinite width membrane was derived.Meanwhile,compared with the Thiele's empirical model,this new model is verified to be more accurate.What's more,the testing data of the off-axial specimens were introduced to such model.It is concluded that such model is feasible to calculate the critical strength of the material with arbitrary angle.In the end,the research fruit was summarized.The author also indicated the future direction of the development.