Study On Mechanical Properties Of An Envelope Material For Airships

With the development of material,control system and energy field,the airship once again becomes a focus of current researches in developed countries for its wide applications in communication,transportation and military area after the explosion of the Hindenburg in 1937.Among them,the research on the stratospheric airship,becomes a top priority in the research filed of the airship.The stratospheric airship is a controllable aircraft floating at around 20 km altitude.Generally,it possesses the ability of stating at a fixed point with long-tern,great load capacity and reusable feature,etc.Therefore,it has invaluable prospect in the field of military and civilian application.As one of the most important parts in airship,the envelope material must be specially developed for the complex space environment in the stratosphere,which is huge temperature difference between day and night(minimum temperature of-55 ℃),ultraviolet radiation,ozone and strong effect of energetic particles,thus the envelope material possesses the following properties: high strength,light weight,low permeability and resistance to environmental degradation through temperature,etc.In this paper,a new airship envelope material called GQ-6 was regarded as the research object,investigated through theoretical methods and experimental research in order to recongnize its mechanical properties.Firstly,the uniaxial tearing performance of the new airship envelope material with central cracks was studied theoretically.Four typical theories used for tear strength analysis were summarized.Based on the stress field consideration theory advanced by Shoji Maekawa,a new theory was improved and proved to be correct through the experiment.To solve the problem of the influence of stress concentration phenomenon on the edge of the specimen,a method based on the advanced stress field consideration theory was presented to determine the reasonable width of the specimen.Secondly,the uniaxial tearing performance of the new airship envelope material with edge notched cracks was studied experimentally.The tearing performance of central cracks and edge notched cracks were compared.The results show that the two methods can be equally analyzed.Meanwhile,the width of the specimen and the width of the slit were used as variables to control the edge notched tear test of different width specimens,a method was proposed that can be used to determine the real critical tear stress through small width of the specimen.Thirdly,the shear behavior of the new airship envelope material was studied experimentally.Three typical theories used for shear behavior test were summarized,then uniaxial and biaxial shear test were carried out and compared.Meanwhile,the shear modulus was calculated by three formulas,and the differences were compared and analyzed.Finally,the welding properties of the new airship envelope material was studied experimentally.Four different welding failure modes were concluded through uniaxial tensile test of different welding width specimens.At the same time,the influence of welding width on the tensile strength and elongation was analyzed.