Study On Tearing Behavior Of Airship Skin Material

Stratospheric airship is a kind of lighter-than-air floats with power propulsion and the ability to control the flight.Stratospheric airship has the advantages of long time in the air,wide detection range,fixed point hovering monitoring and good economy.It has broad application space in the fields of military reconnaissance,high-speed communication,ocean observation,weather forecast and missile early warning.In recent years,the research and development of stratospheric airship has become one of the strategic needs of our country.Among them,the skin of the airship is the main structure to bear the pressure difference between inside and outside and to store gas,which plays a decisive role in realizing the lightweight of the airship and ensuring the structural safety.However,under the action of many adverse factors such as atmospheric temperature,pressure and solar radiation in the adjacent space,the skin material of the airship is easy to produce small cracks,and the crack propagation may lead to the destruction of the entire structure of the stratospheric airship.At present,the research on tearing behavior of airship skin material is a hot topic at home and abroad.In this paper,a new type of skin material made in China will be taken as the research object to carry out experimental analysis,simulation and theoretical research on the tensile and tearing properties of the material.Firstly,through uniaxial tensile test of a new type of skin material made in China,basic mechanical parameters such as elastic modulus and Poisson’s ratio of the skin material were measured.Considering the mechanical characteristics of airship skin material,a uniaxial tear test procedure was established.Uniaxial side tear test and uniaxial center tear test were carried out on the skin material.The influence of different slit sizes on the residual strength of the skin material was evaluated.The effects of different notch shapes on the residual strength of materials were compared under the condition that the equivalent slot size was fixed.The influence of specimen width on the residual strength of the material is discussed under the condition of a certain notch size.To simulate the tearing property of the airship skin material in actual work,a self-made crease manufacturing device was used to take the photos of the surface morphological changes before and after the material damage with the help of an optical microscope.The center tearing test of the creases and the tiny holes generated after wear was carried out.The critical tearing strength of various specimens was obtained through experiments,which provided a basis for further research on tearing property of this type of skin material.Then,the extended finite element method model was established to simulate the crack expansion of film specimens with different crack lengths and specimen widths to verify the validity of the extended finite element simulation.The stress distribution at the tip of the slit and along the expansion path of the slit are studied.The stress distribution of specimens with different slot lengths before and at the moment of crack expansion along the expansion path was studied.By comparing the numerical simulation results with the experimental results,the accuracy of the simulation is verified,and the main reasons for the errors are analyzed.Finally,several existing tear analysis methods are summarized: stress intensity factor analysis method,Thiele empirical method and Maekawa exponential stress field analysis method.By means of numerical simulation,the variation of stress intensity factor(SIF)of specimens under various load conditions and different slot sizes is solved,and the results are compared with those of the analysis method.Based on Maekawa exponential stress field and its modified analysis method,the stress distribution law calculated by numerical simulation and analysis method is compared.Stress concentration coefficient is introduced to discuss the allowable slit length of the skin material of the airship with different sizes under different stress concentration coefficients.