Biaxial Test Methods,Experiments And Mechanical Behavior Of Fabric Membranes

In recent years,membrane structures with beautiful and novel style have attracted considerable attention due to their advantages such as light weight and good self-cleaning.Two typical materials for membrane structures are fabrics and films.In addition,the fabrics also can be used for manufacturing airship and high-altitude balloons which are widely utilized in weather monitoring and communications reconnaissance.This thesis focuses on the fabrics with the method of theoretical analysis and experimental study to investigate the mechanical properties of the fabric membranes under biaxial loading.The main topics include biaxial testing techniques,biaxial shear test,biaxial tensile test as well as biaxial tear test.First,a new biaxial testing machine was developed based on the experience of existing testing machine.The new fixtures of biaxial machine could facilitate to fix specimens.The connecting rod was removed,while the proportional relief valve was mounted directly on the cylinder in order to improve control accuracy.In addition,new test machine with excellent performance of force sensor and electrical systems could improve the accuracy of loading process and measurement.Secondly,biaxial shear test methods and properties of membrane material were studied.As no unified standard on biaxial shear test method,the methods considering test methods and calculation method are necessary.The method need to be considered from test methods and calculation method.Cruciform specimens which has 45° angle between warp direction and loading direction were used to evaluate difference of load curves.New methods of calculating shear strain and shear modulus were discussed.Biaxial shear properties of Uretek5876,Uretek5893 and Uretek3216 LV were tested on biaxial test machine and shear mechanical properties of the three materials were discussed.Thirdly,based on the upgraded test system for displacement control and force control,biaxial tensile tests were conducted for Uretek5876,Uretek5893 and Uretek3216 LV.Different elastic moduli were discussed considering stress ratio of warp and weft.In engineering application,the appropriate moduli were recommended according to different stress ratios.Finally,biaxial tear tests for Uretek3216 LV were carried out to obtain breaking strength and displacement.The effects of slit length,slit angle and stress ratio on breaking strength were studied.