Shizan He’s research while affiliated with Shanghai Jiao Tong University and other places

This paper deals with the fracture failure analysis on plain woven laminated fabrics used in stratospheric airship structures. A series of uniaxial tensile and central slit tearing tests were carefully conducted on bias specimens, and the corresponding tensile and tearing properties, including failure mechanisms and material strengths, of a laminated fabric were discussed. Results show that laminated fabrics are typical direction-depended materials, and their failure characteristics vary greatly with the bias angles. Typical tearing stress–displacement curves of the laminated fabric could be defined as four characteristic regions: a co-deformation region, a yarn extension region (or shear deformation region), a plateau region, and a post peak region. Among bias specimens, there are many obvious differences in tearing behaviors in terms of maximum displacement, damage mode, curve slope, and number of stress peaks, which could be attributed to the material orthotropy and different failure mechanism of constituent materials. Unlike results of tensile strength, there is a W-shaped relationship between tearing strength and off-axis angle, with a local strength peak at 45° angle. Based on the Tsai-hill criterion, a new tearing strength criterion consisting of two parts, including a U-shaped and an inverted V-shaped part, is proposed for this laminated fabric. Comparisons between the experimental and calculated results for the laminated fabric are performed, and the strong agreements demonstrate that the proposed criterion is feasible and accurate.

The use of enhanced plain woven fabrics for aerospace engineering needs essential and accurate mechanical parameters for analyzing structural behavior and performing numerical simulations. The uniaxial tensile tests are direct and effective approaches to investigate these mechanical properties. This study focused on uniaxial monotonic and cyclic mechanical properties of an enhanced plain woven fabrics URETEK 5893 in on-axis and off-axis tension. For uniaxial monotonic mechanical properties, an improved method to determine yield stress was proposed and digital image correlation (DIC) technique was utilized to investigate detailed breaking mechanism. It is found that yield stresses were stable in each loading direction and typical yield stresses in the warp, weft and 45o directions were 5.56 MPa, 8.84 MPa and 1.96 MPa respectively. Moreover, the breaking mechanism in terms of strain propagation process was identified. For cyclic mechanical properties, approximate stable ratcheting strain and elastic modulus were investigated. Nonlinear ratcheting strain was more sensitive near 45o than other directions. Moreover, Poisson ratios in three directions were obtained with DIC technique and the maximum Poisson ratio existed in the 45o direction. The comparisons between experimental and theoretical elastic moduli showed that the best agreement existed in the warp and weft directions and the accuracy of using the theoretical equation to calculate elastic modulus was dependent on material linearity.

This paper presented the development of a novel flexible inflatable Manipulation arm. Both straight beams and rotational joints are made of air-inflated membrane units. In order to minimize the actuation moment, a rotational joint with creases, analogous to spacesuit elbow, was developed. Besides, a tendon driven system was also developed to actuate the arm rotation. Biaxial tension and shear tests were conducted on the flexible PVC fabric of the inflatable arm, and the elastic constants of the membrane materials were obtained according to the orthotropic assumption. Moreover, a finite element model was created to simulate the rotational performance of the inflated arm. The simulation results are compared with those obtained for cylindrical joints with no creases, and the former configuration results in a much lower actuation torque, which well satisfies the design goal for the rotational joint. Furthermore, a prototype of the inflatable arm was designed and made to perform an experimental investigation, and the accuracy of the numerical simulation was validated by the test data. © 2016, Shanghai Jiao Tong University Press. All right reserved.