Zhang Qilin

Experimental analysis of tensile behaviors of polytetrafluoroethylene-coated fabrics subjected to monotonous and cyclic loading

This paper presents the tensile behaviors of polytetrafluoroethylene (PTFE)-coated fabrics subjected to monotonous and cyclic loading. First, uniaxial tensile tests are conducted to study the uniaxial cyclic behaviors, in which the effects of stress amplitude and temperature on the fabrics are studied. Then, biaxial tests are carried out to analyze the biaxial cyclic behaviors with different stress ratios. Finally, the mechanical properties of PTFE-coated fabrics without initial loading and after cyclic loading are compared. The results show that the tensile behaviors of PTFE-coated fabrics are asymmetric and affected obviously by loading protocols, which are concerned with the woven structure of substrate and properties of yarns. After cyclic loading, the significant stiffness strengthening and the linearity of tensile behaviors becomes obvious, while the discrepancy between the elastic modulus of the warp and the weft decreases. Compared with the new material without initial loading, the material tensile strength after cyclic loading remains almost unchanged, which may be related with fewer cycle numbers. The tensile behaviors under cyclic loading are mainly related with stress amplitude, temperature and woven structure of substrate. With temperature increasing, the degree of stiffness strengthening after cyclic loading increases. The effect of loading history on the mechanical properties of PTFE-coated fabric is obvious, and different constitutive constants should be conducted regarding different design stages.

Fracture failure analysis and strength criterion for PTFE-coated woven fabrics

This paper presents the research on fracture failure analysis and failure criterion for PTFE-coated woven fabrics. First, groups of on-axial and off-axial tensile tests are carried out, and the corresponding failure mechanisms are analyzed. Then, the samples with initial defects are tested and the fracture toughness is discussed. Finally, several current strength criteria are compared to predict the failure strength of PTFE-coated woven fabrics and a new strength criterion is proposed. Results show the material failure strength depends on the stress ratio and off-axial angle of sample. The ratio of principal stress decides the material strength, and the angle between the principal stress and yarn orientation decides the failure mode. The predictions of current strength criteria agree well with most of the experiment data, except for the samples of small off-axial angles. The disagreements could be attributed to the unbalanced woven structure due primarily to the crimp interchange in the weaving and coating processes. The new strength criterion can make a good prediction of the failure strength of PTFE-coated woven fabrics.

Incremental finite element solution for nonlinear problems of space trusses

Abstract Based on an updated total Lagrangian formulation, an accurate incremental stiffness matrix and corresponding finite element equation for nonlinear problems of space trusses are derived in this paper. The modified arc-length iteration technique is presented to solve the ultimate strength and the load-deflection curves of space trusses. The stiffness matrix has a symmetric and concise form in which the large defletion effects on structures can be included accurately and the material nonlinearity can be considered easily. Numerical examples show that the incremental finite element method presented in this paper can be used to analyse the elastoplastic large deflection problems of space trusses satisfactorily and effectively.

Integrated CAD Software for Steel Frame Detailing

Steel frames have been widely designed and constructed in China since the end of last century. This paper introduces the primary program principles and techniques of the development of integrated CAD software for detailing design of steel portal frame structure, including the frame work, data structure, 3D modeling algorithm and automatic output of 2D drawings.

Advances in mechanical properties of coated fabrics in civil engineering

Membrane structures are widely used in large span spatial structures due to excellent mechanical behavior and beautiful forms. Mechanical properties of coated fabrics are an important basis of design, analysis, and construction of membrane structures. This paper gives an overview of the research advances in mechanical properties of coated fabrics. First, the basic mechanical indexes of coated fabrics and corresponding test methods are presented. Then, the existing constitutive relations for coated fabrics are discussed. Finally, the effect of environment and other factors on the mechanical properties of coated fabrics are studied. In addition, the future trends on the mechanical behavior of coated fabrics are given, which can be references for design and analysis of coated fabrics in civil engineering.

Numerical Method Based on FE for Heat Flow Computation of Curtain Walls with Complex Sections

As one of the biggest parts of total national energy consumption (TNEC), building energy consumption (BEC) catches public eyes and has been regarded as a crucial problem of the current society. Energy used on windows and curtain walls in buildings account for 50% of the total buildings energy consumption. In this paper the process of heat transfer in curtain wall with complex cross-section is analyzed and simulated using finite element method, in which the influence of convection and radiation in frame and glazing cavity is considered and the fixed conductivity is placed by an effective one. Finally, a numerical example is studied and the results are obtained and compared with ANSYS software. The method presented in this paper provides a basis for the calculation of heat transfer coefficient and will promote the energy efficiency study of windows and curtain walls.

Dynamic analysis of a levy dome

Publisher Summary The chapter discusses dynamic analysis of a levy dome. A simple method is presented for the analysis of a tensegrity system using three steps: the first to form finding (without loading or self-stress), the second to implement self-stress, and the last to study the behavior under external actions. Dynamic characterization of a levy dome under different self-stress levels is described with modal analysis. Dynamic and seismic analyses are carried out for the levy dome. With modal analysis, it is observed that the deformation of lower modes represents motion state as a whole, while for higher modes, adjacent struts have relatively large displacement. Increasing the prestress level can greatly improve mechanical properties of the levy dome. Dynamic responses of tensegrity structures are characterized by infinitesimal mechanism modes. To analyze the dynamic response of pre-stressed tensegrity structures, it is important to compute infinitesimal mechanisms of tensegrity modules and interpret global deformation modes of tensegrity structures in terms of infinitesimal mechanism modes.