| As a new member of directionally oriented knitting structures, multi-layered biaxial weft knitted (MBWK) fabric is attracting more and more interest and attention due to its outstanding mechanical properties and competitive production cost. It possesses a great application potential and bright future in the field of aerospace quality components, automotive frames, marine parts, war industry, construction industry, and so on.The shear properties of MBWK fabrics are most important as far as a forming process is concerned, for it directly decides whether this fabric can transform from its original plane state to 3D curved state without buckling. For the in-plane shear testing, the popular devices include KES-F system, Fast system and Picture-frame shear device. Firstly, this paper mainly discusses the motion law of the widely studied and very potential picture-frame device, and it was found that all the four arms have the same angular speed and angular accelerated speed although they move in different forms. In addition, the "quasi-static state" concept was first put forward, according to which the motion of the picture-frame shear device can be just simplified as quasi-static for a specified shear angle range. The critical shear angle of quasi-static state was given under different loading speeds and frame lengths condition, and the influence of specimen size on this shear angle range is also discussed. Based on the above analysis, the relation between the applied load and the resulted forces on each frame arm was obtained, and Bryan's experimental conclusion was proved in theory, i.e., the stress near frame arms area approximates pure shear. Besides, an improved design is presented in order to tackle the problems of the originally- designed device. Secondly, the shear properties of MBWK fabrics were studied with the aid of picture-frame device. Two methods are presented: 1) according to the structure characteristics of the picture-frame device and bias tensile test, the shearstress-strain curve was obtained. Furthermore, this method can be used to study shear properties of other fabrics, such as plain-weave fabrics, biaxial warp knitted fabrics (containing two bias inserting yarn systems), etc; 2) a shear model was established by using the structural parameters and the inner friction properties of the fabric. The experimental results agreed with the model very well. It will lay a foundation for further study on MBWK fabrics.Finally, hemi-sphere molding forming of fabric was simulated by using the rapid development and widely applied NURBS method with the aid of SUN station, in order to better understand the molding forming properties of fabric, predict whether the final parts can be formed well or not, and provide guidance to a practical forming process. NURBS interpolation surface can't directly show the spatial positions of the inserting yarn's crossovers in the deformed state, and this method itself is very complicated, although the simulated 3-D surface can give a strong solid effect. Therefore, it was decided to use NURBS interpolation curve to simulate the hemi-sphere forming of fabric, which can not only directly show the real yarn spatial positions and orientation in the deformed state, but also simplify the simulating process to a great degree. The simulated 3-D surface by the latter method can also give a strong solid effect. Furthermore, the possible forming defects, such as buckling and wrinkles, can be predicted. And this method will surely provide theoretical support to a concrete forming process. Also, this method can be applied to simulating the forming process of other kinds of flat fabrics.
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