On The Structral Parameters Of Woven Sandwich Fabrics

Woven sandwich fabric is one of the three-dimensional structural fabrics that is made up of warp yarns, weft yarns, and pile yarns. The fabric has an integral core structure as a result of weaving of weft yarn in the skin to the pile yarn in the sandwich layer. Impregnated by resin matrix, the fabric can be,made into reinforced composites, referred to as the woven sandwich fabric composites. The woven sandwich fabric composites are widely used in industrial fields, including aviation, spaceflight, architecture and ship. The composites provide excellent properties such as structural integrity, light weight, good designability and so on. As the reinforcement, the variation of fabric configuration influences largely the mechanical properties of woven sandwich fabric composites. Studies show that the composites made from the sandwich fabric with different thickness have discrepant mechanical properties. As the increasing of the fabric thickness, flat-wise compressive and shear properties of composites gradually decrease, but bending stiffness rises. Therefore, the thickness of the sandwich fabric plays an important role in mechanical properties of the reinforced composites. However, due to the deformation of the pile yarn, it is difficult to determine the thickness of the sandwich fabric if other conditions are not defined.In order to find an appropriate method to determine the thickness of woven sandwich fabric, in this paper, the relationship among the structural parameters of the fabric is investigated in order to find a method in determining the thickness of the fabrics. According to the geometric shape of the pile yarns, five parameters are defined, including the pile height, the pile length, the picks density, the distance along warp direction between the.stitch point in the top skin to the bottom one (called "the stitch distance" for short), the angle between-the tangent line on the stitch point of a pile yarn departing from the skin and the connecting line of the stitch points at the top and bottom skin (called "the orientating angle" for short). Furthermore, following the load-carrying conditions of a pile yarn, a sinusoid is adopted to simulate the pile shape. Equations of the pile shape are obtained and geometric relationship among structural parameters is established.In order to validate the rationality of the geometric relationship, the structural parameters of sandwich fabric samples are measured using the "IamgeJ" software from the cross-section photo of the fabric samples. With the geometric relationship established, the pile height is calculated. By comparing the calculated values with the measured ones of the pile height, it is shown that the geometric relationship established is valid. Pile configurations from the samples of different fabric thicknesses are obtained by tensile and compressive deformation along the fabric thickness direction. The results prove the correctness of the geometric relationship regardless of the sample's thickness deformation. Furthermore, the structural parameters of different fabric samples with various pile configurations are tested and pile heights are calculated using the geometrical relations developed. Influences of the structural parameters in the pile height are discussed. It is shown that the difference of the pile height between the calculation and measurement increases when the orientation angle increases. The difference would be more obviously when the pile length arises. The variation of the pick density has a strong effect on the difference between the calculation and measurement of the pile height for sample fabrics with small thickness. However, the effect is negligible for sample fabrics of great thickness. When the stitch distance increases, the pile height will decrease. However, this effect is more obvious for thin fabrics.