In this study, a high-tenacity polyester was used to produce biaxial weft knitted fabric in three different loop densities. All of the composite samples were manufactured using the vacuum injection process. Epoxy resin was used as the matrix in the composite samples. Tensile tests in the course and wale directions were carried out on all samples. The results showed that the tensile strength and the elastic modulus of the composites were improved by increasing the loop density. On the other hand, multi-scale finite element modeling was employed to predict the elastic constants and the tensile strength of the composites. In this method, unit-cells of biaxial weft knitted fabrics with a script were modeled by ABAQUS finite element software in the meso scale. Periodic boundary conditions were applied to the unit-cells. Stiffness matrices of composites were calculated by a python code. In the macro model, a shell geometry was created and the elastic constants calculated from the meso scale were assigned to the macro model. The tensile strength of composites in the course and wale directions was predicted by the Tsai-Wu failure criterion equations. The numerical results had a good agreement with the experimental ones. According to the numerical results, the difference in the loop densities as the inputs data could be used and elastic constants and strength of composites in the course and wale directions could be obtained. So, this model is a useful method to predict the tensile behavior of biaxial weft knitted composites with different geometries.

In this study, tensile and flexural behavior of biaxial and rib weft-knitted composite is obtained numerically and experimentally. Multi-scale finite element modeling is employed to simulate the tensile and flexural behavior of composite samples. In the finite element modeling, the geometry of a unit cell of each fabric is initially modeled in ABAQUS software, and then periodic boundary conditions were applied to a unit cell. The stiffness matrix for each structure was obtained by a python code via meso scale modeling and used as input data for the macro modeling. To validate the numerical model, two types of weft-knitted fabrics (rib 1 × 1 and biaxial fabrics) are produced by a flat weft knitting machine. Epoxy resin is used to construct composite by the vacuum injection process (VIP). After that, the tensile and three-point bending tests were applied to composite samples. The experimental results showed that tensile strength and tensile modulus of biaxial composites are greater than rib composites, in both wale and course directions. Moreover, in three-point bending test, biaxial composite showed more strength and more stiffness in comparison to rib composite. Finite element results were compared to experimental results in tensile and bending tests. The results showed that good agreement with experimental results in the linear section of tensile and flexural behavior of composites. Consequently, the current multi-scale modeling can be used to predict the stiffness matrix and mechanical behavior of complex composite structures such as knitted composites.

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The purpose of this study is to investigate the role of density and pile height on sound absorption coefficient in Double Base Persian (DBP) rug and possibility of prediction the acoustic behavior of DBP rug using the mathematical model. For this aim, in the first step, three double base rug samples were produced at different base densities (2, 4, and 6 warp yarn/cm) and the sound absorption coefficient of samples was measured with Impedance tube in two thicknesses (15 & 13 mm) to study the pile height effect. Moreover, the sound absorption of the double base zone was also measured by shaving off the pile from the double base rug samples. Three rug samples at different base densities were produced with very thin warp and weft yarns to avoid the base effect in this sample. Besides, the macroscopic empirical model (Johnson–Champoux–Allard (JCA)) was implemented on obtained data. The results showed that the sound absorption of the double base rug samples increases with increasing the pile height and base density. The role of the base zone in the sound absorption of the rug is bolder than the pile zone. What leads to improve the rug sound absorption by increasing density is increasing the sound absorption of base zone and the pile density changes do not play a major role in increasing the rug sound absorption. In addition, by assuming DBP rugs as a two-layer porous (pile + base zone) absorber, JCA model shows a good consistency with experimental data.