Multi-scale finite element modeling of bending behavior of 3D multi-cell spacer weft-knitted composites with different structures

In the present study, a multi-scale finite element model is proposed to predict the linear and nonlinear behavior of the 3D multi-cell spacer weft-knitted composite under bending load. In this study, a unit-cell of the composite which includes plain and biaxial weft-knitted structures was modeled at the meso scale. Periodic boundary conditions were applied to the meso model to calculate the elastic constants of each composite structure. In order to obtain failure parameters of the composites, the Puck failure criterion model was utilized by a VUMAT code for the meso model. Afterward, the elastic constants of the composites based on a Python code were extracted from the meso model. Moreover, failure parameters that include tensile and compressive strength through the fiber and transverse directions were obtained from the meso model. All elastic and failure parameters were used for the macro model which is created with different profiles under bending load. The numerical results at the meso scale showed that the presence of the weft and warp yarns inside the biaxial weft-knitted composite increases the strength of the composite through the course and wale directions. Moreover, the stiffness of the composite would be improved. So, the samples that contained a biaxial composite had more stiffness and bending strength in comparison with plain composite samples because the top and bottom layers were manufactured by the biaxial weft-knitted structure. Besides, the comparison between numerical and experimental force–deflection curves showed that the proposed model could predict the linear and nonlinear behavior of the composites with high accuracy. So, this model can be used for other textile composites with complex shapes to predict the mechanical behavior of them.