The effect of loop density on the tensile behavior of biaxial weft knitted composites using both experimental tests and numerical method

Abstract

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.

Potential fabric-reinforced composites: a comprehensive review

“…Knitted fabrics are composed of course and wales yarns made through knitting process. However, when the fabrics are transformed into composite materials, both the course and wales directions of fabrics showed an improvement in strength with the increased loop density, which showed an agreement with the finite element model analysis [83].…”

Damage and failure mechanisms of biaxial weft-knitted reinforced composites via meso-scale finite element modeling

“…Their aim was to simulate the forming process of BWK fabrics into complex-shaped composites. The effect of loop density on the tensile behavior of BWK composites was investigated by Hesami et al 1 using experimental and numerical approaches. They proposed a meso-scale finite element modeling to predict the Young’s modulus along the wale and course directions.…”

“…Damage and failure mechanisms were predicted by developing a VUMAT user material subroutine based on the 3D Hashin criterion. To verify the numerical results, a comparison was made with the experimental data of Hessami et al 1 It was found that the failure mechanisms of BWK composite are determined by the geometrical parameters of the BWK fabric. Based on the numerical assessments, some recommendations were made to fully exploit the potential of BWK composites as load-bearing structures.…”

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

“…The presence of straight yarns inside the fabric structure leads to the straight yarns playing a significant role during the loading process to reinforce the composite and reduce the stress concentration in other spots. 7 Numerous experimental and numerical studies were carried out on weft-knitted composites. [8][9][10][11][12] Shekarchizadeh et al 13 analyzed the tensile behavior of the weft-knitted composite by micromechanics equations and the finite element model.…”

“…19,20 Recently, researchers have used Vassiliadis et al's 15 model to create weft-knitted loop geometry at the meso scale. 7,9,[21][22][23] In this model, the geometry of the weft-knitted loop based on the coordinate points of the loop geometry is created in a three-dimensional space. Despite all efforts regarding prediction of the mechanical properties of the 3D spacer weft-knitted composites, only some limited researches have been focused on the failure behavior of these structures.…”