This paper deals with investigating the tensile characteristics of biaxial weft-knitted reinforced composites in terms of stiffness, strength and failure mechanism. The biaxial weft-knitted fabric was produced on an electronic flat knitting machine by E-glass yarns and then was impregnated with epoxy resin. Using an accurate geometrical model, the composite unit cell was designed in Abaqus software’s environment. Tensile tests were simulated in different directions on the created unit cell and the stiffness was calculated. By applying the proper failure theories, the composite strength was predicted and then critical regions of the unit cell were determined. In the next step, a micromechanical approach was also applied to estimate the same tensile features. Failure theories were also applied to predict the strength and most susceptible areas for failure phenomenon in the composite unit cell. The tensile properties of the produced composites were measured and compared with outputs of the finite element and micromechanical approaches. The results showed that the meso-scale finite element analysis approach can well predict the composite strength. In contrast, the meso-scale analytical equation model was not able to predict it acceptably because this model ignores the strain concentration. Both meso-scale finite element analysis and meso-scale analytical equation approaches predicted the similar locations for the composite failure in wale and course directions.

Design and analysis of parts constructed from weft-knitted textile composites need the elastic and fracture behavior of the composite. To avoid time-consuming and expensive experimental procedures, micromechanical models and finite element simulations can be used to estimate stiffness matrix of these composites. In the present study, at first, a 3D model of a plain weft-knitted fabric is presented. Then a micromechanical approach is proposed to derive the mechanical properties of the weft-knitted composite using this geometrical model. A finite element simulation is carried out to extract the elastic properties of the composite as an alternative procedure. Finally, obtained moduli from both methods are validated by comparing them with existing experimental values. Results show a good agreement between the calculated and measured data. It can be concluded that the proposed micromechanical approach can predict weft-knitted composite behavior well without any great effort; however, the finite element analysis gives acceptable results too. The effects of composite variables on the stiffness are investigated and discussed.

In this paper, a novel parameter determination technique is developed for material models in continuum mechanics aimed at describing metamaterials. Owing to their peculiar mechanical properties and behaviors, such as extreme elasticity or high strength‐to‐weight ratio, metamaterials are of interest to be simulated by reduced‐order modeling by means of the generalized mechanics. Such models incorporate constitutive parameters to be determined; we develop an automatized optimization process specifically for obtaining metamaterials parameters. The process aims at minimizing a mechanically meaningful error function measuring the deviation of the continuum from a detailed description by using the Trust Region Reflective optimization method. The parameter identification procedure is tested for an exemplary extension experiment of a metamaterial, proving to be robust and reliable.

Pantographic structures are examples of metamaterials with such a microstructure that higher-gradient terms’ role is increased in the mechanical response. In this work, we aim for validating parameters of a reduced-order model for a pantographic structure. Experimental tests are carried out by applying forced oscillation to 3D-printed specimens for a range of frequencies. A second-gradient coarse-grained nonlinear model is utilized for obtaining a homogenized 2D description of the pantographic structure. By inverse analysis and through an automatized optimization algorithm, the parameters of the model are identified for the corresponding pantographic structure. By comparing the displacement plots, the performance of the model and the identified parameters are assessed for dynamic regime. Qualitative and quantitative analyses for different frequency ranges are performed. A good agreement is present far away from the eigenfrequencies. The discrepancies near the eigenfrequencies are a possible indication of the significance of higher-order inertia in the model.