The nonlinear, anisotropic, and multiscale mechanical behavior of knitted textiles is investigated experimentally in this article. The approach is motivated by recent computational work by the authors that revealed, for the first time to their best knowledge, local‐global mechanical behavior effects related to the hierarchical, three‐dimensional structure of this type of materials. The investigation is carried out on single jersey knitted textile specimens. Mechanical testing consisting of tensile loading along the two principal directions was coupled with a noncontact, optical metrology method capable of providing deformation measurements. The effect of globally applied loading on yarn‐to‐yarn interactions was explored using measured data. The results validate the previously obtained computational findings that include the anisotropic behavior between course and wale directions, the pronounced out‐of‐plane motion observed when in‐plane loading is applied, as well as the characteristic nonlinear mechanical behavior of knitted textiles. These effects were linked to direct observations of the loop structure that demonstrated the coupling between local kinematics and kinetics with global mechanical behavior.
A novel failure model updating methodology is presented in this manuscript for composite materials. The innovation in the approach presented is found in both the experimental and computational methods used. Specifically, a dominant bottleneck in data-driven failure model development relates to the types of data inputs that could be used for model calibration or updating. To address this issue, nondestructive evaluation data obtained while performing mechanical testing at the laboratory scale is used in this manuscript to form a damage metric based on a series of processing steps that leverage raw sensing inputs and provide progressive failure curves that are then used to calibrate the damage initiation point computed by full field 3D finite element simulations of fiber-reinforced composite material that take into account both intra- and interlayer damage. Such curves defined based on nondestructive evaluation data are found to effectively monitor the progressive failure process and therefore they could be used as a way to form modeling inputs at different length scales.
Advances in sensing and nondestructive evaluation methods have increased the interest in developing data-driven modeling and associated computational workflows for model-updating, in relation also to a variety of emerging digital twin applications. In this context, of particular interest in this investigation are transient effects that lead to or are caused by deformation instabilities, typically found in the cases of complex material behavior or in interactions between material and geometry. In both cases, deformation localizations are observed which are typically also related to damage effects. This manuscript describes a novel framework to incorporate deformation data into a finite element model (FEM) that has been formulated using non-local mechanics and is capable of receiving such data and using it to describe the development of localizations. Specifically, experimentally measured full field displacement data is used as an input in FEM as an ad-hoc boundary condition at any or every node in the body. To achieve this goal, a plasticity model which includes a spatially averaged non-local hardening parameter in the yield criterion is used to account for associated numerical instabilities and mesh dependence. Furthermore, the introduction of a length scale parameter into the constitutive law allows the connection between material behavior, geometry and localizations. Additional steps remove the experimental data and evolve the computational predictions forward in time. Both one and three-dimensional boundary value problems are used to present results obtained by the proposed framework, while comments are made in terms of its potential uses.
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