A finite beam element multifunctional fabric modeling framework demonstrated with SMA knitted actuators

Multifunctional textiles have gained recent attention due their intrinsic properties that provide actuator, energy dampening, or sensory capabilities within small form factor textiles without external attachments. Such technologies are specifically appealing for medical and aerospace wearables, where active compression, haptic feedback, or the tracking of bodily functions are important tasks that are ideally conducted in a minimally-intrusive fashion. Current design capabilities of multifunctional textile are limited as present predictive tools lack accuracy and universality. This paper presents a finite beam element modeling tool for shape memory alloy (SMA) knitted architectures. The temperature-dependent variation of material properties within the SMA knitted loop affects the macroscopic force-extension behavior of SMA knitted architectures leading to an actuated and a relaxed knitted architecture response. This difference is exploited as the active property in SMA knitted architectures. The modeling architecture defines interfaces between sub-models organized in modules, specifically the material constitutive module, repetitive unit cell module, manufacturing module, contact module, and a boundary condition module. The SMA knitted architecture is modeled utilizing a 1D SMA constitutive model, quarter loop knit unit cell, a differential geometry-based manufacturing model, while assuming 3D Coulomb friction conditions. Kinematically-suitable boundary conditions are applied and the simulation predictions are compared quantitatively to macroscopic tensile experimental results, as well as qualitatively to microscopic X-ray diffraction phase analysis. The verification against experimental data supports the ability of the modeling tool to accurately predict the SMA knitted architecture thermo-mechanical performance with mean force-extension errors of less than 5%. The modeling tool provides the basis to understand, design, and optimize the lightweight, large force and deformation SMA knitted actuator textiles for novel applications. Additionally, the multifunctional textile modeling tool is implemented based on highly interchangeable sub-models to create synergies and propel the modeling of any multifunctional textile.