Layer-resolved thermomechanics and load partitioning in twisted multifilament helical structures

Thermally driven twisted multifilament helical structures redirect anisotropic filament-scale free strains into coupled axial, torsional, and radial responses. A common imposed twist produces radius-dependent helix geometry, yet existing reduced descriptions do not jointly resolve the resulting layer- and constraint-dependent load partitioning, stress localization, and energy storage. We develop a layer-resolved curved-rod model for first-level twisted bundles without macroscopic coiling. The model retains each layer’s radius, helical angle, and filament population, maps these effective deformation modes into bundle-scale responses, and evaluates layer-wise stresses and elastic strain energy relative to a specified mechanical reference state. Three-dimensional finite-element calculations subjected to the bundle-coordinate thermal strain reproduce the analytical trends under complementary constraints and support the internal consistency of the formulation. Within the examined incremental regime, increasing twist reduces the end-constrained axial reaction, whereas torsional and confinement-related radial reactions reach maxima at distinct intermediate twist levels. In the examined bundle, twist also shifts the axial-force share toward inner layers, while outer layers retain disproportionate contributions to torque and radial interaction. Under the fixed-radius constraint, an equivalent single-helix description reproduces selected global outputs with amplitude-normalized root-mean-square errors of about 5 percent or less, but cannot capture layer-wise load fractions or changes in the layers carrying the largest calculated stress magnitudes. Elastic energy storage remains stretching-dominated, although bending and torsional contributions increase with helical obliquity and effective axial and radial deformation mismatch. This work reveals that twist redistributes thermal actuation among response channels and radial layers, providing a mechanics basis for output-specific and stress-aware design.