A numerical analysis of Saint-Venant torsion in strain-gradient bars
Abstract The article addresses the torsion of bars with arbitrary cross sections subject to warping employing the finite element method in the strain-gradient elasticity. Subsequent to extracting the strains and stresses given by the Saint-Venant torsion hypothesis for an infinitesimal deformation, the principle of virtual work is adopted to investigate the weak form of stationary equation. Then, two torsion-warping elements, the former has four nodes and the latter has nine nodes with 6 DoF per node, are constructed for the torsion analysis of bars. To investigate the behaviour of the devised elements, some examples with known cross sections are presented which can be used to examine the accuracy of the developed elements and to study the size-dependent trend in the bars.
Abstract Understanding the atomistic mechanisms of tensile failure in carbon fibers is important for fiber manufacturing and applications. Here we design structural faults with atomistic details, pertaining to polyacrylonitrile (PAN) derived fibers, and probe them using large-scale molecular dynamics simulations to uncover trends and gain insight into the effect of local structure on the strength of the basic structural units (BSUs) and the role of interfaces between regions with different degrees of graphitization. Besides capturing the expected strength degrading with increasing misalignment, the designed basic structural units reveal atomistic details of local structural failure upon tensile loading. Fracture initiation is nearly always associated with the interface of the misoriented crystallite and its environment.