arXiv subjects

Yucai Hu

Publications and source records attributed to Yucai Hu.

4 recordsLinked to original sources

arXiv2026

Influence of twist direction and large deformation on soft material torsional contact

Shear-induced contact area reduction is widely observed in soft contacts, yet recent torsional experiments have revealed a more complex non-monotonic evolution in which the contact area first increases and then decreases with twist angle. The mechanism responsible for this initial area increase and the role of large deformation in the overall area evolution remain unclear. In this study, we experimentally investigate the torsional contact response of soft Polydimethylsiloxane (PDMS) spheres by combining forward-backward twist tests with a systematic variation of the curing-agent-to-base ratio to tune material softness and deformation level. The loading-unloading tests show that the torsional interface is strongly irreversible: during unloading, the contact area follows a decrease-increase-decrease path rather than retracing the loading branch, and repeatable petal-like edges appear, indicating a wrinkle-induced surface instability. By decreasing the mixing ratio, we find that larger deformation strengthens the area-reduction contribution and eventually suppresses the initial area increase, leading to a monotonic area decrease during loading for sufficiently soft PDMS. Softer PDMS also exhibits lower shear strength, weaker torque oscillations, and improved repeatability. The results provide experimental evidence that large deformation can drive shear-induced contact area reduction, while the origin of the initial area increase remains unresolved. These findings narrow the possible mechanisms (e.g., triboelectrification) responsible for the initial area increase and provide a stringent benchmark for frictional contact models of soft interfaces.

cond-mat.soft↗

arXiv2024

Lorentz transformation for the kinematics of degree-4 rigid origami vertices and compatibility of rigid-foldable polygons

We offer new insight into the folding kinematics of degree-4 rigid origami vertices by drawing an analogy to spacetime in special relativity. Specifically, folded states of the vertex, described by pairs of fold angles in terms of cotangent of half-angles, are related through Lorentz transformations in $1+1$ dimensions. Linear ordinary differential equations are derived for the tangent vectors on two-dimensional fold-angle planes, with the coefficient matrix depending exclusively on the sector angles. By taking the limit to the flat state, we generalize the fold-angle multipliers previously defined for flat-foldable vertices to general and collinear developable degree-4 vertices, and obtain a compatibility theorem on the rigid-foldability of polygons with $n$ developable degree-4 vertices. We further explore the rigid-foldable polygons of equimodular type and compose tangent vectors involving fold angles at the creases of the central polygon.

cond-mat.soft↗

arXiv2020

Constructing rigid-foldable generalized Miura-ori tessellations for curved surfaces

Origami has shown the potential to approximate three-dimensional curved surfaces by folding through designed crease patterns on flat materials. The Miura-ori tessellation is a widely used pattern in engineering and tiles the plane when partially folded. Based on constrained optimization, this paper presents the construction of generalized Miura-ori patterns that can approximate three-dimensional parametric surfaces of varying curvatures while preserving the inherent properties of the standard Miura-ori, including developability, flat-foldability and rigid-foldability. An initial configuration is constructed by tiling the target surface with triangulated Miura-like unit cells and used as the initial guess for the optimization. For approximation of a single target surface, a portion of the vertexes on the one side is attached to the target surface; for fitting of two target surfaces, a portion of vertexes on the other side is also attached to the second target surface. The parametric coordinates are adopted as the unknown variables for the vertexes on the target surfaces whilst the Cartesian coordinates are the unknowns for the other vertexes. The constructed generalized Miura-ori tessellations can be rigidly folded from the flat state to the target state with a single degree of freedom.

cs.CE↗

arXiv2020

Folding Simulation of Rigid Origami with Lagrange Multiplier Method

Origami crease patterns are folding paths that transform flat sheets into spatial objects. Origami patterns with a single degree of freedom (DOF) have creases that fold simultaneously. More often, several substeps are required to sequentially fold origami of multiple DOFs, and at each substep some creases fold and the rest remain fixed. In this study, we combine the loop closure constraint with Lagrange multiplier method to account for the sequential folding of rigid origami of multiple DOFs, by controlling the rotation of different sets of creases during successive substeps. This strategy is also applicable to model origami-inspired devices, where creases may be equipped with rotational springs and the folding process involves elastic energy. Several examples are presented to verify the proposed algorithms in tracing the sequential folding process as well as searching the equilibrium configurations of origami with rotational springs.

cs.CE↗