Session: 13-02-02: Advances in the Mechanics of Architected Materials II

Paper Number: 173322

Mechanics of Highly Entangled Matter Through Knitting 

Three-dimensional (3D) printing enables filamentous topologies that are inaccessible to conventional textile machinery, recasting knits as a versatile platform for architected, highly entangled architected materials. We combine multi-material PolyJet additive manufacturing, two-photon lithography, discrete elastic-rod simulation, and multi-axial mechanical testing to translate the canonical Stockinette stitch into a programmable, length-scale-invariant volumetric solid whose behavior is governed by topology as well as the parent-polymer properties. First, two-dimensional knits containing six-by-six stitches are 3D printed. Equi-biaxial tensile experiments up to 40% strain reproduce the anisotropic, hysteretic response of cotton fabrics. Parameterizing loop width, height, depth, curvature, fibre radius, and ply number yields an empirical factor xi that collapses the stress-strain data onto a single master relation, quantified by an entanglement constant β. This universal normalization is captured by a discrete elastic-rod model with Incremental Potential Contact, enabling prediction of yarn strain and frictional sliding.

Exploiting layer-wise fabrication we introduce “volumetric knits” in which the yarn interloops sequentially along the Course (X), Wale (Y) and Pile (Z) directions. The resulting periodic unit cell is assembled from a single continuous filament yet forms a 3D lattice with programmable topology. Uniaxial tests show the Pile axis is roughly an order of magnitude stiffer than the in-plane directions, while triaxial experiments demonstrate that pre-straining one or two axes tunes the stiffness, strength and energy dissipation of the remaining axes over more than an order of magnitude, i.e., by stretching one axis, we can dynamically increase the stiff in the other axes. Such couplings suggest deployable dampers and morphing skins tuned in situ through simple stretching.

Because additive manufacturing is path- rather than topology-limited, the same geometry can be fabricated at any length-scales. We fabricate six-loop-per-side volumetric knits with 50 um loops in IP-Dip photoresist using a Nanoscribe GT2. In-situ tensile testing inside a scanning electron microscope confirms a normalized strength on par with macro-scale counterparts, validating scale invariance while highlighting a stiffness increase caused by partial filament fusion.

The study establishes 3D-printed knits as a bridge between textile and mechanical metamaterials. The universal master curve provides a rapid recipe for targeting specific stress-strain profiles, and the DER-IPC workflow enables predictive exploration of a vast design space. Future integration of multi-material or functional resins could locally tailor friction, embed sensors, or incorporate shape-memory actuation, while miniaturization may produce tissue scaffolds, adaptive filters or impact-mitigating cores. Beyond mechanics, the open internal volume and single-yarn continuity offer new avenues for fluid transport, thermal management, and electrical routing within an intrinsically robust, lightweight, multifunctional scaffold.

Presenting Author: Tian Chen University of Houston

Presenting Author Biography: Dr. Tian (Tim) Chen is the Kamel Salama Assistant Professor of Mechanical Engineering at the University of Houston, leading the Architected Intelligent Matter (AIM) Laboratory. He earned a D.Sc. from ETH Zurich, an MSc from TU Delft, and a BASc from the University of Toronto. Chen’s research vision is to develop programmable matter that is capable of tuning its physical properties and/or shape on demand in response to environmental stimuli. His lab achieves this by utilizing knowledge from mechanics, geometry, computation and manufacturing. Specifically, he leverages multistability, elastic snap-through, magnetic coupling, frictional contact and geometric frustration to encode “if-this-then-that” logic directly into matter. Recent contributions include a mechanical metamaterial with reprogrammable stable memory; bistable auxetic surfaces that deploys stably into curved shells; temperature encoded stress-strain behavior, and self-deploying solar arrays powered solely by elastic origami and shape-memory polymers. These works have appeared in Nature, Science Advances, PNAS and Siggraph, and featured on cable news as well Youtube channels with millions of views. He is Deputy Editor-in-Chief of 3D Printing and Additive Manufacturing and organizers of numerous minisymposia. He is funded by NSF, NASA, DoD and industry partners. Dr. Chen is the recipient of the Haythornthwaite Initiation Grant and the ETH Medal. His research is funded by the NSF, NASA, DoD and industry partners.

Authors:

Tian Chen University of Houston