Jordan R. Raney

We report the formulation and printing of Cu inks composed of binary mixtures of colloidal ∼5 nm Cu nanocrystals (NCs) and ∼500 nm Cu microcrystals (MCs) and postdeposition chemical and low-temperature thermal treatments to achieve micron-thick, high-conductivity metal traces that yield high-performance, printed radio frequency (RF) electronic devices. Solid-state NH 4 Cl treatment of binary Cu NC/MC mixed films removes insulating ligands and surface oxides and establishes Cl – -mediated surface chemistry that drives NC-enabled “nano-soldering” between MCs and increased MC faceting and interparticle necking. Subsequent mild annealing under N 2 promotes further densification to yield micron-scale films with resistivities as low as ∼14.5 times that of bulk Cu for optimized 75 wt % NC/MC films after annealing at 150 °C for 5 min. By formulating these binary NC/MC systems in α-terpineol/ethyl cellulose/poly(vinylpyrrolidone) vehicles, we obtain non-Newtonian inks compatible with both screen printing and direct ink writing (DIW) and we deposit micron-thick patterned conductive traces on flexible substrates. Screen-printed, flexible RF inductively coupled interdigitated capacitors are fabricated from the mixed NC/MC inks and achieve Q = 4.89, corresponding to ∼68% of a bulk-Cu reference. DIW produces over 100 μm thick CAD-defined traces with an average resistivity of 95 ± 22.6 μΩ·cm. We show that NC-enabled processing of mixed NC/MC systems yield manufacturable, high-frequency metal components for printed Internet of Things platforms.

We report the formulation and printing of Cu inks composed of binary mixtures of colloidal ∼5 nm Cu nanocrystals (NCs) and ∼500 nm Cu microcrystals (MCs) and postdeposition chemical and low-temperature thermal treatments to achieve micron-thick, high-conductivity metal traces that yield high-performance, printed radio frequency (RF) electronic devices. Solid-state NH₄Cl treatment of binary Cu NC/MC mixed films removes insulating ligands and surface oxides and establishes Cl^–-mediated surface chemistry that drives NC-enabled “nano-soldering” between MCs and increased MC faceting and interparticle necking. Subsequent mild annealing under N₂ promotes further densification to yield micron-scale films with resistivities as low as ∼14.5 times that of bulk Cu for optimized 75 wt % NC/MC films after annealing at 150 °C for 5 min. By formulating these binary NC/MC systems in α-terpineol/ethyl cellulose/poly(vinylpyrrolidone) vehicles, we obtain non-Newtonian inks compatible with both screen printing and direct ink writing (DIW) and we deposit micron-thick patterned conductive traces on flexible substrates. Screen-printed, flexible RF inductively coupled interdigitated capacitors are fabricated from the mixed NC/MC inks and achieve <i>Q</i> = 4.89, corresponding to ∼68% of a bulk-Cu reference. DIW produces over 100 μm thick CAD-defined traces with an average resistivity of 95 ± 22.6 μΩ·cm. We show that NC-enabled processing of mixed NC/MC systems yield manufacturable, high-frequency metal components for printed Internet of Things platforms.

This study presents a modular pneumatic actuator system for soft robotics, designed to improve reconfigurability, adaptability, and deployment efficiency. The system consists of a standardized and extensible set of functional modules, including elongation, bending, twisting, and stimuli-responsive modules, each systematically characterized by its pressure–deformation behavior. These modules can be (re)assembled according to task-specific requirements, enabling the rapid construction of soft robotic platforms with customized actuation strategies. We demonstrate the versatility of this approach through three representative systems: a bioinspired trunk-like robot, a soft crawling robot, and a reconfigurable three-fingered gripper. Each example highlights key advantages of modularity, such as structural adaptability, environmental responsiveness, and object-specific grasping. The results show that this strategy supports scalable, low-cost, and reusable actuator designs.

Surfaces and structures capable of multiple stable configurations have attracted growing interest for on-demand shape morphing. In this work, we consider an elastic compliant plate coupled to a two-dimensional foundation comprising an array of bistable elements, a system that can form and retain complex continuous morphologies without sustained actuation via creation of stable domain walls separating regions in different stable states. These domain walls exhibit three distinct behaviors: expansion, shrinking, and metastable pinning. These arise from two limits of foundation discreteness. In the continuum limit, where bistable units are strongly coupled, domain walls undergo global phase transitions analogous to first-order phase transitions. In the anti-continuum limit, discreteness introduces Peierls-Nabarro-type energy modulations that lead to metastable pinning. To quantify these behaviors and the transition between the two limits, we develop a reduced-order model that captures the total potential energy of configurations with domain walls and validate it using finite element analysis (FEA). For axisymmetric domain walls, the model yields phase diagrams identifying the regimes of expansion, shrinking, and pinning as functions of bistable-potential asymmetry, relative foundation discreteness, and domain-wall size. We then extend the analysis to non-axisymmetric geometries and establish local geometric criteria that predict the stability of convex and concave polygonal domain walls, confirmed by simulations. Together, these results clarify how discreteness enables stability through energy-landscape modulation, provide predictive design rules for multistable reconfigurable surfaces, and offer insights into domain-wall stability more generally in elastically coupled multistable metamaterials.

Multistable mechanical metamaterials enable programmable transitions between discrete stable states through propagating kink transition waves (TWs). Yet controlling these kinks typically requires local actuation or high-energy deformation, limiting scalability. Here we demonstrate a universal strategy for pinning and depinning TWs using local defects and boundary phonon excitations. Inspired by phonon-dislocation interactions in crystalline solids, we use pairs of phonons that form a beating envelope resonant with the pinned kink's translational mode, which lies within a phononic band gap. This resonant coupling efficiently transfers energy to the kink, allowing it to overcome defect barriers and propagate across impurities. The proposed mechanism enables application of these systems as information processing units in mechanical computing, namely as scalable and more robust mechanical memory.

Multistable mechanical metamaterials enable programmable transitions between discrete stable states through propagating kink transition waves (TWs). Yet controlling these kinks typically requires local actuation or high-energy deformation, limiting scalability. Here we demonstrate a universal strategy for pinning and depinning TWs using local defects and boundary phonon excitations. Inspired by phonon-dislocation interactions in crystalline solids, we use pairs of phonons that form a beating envelope resonant with the pinned kink's translational mode, which lies within a phononic band gap. This resonant coupling efficiently transfers energy to the kink, allowing it to overcome defect barriers and propagate across impurities. The proposed mechanism enables application of these systems as information processing units in mechanical computing, namely as scalable and more robust mechanical memory.

Wing sections with bistable hinges outfitted on trailing edge flaps provide a promising means for passively rejecting gust loads on an aircraft. This study found that there exists a two-way coupling between the aerodynamic loads experienced by the airfoil and the deflection of the bistable hinge and corresponding flap. The current work demonstrates how the energy wells of a bistable hinge system can be configured to introduce decambering of the airfoil when stall limits are approached. By expressing the interdependent coupling between the global flow state and the hinge material properties, a bistable hinge can be designed to produce snap-through transitions when prescribed aerodynamic states are reached. The efficacy of this bistable hinge integration strategy is shown in an experimental campaign, where passive alleviation of aerodynamic loads are produced in the vicinity of airfoil stall limits.

Surfaces and structures capable of multiple stable configurations have attracted growing interest for on-demand shape morphing. In this work, we consider an elastic compliant plate coupled to a two-dimensional foundation comprising an array of bistable elements, a system that can form and retain complex continuous morphologies without sustained actuation via creation of stable domain walls separating regions in different stable states. These domain walls exhibit three distinct behaviors: expansion, shrinking, and metastable pinning. These arise from two limits of foundation discreteness. In the continuum limit, where bistable units are strongly coupled, domain walls undergo global phase transitions analogous to first-order phase transitions. In the anti-continuum limit, discreteness introduces Peierls-Nabarro-type energy modulations that lead to metastable pinning. To quantify these behaviors and the transition between the two limits, we develop a reduced-order model that captures the total potential energy of configurations with domain walls and validate it using finite element analysis (FEA). For axisymmetric domain walls, the model yields phase diagrams identifying the regimes of expansion, shrinking, and pinning as functions of bistable-potential asymmetry, relative foundation discreteness, and domain-wall size. We then extend the analysis to non-axisymmetric geometries and establish local geometric criteria that predict the stability of convex and concave polygonal domain walls, confirmed by simulations. Together, these results clarify how discreteness enables stability through energy-landscape modulation, provide predictive design rules for multistable reconfigurable surfaces, and offer insights into domain-wall stability more generally in elastically coupled multistable metamaterials.

Surfaces and structures capable of multiple stable configurations have attracted growing interest for on-demand shape morphing. In this work, we consider an elastic compliant plate coupled to a two-dimensional foundation comprising an array of bistable elements, a system that can form and retain complex continuous morphologies without sustained actuation via creation of stable domain walls separating regions in different stable states. These domain walls exhibit three distinct behaviors: expansion, shrinking, and metastable pinning. These arise from two limits of foundation discreteness. In the continuum limit, where bistable units are strongly coupled, domain walls undergo global phase transitions analogous to first-order phase transitions. In the anti-continuum limit, discreteness introduces Peierls-Nabarro-type energy modulations that lead to metastable pinning. To quantify these behaviors and the transition between the two limits, we develop a reduced-order model that captures the total potential energy of configurations with domain walls and validate it using finite element analysis (FEA). For axisymmetric domain walls, the model yields phase diagrams identifying the regimes of expansion, shrinking, and pinning as functions of bistable-potential asymmetry, relative foundation discreteness, and domain-wall size. We then extend the analysis to non-axisymmetric geometries and establish local geometric criteria that predict the stability of convex and concave polygonal domain walls, confirmed by simulations. Together, these results clarify how discreteness enables stability through energy-landscape modulation, provide predictive design rules for multistable reconfigurable surfaces, and offer insights into domain-wall stability more generally in elastically coupled multistable metamaterials.

Buckling is a common failure mode in lattice structures, limiting their use in some applications. The tendency of a strut to buckle is related to the local nodal connectivity. In this work, we introduce a pneumatic actuation strategy to actively tune the mechanical behavior of lattice structures by locally reconfiguring their effective nodal connectivity. By selectively inflating pneumatic actuators embedded in the lattice into spatial patterns with varying levels of connectivity, we demonstrate a method to modulate mechanical properties, including stiffness and buckling response. The most reinforced pattern can lead to 121.6% improvement in buckling strength relative to the regular lattice itself. Additionally, the post-buckling behavior of pneumatically controlled lattices can be programmably tuned by varying the input air pressure signals. The pneumatically controlled lattices reduced the peak acceleration by 50.9%, demonstrating enhanced impact mitigation capability. These results show that pneumatic actuation provides a versatile approach to enhancing structural performance under both static and dynamic loading. Since this strategy does not rely on multi-material interfaces or specific cell topologies, it can be broadly applied to optimize a wide range of lattice architectures. Lattice structures enable programmable mechanics but often require complex manufacturing or electronic systems. Xiaoheng Zhu, Yucong Hua and colleagues present a pneumatic control method that is easily reconfigurable and suitable for diverse structural applications

Bicontinuous emulsion gels are mixtures with interpenetrating arrangements of two immiscible liquids stabilized with particles. The structures of such gels are readily made into simple macroscale geometries, like sheets and fibers; however, achieving more complex macroscopic structures while maintaining control over microscopic features and morphological bicontinuity remains a challenge. In this study, the ability to fabricate complex 3D structures of bicontinuous emulsion gels using direct ink writing (DIW) is demonstrated. The emulsion precursors are formulated with a mixture of hydrophilic and hydrophobic fumed silica particles; these precursors exhibit shear-thinning and yield stress behavior necessary for DIW. The thixotropic nature of the precursor further promotes the formation of bicontinuous emulsion gels through vaporization-induced phase separation and stabilization through both interfacial jamming and bulk stabilization mechanisms. This fabrication technique enables the creation of functional bicontinuous structures with complex architectures, paving the way for application in biomedical implants, catalytic reactors, and beyond.

In this work, we study the nonlinear dynamics of tail motion using numerical simulations and experiments. Our simulations are based on a discrete model comprising rigid cylinders (representing vertebrae) coupled by longitudinal, shear, and bending springs (representing tissues). We consider how various parameter combinations, such as geometric and stiffness gradients in the tail, affect the dynamic response of tails subjected to impulse loading. Using numerical and experimental approaches, we quantify pulse propagation in tails, demonstrating that flexible tails can support a stable wavefront. By incorporating a gradient that gradually decreases the length of each vertebra (geometric gradient) and the stiffness of its connecting tissues (stiffness gradient), we significantly enhance the lateral displacement and velocity of the propagating pulse towards the tip. We show that this effect can be used to improve stability of robotic vehicles subjected to impulses.

Nature manufactures structures via decentralized processes involving groups of agents. This is fundamentally different from traditional manufacturing, where objects are produced via sequences of predefined steps. In this work, we explore the idea of using simulated "swarms" of simple agents to generate new designs for architected materials in a decentralized, bioinspired manner. Individual agents choose their own actions based solely on information in their immediate environment, with no centralized control. The structures that these processes produce are the result of the collective action of the individual agents, rather than a predetermined design. We build an integrated platform for determining "rule-structure-property" relationships, analogous to process-structure-property relationships in materials science. The platform simulates agent behaviors to show how different rules and different environments result in different structures. We then three-dimensional print these and perform finite element analysis to experimentally and numerically characterize mechanical properties, including tensile strength and energy dissipation.

Multistable metamaterials, capable of adopting multiple stable configurations, offer versatile control over the shape and mechanical properties of systems. Transition waves (TWs), which propagate spatially through state transitions, provide a promising mechanism for reconfiguring such materials. While TWs in systems with asymmetric energy landscapes propagate stably by transitioning from higher to lower energy states, they require additional energy input to reset the structure. This work explores a multistable system with a reconfigurable surface shape, comprising an elastic slender beam coupled to a foundation of bistable elements, each with a symmetric energy landscape. The symmetric landscape enables TWs with tunable speeds, energy, and propagation distances, which can be controlled by boundary impact speed. The stop position of the TW forms a stable domain wall, separating regions of the beam in distinct stable states. Leveraging the relationship between impact speed and propagation distance, we propose a dynamic strategy for reversible surface shape reconfiguration using sequential impulses to generate targeted configurations. The feasibility of this strategy for shape control of multistable systems has been confirmed experimentally, using buckled double-beams as bistable elements.

Abstract This is a roadmap article with multiple contributors on different aspects of embodying intelligence and computing in the mechanical domain of functional materials and structures. Overall, an IOP roadmap article is a broad, multi-author review with leaders in the field discussing the latest developments, commissioned by the editorial board. The intention here is to cover various topics of adaptive structural and material systems with mechano-intelligence in the overall roadmap, with twelve sections in total. These sections cover topics from materials to devices to systems, such as computational metamaterials, neuromorphic materials, mechanical and material logic, mechanical memory, soft matter computing, physical reservoir computing, wave-based computing, morphological computing, mechanical neural networks, plant-inspired intelligence, pneumatic logic circuits, intelligent robotics, and embodying mechano-intelligence for engineering functionalities via physical computing. In this paper, we view all the sections with equal contributions to the overall roadmap article and thus list the authorship on the front page via alphabetical order of their last names. On the other hand, for each individual section, the authors decide on their own the order of authorship. (Abstract written by Guest Editors Kon-Well Wang (aka K W Wang) and Suyi Li.)

Pneumatic soft robots have several advantages, including facile fabrication, versatile deformation modes, and safe human–machine interaction. However, pneumatic soft robots typically rely on mechatronics to interact with their environment, which can limit their form factors and reliability. Researchers have considered how to achieve autonomous behaviors using the principles of mechanical computing and physical intelligence. Herein, modular responsive valves that can autonomously regulate airflow within pneumatic soft robots in response to various environmental stimuli, including light, water, and mechanical forces, are described. By combining multiple types of valves, autonomous logic gates and more advanced logical operations can be realized. Finally, it is demonstrated that responsive valves can be integrated with pneumatic soft robots, allowing autonomous morphing and navigation. This framework provides a strategy for creating autonomous pneumatic robots that can respond to multiple stimuli in their environment.

Mechanical metamaterials have recently been exploited as an interesting platform for information storing, retrieval and processing, analogous to electronic devices. In this work, we describe the design and fabrication a two-dimensional (2D) multistable metamaterial consisting of building blocks that can be switched between two distinct stable phases, and which are capable of storing binary information analogous to digital bits. By changing the spatial distribution of the phases, we can achieve a variety of different configurations and tunable mechanical properties (both static and dynamic). Moreover, we demonstrate the ability to determine the phase distribution via simple probing of the dynamic properties, to which we refer as mechanical proprioception. Finally, as a simple demonstration of feasibility, we illustrate a strategy for building autonomous kirigami systems that can receive inputs from their environment. This work could bring new insights for the design of mechanical metamaterials with information processing and computing functionalities. This article is part of the theme issue 'Origami/Kirigami-inspired structures: from fundamentals to applications'.

Bamboo has a functionally-graded microstructure that endows it with a combination of desirable properties, such as high failure strain, high toughness, and a low density. As a result, bamboo has been widely used in load-bearing structures. In this work, we study the use of bamboo-inspired void patterns to geometrically improve the failure properties of structures made from brittle polymers. We perform finite element analysis and experiments on 3D-printed structures to quantify the effect of the shape and spatial distribution of voids on the fracture behavior. The introduction of periodic, uniformly distributed voids in notched bend specimens leads to a 15-fold increase in the fracture energy relative to solid specimens. Adding a gradient to the pattern of voids leads to a cumulative 55-fold improvement in the fracture energy. Mechanistically, the individual voids result in crack blunting, which suppresses crack initiation, while neighboring voids redistribute stresses throughout the sample to enable large deformation before failure.

Abstract Architected materials exhibit unique properties and functionalities based on the geometric arrangement of their constituent materials. In most cases, these parameters are fixed, requiring that the system be redesigned and reconstructed if different properties are desired. Both stimuli‐responsive materials and modular designs have been used to enable re‐programmable properties in the past, but often have limitations, such as the need for a continuous application of external stimuli or power, or unwanted global morphing. In this study, a locally stable anti‐tetra chiral (LSAT) metamaterial is introduced consisting of independently multistable units that can deform and change state without inducing changes in the global morphology. Adjacent cells are only weakly coupled, allowing the collective metamaterial to be switched between many different possible states. Local bistability enables re‐programmable heterogeneity, such as the snapping of cells along an edge or diagonally within the architected material. Utilizing finite element analysis (FEA), the influence of key geometric parameters on the re‐programmability of the metamaterials is systematically investigated. The effect of these parameters on properties such as shear stiffness, Poisson's ratio, and vibration are also investigated using experimental prototypes. This re‐programmable metamaterial promises to expand the design space for mechanical systems, with potential applications in non‐traditional computation, robotic actuation, and adaptive structures.

In recent years, mechanical metamaterials have been developed that support the propagation of an intriguing variety of nonlinear waves, including transition waves and vector solitons (solitons with coupling between multiple degrees of freedom). Here we report observations of phase transitions in 2D multistable mechanical metamaterials that are initiated by collisions of soliton-like pulses in the metamaterial. Analogous to first-order phase transitions in crystalline solids, we observe that the multistable metamaterials support phase transitions if the new phase meets or exceeds a critical nucleus size. If this criterion is met, the new phase subsequently propagates in the form of transition waves, converting the rest of the metamaterial to the new phase. More interestingly, we numerically show, using an experimentally validated model, that the critical nucleus can be formed via collisions of soliton-like pulses. Moreover, the rich direction-dependent behavior of the nonlinear pulses enables control of the location of nucleation and the spatio-temporal shape of the growing phase.

Mechanical metamaterials enable the creation of structural materials with unprecedented mechanical properties. However, thus far, research on mechanical metamaterials has focused on passive mechanical metamaterials and the tunability of their mechanical properties. Deep integration of multifunctionality, sensing, electrical actuation, information processing, and advancing data-driven designs are grand challenges in the mechanical metamaterials community that could lead to truly intelligent mechanical metamaterials. In this perspective, we provide an overview of mechanical metamaterials within and beyond their classical mechanical functionalities. We discuss various aspects of data-driven approaches for inverse design and optimization of multifunctional mechanical metamaterials. Our aim is to provide new roadmaps for design and discovery of next-generation active and responsive mechanical metamaterials that can interact with the surrounding environment and adapt to various conditions while inheriting all outstanding mechanical features of classical mechanical metamaterials. Next, we deliberate the emerging mechanical metamaterials with specific functionalities to design informative and scientific intelligent devices. We highlight open challenges ahead of mechanical metamaterial systems at the component and integration levels and their transition into the domain of application beyond their mechanical capabilities.

Variational quantum algorithms exploit the features of superposition and entanglement to optimize a cost function efficiently by manipulating the quantum states. They are suitable for noisy intermediate-scale quantum (NISQ) computers that recently became accessible to the worldwide research community. Here, we implement and demonstrate the numerical processes on the 5-qubit and 7-qubit quantum processors on the IBM Qiskit Runtime platform. We combine the commercial finite-element-method (FEM) software ABAQUS with the implementation of Variational Quantum Eigensolver (VQE) to establish an integrated pipeline. Three examples are used to investigate the performance: a hexagonal truss, a Timoshenko beam, and a plane-strain continuum. We conduct parametric studies on the convergence of fundamental natural frequency estimation using this hybrid quantum-classical approach. Our findings can be extended to problems with many more degrees of freedom when quantum computers with hundreds of qubits become available in the near future.

In this work, we show that collisions of one type of nonlinear wave can lead to generation of a different kind of nonlinear wave. Specifically, we demonstrate the formation of topological solitons (or transition waves) via collisions of elastic vector solitons, another type of nonlinear wave, in a multistable mechanical system with coupling between translational and rotational degrees of freedom. We experimentally observe the nucleation of a phase transformation arising from colliding waves, and we numerically investigate head-on and overtaking collisions of solitary waves with vectorial properties (i.e., elastic vector solitons). Unlike KdV-type solitons, which maintain their shape despite collisions, our system shows that collisions of two vector solitons can cause nucleation of a new phase via annihilation of the vector solitons, triggering the propagation of transition waves. The propagation of these depends both on the amount of energy carried by the vector solitons and on their respective rotational directions. The observation of the initiation of transition waves with collisions of vector solitons in multistable mechanical systems is an unexplored area of fundamental nonlinear wave interactions and could also prove useful in applications involving reconfigurable structures.

Robots typically interact with their environments via feedback loops consisting of electronic sensors, microcontrollers, and actuators, which can be bulky and complex. Researchers have sought new strategies for achieving autonomous sensing and control in next-generation soft robots. We describe here an electronics-free approach for autonomous control of soft robots, whose compositional and structural features embody the sensing, control, and actuation feedback loop of their soft bodies. Specifically, we design multiple modular control units that are regulated by responsive materials such as liquid crystal elastomers. These modules enable the robot to sense and respond to different external stimuli (light, heat, and solvents), causing autonomous changes to the robot's trajectory. By combining multiple types of control modules, complex responses can be achieved, such as logical evaluations that require multiple events to occur in the environment before an action is performed. This framework for embodied control offers a new strategy toward autonomous soft robots that operate in uncertain or dynamic environments.

In this Letter, we investigate the propagation of nonlinear pulses along the free surface of flexible metamaterials based on the rotating squares mechanism. While these metamaterials have previously been shown to support the propagation of elastic vector solitons through their bulk, here, we demonstrate that they can also support the stable propagation of nonlinear pulses along their free surface. Furthermore, we show that the stability of these surface pulses is higher when they minimally interact with the linear dispersive surface modes. Finally, we provide guidelines to select geometries that minimize these interactions.

Bamboo has a functionally-graded microstructure that endows it with a combination of desirable properties, such as high failure strain, high toughness, and a low density. As a result, bamboo has been widely used in load-bearing structures. In this work, we study the use of bamboo-inspired void patterns to geometrically improve the failure properties of structures made from brittle polymers. We perform finite element analysis and experiments on 3D-printed structures to quantify the effect of the shape and spatial distribution of voids on the fracture behavior. The introduction of periodic, uniformly distributed voids in notched bend specimens leads to a 15-fold increase in the work of fracture relative to solid specimens. Adding a gradient to the pattern of voids leads to a cumulative 55-fold improvement in the work of fracture. Mechanistically, the individual voids result in crack blunting, which suppresses crack initiation, while neighboring voids redistribute stresses throughout the sample to enable large deformation before failure. In addition, we conduct qualitative, low-energy impact experiments on PMMA plates with laser-cut void patterns, illustrating the broader potential for this strategy to improve damage tolerance and energy absorption in a wide range of materials systems.

In this work, we show that collisions of one type of nonlinear wave can lead to generation of a different kind of nonlinear wave. Specifically, we demonstrate the formation of topological solitons (or transition waves) via collisions of elastic vector solitons, another type of nonlinear wave, in a multi-stable mechanical system with coupling between translational and rotational degrees of freedom. We experimentally observe the nucleation of a phase transformation arising from colliding waves, and we numerically investigate head-on and overtaking collisions of solitary waves with vectorial properties (i.e., elastic vector solitons). Unlike KdV-type solitons, which maintain their shape despite collisions, our system shows that collisions of two vector solitons can cause nucleation of a new phase via annihilation of the vector soltions, triggering the propagation of transition waves. The propagation of these depends both on the amount of energy carried by the vector solitons and on their respective rotational directions. The observation of the initiation of transition waves with collisions of vector solitons in multistable mechanical systems serves as an example of new fundamental nonlinear wave interactions, and could also prove useful in applications involving reconfigurable structures.

In this work, we present a multifidelity Bayesian optimization framework for designing architected materials with optimal energy absorption during compression. Data from both physical experiments (high fidelity) and numerical simulations (low fidelity) are fed in parallel to train the surrogate model, which iteratively decides the next sets of experiments and simulations to run in order to find the optimal structural parameters. We show that having multifidelity data sources allows the optimization framework to find the optimum after fewer iterations relative to using a single high-fidelity source. This saves both material costs and time in the optimization process. Finally, we also apply constraints (on relative density and stress variations) to the optimization process, finding optimal structures within the bounds of the constraints. This framework can be translated to other problems that require complex, high-fidelity, labor-intensive experiments while automating low-fidelity simulations.

In this work, we report observations of phase transitions in 2D multistable mechanical metamaterials that are initiated by collisions of soliton-like pulses in the metamaterial. Analogous to first-order phase transitions in crystalline solids, we experimentally and numerically observe that the multistable metamaterials support phase transitions if the new phase meets or exceeds a critical nucleus size. If this criterion is met, the new phase subsequently propagates in the form of transition waves, converting the rest of the metamaterial to the new phase. More interestingly, we observe that the critical nucleus can be formed via collisions of soliton-like pulses. Moreover, the rich direction-dependent behavior of the nonlinear pulses enables control of the location of nucleation and the spatio-temporal shape of the growing phase.

In this work, we investigate toughening mechanisms in soft polymers reinforced with stiff fibers, particularly focusing on the effect of the strength of the fiber-matrix bond on the toughness. We print polydimethylsiloxane with short milled glass fibers using direct ink writing, an extrusion-based 3D printing method. This process produces composites with aligned fibers. Fibers can be treated with acid prior to printing, which improves the strength of the fiber-matrix bond. This results in higher yield stress and toughness. The higher toughness of the composites can be attributed to intrinsic mechanisms such as matrix deformation and fiber pullout, as well as to extrinsic mechanisms like mechanical dissipation. The intrinsic toughness of the composites is analytically estimated using a micro-mechanical model and experimentally measured by stretching the composites in the direction of fiber alignment. Finally, we demonstrate partial healing of the fiber-matrix bond after initial pre-stretch. Thermal treatment of the damaged composites results in partial recovery of stiffness and toughness.