Experimental Investigation of the Mechanisms and Performance of Active Auxetic and Shearing Textiles

Anisotropic textiles are commonly used in wearable applications to achieve varied bi-axial stress-strain behavior around the body. Auxetic textiles, specifically those that exhibit a negative Poisson’s ratio (v), likewise exhibit intriguing behavior such as volume increase in response to impact or variable air permeability. Active textiles are traditional textile structures that integrate smart materials, such as shape memory alloys, shape memory polymers, or carbon nanotubes, to enable spatial actuation behavior, such as contraction for on-body compression or corrugation for haptic feedback. This research is a first experimental investigation into active auxetic and shearing textile structures. These textile structures leverage the bending- and torsional-deformations of the fibers/filaments within traditional textile structures as well as the shape memory effect of shape memory alloys to achieve novel, spatial performance. Five textile structures were fabricated from shape memory alloy wire deformed into needle lace and weft knit textile structures. All active structures exhibited anisotropic behavior and four of the five structures exhibited auxetic behavior upon free recovery, contracting in both x- and y-axes upon actuation (v = −0.3 to −1.5). One structure exhibited novel shearing behavior, with a mean free angle recovery of 7°. Temperature-controlled biaxial tensile testing was conducted to experimentally investigate actuation behavior and anisotropy of the designed structures. The presented design and performance of these active auxetic, anisotropic, and shearing textiles inspire new capabilities for applications, such as smart wearables, soft robotics, reconfigurable aerospace structures, and medical devices.

A Three-Row Opposed Gripping Mechanism With Radial Configuration for Wall-Climbing Robots

This paper presents a three-row opposed gripping mechanism with radial configuration for wall-climbing robots inspired by the structure of the gripper of LEMUR IIB. The mechanism builds upon a kind of microspines for climbing robots. This work utilizes an opposed spoke configuration with 3 rows of 31 microspines on each linkage array, splayed around a central bracket. A single motor drives the 3 linkage arrays by a set of gears to achieve attachment and detachment procedures, and the trajectory of each linkage array tip makes the miniature spines easy to penetrate in and pull off the surfaces. The mechanism designed as a foot of climbing robots can vertically resist at least 1kg of load on rough surface. The findings provide a foundation for constructing a system for a rough-wall-climbing robot.

Photo-Triggered Soft Materials With Differentiated Diffusive Pathways

Controlled diffusive transport between regions within a compartmentalized structure is an essential feature of cellular-inspired materials. Using the droplet interface bilayer (DIB) technique, biomolecular soft materials can be constructed in an oil medium by connecting multiple lipid-coated microdroplets together through interfacial bilayers. While traditionally achieved through the incorporation of pore forming toxins (PFTs), signal propagation within DIB assemblies can be remotely controlled through the integration of photopolymerizable phospholipids (23:2 DiynePC) into the aqueous phase. Since such strategy allows for the formation of UV-C triggered pathways only between droplets both containing DiynePC, polymerizable phospholipids have shown an advantage of reducing undesired diffusion and forming conductive pathways. The partial polymerization of lipid bilayers formed through the DIB platform is still to this date underexplored in the literature. In a previous work, we have shown that the incorporation of 23:2 DiynePC into lipid bilayers allows for the creation of patterned conductive pathways in a 2D DIB structure. The properties of photosensitive bilayers were also investigated but not their channel activity. The functionalization of bilayers-based photosensitive structures through transmembrane channels remains an under-investigated mean of achieving further differentiated conductive channels. This work explores the reconstitution of several transmembrane channels such as alpha-hemolysin (αHL) and alamethicin (ALM) into partially polymerized lipid bilayers. We believe that the ability to incorporate transmembrane channels into photosensitive DIB soft structures allows for further differentiation of signal propagation pathways by including both edge-defect induced pores as well as more traditional and bio-derived transporters.

On the Design of a Long-Stroke Beam-Based Compliant Mechanism Providing Quasi-Constant Force

In this paper the design of a linear long-stroke quasi-constant force compliant mechanism (CM) is presented and discussed. Starting from a flexure-based slider-crank mechanism, providing the required constant force within a rather limited deflection range, the paper reports about the shape optimization carried out with the specific aim of extending the available CM operative range. The proposed device is suitable in several precision manipulation systems, which require to maintain a constant-force at their contact interface with the manipulated object. Force regulation is generally achieved by means of complex control algorithms and related sensory apparatus, resulting in a flexible behavior but also in high costs. A valid alternative may be the use of a purposely designed CM, namely a purely mechanical system whose shape and dimensions are optimized so as to provide a force-deflection behavior characterized by zero stiffness. In the first design step, the Pseudo-Rigid Body (PRB) method is exploited to synthesize the sub-optimal compliant configuration, i.e. the one characterized by lumped compliance. Secondly, an improved design alternative is evaluated resorting to an integrated software framework, comprising Matlab and ANSYS APDL, and capable of performing non-linear structural optimizations. The new embodiment makes use of a variable thickness beam, whose shape and dimensions have been optimized so as to provide a constant reaction force in an extended range. Finally, a physical prototype of the beam-based configuration is produced and tested, experimentally validating the proposed design method.

Design-Oriented Multifidelity Fluid Simulation Using Machine Learned Fidelity Mapping

A machine learning algorithm that performs multifidelity domain decomposition is introduced. While the design of complex systems can be facilitated by numerical simulations, the determination of appropriate physics couplings and levels of model fidelity can be challenging. The proposed method automatically divides the computational domain into subregions and assigns required fidelity level, using a small number of high fidelity simulations to generate training data and low fidelity solutions as input data. Unsupervised and supervised machine learning algorithms are used to correlate features from low fidelity solutions to fidelity assignment. The effectiveness of the method is demonstrated in a problem of viscous fluid flow around a cylinder at Re ≈ 20. Ling et al. built physics-informed invariance and symmetry properties into machine learning models and demonstrated improved model generalizability. Along these lines, we avoid using problem dependent features such as coordinates of sample points, object geometry or flow conditions as explicit inputs to the machine learning model. Use of pointwise flow features generates large data sets from only one or two high fidelity simulations, and the fidelity predictor model achieved 99.5% accuracy at training points. The trained model was shown to be capable of predicting a fidelity map for a problem with an altered cylinder radius. A significant improvement in the prediction performance was seen when inputs are expanded to include multiscale features that incorporate neighborhood information.

Design and Realization of Temperature-Driven Smart Structure Based on Shape Memory Polymer in 4D Printing

In the traditional 4D printing method using Shape Memory Polymer (SMP), the design process and preparation of 4d printing are complex. In this research, we proposed a design method of a temperature-driven SMP smart structure and made Realization. This smart structure also a bilayer structure use an SMP material in one printing process to realize the deformation in 4D printing. The design of the smart structure is mainly realized by parameter allocation in the printing process, such as print line width, print line height, print temperature, simulation temperature, and fill the form in Fused Deposition Modelling (FDM). Through experimental determination and analysis of statics and thermodynamics, our method fitting out the model relationship between process parameters and the curvature and strain of smart structure. This bilayer smart structure widely applied to the self-folding. In the example stage, this paper mainly uses PLA as an SMP material for the preparation of structure. Observing that the motion behaviors of the smart structure conformed to the model measured in this paper, the average accuracy of the strategy reaches 95%.

An FE Based Surrogate Model for Predicting the Impact of a SMA Twist System on the Helicopter Performance

This work focuses on a surrogate predictive model, conceived to estimate the impact on blade twist law of a Shape Memory Alloy actuation system. The basic idea is to integrate the pre-existing blade structure with a pre-twisted SMA tube. Due to the specific property of recovering deformation during phase transition, the SMA element can transmit angular deformations and alter the original twist to improve performance when required. The model includes two main modules. The first one targets the SMA actuator and simulates the transmission of twist against some critical parameters (tube extension and location along the blade span and level of activation). The second module receives as input the modified twist law and the updated mechanical features due to the SMA and gives in output an estimate of the performance produced by the system. After an overview on input and output parameters and their cross link, a description of the SMA predicting core is provided. A parameterization is then organized to illustrate the impact of the morphing system onto the blade and on the twist law. On this basis, an additional parameterization is implemented, now focusing on the effects on performance of the proposed system.

Nonreciprocal Wave Transmission in Metastable Modular Metastructures Utilizing Asymmetric Dual-Threshold Snap-Through

In this research, the nonreciprocal wave transmission features in one-dimensional and two-dimensional metastable modular metastructures are studied. Unlike previous work, in which the nonreciprocal transmission in metastable metastructures is realized by utilizing the supratransmission phenomenon when the excitation frequency is inside the linearized bandgap, a new approach is explored to achieve nonreciprocal wave transmission exploiting metastability and asymmetric dual-threshold snap-through. It is found that because of the asymmetry of potential energy wells of the equilibria, there will be two excitation amplitude thresholds for a metastable component when it is initially at the high-potential-energy equilibrium with excitation frequency within the passband. When the excitation amplitude increases and exceeds the first threshold, the metastable component will snap to the low-potential-energy equilibrium and maintain intrawell motion around this stable point, which will cause a significant decrease of the wave transmission. And when the excitation amplitude exceeds the second threshold, the metastable component will start to perform interwell motion, and now the wave transmission will increase suddenly. By using this “dual-threshold” phenomenon, nonreciprocal wave transmission in a one-dimensional structure is realized by connecting a metastable chain with a linear periodic part. Because of the wave attenuation effect of the linear part of the system, the excitation amplitude thresholds on different sides of the one-dimensional structure will be discrepant. Therefore, nonreciprocal wave transmission can be developed when the excitation amplitude is within certain ranges. It is interesting to note that the direction of nonreciprocal wave transmission can be changed by setting the excitation amplitude to different values. By changing the configuration of the metastable chain, the operation frequency and excitation amplitude ranges of the nonreciprocal transmission can be tuned. For a two-dimensional metastable metastructure, nonreciprocal wave transmission can be realized by adjusting the parameters of some metastable modules in the metastructure in the manner that the potential energy and energy thresholds of the adjusted modules and the unadjusted modules are different, but the passbands of the adjusted modules and the unadjusted modules will overlap in some frequency regions. Numerical studies provide clear insight of the proposed nonreciprocal wave transmission approach.

Active Thermal Management of FRP Composites via Embedded Vascular Networks

Fibre-reinforced polymer (FRP) composite materials are limited in high temperature applications by the matrix glass transition temperature, Tg. At and above this temperature, significant mechanical performance is lost, and degradation processes accelerated. This research explores the use of internal passages, or vascules, within the laminate to carry a coolant fluid, absorbing heat energy and cooling the material. A custom thermal chamber and four-point flexural test fixture were developed to perform in-situ thermo-mechanical testing. Vascular and non-vascular carbon/epoxy specimens were manufactured, containing arrays of four 1.1 mm diameter vascules. Specimens were exposed to temperatures from ambient to 170 °C (Tg = 200 °C). Flexural modulus varied little with temperature across all tests. Non-vascular specimens at 170 °C showed a reduction in ultimate strength of 21 % compared to under ambient conditions. The presence of vascules caused a small improvement in flexural modulus and strength, due to displacement of a small number of 0° fibre tows further from the neutral axis as a result of the manufacturing process. At 15 L·min−1 coolant flow, vascular specimens showed full retention of strength compared to non-vascular specimens at ambient, demonstrating the potential mechanical performance benefits.

Compact Telescopic Morphing Lattice Boom

This paper reports on the design and manufacture of a compact telescopic morphing lattice (CTML) space boom. This boom stows within a 1U CubeSat volume and weighs only 0.475kg. Once deployed, the CTML has a total length of 2m, 20 times the stowed height. The device consists of three multi-stable cylindrical composite lattices connected in series. To improve packaging efficiency, these lattices nest inside one another in the stowed configuration. The morphing lattice is a structure that uses prestress and lamina orientation to seamlessly morph from a short stowed state to a long deployed state. By tailoring the manufacturing parameters, the lattices in the boom have been designed to maximize the deployment force and to be self-deploying. Therefore, the CTML only requires a small, lightweight mechanism to regulate the deployment speed. The deployment speed regulator can also potentially retract the boom back to the stowed state, facilitating reconfigurability.