Deployable vortex generators for low Reynolds numbers applications powered by cephalopods inspired artificial muscles.

This paper proposes deployable vortex generators (VGs) powered by twisted spiral artificial muscles (TSAMs). TSAMs take inspiration from cephalopods' papillae and can protrude out of plane upon electro-thermal actuation with an output strain of 2000% and an input voltage of 0.2 V/cm. Unlike passive VGs, designed for specific flow conditions, this technology can adjust to changes in flow conditions by overcoming the limitations of existing active flow control devices in terms of portability and power requirements. Our technology can deploy different VGs configurations on demand, and match a desired target configuration, optimized for a specific flow condition. Experiments were conducted in a wind tunnel using a NASA Langley Research Center LS (1)-0417 GA(W)-1 airfoil. Stall delays and lift increase have been demonstrated for different flow conditions, with Reynolds numbers between 100,000 and 140,000. These findings are promising for enhancing efficiency in small unmanned aerial vehicles operating at low Reynolds numbers.

Octopus-Inspired Muscular Hydrostats Powered By Twisted and Coiled Artificial Muscles.

Traditional robots are characterized by rigid structures, which restrict their range of motion and their application in environments where complex movements and safe human-robot interactions are required. Soft robots inspired by nature and characterized by soft compliant materials have emerged as an exciting alternative in unstructured environments. However, the use of multicomponent actuators with low power/weight ratios has prevented the development of truly bioinspired soft robots. Octopodes' limbs contain layers of muscular hydrostats, which provide them with a nearly limitless range of motions. In this work, we propose octopus-inspired muscular hydrostats powered by an emerging class of artificial muscles called twisted and coiled artificial muscles (TCAMs). TCAMs are fabricated by twisting and coiling inexpensive fibers, can sustain stresses up to 60 MPa, and provide tensile strokes of nearly 50% with <0.2 V/cm of input voltage. These artificial muscles overcome the limitations of other actuators in terms of cost, power, and portability. We developed four different configurations of muscular hydrostats with TCAMs arranged in different orientations to reproduce the main motions of octopodes' arms: shortening, torsion, bending, and extension. We also assembled an untethered waterproof device with on-board control, sensing, actuation, and a power source for driving our hydrostats underwater. The proposed TCAM-powered muscular hydrostats will pave the way for the development of compliant bioinspired robots that can be used to explore the underwater world and perform complex tasks in harsh and dangerous environments.

A hybrid soft material robotic end-effector for reversible in-space assembly of strut components.

Based on the NASA in-Space Assembled Telescope (iSAT) study (Bulletin of the American Astronomical Society, 2019, 51, 50) which details the design and requirements for a 20-m parabolic in-space telescope, NASA Langley Research Center (LaRC) has been developing structural and robotic solutions to address the needs of building larger in-space assets. One of the structural methods studied involves stackable and collapsible modular solutions to address launch vehicle volume constraints. This solution uses a packing method that stacks struts in a dixie-cup like manner and a chemical composite bonding technique that reduces weight of the structure, adds strength, and offers the ability to de-bond the components for structural modifications. We present in this paper work towards a soft material robot end-effector, capable of suppling the manipulability, pressure, and temperature requirements for the bonding/de-bonding of these conical structural components. This work is done to investigate the feasibility of a hybrid soft robotic end-effector actuated by Twisted and Coiled Artificial Muscles (TCAMs) for in-space assembly tasks. TCAMs are a class of actuator which have garnered significant recent research interest due to their allowance for high force to weight ratio when compared to other popular methods of actuation within the field of soft robotics, and a muscle-tendon actuation design using TCAMs leads to a compact and lightweight system with controllable and tunable behavior. In addition to the muscle-tendon design, this paper also details the early investigation of an induction system for adhesive bonding/de-bonding and the sensors used for benchtop design and testing. Additionally, we discuss the viability of Robotic Operating System 2 (ROS2) and Gazebo modeling environments for soft robotics as they pertain to larger simulation efforts at LaRC. We show real world test results against simulation results for a method which divides the soft, continuous material of the end-effector into discrete links connected by spring-like joints.

Carbon Fiber-Based Twisted and Coiled Artificial Muscles (TCAMs) for Powered Ankle-Foot Orthoses.

Ankle foot orthoses (AFOs) control the position and motion of the ankle, compensate for weakness, and correct deformities. AFOs can be classified as passive or powered. Powered AFOs overcome the limitations of passive AFOs by adapting their performance to meet a variety of requirements. However, the actuators currently used to power AFOs are typically heavy, bulky, expensive, or limited to laboratory settings. Thus, there is a strong need for lightweight, inexpensive, and flexible actuators for powering AFOs. In this technical brief, carbon fiber/silicone rubber (CF/SR) twisted and coiled artificial muscles (TCAMs) are proposed as novel actuators for powered AFOs. CF/SR TCAMs can lift to 12,600 times their weight with an input power of only 0.025 W cm-1 and are fabricated from inexpensive materials through a low-cost manufacturing process. Additionally, they can provide a specific work of 758 J kg-1 when an input voltage of 1.64 V cm-1 is applied. Mechanical characterization of CF/SR TCAMs in terms of length/tension, tension/velocity, and active-passive length/tension is presented, and results are compared with the performance of skeletal muscles. A gait analysis demonstrates that CF/SR TCAMs can provide the performance required to supplement lower limb musculature and replicate the gait cycle of a healthy subject. Therefore, the preliminary results provided in this brief are a stepping stone for a dynamic AFO powered by CF/SR TCAMs.

Enabling Superhydrophobicity-Guided Superwicking in Metal Alloys via a Nanosecond Laser-Based Surface Treatment Method.

Enabling capillary wicking on bulk metal alloys is challenging due to processing complexity at different size scales. This work presents a laser-chemical surface treatment to fabricate superwicking patterns guided by a superhydrophobic region over a large-area metal alloy surface. The laser-chemical surface treatment generates surface micro/nanostructures and desirable surface chemistry simultaneously. The superhydrophobic surface was first fabricated over the whole surface by laser treatment under water confinement and fluorosilane treatment; subsequently, superwicking stripes were processed by a second laser treatment in air and cyanosilane treatment. The resultant surface shows superwicking regions surrounded by superhydrophobic regions. During the process, superwicking regions possess dual-scale structures and polar nitrile surface chemistry. In contrast, random nanoscale structures and fluorocarbon chemistry are generated on the superhydrophobic region of the aluminum alloy 6061 substrates. The resultant superwicking region demonstrates self-propelling anti-gravity liquid transport for methanol and water. The combination of the capillary effect of the dual-scale surface microgrooves and the water affinitive nitrile group contributes toward the self-propelling movement of water and methanol at the superwicking region. The initial phase of wicking followed Washburn dynamics, whereas it entered a non-linear regime in the later phase. The wicking height and rate are regulated by microgroove geometry and spacing.

Interfacial Force-Focusing Effect in Mechanophore-Linked Nanocomposites.

Enhanced force transmission to mechanophores is demonstrated in polymer nanocomposite materials. Spiropyran (SP) mechanophores that change color and fluorescence under mechanical stimuli are functionalized at the interface between SiO2 nanoparticles and polymers. Successful mechanical activation of SP at the interface is confirmed in both solution and solid states. Compared with SP-linked in bulk polymers, interfacial activation induces greater conversion of SP to its colored merocyanine form and also significantly decreases the activation threshold under tension. Experimental observations are supported by finite element simulation of the interfacial stress state. The interfacial force-focusing strategy opens a new way to control the reactivity of mechanophores and also potentially indicates interfacial damage in composite materials.