Mechanical Engineering

High-performance, all-aromatic, insoluble, engineering thermoplastic polyimides, such as pyromellitic dianhydride and 4,4'-oxydianiline (PMDA-ODA) (Kapton), exhibit exceptional thermal stability (up to ≈600 °C) and mechanical properties (Young's modulus exceeding 2 GPa). However, their thermal resistance, which is a consequence of the all-aromatic molecular structure, prohibits processing using conventional techniques. Previous reports describe an energy-intensive sintering technique as an alternative technique for processing polyimides with limited resolution and part fidelity. This study demonstrates the unprecedented 3D printing of PMDA-ODA using mask-projection stereolithography, and the preparation of high-resolution 3D structures without sacrificing bulk material properties. Synthesis of a soluble precursor polymer containing photo-crosslinkable acrylate groups enables light-induced, chemical crosslinking for spatial control in the gel state. Postprinting thermal treat...

All-aromatic polyimides have degradation temperatures above 500 °C, excellent mechanical strength, and chemical resistance, and are thus ideal polymers for high-temperature applications. However, their all-aromatic structure impedes additive manufacturing (AM) because of the lack of melt processability and insolubility in organic solvents. Recently, our group demonstrated the design of UV-curable polyamic acids (PAA), the precursor of polyimides, to enable their processing using vat photopolymerization AM. This work leverages our previous synthetic strategy and combines it with the high solution viscosity of nonisolated PAA to yield suitable UV-curable inks for UV-assisted direct ink write (UV-DIW). UV-DIW enabled the design of complex three-dimensional structures comprising of thin features, such as truss structures. Dynamic mechanical analysis of printed and imidized specimens confirmed the thermomechanical properties typical of all-aromatic polyimides, showing a storage modulus a...

Abstract In this study, we report a multimodal energy harvesting device that combines electromagnetic and piezoelectric energy harvesting mechanism. The device consists of piezoelectric crystals bonded to a cantilever beam. The tip of the cantilever beam has an attached permanent magnet which, oscillates within a stationary coil fixed to the top of the package. The permanent magnet serves two purpose (i) acts as a tip mass for the cantilever beam and lowers the resonance frequency, and (ii) acts as a core which oscillates ...

Electromagnetic actuators have been commonly deployed in robotics technology for obtaining expressions and other motion. However, the current technology is unable to meet the requirement of space limitation and at the same time provide high displacement and force (22–25 mm and force 2–7 N). The loss of space due to bulky motors prohibits the possibility of installing processing and control cards inside the skull of humanoid robot which is required to realize a smart expressive face. Our study shows the feasibility of utilizing ...

abstract An unmanned underwater vehicle (UUV) was designed inspired by the form and functionality of a Jellyfish. These natural organisms were chosen as bio-inspiration for a multitude of reasons including: efficiency of locomotion, lack of natural predators, proper form and shape to incorporate payload, and varying range of sizes. The structure consists of a hub body surrounded by bell segments and microcontroller based drive system. The locomotion of UUV was achieved by shape memory alloy" Biometal Fiber" actuation which ...

Abstract This study focuses on the synthesis and characterization of thick and thin film polypyrrole (PPy)–metal composite actuators for application as artificial muscles in facial robotics. The fabrication method consists of three steps based upon the approach proposed by Ding et al (2003 Synth. Met. 138 391–8):(i) winding the conductive spiral structure around the platinum (Pt) wire core,(ii) deposition of PPy film on the Pt wire core, and (iii) removal of the Pt wire core. This approach yielded good performance from the synthesized actuators, ...

Mimicking facial structure for a robotic head is a challenging issue and requires information on design and control of muscle actuation, architecture of the linkages between actuation points within skin, and deformation matrix with respect to global coordinates for a specific expression. This manuscript presents:(1) a functional relationship between deformation vector of facial control points and actuator parameter, skin elasticity and angular position of actuator. The actuation method is applicable to any rotary actuator technology utilized for ...

ABSTRACT Artificial skin materials were synthesized using platinum-cured silicone elastomeric material (Reynolds Advanced Materials Inc.) as the base consisting of mainly polyorganosiloxanes, amorphous silica and platinum-siloxane complex compounds. Systematic incorporation of porosity in this material was found to lower the force required to deform the skin in axial direction. In this study, we utilized foaming agents comprising of sodium bicarbonate and dilute form of acetic acid for modifying the polymeric chain and ...

Abstract Composite stripe and zigzag actuators consisting of a sandwich polypyrrole (PPy)/polyvinylidene difluoride (PVDF)/PPy structure were synthesized using potentiodynamic film growth on gold electrodes. The synthesis was done from an aqueous solution containing tetrabutylammonium perchlorate and pyrrole by polymerization at room temperature. The actuator displacement was modeled using finite element simulations. For depositing thin PPy films and thereby minimizing the response time, experimental ...

The numerical simulation of shape memory alloy actuators requires the solution of the coupled thermo-mechanical, phase transformation, and constitutive relationship equations. Simulation results are highly affected by parametric values as well as modeling equations. Specifically, the martensite fraction affects the simulation results of the actuator significantly for various input excitation as fraction of martensite is often modeled with a switching function. Depending on the assumed model this may cause changes in other properties of ...

ABSTRACT Artificial skin materials were synthesized using platinum-cured silicone elastomeric material (Reynolds Advanced Materials Inc.) as the base consisting of mainly polyorganosiloxanes, amorphous silica and platinum-siloxane complex compounds. Systematic incorporation of porosity in this material was found to lower the force required to deform the skin in axial direction. In this study, we utilized foaming agents comprising of sodium bicarbonate and dilute form of acetic acid for modifying the polymeric chain and ...

abstract An unmanned underwater vehicle (UUV) was designed inspired by the form and functionality of a Jellyfish. These natural organisms were chosen as bio-inspiration for a multitude of reasons including: efficiency of locomotion, lack of natural predators, proper form and shape to incorporate payload, and varying range of sizes. The structure consists of a hub body surrounded by bell segments and microcontroller based drive system. The locomotion of UUV was achieved by shape memory alloy" Biometal Fiber" actuation which ...

Abstract. Recently, bio-inspired shape memory alloy composite (BISMAC) actuators have been shown to mimic the deformation characteristics of natural jellyfish medusa. In this study, a constant cross-section BISMAC actuator was characterized in terms of bending deflection and force in conjunction with microscopy to understand its deformation mechanism. The actuator showed bending deflection of 111% with respect to the active length along with a blocking force of 0.061 N. The resulting energy density of the ...