Zhangxian Deng

Inflatable structures, promising for future deep space exploration missions, are vulnerable to damage from micrometeoroid and orbital debris impacts. Polyvinylidene fluoride-trifluoroethylene (PVDF-trFE) is a flexible, biocompatible, and chemical-resistant material capable of detecting impact forces due to its piezoelectric properties. This study used a state-of-the-art material extrusion system that has been validated for in-space manufacturing, to facilitate fast-prototyping of consistent and uniform PVDF-trFE films. By systematically investigating ink synthesis, printer settings, and post-processing conditions, this research established a comprehensive understanding of the process-structure-property relationship of printed PVDF-trFE. Consequently, this study consistently achieved the printing of PVDF-trFE films with a thickness of around 40 µm, accompanied by an impressive piezoelectric coefficient of up to 25 pC N⁻¹. Additionally, an all-printed dynamic force sensor, featuring a sensitivity of 1.18 V N⁻¹, was produced by mix printing commercial electrically-conductive silver inks with the customized PVDF-trFE inks. This pioneering on-demand fabrication technique for PVDF-trFE films empowers future astronauts to design and manufacture piezoelectric sensors while in space, thereby significantly enhancing the affordability and sustainability of deep space exploration missions.

Surface acoustic wave (SAW) devices are a subclass of micro-electromechanical systems (MEMS) that generate an acoustic emission when electrically stimulated. These transducers also work as detectors, converting surface strain into readable electrical signals. Physical properties of the generated SAW are material dependent and influenced by external factors like temperature. By monitoring temperature-dependent scattering parameters a SAW device can function as a thermometer to elucidate substrate temperature. Traditional fabrication of SAW sensors requires labor- and cost- intensive subtractive processes that produce large volumes of hazardous waste. This study utilizes an innovative aerosol jet printer to directly write consistent, high-resolution, silver comb electrodes onto a Y-cut LiNbO₃ substrate. The printed, two-port, 20 MHz SAW sensor exhibited excellent linearity and repeatability while being verified as a thermometer from 25 to 200 ^∘C. Sensitivities of the printed SAW thermometer are $$-96.9\times 1{0{}^{-6}}^{\circ }$$ − 96.9 × 1 0 − 6 ∘ C⁻¹ and $$-92.0\times 1{0{}^{-6}}^{\circ }$$ − 92.0 × 1 0 − 6 ∘ C⁻¹ when operating in pulse-echo mode and pulse-receiver mode, respectively. These results highlight a repeatable path to the additive fabrication of compact high-frequency SAW thermometers.

Soft structural textiles, or softgoods, are used within the space industry for inflatable habitats, parachutes and decelerator systems. Evaluating the safety and structural integrity of these systems occurs through structural health monitoring systems (SHM), which integrate non-invasive/non-destructive testing methods to detect, diagnose, and locate damage. Strain/load monitoring of these systems is limited while utilizing traditional strain gauges as these gauges are typically stiff, operate at low temperatures, and fail when subjected to high strain that is a result of high loading classifying them as unsuitable for SHM of soft structural textiles. For this work, a capacitance based strain gauge (CSG) was fabricated via aerosol jet printing (AJP) using silver nanoparticle ink on a flexible polymer substrate. Printed strain gauges were then compared to a commercially available high elongation resistance-based strain gauge (HE-RSG) for their ability to monitor strained Kevlar straps having a 26.7 kN (6 klbf) load. Dynamic, static and cyclic loads were used to characterize both types of strain monitoring devices. Printed CSGs demonstrated superior performance for high elongation strain measurements when compared to commonly used HE-RSGs, and were observed to operate with a gauge factor of 5.2 when the electrode arrangement was perpendicular to the direction of strain.

Structural vibrations in rotating machinery may lead to imprecise motion control, excessive noise, or even structural damage. Magnetostrictive materials can dissipate unwanted vibrations via hysteresis, eddy currents, and joule heating while exhibiting an electrically-tunable elastic modulus. Harnessing this feature, this article presents a shunted magnetostrictive device that includes an iron-gallium (Galfenol) rod, a permanent magnet array, a flux return path, and shunt circuits. The stiffness tunability and damping of this passive device are measured under a 750 Hz sinusoidal axial compression for resistive, capacitive, and inductive shunt circuits. The effect of eddy currents stiffness and damping is investigated for the first time by comparing results from laminated and solid Galfenol rods. Solid Galfenol produces larger eddy current-based damping, while laminated Galfenol enables larger stiffness variation and total damping. This device demonstrates a power density of 19.83 mW cm⁻³ for vibration energy harvesting. The frequency-dependent behavior of the shunted device is tested from 5 Hz to 1 kHz for selected electrical loads.

This article reports means to significantly enhance the adaptation of static and dynamic properties using magnetorheological elastomers and demonstrates the enhancements experimentally. The tunability of traditional magnetorheological elastomers is limited by magnetic field strength and intrinsic magnetic–elastic coupling. This contrasts with recent efforts that have revealed large static and dynamic properties change in elastomeric metamaterials via exploiting internal void architectures and collapse mechanisms, although design guidelines have not been developed to adapt properties in real-time. Considering these benchmark efforts, this research integrates concepts from topologically controlled metamaterials and active magnetorheological elastomers to create and study magnetoelastic metamaterials that mutually leverage applied magnetic fields and reconfiguration of internal architectures to achieve real-time tuning of magnetoelastic metamaterial properties across orders of magnitude. Following detailed descriptions of the manufacturing procedures of magnetoelastic metamaterials, this article describes experiments that characterize the static and dynamic properties adaptation. It is found that by the new integration of internal collapse mechanisms and applied magnetic fields, magnetoelastic metamaterials can be reversibly switched from near-zero to approximately 10 kN/m in one-dimensional static stiffness and tailored to double or halve resonant frequencies for dynamic properties modulation. These ideas may fuel new research where geometry, magnetic microstructure, and structural design intersect, to advance state-of-the-art utilization of magnetorheological elastomers.

An optimization algorithm is proposed to determine the parameters of a discrete energy-averaged (DEA) model for Galfenol alloys. A new numerical approximation approach for partial derivative expressions is developed, which improves computational speed of the DEA model by 61% relative to existing partial derivative expressions. Initial estimation of model parameters and a two-step optimization procedure, including an-hysteresis and hysteresis steps, are performed to improve accuracy and efficiency of the algorithm. Initial estimation of certain material properties such as saturation magnetization, saturation magnetostriction, Young’s modulus, and anisotropy energies can improve the convergence and enhance efficiency by 41% compared to the case where these parameters are not estimated. The two-step optimization improves efficiency by 28% while preserving accuracy compared to one-step optimization. Proposed algorithm is employed to find the material properties of Galfenol samples with different compositions and heat treatments. The trends obtained from these optimizations can guide future Galfenol modeling studies.

The axis of most commercially available bulk Terfenol-D rods is misaligned with the pseudo-cubic Terfenol-D crystals. Thus, the development of efficient and accurate constitutive models for Terfenol-D has traditionally been challenging. This study presents a fully coupled and efficient discrete energy-averaged model that describes the nonlinear magnetostrictive behavior of Terfenol-D. The model is built on the basis of the Stoner-Wohlfarth particle approximation, where the anhysteresis bulk response of magnetostrictive materials is considered as a weighted sum of local magnetic domain responses and the material hysteresis is defined by an evolution function for the weights. The local responses are explicitly calculated through minimizing the free energy of individual magnetic domains; the weights, also known as the domain volume fractions, are described by an energy-based Boltzmann distribution. Advanced computation algorithms are developed to further improve the model efficiency. The model is used to interpret magnetic flux density and strain measurements from multiple [112]-oriented Terfenol-D rods. According to the modeling results, the explicit constitutive model developed in this study is three to five times faster than the previous implicit discrete energy-averaged model while preserving accuracy.

A study on iron-gallium (Galfenol) unimorph harvesters is presented which is focused on extending the power density and frequency bandwidth of these devices. A thickness ratio of 2 (ratio of substrate to Galfenol thickness) has been shown to achieve maximum power density under base excitation, but the effect of electrical load capacitance on performance has not been investigated. This article experimentally analyzes the influence of capacitive electrical loads and extends the excitation type to tip impulse. For resistive-capacitive electrical loads, the maximum energy conversion efficiency achieved under impulsive excitation is 5.93%, while the maximum output power and output power density observed for a 139.5 Hz, 3 [Formula: see text] amplitude sinusoidal base excitation is 0.45 W and 6.88 [Formula: see text], respectively, which are 8% higher than those measured under purely resistive loads. A finite element model for Galfenol unimorph harvesters, which incorporates magnetic, mechanical, and electrical dynamics, is developed and validated using impulsive responses. A buckled unimorph beam is experimentally investigated. The proposed bistable system is shown to extend the harvester’s frequency bandwidth.

The ΔE effect (Young's modulus variation of magnetostrictive materials) is useful for tunable vibration absorption and stiffness control. The ΔE effect of iron-gallium (Galfenol) has not been fully characterized. In this study, major and minor strain-stress loops were measured under different bias magnetic fields in solid, research grade, ⟨100⟩-oriented, highly-textured polycrystalline Fe81.6Ga18.4 Galfenol. A 1 Hz, constant amplitude compressive stress was applied from −0.5 MPa to −63.3 MPa for major loop responses. Minor loops were generated by simultaneously applying a 4 Hz, 2.88 MPa amplitude sinusoidal stress and different bias stresses ranging from −5.7 MPa to −41.6 MPa in increments of about 7.2 MPa. Bias magnetic fields were applied in two ways, a constant field in the sample obtained using a proportional-integral (PI) controller and a constant current in the excitation coils. The ΔE effect was quantified from major and minor loop measurements. The maximum ΔE effect is 54.84% and 39.01% for constant field and constant current major loops, respectively. For constant field and constant current minor loops, the maximum ΔE effect is 37.90% and 27.46%, respectively. A laminated sample of the same material was tested under constant current conditions. The saturation modulus of this material is 59.54 GPa, or 82.65% of the solid rod's saturation modulus, due in part to the soft adhesive layers. The minimum modulus calculated from major loops is 36.31 GPa, which corresponds to a 39.02% ΔE effect. A new optimization procedure is presented on the basis of an existing discrete energy-averaged model to incorporate measurement uncertainties. The model was optimized to both major and minor loop data; model parameters with 95% confidence intervals are presented.

Whether serving as mounts, isolators, or dampers, elastomer-based supports are common solutions to inhibit the transmission of waves and vibrations through engineered systems and therefore help to alleviate concerns of radiated noise from structural surfaces. The static and dynamic properties of elastomers govern the operational conditions over which the elastomers and host structures provide effective performance. Passive-adaptive tuning of properties can therefore broaden the useful working range of the material, making the system more robust to varying excitations and loads. While elastomer-based metamaterials are shown to adapt properties by many orders of magnitude according to the collapse of internal void architectures, researchers have not elucidated means to control these instability mechanisms such that they may be leveraged for on-demand tuning of static and dynamic properties. In addition, while magnetorheological elastomers (MREs) exhibit valuable performance-tuning control due to their intrinsic magnetic-elastic coupling, particularly with anisotropic magnetic particle alignment, the extent of their properties adaptation is not substantial when compared to metamaterials. Past studies have not identified means to apply anisotropic MREs in engineered metamaterials to activate the collapse mechanisms for tuning purposes. To address this limited understanding and effect significant performance adaptation in elastomer supports for structural vibration and noise control applications, this research explores a new concept for magnetoelastic metamaterials (MM) that leverage strategic magnetic particle alignment for unprecedented tunability of performance and functionality using non-contact actuation. MM specimens are fabricated using interrelated internal void topologies, with and without anisotropic MRE materials. Experimental characterization of stiffness, hysteretic loss, and dynamic force transmissibility assess the impact of the design variables upon performance metrics. For example, it is discovered that the mechanical properties may undergo significant adaptation, including two orders of magnitude change in mechanical power transmitted through an MM, according to the introduction of a 3 T free space external magnetic field. In addition, the variable collapse of the internal architectures is seen to tune static stiffness from finite to nearly vanishing values, while the dynamic stiffness shows as much as 50% change due to the collapsing architecture topology. Thus, strategically harnessing the internal architecture alongside magnetoelastic coupling is found to introduce a versatile means to tune the properties of the MM to achieve desired system performance across a broad range of working conditions. These results verify the research hypothesis and indicate that, when effectively leveraged, magnetoelastic metamaterials introduce remarkably versatile performance for engineering applications of vibration and noise control.

Magnetostrictive materials exhibit coupling between magnetic and mechanical energies. This bidirectional energy exchange can be employed for actuation, sensing, and energy harvesting. All ferromagnetic materials exhibit the magnetostrictive effect, but only certain iron–rare earth alloys, iron–gallium alloys, amorphous metals, and iron‐ aluminum alloys exhibit sufficiently high magnetostriction for commercial use. Because the magnetostrictive effect is an intrinsic material property that is robust against external factors such as stress and cyclic fatigue, magnetostrictive devices are suitable for harsh environments.

This article provides an overview ofmagnetostrictivematerials and devices, particularly focused on Metglas, Terfenol‐D, and Galfenol. Various transducer topologies are presented and discussed, along with quantification of performance metrics and experimental aspects related to understanding and harnessing the intrinsic nonlinearities of magnetostrictive materials. Selected modeling approaches considering both constitutive material behavior and system response are presented.

This paper presents a fully coupled, nonlinear electromagnetic-mechanical-thermal model for Terfenol-D devices which include active magnetostrictive materials and passive components. The model includes two parts: (1) a material-level discrete energy-averaged model (DEAM) to describe the magnetomechanical coupling and thermal effect of Terfenol-D and (2) a system-level finite element model formulated in weak form using Maxwell's equations, Newton's law, and heat transfer equations. The objective is to describe the electromagnetic, mechanical, and thermal dynamics of the device. The system finite element model is constructed in COMSOL Multiphysics, and the nonlinear behavior of Terfenol-D is coupled through lookup tables generated by the DEAM. Preliminary results of the output capacity of a Terfenol-D actuator with respect to ambient temperature are presented in terms of blocked force, free displacement, and output power. The blocked force and free displacement decrease by 8.0% and 29.8%, respectively, for a 12 A (RMS) excitation current, as the temperature increases from 20 °C to 180 °C. One of the key contributions of this study is that it accounts for both the temperature-dependent Terfenol-D properties and the thermal effects of surrounding passive systems.

This paper focuses on the development of a 3D hysteretic Galfenol model which is implemented using the finite element method (FEM) in COMSOL Multiphysics^®. The model describes Galfenol responses and those of passive components including flux return path, coils and surrounding air. A key contribution of this work is that it lifts the limitations of symmetric geometry utilized in the previous literature and demonstrates the implementation of the approach for more complex systems than before. Unlike anhysteretic FEM models, the proposed model can describe minor loops which are essential for both Galfenol sensor and actuator design. A group of stress versus flux density loops for different bias currents is used to verify the accuracy of the model in the quasi-static regime. Through incorporating C code with MATLAB, the computational efficiency is improved by 78% relative to previous work.

Major and minor magnetization versus stress loops under different bias magnetic fields from 0.8 kA/m to 8.0 kA/m in 0.8 kA/m steps were measured in research grade, ⟨100⟩ oriented, textured polycrystalline Fe81.6Ga18.4. Both compressive and tensile stresses were applied from −63 MPa to 63 MPa for major loop analysis. Minor loops were generated by superimposing a 4.0 Hz, 2.8 MPa amplitude sinusoidal stress on different dc compressive stresses ranging from −40.7 MPa to −5.6 MPa in 7.0 MPa increments. Bias magnetic fields were applied in two ways, constant field in the sample obtained using a controller and constant current to the excitation coils. An energy-averaged model and related optimization method are presented to compare the experiments with simulations. The slope of magnetic flux density versus stress, i.e., the material's sensitivity to stress, is quantified from major and minor loop measurements. The peak sensitivity at constant field is about 75 T/GPa for constant-field major loops, whereas it is 41 T/GPa for constant-current major loops. The sensitivity for minor loops is consistently lower than for major loops, whether at constant field or constant current.