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Friction stir processing (FSP), an innovative local microstructural modification technique for bulk material, has been used to process Monel alloy. A detailed microstructural analysis was conducted by acquiring high-resolution electron backscatter diffraction (EBSD). The local tensile properties and hardness nanoindentation were obtained for the different FSP area zones. The coarse equiaxed grain structure of 18.9 μm average grain size at the base material (BM) has been dynamically recrystallized refined equiaxed grains of an average grain size of 3.6 μm in the stir zone (SZ) where the thermomechanically affected zone (TMAZ) has an average grain size of 10.7 μm. The grain structure at the interface of the SZ and TMAZ consisted of mixed fine recrystallized grains and coarse deformed grains. The SZ is dominated by significantly refined grains, with the highest fraction of high-angle grain boundaries (HAGBs) of about 71%. The point-to-point misorientation measured by Kernel Average Misorientation (KAM) indicates low values in the SZ compared with the highest values at the interface between SZ and TMAZ. In terms of tensile properties, the yield strength of TMAZ and SZ improved to 380 and 440 MPa, respectively. The ultimate tensile strength (UTS) also increased by 18% from 499 to 593 MPa in TMAZ and 37% from 499 to 699 MPa in the SZ. The maximum nano hardness found in the TMAZ of about 7.13±1.92 GPa due to the high density of the substructure. However, the SZ slightly increased to 3.88±0.22 GPa from 3.33±0.17 GPa of the BM.

Developing stretchable/wearable strain sensors in different application scenarios is a global demand for creating a smart society and promoting healthcare, whereas existing hydrogel-based strain sensors suffer from limited sensitivity, low conductance and hydrophilicity, making them difficult to operate underwater. In this work, a highly sensitive, stretchable, and hydrophobic strain sensor is fabricated by coating a layer of reduced graphene oxide (rGO) sheets on the surface of organohydrogel. Furthermore, a facile solvent-replacement approach is utilized to enhance the anti-freezing and anti-drying abilities of hydrogel simultaneously by incorporating propanediol in the solvent. Consequently, the obtained rGO-organohydrogel composite strain sensor features a high gauge factor of 140, a low detection limit of 0.1% strain, a wide detection range (0–400% strain), a fast response time of 190 ms, excellent stability and repeatability, and high hydrophobicity (contact angle of 122°), making it applicable for a wide range of application scenarios, such as the real-time and continuous monitoring of various human motions in extremely cold (−60 °C), dry, and underwater environments. The sensitivity of an rGO-modified organohydrogel strain sensor is more than 30 times higher than that of its unmodified counterpart, which is attributed to the cracking and tunneling effects introduced by the highly conductive rGO surface layer upon stretching.

A non-equiatomic interstitial-strengthened high entropy alloy (iHEA), Fe49.5Mn30Co10Cr10C0.5 (at.%), is manufactured by laser powder-bed fusion (LPBF) with stripe and chessboard scanning strategies. The present study highlights the correlation between the laser scanning strategies with resulting microstructure, textures, and anisotropic mechanical properties in as-built iHEA. The results show that the LPBF processed iHEA exhibits an excellent strength-ductility synergy due to the combined deformation mechanisms of dislocation slip, martensite phase transformation- and nano twinning-induced plasticity. The samples printed by the stripe scanning strategy show more evident mechanical anisotropy than that of the chessboard-scanned samples. The difference in the degree of mechanical anisotropy is mainly attributed to the heterogeneous grain morphology and crystallographic texture resulted from different scanning strategies.

This paper summarizes the submissions to a recently announced contact-mechanics modeling challenge. The task was to solve a typical, albeit mathematically fully defined problem on the adhesion between nominally flat surfaces. The surface topography of the rough, rigid substrate, the elastic properties of the indenter, as well as the short-range adhesion between indenter and substrate, were specified so that diverse quantities of interest, e.g., the distribution of interfacial stresses at a given load or the mean gap as a function of load, could be computed and compared to a reference solution. Many different solution strategies were pursued, ranging from traditional asperity-based models via Persson theory and brute-force computational approaches, to real-laboratory experiments and all-atom molecular dynamics simulations of a model, in which the original assignment was scaled down to the atomistic scale. While each submission contained satisfying answers for at least a subset of the posed questions, efficiency, versatility, and accuracy differed between methods, the more precise methods being, in general, computationally more complex. The aim of this paper is to provide both theorists and experimentalists with benchmarks to decide which method is the most appropriate for a particular application and to gauge the errors associated with each one.

Despite rapid advancements in the development of triboelectric nanogenerators (TENG), mechanical defects generated during their working condition limit the service lifetime of these devices. Polyester-based vitrimers can offer a solution to solve this issue via their dynamic bond exchange reactions. However, they often require high temperatures and a long time to crosslink, rendering them not useful for large-scale TENG fabrication. To solve these issues, a self-healable vitrimer-based triboelectric nanogenerator (VITENG) is developed based on diacrylate poly(dimethylsiloxane) (AA-PDMS) via a fast thiol-Michael reaction. By including 2,3-dihydroxypropyl methacrylate (DHPMA), hydroxy end dangling side chains are generated in the matrix, which increased the PDMS network's flexibility and transesterification efficiency. Efficient transesterification occurs on the abundant dynamic β-hydroxy ester bonds in the PDMS network, resulting in 100% efficient mechanical damage repair. The VITENG demonstrates a good performance with an output voltage of 135 V under a load of 10 N, demonstrating the potential for mechanical energy harvesters with long lifetimes and high design flexibility.

Elastomer-based wearables can improve people's lives; however, frictional wear caused by manipulation may pose significant concerns regarding their durability and sustainability. To address the aforementioned issue, a new class of advanced scalable supersoft elastic transparent material (ASSETm) is reported, which offers a unique combination of scalability (20 g scale), stretchability (up to 235%), and enzymatic degradability (up to 65% in 30 days). The key feature of our design is to render native dextrin hydrophobic, which turns it into a macroinitiator for bulk ring-opening polymerization. Based on ASSETm, a self-powered touch sensor (ASSETm-TS) for touch sensing and non-contact approaching detection, possessing excellent electrical potential (up to 65 V) and rapid response time (60 ms), is fabricated. This work is a step toward developing sustainable soft electronic systems, and ASSETm's tunability enables further improvement of electrical outputs, enhancing human-interactive applications.

Seals can detect prey up to 180 m away using only their flow-sensing whiskers. The unique undulating morphology of Phocid seal whiskers reduces vortex-induced vibrations (VIVs), rendering seals highly sensitive to biologically relevant flow stimuli. In this work, digital models of harbor and grey seal whiskers are extracted using 3D scanning and a mathematical framework that accurately recreates their undulating geometry is proposed. Through fluid-structure interaction studies and experimental investigations involving a whisker array mounted on 3D-printed microelectromechanical systems sensors, the vibration characteristics of the whisker array and the interaction between neighboring whiskers in steady flows and fish-wake-like vortices are explained for the first time. Results reveal that the downstream vortices intensity and resulting VIVs are consistently lower for grey than harbor seal whiskers and a smooth cylinder, suggesting that the grey seal whisker geometry can be an ideal template for the biomimetic design of VIV-resistant underwater structures. In addition, neighboring whiskers in an array influence one another by resulting in greater flow vorticity fluctuation and distribution area, thus causing increased vibrations than an isolated whisker, which indicates the possibility of a signal-strengthening effect in whisker arrays.

Flexible piezocapacitive sensors utilizing nanomaterial-polymer composite based nanofibrous membranes offer an attractive alternative to more traditional piezoelectric and piezoresistive wearable sensors owing to their ultralow powered nature, fast response, low hysteresis, and insensitivity to temperature change. In this work we propose a facile method of fabricating electrospun graphene dispersed PVAc nanofibrous membrane based piezocapacitive sensors for applications in IoT enabled wearables and human physiological function monitoring. A series of electrical and material characterization experiments were conducted on both the pristine and graphene dispersed PVAc nanofibers to understand the effect of graphene addition on nanofiber morphology, dielectric response, and pressure sensing performance. Dynamic uniaxial pressure sensing performance evaluation tests were conducted on the pristine and graphene loaded PVAc nanofibrous membrane-based sensors for understanding the effect of two-dimensional (2D) nanofiller addition on pressure sensing performance. Almost twofold increase in dielectric constant and pressure sensing performance was observed for graphene loaded nanofiber sensors and subsequently, micro dipole formation model was invoked to explain the nanofiller induced dielectric constant enhancement. The robustness and reliability of the sensor has been underscored by conducting accelerated lifetime assessment experiments entailing at least 3000 cycles of periodic tactile force loading. A series of tests involving human physiological parameters monitoring were conducted to underscore the applicability of the proposed sensor for IoT enabled personalized health care, soft robotics, and next generation prosthetic devices. Finally, easy degradability of the sensing elements is demonstrated to emphasize their suitability for transient electronics applications.

We present the design and experimental validation of source seeking control algorithms for a unicycle mobile robot that is equipped with novel 3D-printed flexible graphene-based piezoresistive airflow sensors. Based solely on a local gradient measurement from the airflow sensors, we propose and analyze a projected gradient ascent algorithm to solve the source seeking problem. In the case of partial sensor failure, we propose a combination of Extremum-Seeking Control with our projected gradient ascent algorithm. For both control laws, we prove the asymptotic convergence of the robot to the source. Numerical simulations were performed to validate the algorithms and experimental validations are presented to demonstrate the efficacy of the proposed methods., Published in IEEE Transactions on Robotics

During the past few decades, a significant amount of research effort has been dedicated toward developing skin-inspired sensors for real-time human motion monitoring and next-generation robotic devices. Although several flexible and wearable sensors have been developed in the past, the need of the hour is developing accurate, reliable, sophisticated, facile yet inexpensive flexible sensors coupled with neuromorphic systems or spiking neural networks to encode tactile information without the need for complex digital architectures, thus achieving true skin-like sensing with limited resources. In this work, we propose an approach entailing carbon nanofiber-polydimethylsiloxane composite-based piezoresistive sensors, coupled with spiking neural networks, to mimic skin-like sensing. The strain and pressure sensors have been combined with appropriately designed neural networks to encode analog voltages to spikes to recreate bioinspired tactile sensing and proprioception. To further validate the proprioceptive capability of the system, a gesture tracking smart glove, combined with a spiking neural network, was demonstrated. Wearable and flexible sensors with accompanying neural networks such as the ones proposed in this work will pave the way for a future generation of skin-mimetic sensors for advanced prosthetic devices, apparel integrable smart sensors for human motion monitoring, and human-machine interfaces.

Both shape memory and self-healing polymers have received significant attention from the materials science community. The former, for their application as actuators, self-deployable structures, and medical devices; and the latter, for extending the lifetime of polymeric products. Both effects can be stimulated by heat, which makes resistive heating a practical approach to trigger these effects. Here we show a conductive polyketone polymer and carbon nanotube composite with cross-links based on the thermo-reversible furan/maleimide Diels–Alder chemistry. This approach resulted in products with efficient electroactive shape memory effect, shape reprogrammability, and self-healing. They exhibit electroactive shape memory behavior with recovery ratios of about 0.9; requiring less than a minute for shape recovery; electroactive self-healing behavior able to repair microcracks and almost fully recover their mechanical properties; requiring a voltage in the order of tens of volts for both shape memory and self-healing effects. To the best of our knowledge, this is the first report of electroactive self-healing shape memory polymer composites that use covalent reversible Diels–Alder linkages, which yield robust solvent-resistant polymer networks without jeopardizing their reprocessability. These responsive polymers may be ideal for soft robotics and actuators. They are also a step toward sustainable materials by allowing an increased lifetime of use and reprocessability.

This work reports the fabrication of a titanium carbide nanoparticle-based inkjet printed flexible bidirectional flow sensor. The design of the flow sensor consists of an inkjet printed titanium carbide piezoresistive strain gauge on a polyester cantilever. The sensors demonstrated a normalized flow sensitivity of 1.043/(ms-1) in the velocity range ~ 0.15 – 0.55 m/s (for water flow). The fabrication method reported in this work potentially opens a new direction for fabrication of a class of robust, repeatable, and inexpensive flexible flow sensors.

Terrain adaptation and amphibious landing pose the greatest challenges for soft amphibious robots. Based on the principles of tortoises, this paper presents a fully 3D-printed soft amphibious robot with four pneumatic bionic legs that are capable of bending in three dimensions. The gaits of the robot are described in six different ways and a dynamic model is developed for its control. In addition to linear motion (0.97 BL s−1) and turning (25.4° s−1) on rigid terrain, the robot can also maneuver on various surface conditions (such as hills, gaps, smooth slopes, gravel, sand, muddy terrain, and water), and even make an amphibious landing. These properties, together with the soft amphibious robot's continuous obstacle avoidance capabilities, high load-carrying capacity (28 times its own weight), low cost, and high camouflage, allow for a wide variety of applications.

Multiwalled carbon nanotubes (MWCNT) and carbon black (CB) have been widely used as conductive fillers in electroactive polymer composites. MWCNT-based composites generally have lower resistivity and percolation thresholds, while CB-based ones are considerably cheaper. To balance these pros and cons, ternary composites (TCs) (polymer-MWCNT-CB) can be formulated. Here, we prepared electroactive MWCNT-CB TCs capable of self-healing and with shape memory properties, based on polyketones reversibly-crosslinked via Diels-Alder chemistry. Unexpectedly, the cheaper CB-rich formulations had lower resistivities, thus better electroactive self-healing and shape memory responses. Nonetheless, not all electroactive MWCNT-CB TCs have this clear cost-effectiveness. We evaluated the cost-performance of multiple reported MWCNT-CB TCs systems and found different general trends (positive, negative, and synergistic cost-efficiency relationships). Thus, the cost-effectiveness of these fillers (and their combination) greatly depends on each composite system and what it is intended for. This work includes the first systematic report on cost-performance of MWCNT and CB as conductive fillers.

The development of stimuli-responsive drug nanocarriers is an increasingly important area in nanomedicine because efficient delivery of toxic drugs to targeted tissues minimizes side effects. The specific objective of this study was to synthesize and characterize a novel pH-responsive drug carrier based on halloysite nanotubes for the controlled release of the anticancer drug doxorubicin. Poly(N,N-dimethylaminoethyl methacrylate) brushes were grafted from the surface of halloysite nanotubes using the combination of mussel-inspired polydopamine surface modification and activators regenerated by electron transfer in atom transfer radical polymerization. The chemical structure and morphology of the modified halloysite nanotubes were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermal gravimetric analysis as well as scanning and transmission electron microscopies. Dynamic light scattering and zeta potential analysis were carried out to evaluate the pH-responsivity of the functionalized halloysite nanotubes. The results of the drug loading and release study of pristine and functionalized halloysite nanotubes showed that grafting of poly(N,N-dimethylaminoethyl methacrylate) brushes on the polydopamine-modified halloysite nanotubes surface leads to a drastic increase in doxorubicin loading capacity and a highly pH-sensitive release behaviour. Less than 10 % of the loaded doxorubicin was released from poly (N,N-dimethylaminoethyl methacrylate)-grafted halloysite nanotubes at pH 7.4 after 24 h; in contrast, at pH 5.5 there was a continuous release of doxorubicin totalling 13 % in the first 30 min, i.e. lower than for the pristine halloysite nanotubes (32 %), but reaching 48 % after 24 h. Poly (N,N-dimethylaminoethyl methacrylate)-grafted halloysite nanotubes can hence be considered as a potential candidate for delivering highly toxic drug molecules to the acidic target sites.

Wire and arc additive manufacturing (WAAM) technology was used for the fabrication of NiTiTa (2.5 at. % Ta) shape memory alloys (SMAs) for the first time, using commercialy available NiTi wire and Ta foil as the feedstock materials. The addition of Ta significantly increased the phase transformation temperatures, leading to a room-temperature microstructure composed of both B19′ martensite and B2 austenite, and (Ti,Ta)2Ni precipitates distributed at the grain boundaries. Compared with the WAAM fabricated NiTi counterpart, the corrosion potential (Ecorr) of the NiTiTa material increased from − 0.55 to − 0.44 V, while the corrosion current density (Icorr) decreased from 1.90 × 10−6 to 4.2 × 10−7 A/cm2. The X-ray brightness increased from 19.6 to 56.4 %. These results indicate that the addition of Ta can enhance the corrosion resistance and X-ray visibility of NiTiTa parts. Furthermore, the WAAM fabricated NiTiTa material was able to retain a stable superelastic response under 10 loading-unloading cycles, highlighting the great potential application value in the biomedical field. Our work provides an innovative method for additively manufacturing NiTi-based multi-component SMAs through WAAM.

Wire and arc additive manufacturing (WAAM) has received increasing attention due to its low cost and high productivity compared to traditional techniques for manufacturing high strength steels. In the present work, WAAM was used to fabricate bimetallic laminated steel structure (BLSS) with enhanced strength-ductility synergy by alternately depositing 304 stainless steel (304 SS) and low carbon steel (LCS) on Q345 substrate. The microstructure and mechanical properties of additive manufactured BLSS were investigated in detail. The 304 SS layer is composed of martensite, different from the vermicular ferrite distributed in the austenite matrix of the single-304 SS structure. While the LCS layer has no obvious change compared to the single-LCS structure, except for the refinement of the blocky ferrite. Meanwhile, fine grains formed at the interface between the LCS and 304 SS layers. The differences in element content, phase constituent and grain size between different layers lead to changes in the mechanical properties of this BLSS along different loading directions. The tensile strength and elongation in the longitudinal (Y) direction reached 999.8 MPa and 28.2%, respectively, where the strength was almost twice that of single-material 304 SS and LCS structure with the elongation between them. Digital image correlation (DIC) was used to observe the strain distribution of the BLSS during tensile process, and a significant stress concentration was observed in the transversal (Z) direction, resulting in a decrease in its tensile properties compared to the Y direction. Fracture topography analysis of specimens with different loading directions revealed a brittle-ductile mixed fracture mode. Our work provides a feasible and flexible method for the fabrication of BLSS with superior mechanical properties, which have potential applications in fields such as architectural and civil engineering structures.

Many marine animals perform fascinating survival hydrodynamics and perceive their surroundings through optimally evolved sensory systems. For instance, phocid seal whiskers have undulations that allow them to resist noisy self-induced vortex-induced vibrations (VIV) while locking their vibration frequencies to wakes generated by swimming fishes. In this work, fully 3D-printed microelectromechanical systems (MEMS) sensors with high gauge factor graphene nanoplatelets piezoresistors are developed to explain the exquisite sensitivity of whisker-inspired structures to upstream wakes. The sensors are also used to measure natural frequencies of excised harbor (Phoca vitulina) and grey (Halichoerus grypus) seal whiskers and determine the effect of whisker orientation on the VIV, which can explain the possible natural orientation of whiskers during active hunting. Experimental investigations conducted in a recirculating water flume show that whisker-inspired sensors successfully sense an upstream wake located up to 10× the whisker diameter by locking to the frequency of the wake generator, thus mimicking the sensing mechanism of the seal whisker. The combination of VIV reduction and frequency-locking with the upstream wake generator demonstrates the whisker-inspired sensor's high signal-to-noise ratio, indicating its efficiency in long-distance wake sensing as well as its potential as an alternative to visual and acoustic sensors in underwater robots.

Ultrasonic spot welding (USW) has attracted increasing attention due to its high-throughput solid-state bonding mechanism, which shows great potential in the semiconductor and automotive industries for joining of metal sheets. However, the short welding cycle makes it challenging to effectively monitor the temperature history and deformation of the workpieces during the process. In this study, a three-dimensional (3D) finite element analysis model for USW of superelastic NiTi shape memory alloy (SMA) with Cu interlayer was developed using ansysworkbench. The thermal-stress coupled phenomena including the heat generation and stress distribution during the welding process were simulated and analyzed. First, a superelastic constitutive model for NiTi SMAs was constructed. The distribution of temperature and stress fields was then obtained by thermal-stress analysis using the direct coupling method, and the superelasticity of SMAs was observed. The simulation results showed that the highest temperature occurred in the center of the welding area during USW, which is proportional to the welding time and inversely proportional to the clamping pressure. In addition, the maximum stress occurred at the center of the contact surface between upper NiTi and Cu interlayer. After that, the validity of the simulation results was verified by setting up a thermocouple temperature measurement platform to collect the temperature data, which exhibited a good agreement with the simulated results. The simulation procedure demonstrates its potential to predict temperature and stress distributions during the USW process.

To improve the mechanical and tribological properties of diamond-like carbon (DLC) film on nitrile butadiene rubber, the DLC/Ti-C bilayer films are fabricated by a dual-target magnetron sputtering method. The morphological characterization results indicate that the roughness of DLC/Ti-C first decreases and then increases slightly with the increase of Ti content and surface roughness of all modified samples is lower than that of nitrile butadiene rubber (NBR). Raman spectra show that the change of Ti content in the Ti-C interlayer has no effect on the ratio of sp2 to sp3 bonds of surface DLC film. The nanoindentation results show that the Ti content significantly affects the hardness, Young’s modulus, hrex/hmax and elastic recovery (%). Notably, the DLC/Ti-C films with a Ti content of 12.32 ∼ 14.77 at. % show the lowest coefficient of friction (CoF, 0.1 ∼ 0.2) and superior wear resistance due to the increased transformation of sp2 into sp3 in the films. This study unravels that the DLC films' superior mechanical and tribologic performance could be realized by regulating the Ti content in the Ti-C interlayer.

This study reports on the ultralubricity of a high-temperature resilient nanocomposite WS2/a-C tribocoating. The coefficient of friction of this coating remains at around 0.02 independently of a thermal treatment up to ∼500 °C, as confirmed by high-temperature tribotests. Moreover, the coating annealed at 450 °C keeps exhibiting a similar ultralubricity when cooled back down to room temperature and tested there, implying a tribological self-adaptation over a broad temperature range. High-resolution TEM observations of the tribofilms on the wear track unveil that WS2 nanoplatelets form dynamically via atomic rearrangement and extend via unfaulting geometrical defects (bound by partial climb dislocations). The (002) basal planes of the WS2 nanoplatelets, reoriented parallel to the tribo-sliding direction, contribute to a sustainable ultralubricity. The declining triboperformance beyond 500 °C is associated with sulfur loss rather than the transformation of WS2 into inferior WO3 via oxidation as suggested earlier. This self-adaptive WS2/a-C tribocoating holds promise for a constant ultralubrication with excellent thermal performance.

NiTi thin sheets were ultrasonic spot welded with a Cu interlayer, where different welding vibration amplitudes were applied to study the influence on the surface and interface microstructural characteristics, phase transformation behavior and mechanical response of the joints, which aimed to enhance the joint performance by proper optimization of the process parameters. An excellent bonding interface was achieved when an optimized vibration amplitude was applied, with a recrystallized microstructure formed in the Cu foil side near the bonding interface, which helped to improve the mechanical performance of the joints. Joints made with vibration amplitude of 55 mu m had an improved strength compared to the NiTi base material.

The present study is dedicated to explore the effect of grain refinement on cracking resistance of hot-dip galvanized Zn–Al–Mg coatings on steel substrate. In this work, we demonstrate the enhancement of plastic deformation and cracking resistance by refining the microstructure (primary zinc grains) of the Zn–Al–Mg coatings. For this purpose, two types of Zn–Al–Mg coatings namely, fine grained and coarse grained microstructures are investigated utilizing in-situ scanning electron microscopy tensile tests. Electron backscatter diffraction technique is used to illuminate the deformation behavior at the scale of grains (and/or within grains). The results reveal that the coating with fine grained microstructure possesses higher ductility and cracking resistance, whereas the coating with coarse grain microstructure induces more transgranular cracking during deformation. Moreover, primary zinc grain refinement has been shown to decrease the fraction of coarse deformation twins that serve as undesirable sites of micro-cracking. In particular, both deformation mechanisms and cracking behavior are found to be grain size-dependent in these coatings.

Recent advances in 3D printing technology have enabled unprecedented design freedom across an ever-expanding portfolio of materials. However, direct 3D printing of soft polymeric materials such as polydimethylsiloxane (PDMS) is challenging, especially for structural complexities such as high-aspect ratio (>20) structures, 3D microfluidic channels (∼150 μm diameter), and biomimetic microstructures. This work presents a novel processing method entailing 3D printing of a thin-walled sacrificial metallic mold, soft polymer casting, and acidic etching of the mold. The proposed workflow enables the facile fabrication of various complex, bioinspired PDMS structures (e.g., 3D double helical microfluidic channels embedded inside high-aspect ratio pillars) that are difficult or impossible to fabricate using currently available techniques. The microfluidic channels are further infused with conductive graphene nanoplatelet ink to realize two flexible piezoresistive microelectromechanical (MEMS) sensors (a bioinspired flow/tactile sensor and a dome-like force sensor) with embedded sensing elements. The MEMS force sensor is integrated into a Philips 9000 series electric shaver to demonstrate its application in "smart"consumer products in the future. Aided by current trends in industrialization and miniaturization in metal 3D printing, the proposed workflow shows promise as a low-temperature, scalable, and cleanroom-free technique of fabricating complex, soft polymeric, biomimetic structures, and embedded MEMS sensors.

Surface roughness of laser powder bed fusion (L-PBF) printed overhang regions is a major contributor to deteriorated shape accuracy/surface quality. This study investigates the mechanisms behind the evolution of surface roughness (Ra) in overhang regions. The evolution of surface morphology is the result of a combination of border track contour, powder adhesion, warp deformation, and dross formation, which is strongly related to the overhang angle (θ). When 0° ≤ θ ≤ 15°, the overhang angle does not affect Ra significantly since only a small area of the melt pool boundaries contacts the powder bed resulting in slight powder adhesion. When 15° < θ ≤ 50°, powder adhesion is enhanced by the melt pool sinking and the increased contact area between the melt pool boundary and powder bed. When θ > 50°, large waviness of the overhang contour, adhesion of powder clusters, severe warp deformation and dross formation increase Ra sharply.

Cerebral hemodynamics play an important role in the development of cerebrovascular diseases. In this work, we propose a numerical framework for modeling patient-specific cerebral blood flow, using commonly available clinical datasets. Our hemodynamic model was developed using Simscape Fluids library in Simulink, based on a block diagram language. Medical imaging data obtained from computerized tomography angiography (CTA) in 59 patients with aneurysmal subarachnoid hemorrhage was used to extract arterial geometry parameters. Flow information obtained from transcranial Doppler (TCD) measurement was employed to calibrate input parameters of the hemodynamic model. The results show that the proposed numerical model can reproduce blood flow in the circle of Willis (CoW) per patient per measurement set. The resistance at the distal end of each terminal branch was the predominant parameter for the flow distribution in the CoW. The proposed model may be a promising tool for assessing cerebral hemodynamics in patients with cerebrovascular disease.

While the automotive industry is striving for the reduction of car body weight to increase the fuel efficiency and to reduce CO2 emission without compromising the safety and crashworthiness of vehicles, a new generation of advanced high strength steels (AHSS) have emerged as excellent candidates to meet these requirements. However, their integration into the car body structure is associated with welding-related problems. This research utilizes a novel approach to establish a fundamental correlation between welding parameters, microstructure and mechanical performance of AHSS resistance spot welds. In-situ micro-cantilever bending experiments are executed and analyzed in a quantitative manner to evaluate the effect of texture and post-welding heat treatment on the local fracture toughness of spot welds. A striking finding is that, through a switch from single to double pulse weld scheme, the texture of martensite formed in the fusion zone becomes responsible for a significantly higher fracture toughness of the area in front of the pre-crack. In addition, it is found that paint baking heat treatment also results in a much enhanced fracture toughness through tempering of the martensitic microstructure. A quantitative correlation is made between the micro-scale fracture toughness and macro-scale mechanical performance of advanced high strength steel welds.

Recently, 3D porous graphene–polymer composite-based piezoresistive sensors have gained significant traction in the field of flexible electronics owing to their ultralightweight nature, high compressability, robustness, and excellent electromechanical properties. In this work, we present an improved facile recipe for developing repeatable, reliable, and linear 3D graphene–polydimethylsiloxane (PDMS) spongy sensors for internet of things (IoT)-enabled wearable systems and smart consumer products. Fundamental morphological characterization and sensing performance assessment of the piezoresistive 3D graphene–polymer sensor were conducted to establish its suitability for the development of squeezable, flexible, and skin-mountable human motion sensors. The density and porosity of the sponges were determined to be 250 mg cm−3 and 74% respectively. Mechanical compressive loading tests conducted on the sensors revealed an average elastic modulus as low as ∼56.7 kPa. Dynamic compressive force-resistance change response tests conducted on four identical sensors revealed a linear piezoresistive response (in the compressive load range 0.42–2.18 N) with an average force sensitivity of 0.3470 ± 0.0794 N−1. In addition, an accelerated lifetime test comprising 1500 compressive loading cycles (at 3.90 N uniaxial compressive loading) was conducted to demonstrate the long-term reliability and stability of the sensor. To test the applicability of the sensors in smart wearables, four identical graphene–PDMS sponges were configured on the fingertip regions of a soft nitrile glove to develop a pressure sensing smart glove for real-time haptic pressure monitoring. Similarly, the sensors were also integrated into the Philips 9000 series electric shaver to realize smart shaving applications with the ability to monitor shaving motions. Furthermore, the readiness of our system for next-generation IoT-enabled applications was demonstrated by integrating the smart glove with an embedded system software utilizing the an open source microcontroller platform. The system was capable of identifying real-time qualitative pressure distribution across the fingertips while grasping daily life objects, thus establishing the suitability of such sensors for next-generation wearables for prosthetics, consumer devices, and personalized healthcare monitoring devices.

In this work, we report a class of fabric-like flexible and wearable capacitive sensors utilizing electrospun polyvinyl acetate (PVAc)-graphene nanofibers for human movement monitoring applications. The sensor reported in this work features flexible PVAc-graphene thin film sandwiched between two layers of conductive fabric and fully encapsulated in transparent adhesive films. The fabricated pressure sensor demonstrates two linear regimes with sensitivity figures of 0.0136 kPa-1 (pressure < 75 kPa) and 0.0063 kPa-1 (pressure > 75 kPa), respectively. The realized pressure sensor is flexible, apparel integrable, and the facile fabrication method will enable reliable and repeatable performance over roll-to-roll manufacturing suitable for mass production.

Seal whiskers have been well studied in view of their remarkable hydrodynamic trail tracking capability. The considerable variation in the whisker lengths indicates that the whiskers have different natural frequencies sensitive to various frequency bands of hydrodynamic stimuli. However, a thorough experimental investigation of the natural frequencies of seal whiskers has not been conducted before. Here, we develop a novel and low-cost methodology for easy measurements of the natural frequencies of seal whiskers using a 3D-printed MEMS cantilever sensor featuring a graphene nanoplatelet piezoresistor and a soft encapsulation of the whisker base at the distal end of the cantilever.

Zn-Al-Mg coatings are important materials in coatings science and technology that are widely utilized in automotive and construction applications. These coatings which are mainly produced by the hot-dip galvanization process, offer excellent corrosion resistance and anti-galling performance for the steel substrates. In contrast, they currently exhibit a high cracking tendency when subjected to plastic deformation and forming processes. The formability properties of these coatings are limited due to the adverse and severe cracking. The generated cracks with a large opening on the coating surface enable the penetration of corrosive media into the coating and subsequently can facilitate the corrosion and degradation of the steel substrates. Therefore, the mechanical integrity and durability of Zn-Al-Mg coated steel sheets are strongly related to the fundamental understanding of the deformation, cracking behavior and formability of the coating. Only through such comprehension, it is possible to generate a scientific guideline to improve the cracking resistance of these coatings. The principal aims of the present thesis are therefore (1) to unravel the origin and mechanism of cracking in Zn-Al-Mg coatings, (2) to resolve the long-lasting cracking and formability problems associated with these coatings. To these ends, comprehensive evaluations on the structure-properties relationship are realized in this thesis. Step-wise and dedicated research works are carried out and in the light of the knowledge obtained, synergic solutions and strategies are applied in order to accomplish crack-resistant and highly-formable Zn-Al-Mg coatings.

With the steady rise in average life expectancy across the globe in the last century, lifestyle related diseases are causing a burden on existing healthcare infrastructure. Emerging complex diseases cause significant impact on productive man hours and burden the existing healthcare system. For instance, people suffering from progressive neurodegenerative disorders like Parkinson’s disease, multiple sclerosis, and Huntington’s disease must be monitored frequently to track the progress of the diseases. Due to the life altering nature of these neurodegenerative diseases, it becomes very difficult for the patients to return to their daily routine, considering the fact that a significant amount of their time is spent in hospital-based diagnostic and rehabilitation centres. Other less serious complications, like sleep apnoea, post-trauma recovery, and similar conditions also need regular progress tracking and medical intervention (if necessary) and can cause disruptions to daily life due to frequent hospital stays. Inexpensive, accurate, and power efficient wearable sensors will be playing a major role in facilitating the health 3.0 in the foreseeable future. Particularly, the onslaught of COVID-19 pandemic since late 2019 have fuelled the demand for wearable sensors capable of human physiological vitals monitoring. The need of the hour is efficient, non-invasive, wearable sensors capable of gathering vital human physiological parameters round the clock and store the data in cloud for remote access by healthcare specialists. However, for any sensor to be considered seriously in healthcare space, parameters like sensitivity, ease of use, cost effectiveness, long term reliability and most importantly, low power budget are of paramount importance. Other than applications in human physiological monitoring, flexible sensors are relevant for applications involving artificial skins for next generation prosthesis, soft human-machine interface, and robotics assisted medical facilities. Nature is full of unique designs to tackle interesting problems we encounter daily. For instance, the seamless entry of a Kingfisher from a low resistance medium (air) to a high resistance medium (water) is nothing short of an extraordinary aerodynamic design marvel. Interfacing nanotechnology with biomimetics is important in the context of next generation wearables as it can lead to the development of a class of highly reliable and inexpensive wearable sensors tailored to cater the urgent needs of physiological parameter monitoring. This thesis has been a humble effort towards creating a seamless integration between the concepts of bioinspiration and Microsystems-enabled miniaturized sensors for tackling a wide variety of problems we encounter in our daily life. Two most widely used and traditional mechanisms of sensing entailing piezoresistive and capacitive sensing were investigated and a bioinspiration approach was taken to device next generation flexible and wearable devices. A wide variety of practical problems ranging from human gait monitoring to low powered flow sensing has been tackled taking inspiration from nature.

In the present work, the effects of laser surfacing aiming at modifying the surface roughness on NiTi sheets prior to the application of ultrasonic welding (USW) were investigated. Three different configurations joining original and laser surfaced specimens were performed: original/original (referred as O/O), original/treated (referred as O/T), and treated/treated (referred as T/T). The influence of surface roughness on the interface formation, diffusion, and mechanical properties was investigated. It is observed that when both bonding surfaces becomes rougher (T/T configuration), the joint strength is the highest, followed by both smooth bonding surfaces (O/O configuration), and the strength of the joint is the lowest when only one of the bonding surfaces was roughened (O/T configuration), which is related to the degree of plastic deformation at the joining interface. The main joining mechanism of NiTi to the Al interlayer was a metallic bonding caused by shear plastic deformation and formation and growth of micro welds at the joining interfaces. Laser surfacing facilitates the metallic bonding, which is directly reflected in the change of the thickness of the Al interlayer after USW. This also helps to produce a mechanical interlocking at the interface, although there is no significant difference in the elemental diffusion. Interfacial failure occurred in all joints tested under different surface contact conditions and exhibited ductile-like fracture characteristics.

Wave energy has gained its popularity in recent decades due to the vast amount of untapped wave energy resources. There are numerous types of wave energy convertor (WEC) being proposed and to be economically viable, various means to enhance the power generation from WECs have been studied and investigated. In this paper, a novel pontoon-type WEC, which is formed by multiple plate-like modules connected by hinges, are considered. The power enhancement of this pontoon-type WEC is achieved by allowing certain level of structural deformation and by utilizing a series of optimal variable power take-off (PTO) system. The wave energy is converted into useful electricity by attaching the PTO systems on the hinge connectors such that the mechanical movements of the hinges could produce electricity. In this paper, various structural rigidity of the interconnected modules are considered by changing the material Young's modulus in order to investigate its impact on the power enhancement. In addition, the genetic algorithm optimization scheme is utilized to seek for the optimal PTO damping in the variable PTO system. It is observed that under certain condition, the flexible pontoon-type WEC with lesser connection joints is more effective in generating energy as compared to its rigid counterpart with higher connection joints. It is also found that the variable PTO system is able to generate greater energy as compared to the PTO system with constant/uniform PTO damping. Keywords: Power generation enhancement, Pontoon-type wave energy convertor, Very large floating structure (VLFS), Hydroelastic response, Variable power take-off system, Genetic algorithm optimization

Three-dimensional interconnected nanoporous graphene (NPG) microfoams and nanofoams are developed via a new approach of solid-state catalytic growth. Both NPG microfoam and nanofoam exhibit similar nanoporous structures that contain close tubular pores and open non-tubular pores but with different particle sizes. As electrochemical reactors for sulfur cathodes, sulfur is encapsulated inside the tubular pores. It is found that NPG nanoreactors can enhance the electrochemical performances in comparison with NPG microreactors, including improved reversible capacities, cyclic performances and rate performances in particular. The electrochemical impedance spectroscopy analysis reveals that NPG nanoreactors facilitate Li+ transportation and decrease the charge-transfer resistance in comparison with the microreactors, promoting the redox kinetics of multi-step conversions between sulfur and lithium sulfides. This work demonstrates a significant particle size effect of nanoporous graphene on the Li–S electrochemistry and can be useful for designing Li–S batteries as well as other electrochemical energy storage systems.

Chloridazon has been a widely used herbicide during the past decades, especially in sugar-beet cultivation. UV-induced degradation of chloridazon leads to the formation of desphenyl counterparts, i.e. desphenyl-chloridazon and methyl-desphenyl-chloridazon. Even if accumulation of these residues in natural waters is far from alarming, a low-cost effective and environmentally friendly adsorbent, capable of binding chloridazon and its degradation products is desirable to reduce their concentration in water even further below legal limits. Here we show that pillared smectite clay, prepared by cation exchange of sodium with copper complexed, cage-shaped polyhedral oligomeric silsesquioxane (Cu2+@POSS) could be a promising candidate for this purpose. X-ray diffraction and high resolution transmission electron microscopy evidenced a homogeneous layered structure where the interlayer spacing is enlarged by 7.1 ± 0.2 Å (the diameter of Cu2+@POSS) with respect to the pristine clay. Exposure of this pillared smectite clay to chloridazon and its metabolites in water showed that Cu2+@POSS intercalation significantly improved its adsorption capacity. In addition, after several thermal regeneration cycles, Cu2+@POSS_SWy-2 still exhibited excellent adsorption properties. These findings demonstrate that smectite clay pillared with copper complexed polyhedral oligosilsesquioxane is a promising environmentally friendly and relatively low cost material for herbicide waste remediation.

Biocompatible antimicrobial coatings may enhance the function of many orthopedic implants by combating infection. Hydroxyapatite is a choice mineral for such a coating as it is native to bone and silver would be a possible antimicrobial agent as it is also commonly used in biomedical applications. The aim of the research is to develop a silver-containing calcium phosphate (Ag/Ca-P) coating via electrochemical deposition on titanium substrates as this allows for controlled coating buildup on complex shapes and porous surfaces. Two different deposition approaches are explored: one-step Ag/Ca-P(1) deposition coatings, containing silver ions as microsized silver phosphate particles embedded in the Ca-P matrix; and via a two-step method (Ag/Ca-P(2)) where silver is deposited as metallic silver nanoparticle on the Ca-P coating. The Ag/Ca-P(1) coating displays a bacterial reduction of 76.1 +/- 8.3% via Ag-ion leaching. The Ag/Ca-P(2) coating displays a bacterial reduction of 83.7 +/- 4.5% via contact killing. Interestingly, by preincubation in phosphate-buffered saline solution, bacterial reduction improves to 97.6 +/- 2.7 and 99.7 +/- 0.4% for Ag/Ca-P(1) and Ag/Ca-P(2) coatings, respectively, due to leaching of formed AgClx(x-1)- species. The biocompatibility evaluation indicates that the Ag/Ca-P(1) coating is cytotoxic towards osteoblasts while the Ag/Ca-P(2) coating shows excellent compatibility. The electrochemical deposition of highly bactericidal coatings with excellent biocompatibility will enable us to coat future bone implants even with complex or porous structures.

Titanium dioxide film as a stable material plays an important role in photocatalytic degradation of pollutants. One of the ways to improve photocatalytic efficiency is to increase the active sites on the semiconductor surface. Photolithography is a manufacturing technique for controlling precisely micrographics on surface. Here grating-structured, square-structured and hexagon-structured TiO2 films were prepared by photolithography and the effects of various surface structures on photocatalysis were studied. It was demonstrated that the photocatalytic activity of TiO2 film was not always improved as the surface area increased. The micro-patterned surface would also impede the mass transfer in the process of photocatalysis. (C) 2019 Elsevier B.V. All rights reserved.

A series of heterogeneous catalysts consisting of highly dispersed Pt nanoparticles supported on nanosized ZrO2 (20 to 60 nm) was synthesized and investigated for the one-pot transfer hydrogenation between glycerol and cyclohexene to produce lactic acid and cyclohexane, without any additional H-2. Different preparation methods were screened, by varying the calcination and reduction procedures with the purpose of optimizing the dispersion of Pt species (i.e., as single-atom sites or extra-fine Pt nanoparticles) on the ZrO2 support. The Pt/ZrO2 catalysts were characterized by means of transmission electron microscopy techniques (HAADF-STEM, TEM), elemental analysis (ICP-OES, EDX mapping), N-2-physisorption, H-2 temperature-programmed-reduction (H-2-TPR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Based on this combination of techniques it was possible to correlate the temperature of the calcination and reduction treatments with the nature of the Pt species. The best catalyst consisted of subnanometer Pt clusters (

Polarization curves and mass losses of SAF3207 hyper-duplex stainless steel under various conditions were measured. The damaged surfaces after erosion-corrosion tests were characterized by scanning electron microscopy. The results showed that an increase in flow velocity could enhance the electrochemical corrosion and consequently decrease the passivation properties of the steel. The erosion-corrosion damage of the samples increased substantially when the flow velocity exceeded the critical value of 4 m.s(-1). The mass loss rate increased as the sand content increased, reaching a maximum at 7wt% sand content, corresponding to the most severe electrochemical corrosion damage. When the sand content was increased further, however, the mass loss rate decreased and then tended stable. The mass loss was divided into incubation, sustained, and stationary periods, with a maximum mass loss rate of 12.97 g.h(-1).m(-2) after an erosion period of 2.5 h. The erosion-corrosion mechanism was investigated in detail.

The effect of the initial structure on the microstructure and texture of the friction stir welded Monel 400 alloy joints was investigated. For this aim, Monel 400 alloy of two initially treated conditions, annealed and rolled, was studied. Orientation imaging microscopy with a step size of 70nm was used to characterise the microstructures of the joints. The mechanical properties were evaluated using Vickers hardness and nanoindentation tests. In the joint of the initial annealed alloy, continuous dynamic recrystallisation governed the grain structure formation. However, in the case of the initial rolled base material, discontinuous dynamic recrystallisation also occurred to cause more random texture, smaller grains, much more high-angle grain boundaries and higher dislocation densities. In the stir zone, the hardness and yielding strength increased respectively from 177 HV to 192 HV and 215.9 to 238.8MPa by changing the base metal from the initial annealed to rolled condition. In addition, the microstructural features of the different zones containing the texture components and grain boundaries were scrutinised thoroughly.

Zn-Al-Mg coatings are important materials for the corrosion protection of steel sheets. However, susceptibility towards cracking limits the formability performance of these coatings. In this study, we focus on the effect of the underlying steel substrate on cracking behavior in these coatings. In order to elucidate this, a high-strength low-alloy (HSLA) steel substrate and an interstitial-free (IF) steel substrate are coated with two different ZnAlMg coatings with and without binary eutectic microstructures. Meticulous in-situ tensile and bending tests are conducted in a scanning electron microscope. To quantify the strain distribution and damage incidents, micro and macro digital image correlation techniques are utilized in order to illuminate the associated cracking causes across length scales. Furthermore, electron backscatter diffraction method is applied to study the role of crystallographic orientation on the cracking tendency. Crack opening and crack area fractions are correlated with the applied strain and bending angles. The findings denote that the discontinuous yielding (Luders banding) of the HSLA steel substrate generates substantial surface roughening and heterogeneous deformation in the coatings that facilitates cracking. In contrast, the IF steel induces a more uniform deformation within the coatings leading to much reduced crack size and crack area fraction. This study has resulted in a key element of a guideline towards crack-resistant and formable Mg-alloyed zinc coatings.

In this work, we report a class of wearable, stitchable, and sensitive carbon nanofiber (CNF)-polydimethylsiloxane (PDMS) composite-based piezoresistive sensors realized by carbonizing electrospun polyacrylonitrile (PAN) nanofibers and subsequently embedding in PDMS elastomeric thin films. Electro-mechanical tactile sensing characterization of the resulting piezoresistive strain sensors revealed a linear response with an average force sensitivity of ~1.82 kN−1 for normal forces up to 20 N. The real-time functionality of the CNF-PDMS composite sensors in wearable body sensor networks and advanced bionic skin applications was demonstrated through human motion and gesture monitoring experiments. A skin-inspired artificial soft sensor capable of demonstrating proprioceptive and tactile sensory perception utilizing CNF bundles has been shown. Furthermore, a 16-point pressure-sensitive flexible sensor array mimicking slow adapting low threshold mechanoreceptors of glabrous skin was demonstrated. Such devices in tandem with neuromorphic circuits can potentially recreate the sense of touch in robotic arms and restore somatosensory perception in amputees.

17–4 PH (precipitation hardening) stainless steel is commonly used for the fabrication of complicated molds with conformal cooling channels using laser powder bed fusion process (L-PBF). However, their microstructure in the as-printed condition varies notably with the chemical composition of the feedstock powder, resulting in different age-hardening behavior. In the present investigation, 17–4 PH stainless steel components were fabricated by L-PBF from two different feedstock powders, and subsequently subjected to different combinations of post-process heat treatments. It was observed that the microstructure in as-printed conditions could be almost fully martensitic or ferritic, depending on the ratio of Creq/Nieq of the feedstock powder. Aging treatment at 480 °C improved the yield and ultimate tensile strengths of the as-printed components. However, specimens with martensitic structures exhibited accelerated age-hardening response compared with the ferritic specimens due to the higher lattice distortion and dislocation accumulation, resulting in the “dislocation pipe diffusion mechanism”. It was also found that the martensitic structures were highly susceptible to the formation of reverted austenite during direct aging treatment, where 19.5% of austenite phase appeared in the microstructure after 15 h of direct aging. Higher fractions of reverted austenite activates the transformation induced plasticity and improves the ductility of heat treated specimens. The results of the present study can be used to tailor the microstructure of the L-PBF printed 17–4 PH stainless steel by post-process heat treatments to achieve a good combination of mechanical properties.

In this work, we report the green production of few-layer bio-Graphene (bG) through liquid exfoliation of graphite in the presence of bovine serum albumin. Microscopic characterization evaluated the quality of the produced nanomaterial, showing the presence of 3–4-layer graphene. Moreover, spectroscopic techniques also confirmed the quality of the resulted bG, as well as the presence of bovine serum albumin on the graphene sheets. Next, for the first time, bG was used as support for the simultaneous covalent co-immobilization of three enzymes, namely β-glucosidase, glucose oxidase, and horseradish peroxidase. The three enzymes were efficiently co-immobilized on bG, demonstrating high immobilization yields and activity recoveries (up to 98.5 and 90%, respectively). Co-immobilization on bG led to an increase of apparent KM values and a decrease of apparent Vmax values, while the stability of the nanobiocatalysts prevailed compared to the free forms of the enzymes. Co-immobilized enzymes exhibited high reusability, preserving a significant part of their activity (up to 72%) after four successive catalytic cycles at 30 °C. Finally, the tri-enzymatic nanobiocatalytic system was applied in three-step cascade reactions, involving, as the first step, the hydrolysis of p-Nitrophenyl-β-D-Glucopyranoside and cellobiose.

Wind energy harvesting and sensing have a huge prospect in constructing self-powered sensor nodes, but the energy transducing efficiency at low and ultra-low wind speeds is still limited. Herein, we proposed a Kármán vortex street driven membrane triboelectric nanogenerator (KVSM-TENG) for ultra-low speed wind energy harvesting and flow sensing. By introducing Kármán vortex in the KVSM-TENG, the cut-in wind speed of the KVSM-TENG decreased from 1 to 0.52 m/s that is the lowest cut-in wind speed in current TENGs. The instantaneous output density of the KVSM-TENG significantly increased by 1000 times and 2.65 times at the inlet wind speeds of 1 and 2 m/s, respectively. In addition, with the excellent energy transducing performance at the ultra-low speed range, the KVSM-TENG was successfully demonstrated to detect a weak leakage of gas pipeline (∼0.6 m/s) for alarming with high sensitivity. The interaction mechanism between the vortex and KVSM-TENG was systematically investigated. Through the simulation and experimental validation, the enhancement mechanism of vortex dependence on the cylinder diameter and placement location of KVSM-TENG was investigated in detail. The influence of parameters such as membrane length, width, thickness, and electrode gap on the performance of the KVSM-TENG was systematically studied. This work not only provided an ingenious strategy for ultra-low speed wind energy harvesting but also demonstrates the promising prospects for monitoring the air flow in the natural gas exploitation and transportation.

Mg-alloyed zinc coatings suffer from early cracking during deformation due to the combined influences of detrimental constituents (e.g., Zn/MgZn2 binary eutectic), unfavorable crystal orientations and incompatible local plastic deformation. This study addresses the crack resistance and deformation mechanisms of a ZnAlMg coating, in the absence of binary eutectic, by using correlative in-situ scanning electron microscopy tensile tests, electron backscatter diffraction, scanning transmission electron microscopy and micro digital image correlation methods. The plasticity and strengthening mechanisms of the binary eutectic-free ZnAlMg coating are thoroughly unravelled via theoretical and experimental approaches including dislocation slip trace analysis, Taylor factor calculations, quantitative dislocation density determination and slip/strain transfer across the grain boundaries. It has been found that the microstructure of the coating, comprising of primary zinc and ternary eutectic, effectively accommodates the applied strain without cracking till fracture of steel substrate. The absence of binary eutectic and the activation of abundant deformation mechanisms in the coating microstructure, promote local compatible plastic deformation and inhibit early damage. Effective slip transfer is unveiled by activation of pyramidal slip in addition to primary dislocation slip systems. The present findings deliver significant insights and solution for improvement in the formability of Mg-alloyed zinc coatings on steel sheets by tailoring the microstructure.

In this work, metal foam current collectors (CCs, i.e. nickel [Ni] and copper [Cu]) were treated by thermal oxidation to create a lithiophilic oxide surface that exhibited enhanced electrochemical performances of lithium anodes such as the cyclic stability of Coulombic efficiency at different current densities for various capacities compared to pristine CCs. The oxidized CCs facilitated much increased diffusivities of ions for lithium growth than pristine CCs. It was found that an inhomogeneous solid electrolyte interphase (SEI) formed on pristine CCs while a uniform SEI formed on oxidized CCs. Uniform lithium (Li) deposition can be achieved on oxidized CCs owing to the lithiophilic oxide surface containing metal nanoparticles and the ionic compound lithium oxide (Li 2O) matrix that led to a uniform SEI film and many nucleation sites. In addition, the porous and non-porous composite anodes exhibited different electrochemical performances. The porous composite anodes showed initial lower voltage hysteresis but shorter lifetime with carbonate-based electrolyte than non-porous composite anodes. The porous composite anodes showed better rate performances in full-cell measurements while the non-porous composite anodes displayed better stability. The interfacial modification of porous hosts by lithiated oxides and the effects of porous structure on battery performances can be also useful for designing other electrodes (e.g. sodium [Na], potassium [K], zinc [Zn]).

Piezoresistive sponges represent a popular design for highly flexible pressure sensors and are typically fabricated using templating methods. In this work, we used stereolithography (SLA) to 3D-print an elastomeric body-centered cubic (BCC) lattice structure with a relative density of 21% and an elastic modulus of 31.5 kPa. The lattice was dip-coated with graphene nanoplatelets to realize a piezoresistive pressure sensor with excellent performance (gauge factor = 3.25, sensitivity = 0.1 kPa-1), high deformability (up to 60 % strain), and repeatability. The novel approach outlined in this work offers greater control over the microstructure and can be used to fabricate sensors with tunable properties.