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5
Date Added: Jan 24, 2022
Date Added: Jan 24, 2022
As more roboticists are turning to Nature for design inspiration, it is becoming increasingly apparent that multisystem-level investigations of biological processes can frequently lead to unexpected advances in the development of experimental research platforms. Inspired by these efforts, we present here a holistic approach to developing an autonomous starfish-inspired soft robot that embodies a number of key design, fabrication, and actuation principles. These key concepts include integrated and sequentially deployable magnetic tube feet for site-specific and reversible substrate attachment, individually addressable flexible arms, and highly efficient and self-contained fluidic engines. These individual features offer a level of synergistic motion control not previously seen in other starfish-inspired robots. For example, our bistable dome-like tube feet are capable of achieving high adhesion forces to ferrous surfaces and low removal forces. These tube feet are further integrated with a fluidic engine to drive the entire arm while maintaining the ability to accurately control the arm position with a 270° range of motion. Furthermore, the arm and fluidic engine are modular, allowing each of the five arms to be replaced in seconds or enabling the exploration of a variety of limb geometries. Through the incorporation of these different design elements, the ASTER-bot (named for its star-like body plan) is capable of locomotion on ferrous surfaces, above and below water, and on nonplanar surfaces. This article further describes the design, fabrication, and integration strategies and characterizes the energetic and locomotory performance of this pentaradial robotic prototype.
Paper
6
Date Added: Jan 4, 2022
Date Added: Jan 4, 2022
The fatigue performance of additively manufactured auxetic meta-biomaterials made from commercially pure titanium has been studied only recently. While certain assumptions have been made regarding the mechanisms underlying their fatigue failure, the exact mechanisms are not researched yet. Here, we studied the mechanisms of crack formation and propagation in cyclically loaded auxetic meta-biomaterials. Twelve different designs were subjected to compression-compression fatigue testing while performing full-field strain measurement using digital image correlation (DIC). The fatigue tests were stopped at different points before complete specimen failure to study the evolution of damage in the micro-architecture of the specimens using micro-computed tomography (micro-CT). Furthermore, finite element models were made to study the presence of stress concentrations. Structural weak spots were found in the inverted nodes and the vertical struts located along the outer rim of the specimens, matching the maximum principal strain concentrations and fracture sites in the DIC and micro-CT data. Cracks were often found to originate from internal void spaces or from sites susceptible to mode-I cracking. Many specimens maintained their structural integrity and exhibited no signs of rapid strain accumulation despite the presence of substantial crack growth. This observation underlines the importance of such microscale studies to identify accumulated damage that otherwise goes unnoticed. The potential release of powder particles from damaged lattices could elicit a foreign body response, adversely affecting the implant success. Finding the right failure criterion, therefore, requires more data than only those pertaining to macroscopic measurements and should always include damage assessment at the microscale.
6
Date Added: Jan 20, 2022
Date Added: Jan 20, 2022
Swarms of tiny flying robots hold great potential for exploring unknown, indoor environments. Their small size allows them to move in narrow spaces, and their light weight makes them safe for operating around humans. Until now, this task has been out of reach due to the lack of adequate navigation strategies. The absence of external infrastructure implies that any positioning attempts must be performed by the robots themselves. State-of-the-art solutions, such as simultaneous localization and mapping, are still too resource demanding. This article presents the swarm gradient bug algorithm (SGBA), a minimal navigation solution that allows a swarm of tiny flying robots to autonomously explore an unknown environment and subsequently come back to the departure point. SGBA maximizes coverage by having robots travel in different directions away from the departure point. The robots navigate the environment and deal with static obstacles on the fly by means of visual odometry and wall-following behaviors. Moreover, they communicate with each other to avoid collisions and maximize search efficiency. To come back to the departure point, the robots perform a gradient search toward a home beacon. We studied the collective aspects of SGBA, demonstrating that it allows a group of 33-g commercial off-the-shelf quadrotors to successfully explore a real-world environment. The application potential is illustrated by a proof-of-concept search-and-rescue mission in which the robots captured images to find “victims” in an office environment. The developed algorithms generalize to other robot types and lay the basis for tackling other similarly complex missions with robot swarms in the future.
4
Date Added: Jan 5, 2022
Date Added: Jan 5, 2022
Swirl cooling is one of the latest and promising internal cooling strategies, which has been widely reported in the designs of the turbine blade leading edges. Based on the traditional single-stage swirl cooling configuration, this paper introduces a novel conception of multistage swirl cooling configuration (two and three stage), aiming to improve the cooling performances of the leading edges without increasing the cooling air consumption. In the new multistage configurations, the vortex chamber is divided into several stages, so that the tangential velocity of cooling air is significantly increased. To reveal the heat transfer and flow characteristics of cooling air in the multistage swirl cooling configuration, a series of numerical simulations are conducted by conjugate heat transfer algorithm under the realistic conditions of gas turbine operations and the real leading edge model of a VKI turbine blade. The numerical results indicate that: under the same coolant mass flow rate, the averaged Nusselt number in the three-stage swirl cooling structure is at least over 75% higher than that in the single-stage structure, and the Nusselt number distribution is also more uniform. At ReD = 40,000, the surface temperature averaged over the entire leading edge wall of the three-stage swirl cooling structure can be nearly 100 K lower than that in the single-stage one. The significant heat transfer enhancement of multistage swirl cooling is at the cost of a higher total pressure loss. However, if the bends connecting the adjacent stages are modified into round-shaped, the pressure loss can be significantly decreased, therefore the thermal performances of the multistage swirl cooling models are higher than that of the single-stage model.
Paper
4
Date Added: Jan 5, 2022
Date Added: Jan 5, 2022
Nickel-iron alloy is broadly utilized in the industrial field due to its fabulous mechanical properties. How to prepare nickel-iron alloy with better corrosion resistance more efficiently is an important concern. Based on this, the WC particles enhanced nickel-iron coatings were fabricated by jet electrodeposition (JED) at a high current density of 100A/dm2. It was found that increasing the deposition temperature appropriately during JED isbeneficial to obtain Ni-Fe-WC coating with the higher number of hard particles. Specifically, the maximum WC particles proportion reaches 4.47 wt% at 55 C. The electrochemical corrosion behavior of coating was measured by polarization curve and electrochemical impedance spectroscopy (EIS). The polarization curve test results displayed that the Ecorr positively shifted from 0.402 to 0.281 V and the icorr reduced from 25.13 to 7.05 mA/cm2 with the increase of WC particles roportion. Meanwhile, the EIS test results exhibited that the impedance of coating enhanced from 12,720 to 59,140 U cm2 . The neutral salt spray test (NSS) was used to simulate the corrosion of coating in a seawater environment. The NSS results showed that with the increase of WC particles, the corrosion products decreased gradually and the degree of corrosion decreased. The analysis showed that WC particles can help the grain growth and release the internal stress in the coating. Larger grain sizes reduces intergranular corrosion and smaller internal stress help to alleviate stress corrosion cracking. The above research can provide theoretical support for the efficient preparation of particle enhanced composite coating with strong corrosion resistance.
Paper
4
Date Added: Jan 24, 2022
Date Added: Jan 24, 2022
The fretting wear behavior of copper–magnesium alloy (Cu–Mg alloy) used for high-speed railway catenary system was investigated. Fretting tests of Cu–Mg alloy cylinder against Cu–Mg alloy cylinder at vertical cross contact configuration were carried out on a fretting wear rig at room temperature. The running condition fretting map (RCFM) composed of partial slip regime (PSR), gross slip regime (GSR), and mixed fretting regime (MFR) was constructed depending on different normal loads and displacement amplitudes. In PSR, only slight surface damage was detected on the wear scar. In MFR, the morphologies of the wear scar displayed a clear subdivision in the central stick zone and the surrounding annular slip zone. Fatigue cracks initiated and propagated at the boundary between the stick zone and slip zone. The damage mechanism is the combination of fretting fatigue and fretting wear which combines adhesion, surface fatigue and slight tribochemical reactions. In GSR, fretting wear is predominant. The wear mechanisms were mainly abrasion, surface fatigue and severe tribochemical reactions dominated by oxidation
4
Date Added: Jan 24, 2022
Date Added: Jan 24, 2022
Taperosis/trunnionosis is a scientific term for describing tribocorrosion (fretting corrosion) at the head-neck taper junction of hip implants where two contacting surfaces are undergone oscillatory micromotions while being exposed to the body fluid. Detached ions and emitted debris, as a result of taperosis, migrate to the surrounding tissues and can cause inflammation, infection, and aseptic loosening with an ultimate possibility of implant failure. Improving the tribocorrosion performance of the head-neck junction in the light of minimising the surface damage and debris requires a better understanding of taperosis. Given its complexity associated with both the mechanical and electrochemical aspects, computational methods such as the finite element method have been recently employed for analysing fretting wear and corrosion in the taper junction. To date, there have been more efforts on the fretting wear simulation when compared with corrosion. This is because of the mechanical nature of fretting wear which is probably more straightforward for modelling. However, as a recent research advancement, corrosion has been a focus to be implemented in the finite element modelling of taper junctions. This paper aims to review finite element studies related to taperosis in the head-neck junction to provide a detailed understanding of the design parameters and their role in this failure mechanism. It also reviews and discusses the methodologies developed for simulating this complex process in the taper junction along with the simplifications, assumptions and findings reported in these studies. The current needs and future research opportunities and directions in this field are then identified and presented.
6
Date Added: Jan 23, 2022
Date Added: Jan 23, 2022
Small soft robotic systems are being explored for myriad applications in medicine. Specifically, magnetically actuated microrobots capable of remote manipulation hold significant potential for the targeted delivery of therapeutics and biologicals. Much of previous efforts on microrobotics have been dedicated to locomotion in aqueous environments and hard surfaces. However, our human bodies are made of dense biological tissues, requiring researchers to develop new microrobotics that can locomote atop tissue surfaces. Tumbling microrobots are a sub-category of these devices capable of walking on surfaces guided by rotating magnetic fields. Using microrobots to deliver payloads to specific regions of sensitive tissues is a primary goal of medical microrobots. Central nervous system (CNS) tissues are a prime candidate given their delicate structure and highly region-specific function. Here we demonstrate surface walking of soft alginate capsules capable of moving on top of a rat cortex and mouse spinal cord ex vivo, demonstrating multi-location small molecule delivery to up to six different locations on each type of tissue with high spatial specificity. The softness of alginate gel prevents injuries that may arise from friction with CNS tissues during millirobot locomotion. Development of this technology may be useful in clinical and preclinical applications such as drug delivery, neural stimulation, and diagnostic imaging.
Paper
2
Date Added: Jan 9, 2022
Date Added: Jan 9, 2022
Nickel-based single crystal creep’s properties are commonly calculated according to the rupture strength under constant load. The creep deformation of turbine blades is not only occurred under constant loading but also the variable loading. The influence of variable load on creep deformation should also be considered. Based on this background, in the present study, gradient loading creep tests of DD6 nickel-based single crystal are carried out under two modes. Take load and holding times into account, the creep characteristics and microstructure evolution is studied. The results show that the load and holding time have significant effects on the creep properties of nickel-based single crystals. The change of load induces an instantaneous jump on the creep deformation and strain rate. The holding time of each loading stage mainly affects the evolution of the internal microstructure of nickel-based single crystal. The research on creep behavior of nickel-based single crystal under gradient load in this paper not only enriches the service performance evaluation of nickel-based single crystal under complex environment but also provides a reference for material design and performance optimization.
5
Date Added: Jan 2, 2022
Date Added: Jan 2, 2022
Field-controlled micro–nano manipulations and micro–nano robots have attracted increasing attention in the fields of medicine, environment, engineering, and energy due to their outstanding characteristics which include small size, strong controllability, cluster action, and strong penetrability; thus, they have gradually become an important research focus in micro–nano manufacturing and in vivo detection. However, precise cluster control, targeted drug delivery in vivo, and cellular micro–nano operation remain challenges. Herein, the scientific research results produced in recent years to meet these challenges are studied. Considering the current research enthusiasm and application challenges, the micro–nano manipulations and micro–nano robots driven by physical fields (magnetic field, sound field, and light field) are mainly discussed. This review includes detailed analysis of control mechanism, control objectives, and supporting technologies; analysis of recent research results, and advantages and future development trends driven by physic fields, etc. This review involves the crossover and integration of multiple disciplines (including microelectronic technology, micro–nano processing technology, biology, physics, chemistry, machinery, and automation, etc.), hoping to inspire relevant practitioners to create new research perspectives, and promote the development of micro–nano robotics.
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