High‐resolution images from Chandrayaan‐1 Terrain Mapping Camera and Lunar Reconnaissance Orbiter Camera reveal landslides and gully formation on the interior wall of a 7 km‐diameter simple crater ...emplaced in Schrödinger basin on the farside of the Moon. These features occur on the steep upper crater wall, where the slope is ~35°. The gullies show a typical alcove‐channel‐fan morphology. Some gullies incise bedrock, where impact‐related faults are present. Slope failure along the concentric faults also led to formation of landslides. Dark slope streaks are abundant at the bright gully regions, especially near the fan and channel deposits. Spectral characteristics inferred from data obtained by Hyperspectral Imager and Moon Mineralogy Mapper on board Chandrayaan‐1 show that the gullies and landslides are characterized by high optical immaturity and devoid of prominent spectral absorption features related to water or hydroxyl molecules, suggesting youthful dry‐granular flows. Mass movements on the crater wall led to the formation of arcuate ridges and ponding of fine‐grained sediments on the crater floor. Runout flows from small impact craters on the slopes indicate that impact‐induced seismic shaking was responsible for the downslope mass movements. Crater size‐frequency distributions suggest a minimum age of 18–2 Ma for the gullies and 2 Ma for the landslides, while age of the host crater ejecta was inferred to be about 175 Ma. The gullies and landslides also occur on the interior wall of other impact craters elsewhere on the Moon and probably formed by similar processes.
Key Points
Gullies and landslides are present in fresh lunar impact craters
Gullies and landslides are dry‐granular flows
Gullies and landslides are formed long after the host crater
Surface finish greatly affects the friction, wear, corrosion, heat transfer and lubrication properties of internal surfaces which find wide applications in medical, automobile, aerospace and mould ...and die industries. However, improving the internal surface finish is extremely challenging due to the restricted tool accessibility of conventional manufacturing processes. This paper develops a novel magnetic polishing tool to deterministically polish internal surfaces. Repeatability tests, single point polishing experiments and gap variation experiments are conducted to evaluate the performance of the proposed polishing tool. Experimental results substantiate the good repeatability and localized polishing capability with a material removal rate of 15 μm/min and achievable surface roughness of 0.258 μm Ra. Furthermore, a theoretical model is developed to reveal the material removal mechanism based on the contact mechanics model and sliding wear theory. The developed model can successfully predict the two-dimensional and three-dimensional polished profiles under different gaps which are defined by the distance between the externally driven magnet and the outer surface of the workpiece. The localized polishing capability is, for the first time, achieved in internal surface finishing and the theoretical study establishes a novel framework for modelling the polished profile evolution in pressure-copying polishing processes.
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•Localized polishing capability is for the first time achieved in internal finishing.•Material removal rate reaches 15 μm/min and surface roughness improvement is 88%.•Gap is the dominant factor influencing material removal rate.•A material removal model is developed based on contact mechanics and wear theory.
Innovative techniques have been proposed to overcome the challenge of the strong tendency of brittle materials to crack during machining. One of them is the use of an epoxy coating to serve as a ...crack formation restraint. However, this only serves to achieve ductile-mode grinding along the uncut shoulders. Therefore, this study evaluates the effect of a layer of epoxy resin on the machined surface perpendicular to the micro-cutting direction of a brittle material, single-crystal calcium fluoride. An increase in the ductile–brittle transition was observed in micro-cutting experiments on the (111) plane of calcium fluoride with the use of a 4-μm thick epoxy resin coating, ranging from 167–347 nm to 213–476 nm for the 0° rake angled tool. A similar increase was also observed with the +5° rake angle, ranging from 91–233 nm to 187–310 nm. An energy-based ductile–brittle transition predictive model is introduced, which characterises the anisotropic behaviour of the single crystal and incorporates the additional stress induced during cutting with a coating as a fraction of the coating hardness. The analytical model accurately predicts a consistent range of improvement from 69–325 nm to 257–485 nm for the 0° rake angle and from 62–285 nm to 215–460 nm for the +5° rake angle. The ductile-mode cutting energy increases to preserve its dominance over brittle-mode cutting and delays the onset of brittle-mode activation. The validity of the model extends the understanding of a surface coating as a restraining technology to include the beneficial stress acting in the deformation zone during cutting.
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•Epoxy resin coating can enhance ductile-mode cutting of CaF2 single-crystal.•Ductile–brittle transitions increase by at least 27.5 % with epoxy coating.•An anisotropic ductile–brittle transition predictive model is proposed.•The coating increases ductile-mode energy dominance to improve machinability.•Additional stress induced in the workpiece is a function of coating hardness.
Multimaterial soft robots, composing of integrated soft actuators and a relatively harder body, show great potential to exert higher payloads and support their own weights. This paper proposed a ...systemic framework to automatically design and fabricate this kind of robots. The multimaterial design problem is mathematically modeled under the framework of topology optimization in which the structure and material distribution are obtained simultaneously. Herein, a multimaterial pneumatic soft finger, modeled as a compliant mechanism, is optimized to achieve its maximal bending deflection and further customized to practical applications on grippers, rehabilitation, and an artificial hand. These optimized multimaterial soft fingers are fabricated by combining molding and three-dimensional printing technique. Experimental results show that the soft gripper can manipulate a large variety of objects with different shapes (from M4 screws to complicated sunglasses) and weights (up to 168 g), the rehabilitation finger can facilitate human safely in two modes, and the artificial hand can perform various gestures. This paper represents an important step toward the realm of high-performance soft robots.
As the simple grounding electrodes alone may not provide the required low impedance beyond the effective length, a new electrode configuration of optimum impedance is proposed for lightning ...transients. The proposed grounding electrode configuration comprises a primary vertical electrode connected with the optimum count of horizontal enhancement electrodes. Exhaustive impulse test simulations are carried out on the primary electrode integrated with multiple enhancement electrodes whose effective lengths are estimated in previous research works. From the simulations, the effective count of enhancements (ECEs) is determined by an optimum impedance reduction approach to arrive at an impulse-efficient electrode configuration. The proposed electrode configurations' resistances and impedances are computed to obtain the impulse coefficients. The reductions of impedances and impulse coefficients in the proposed electrode configurations are calculated. An empirical expression is derived to estimate the ECE using numerical methods. The proposed electrode configuration and the ECE expression are verified with the field experiments.
Micro-wire-cut electrode discharge machining (EDM) is an emerging manufacturing process in the field of micro-manufacturing to fabricate the complex profiles of micro-components. It is a complex ...process involving various process parameters such as pulse on time, pulse off time, wire speed, wire tension and current. In addition to micro-fabrication, this process can also be extended in the field of tool design and developments such as dies, moulds, precision manufacturing, contour cutting, etc., where complex shapes need to be generated with high-grade dimensional accuracy and surface finish. In this research work, an attempt is made to investigate the effect of process parameters on the output variables such as material removal rate (MRR), surface finish and the cutting width (kerf) of wire-cut EDM for duplex stainless steel (DSS). Scanning electron microscopy (SEM) has been used to capture the images of the kerf width, and the measurements are taken with the help of the welding expert system and software. An optimization technique (Taguchi method) has been employed to identify the optimum parameters of the micro-wire-cut EDM process for cutting 2205 grade duplex stainless steel. The effect of each control parameter on the performance measure is studied individually using the plots of signal to noise ratio.
Nanofluids are widely used in heat transfer applications. This article presents the effect of heat transfer and pressure drop of the TiO
2
–water nanofluids flowing in a double-tube counter-flow heat ...exchanger with various flow patterns. In this experimental work, performance of TiO
2
–water nanofluid on heat transfer in three different cases such as laminar, transition and turbulent flow region were analyzed. TiO
2
nanoparticles with average diameters of 20 nm dispersed in water with three volume concentrations of 0.1, 0.3 and 0.5 vol% were used as the test fluid. The results show that the heat transfer of nanofluids is higher than that of the base liquid (water) and increased with the increase in Reynolds number and particle concentrations. The heat transfer rate of nanofluid with 0.5 vol% was 25% greater than that of base liquid, and the results also show that the heat transfer coefficient of the nanofluids at a volume concentration of 0.5 vol% was 15% higher than that of base fluid at given conditions. Pressure drop of nanofluid was increased with increase in volume concentration, and it is slightly higher than that of the base fluid.
Task allocation within the cloud computing environment is a nondeterministic polynomial time class problem that is laborious to get the best solution. It is an important issue in the cloud computing ...setting. The usage of cloud based applications and cloud users are increasing tremendously. In order to handle the massive cloud user’s requests, effective multi-objective Hybrid Genetic Algorithm–Ant Colony Optimization (HGA–ACO) based task allocation technique is proposed in this paper. Utility based scheduler identifies the task order and suitable resources to be scheduled. The proposed HGA–ACO considers the utility based scheduler output and finds the best task allocation method based on response time, completion time and throughput. The HGA–ACO algorithm combines Genetic and Ant Colony Optimization algorithms together. Genetic algorithm (GA) initializes the effective pheromone for ant colony optimization (ACO). ACO is used to enhance the GA solutions for crossover operation of GA. The experimental results show that the proposed framework has better performance in task allocation and ensuring quality of service parameters.
Carbon fiber reinforced polymer (CFRP) has a wide range of applications in aerospace, automobile, marine, and other industries, due to its remarkable mechanical properties and lightweight. It can ...enhance the performance of the structural components and has been presented to be a good alternative over conventional materials. Adhesive bonding has been widely employed, and research studies on the surface modification of CFRP have been conducted to improve the load resistance of adhesive bonding, of which atmospheric pressure (AP) plasma is the most preferred method. However, there is still a lack of study on the effectiveness and strategies of AP plasma surface modification. To gain more insight, possible sources that would have influence on the adhesive bonding were analyzed by preparation of different surface configurations of CFRP. It is confirmed that AP plasma can increase the surface polarity and wettability of the carbon fiber surface. It can contribute to the removal of surface contamination element as well. Although the surface morphology and surface roughness before and after the AP plasma treatment does not show noticeable changes, the single‐lap shear strength of the contaminated samples can be effectively improved. This study validates that AP plasma is effective on surface contamination removal and bonding quality improvement, which provides a potential alternative for the adhesive bonding improvement and surface modification of carbon fiber.
Highlights
Surface polarity and wettability increase of CFRP by AP plasma.
Surface contamination removal and bonding quality improvement by AP plasma.
AP plasma provides a potential alternative method for adhesive bonding pre‐treatment.
AP plasma surface modification mechanism analysis via surface characterization.
AP plasma improved ashesive bonding on CFRP.
Opportunities for new applications of lightweight Mg alloys are emerging in bio-medical fields, especially in medical devices and implants. The biodegradable Mg-based alloys wield advantages over ...their counterparts of SS 316 L, Co-Cr, and Ti-based alloys due to good biocompatibility observed during in-vivo and in-vitro assessments. However, in such aqueous environments, biodegradable magnesium alloys experience the limitation of higher corrosion rates, which causes loosening of the fixation implant. More importantly, it causes an undesirable chemical imbalance in the human body. This undesirable side effect of the promising Mg alloys can be subdued by improving the quality of the implant’s surface which interacts with the human biology. One way to do it is by imparting compressive stress via mechanical processing such as tool-based machining process. Mechanical micro-machining, especially the ultra-precision turning, could be a viable method to fabricate Mg alloy implants and components with the high surface finish necessary for superior corrosion resistance. However, the cutting mechanics of Mg alloy is poorly understood due to the scarcity of processing data and cutting parameters at ultra-precision level. In this paper, with ultra-precise cutting of Mg alloy (AZ91D), a novel “burnishing-like” surface finishing phenomena has been established. Additionally, some of the critical machining results are identified that are crucial for the comprehension of the cutting mechanics. These entities are cutting edge radius effect on the chip formation, material flow angle, machining-induced stress, surface burn marks, chip-tool contact surface, and the fallacy of “no chip formation” phenomenon. Therefore, knowledge derived from this study will enhance the understanding of cutting mechanics at ultra-precision level, and consequently improve the machining results of Mg alloy for bio-medical, electro-mechanical, and space-telecommunication applications.
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