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Plasma electrolytic oxidation (PEO) coating on Zr alloy was prepared, and the corrosion behavior was investigated under 400 °C/10.3 MPa steam condition. The surface morphology, roughness, element distribution, and microstructure of PEO coating after corrosion were analyzed. The results indicate that the PEO coating after corrosion presents the typical pores and pancake structure feature, and the surface roughness of PEO coating decreases after corrosion. The PEO coating corroded for 45 days shows the best electrochemical performance because the newly formed oxide gathers to repair the pores and cracks in the oxide/metal interface. The corrosion resistance of PEO coating decreases with the corrosion time increase because the microcrack in PEO coating is connected to generate a large transverse crack, and the corrosion media can access to oxidize the substrate through the crack during the long-term corrosion process. [ABSTRACT FROM AUTHOR]

H62 brass material is one of the important materials in the process of electrical energy transmission and signal transmission, and has excellent performance in all aspects. Since the wear behavior of electrical contact pairs is particularly complex when they are in service, we evaluated the effects of load, sliding velocity, displacement amplitude, current intensity, and surface roughness on the changes in contact resistance. Machine learning (ML) algorithms were used to predict the electrical contact performance of different factors after wear to determine the correlation between different factors and contact resistance. Random forest (RF), support vector regression (SVR) and BP neural network (BPNN) algorithms were used to establish RF, SVR and BPNN models, respectively, and the experimental data were trained and tested. It was proved that BP neural network model could better predict the stable mean resistance of H62 brass alloy after wear. Characteristic analysis shows that the load and current have great influence on the predicted electrical contact properties. The wear behavior of electrical contacts is influenced by factors such as load, sliding speed, displacement amplitude, current intensity, and surface roughness during operation. Machine learning algorithms can predict the electrical contact performance after wear caused by these factors. Experimental results indicate that an increase in load, current, and surface roughness leads to a decrease in stable mean resistance, while an increase in displacement amplitude and frequency results in an increase in stable mean resistance, leading to a decline in electrical contact performance. To reduce testing time and costs and quickly obtain the electrical contact performance of H62 brass alloy after wear caused by different factors, three algorithms (random forest (RF), support vector regression (SVR), and BP neural network (BPNN)) were used to train and test experimental results, resulting in a machine learning model suitable for predicting the stable mean resistance of H62 brass alloy after wear. The prediction results showed that the BPNN model performed better in predicting the electrical contact performance compared to the RF and SVR models. [ABSTRACT FROM AUTHOR]

The turtle has survived for over several hundred million years and evolved excellent shell structure to resist high-stress repeated impact by stone and predators. Based on the impact resistance performance of turtle shell, a new bionic composite coating (BCC) was proposed and prepared, which is composed of porous micro-arc oxidation (MAO) inner layer, Si transition middle layer, and different-element (H, Si, and Cr)-doped diamond-like carbon (DLC) outer layer. This study aims to investigate the impact response, energy absorption, and damage characteristics of BCC in low-speed impact conditions. Results indicate that the impact behavior of BCC is superior to substrate and the BCC presents a lower peak force and higher energy absorption. Thus, the outer DLC layer could resist the impact force to reduce damage. The porous structure in MAO layer could act as a buffer and deform to absorb energy. The BCC-Si shows the best impact resistance with the lowest wear volume due to the Si-DLC layer with a good balance of toughness and hardness. [ABSTRACT FROM AUTHOR]

As a typical keratinous material, the mechanical properties of pangolin scales are affected by hydration. Clarifying the mechanism of influence of hydration on dynamic response of materials may provide valuable inspiration for bio-inspired design. In this study, mechanical properties and impact wear behaviors of pangolin scales from different hydrated levels were investigated on a low-velocity impact wear tester. The dynamic response and damage behavior of these pangolin scales were systematically analyzed. Results showed that the energy absorption and impact contact force were considerably distinct with different hydrated levels. The maximum values of the impact contact force are similar to each other in various impact cycles. However, the damage extent of scales was not the same in varied impact cycles. Impact worn scars size of scales increased as the impact cycles increased. Under varied hydrated levels, energy absorption initially decreased and then increased with the increase in moisture content. Specifically, for a hydrated level of 10.5%, the energy absorption had the lowest rate, down to 26.6%, and the impact force decreased. Finally, the mechanisms and factors affecting the dynamic response and impact wear of scales were investigated. This study promoted a bio-inspired design for improving impact wear resistance properties. [ABSTRACT FROM AUTHOR]

Based on the trabecular bone structure, a porous micro-arc oxidation (MAO) coating and a MAO/Al composite coating were fabricated on AZ31D Mg alloy. Surface morphology, cross-section morphology, coating composition, and coating thickness were observed by scanning electron microscopy, energy dispersive spectrometry, and x-ray diffraction. Then, force-dampening and energy-absorbing effects of the coatings were explored by a constant kinetic energy impact experiment, to explore their dampening stress and reducing vibration values applying in engineering structure subjected to impact or vibration stress. Results show that large plastic deformation and cracks formed in the AZ31D Mg alloy after impact, and the MAO coating hindered the formation of the defects due to its higher stiffness. In addition, MAO enhanced the energy-absorbing ability of the Mg alloy, which is beneficial for vibration reduction. However, the MAO coating had a rough and brittle surface, and when Al was used to protect it, its force-dampening effect, energy-absorbing effect, and plastic deformation resistance had the evolution trend approaching the Mg alloy substrate but with improved crack resistance. MAO can be an optimization method for enhancing the plastic deformation resistance and vibration reduction effect of Mg alloy as structure material, and Al can be used to enhance its crack resistance. [ABSTRACT FROM AUTHOR]

The impact tests were conducted on metallic materials with different bulk hardness and Young's moduli. Analysis of the dynamics response during the tribological process showed that the tested materials had similar energy absorption, where the peak contact force increased as the tests continued. Moreover, wear volume decreased with the increase in Young's modulus of metals, except for Cr with a relatively low hardness. Wear rate was gradually reduced to a steady stage with increasing cycles, which was attributed to the decrease in contact stress and work-hardening effect. The main wear mechanism of impact was characterized by delamination, and the specific surface degradation mechanisms were depending on the mechanical properties of materials. The absorbed energy was used to the propagation of micro-cracks in the subsurface instead of plastic deformation, when resistance of friction wear and plastic behavior was improved. Hence, both the hardness and Young's modulus played important roles in the impact wear of metallic materials. [ABSTRACT FROM AUTHOR]

The impact fretting wear has largely occurred at nuclear power device induced by the flow-induced vibration, and it will take potential hazards to the service of the equipment. However, the present study focuses on the tangential fretting wear of alloy 690 tubes. Research on impact fretting wear of alloy 690 tubes is limited and the related research is imminent. Therefore, impact fretting wear behavior of alloy 690 tubes against 304 stainless steels is investigated. Deionized water is used to simulate the flow environment of the equipment, and the dry environment is used for comparison. Varied analytical techniques are employed to characterize the wear and tribochemical behavior during impact fretting wear. Characterization results indicate that cracks occur at high impact load in both water and dry equipment; however, the water as a medium can significantly delay the cracking time. The crack propagation behavior shows a jagged shape in the water, but crack extended disorderly in dry equipment because the water changed the stress distribution and retarded the friction heat during the wear process. The SEM and XPS analysis shows that the main failure mechanisms of the tube under impact fretting are fatigue wear and friction oxidation. The effect of medium(water) on fretting wear is revealed, which plays a potential and promising role in the service of nuclear power device and other flow equipments. [ABSTRACT FROM AUTHOR]

Under different simulated oral environments (distilled water, artificial saliva, and a cola soft drink) and with a small-amplitude reciprocating apparatus, the friction and wear behaviors of 5 types of indirect dental restorative composites relative to uniform SiN balls were investigated. Test parameters were: normal load with 20 N, reciprocating amplitude (1,000 μm), and frequency (0.25 Hz). Tests lasting up to 5,000 cycles were conducted. The wear damage characteristics are discussed in detail based on an analysis of friction behaviors, SEM observations, and 2- and 3-D profile microscopy. The results indicated that the hybrid resin composites with high filler weight and well filler distributions, such as Filtek P60, possess better wear resistance than nano-filled composites, such as VITA ZETA and VITA LC, with relatively low filler weight. Artificial saliva and a cola soft drink could play important roles in lowering the friction coefficient and wear loss of dental composites. The cola soft drink displayed a better lubrication effect. The degree of sensitivity to changes in lubrication conditions varies with different dental composites. Abrasive wear is the main wear mechanism for the 5 composites, but brittle cracks and delamination are more common for VITA ZETA and VITA LC. [ABSTRACT FROM AUTHOR]

The mechanical and wear properties of CFRP laminate were investigated using a method of cycling low velocity impact, to study the trend and mechanism of impact resistance of the CFRP laminate under repeated impact during its service process. The interface responses of CFRP laminate under different impact kinetic energy during the cycling impact process were studied were studied experimentally, such as impact contact duration, deformation and energy absorption. The worn surface morphologies were observed through optical microscopy and a 3-D surface profiler and the cross-sectional morphologies were observed through SEM to investigate the mechanism of impact material damage. Based on a single-degree-of-freedom damping vibration model, the normal contact stiffness and contact damping of the material in different wear stages were calculated. It shows the failure process of CFRP laminate damaged by accumulated absorption energy under the cycling impact of different initial kinetic energy. The results indicate that the stiffness and damping coefficients will change at different impact velocities or cycle numbers. The damage mechanism of CFRP laminates under cycling low kinetic energy is delamination. After repeated experiments, it was found that there was a threshold value for the accumulated absorption energy before the failure of the CFRP laminate. [ABSTRACT FROM AUTHOR]

Please note that the correct surname of the first author of this article is 'Wang' (not 'Wan' as it was given in the article as originally published). [ABSTRACT FROM AUTHOR]