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Abstract The beetle has evolved over several hundred million years and possess perfect structure, as well as performance. According to the excellent structure and performance of beetle forewing, a bionic structural material (BSM) was designed and manufactured to improve its low-velocity impact resistance behavior. The surface layer of BSM is carbon-fiber-reinforced plastic (CFRP), and the cores of BSM are aluminum honeycomb. This study aims to investigate the dynamic response, energy absorption, and damage characteristics of BSM in low-velocity and high-cycle impact condition. Results showed that the BSM is superior to single CFRP, with lower peak force, higher energy absorption, and deformation. The damage mechanism of CFRP under cycling low kinetic energy is delamination and then fracture. Meanwhile, the damage of CFRP in sandwich structures is lower than in single CFRP, indicating an excellent impact resistance behavior of BSM, which is useful for practical engineering applications. Graphical abstract The structure of the beetle forewing and impact resistance composite design.(a) Adult beetle. (b) Outline sketch of the forewing (c) surface and (d-h) cross-section and a simple model and microstructure of beetle forewing (i). Image 1 [ABSTRACT FROM AUTHOR]

F6NM martensitic stainless steel was exposed to 350 °C water condition for 500, 1500, and 2500 h to simulate pressurized water reactor (PWR) condition. The characterization and corrosion behavior of the oxide film were investigated. Results indicate that the exposed steel surface formed a double-layer oxide film. The outer oxide film is Fe-rich and contains two type oxide particles. However, the inner oxide film is Cr-rich, and two oxide films, whose thicknesses increase with increasing exposure time. The oxide film reduces the corrosion behavior because the outer oxide film has many crack and pores. Finally, the mechanism and factors affecting the formation of the oxide film were investigated. [ABSTRACT FROM AUTHOR]

Study of the properties of natural biomaterials provides a reliable experimental basis for the design of biomimetic materials. The mechanical properties and impact wear behaviors of turtle shell with different soaking time were investigated on a micro-amplitude impact wear tester. The damage behavior of turtle shells with different soaking time and impact cycles were systematically analyzed, also the impact dynamics behavior was inspected during the impact wear progress. The results showed that the energy absorption and impact contact force were significantly different with varied soaking time. Under different impact cycles, the peak contact force of shell samples with same soaking time were approximate to each other in value and the values of impact contact time change in a small range. However, the damage extent of shells were distinct with varied impact cycles. It was found that impact worn scars of shells increase with impact cycles increasing. However, under the same impact cycles, energy absorption and contact time increased with the extending of soaking time, but the peak contact force decrease. Especially shell without soaking, the absorption rate is the lowest. [ABSTRACT FROM AUTHOR]

This study investigated the effects of electrical contact resistance (ECR) on pogo pins used in mobile phones, chargers, digital cameras, Bluetooth headsets, medical equipment, and other electronic products with different surface roughness. Experimental results revealed that metallic wear debris is generated by fretting motion and formation of a third body on rough surfaces without removal by fretting motion, thus increasing ECR. Wear debris does not easily form the third body at contact areas of smooth surfaces and causes formation of metal–metal contact pattern. Results showed low ECR with fretting motion. 3D and 2D profiles of contact area verified the definition of contacting high spots, further explaining increases in ECR. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the impact fretting wear behavior of thin-walled tubes under different support interfaces with a novel impact wear testing rig. A tube/cylindrical contact model was used, and V-shaped fixtures with varied angles were applied. The 304 stainless steel tubes with varied lengths and a GCr15 bearing steel roller were used as the test materials. The interface deformation, impact energy absorption, and damage behavior were investigated in terms of the influence of the support angle, tube length, and the initial impact energy. After the test, the wear mechanism of the tube was investigated. The results showed that under the same lengths, when the support angle increased, the deformation displacement increased, but the contact peak force, energy absorption, and the area of worn scars decreased. The increasing length increased the contact force, energy absorption ratio, and serious damage but reduced the deformation. The increasing kinetic energy of the initial impact will decrease the energy absorption ratio. Contact fatigue spalling and oxidation are the wear mechanisms of the impact fretting wear of 304 stainless steel. [ABSTRACT FROM AUTHOR]

Dual-rotary fretting (DRF) is a complex fretting wear mode combining torsional fretting with rotational fretting. Two different typical friction-induced convex topographies (Type I and Type II) in contact area were showed, which are under the control of torsional and rotational fretting components, respectively. To investigate their evolution characteristics and formation mechanism, the convex topographies were analyzed by SEM, XPS, a nano-hardness tester and surface profilometry, etc. The results show that the convex topographies significantly depended on the test parameters and environmental conditions. The initiation and propagation of fretting fatigue cracks were found related with the convex topography under the fretting wear. [ABSTRACT FROM AUTHOR]

The fretting corrosion behavior of quench–polish–quench (QPQ)-treated TP316H steel was investigated in liquid sodium at 450 °C. The surface of the sample after QPQ is a multi-layer structure, consisting of the outermost oxide layer, the middle nitriding layer, and an underneath diffusion layer. The fretting wear and corrosion increased the material damage. With increasing thickness of the nitriding layer, the cross-sectional hardness and wear resistance remarkably increased, the fretting corrosion volume decreased. The effect of multilayer structure anti-wear and anti-corrosion were examined. Possible fretting corrosion mechanisms of the multilayer structure prepared by QPQ on TP316H in liquid sodium are discussed. • Time of QPQ treatments influence the multilayer structure of modified surface. • The high-hardness nitriding layer exerts the main anti-wear effect. • The diffusion layer exerts better anti-corrosion effect, and decomposes into the harder CrN and α-Fe phases. • QPQ treatments are promising for combating fretting corrosion of TP316H in liquid sodium. [ABSTRACT FROM AUTHOR]

The fretting corrosion behavior of zirconium (Zr) alloy under different pH conditions was investigated. The morphology, microstructure, and wear mechanism of Zr alloy under different pH condition was analyzed. The results indicate that the wear scar Zr alloy in acid condition presents a typical feature of wear debris, furrow, and delamination, indicating that the wear mechanism is oxidation wear and abrasive wear. The microstructure beneath the wear scar is composed of a thick wear debris layer (WDL), deformation layer (DL), and thin tribologically transformed structure (TTS). The WDL is a nano-sized grainy structure and the micro-crack is mainly formed on the interface of WDL and TTS. The largest wear volume belongs to the wear scar in pH of 1 condition. Because the corrosion and corrosion induced by wear would destroy the surface protective film and form a thick WDL, which is easy to separate to increase the material loss volume. The Zr alloy in pH of 1 condition shows the largest volume ratio of wear induced by corrosion and corrosion induced by wear. • The material loss volume by tribocorrosion is lowest at intermediate pH and highest at low pH. • The thick WDL at low pH is generated by the quick oxidation of TTS/DL and the accumulation of oxide particles. • The wear mechanism of Zr alloy at intermediate pH is abrasive wear and at low pH is oxidation wear and abrasive wear. [ABSTRACT FROM AUTHOR]

Abstract: Ti6Al7Nb is a high-strength titanium alloy used in replacement hip joints that possesses the excellent biocompatibility necessary for surgical implants. Ti6Al7Nb treated with nitrogen gas (N2) plasma immersion ion implantation–deposition (PIII–D) was investigated. Torsional fretting wear tests of untreated and nitrogen-ion-implanted Ti6Al7Nb alloys against a Zr2O ball (diameter 25.2mm) were carried out under simulated physiological conditions (serum solution) in a torsional fretting wear test rig. Based on the analyses of the frictional kinetics behavior, the observation of 3D profiles, SEM morphologies and surface composition analyses, the damage characteristics of the surface modification layer and its substrate are discussed in detail. The influence of nitrogen ion density on the implantation and torsional angular displacement amplitudes were investigated. The results indicated that ion implantation layering can improve resistance to torsional fretting wear and thus has wide potential application for the prevention of torsional fretting damage in artificial implants. The damage mechanism prevented by the ion implantation layer on the Ti6Al7Nb alloy is a combination of oxidative wear, delamination and abrasive wear. An increase in ion implantation concentration inhibited detachment by delamination. [Copyright &y& Elsevier]

Abstract: Fretting displacements of a shrink-fitted PMMA shaft subjected to rotating bending by a newly produced bending fretting device are observed and measured in situ, which are also analyzed by numerical simulations. The results show that the fretting mode of the shrink-fitted shaft is a kind of composite tangential fretting combining both axial and transverse motions and the relative sliding trajectory is approximately in a spindle shape. Besides, the fretting could be transitional between the partial slip and gross slip and the sliding velocity is also continuously varied. [Copyright &y& Elsevier]

Abstract: Radial fretting tests on human femur cortical bone with a ball-on-flat configuration were carried out in vitro under different normal contact loads. The kinetics behaviors and damage characteristics of the cortical bone were analyzed using the load versus displacement (F–D) curves. The fretting scars were examined using laser confocal scanning microscopy (LCSM) and scanning electron microscopy (SEM). A nano-indenter was used to characterize the mechanical property of the osteon of the cortical bone. Morphologies showed that the primary damage form was due to micro-cracking. Around the osteon, three kinds of micro-crack configurations were observed; i.e. annular cracks—located at the concentric lamellae; radial cracks—initiated from the Harversion canal; and interstitial cracks—initiated and propagated between the interstitial lamellae. Plenty of interstitial cracks occurred in the wear scar, which indicated that the interstitial tissue was the weak zone in the structure of cortical bone. In addition, the contact stresses under the radial fretting condition were calculated by the finite element method analysis (FEMs) and the behaviors of cracking were explained. The results demonstrated that the stress concentration that occurred around the Harversian canal and osteon system resulted in a better resistance than that from the interstitial tissue. The concentric lamellae presented a better radial-fretting resistance and contact fatigue resistance than that from the interstitial lamellae. [Copyright &y& Elsevier]

Abstract: Four simple fretting modes are defined according to relative motion: tangential, radial, rotational, and torsional fretting. This paper presents a new test rig that was developed from a low-speed reciprocating rotary system to show torsional fretting wear under ball-on-flat contact. Torsional fretting behavior was investigated for LZ50 steel flats against AISI52100 steel balls under various angular displacement amplitudes and normal loads. The friction torques and dissipation energy were analyzed in detail. Two types of T–θ curves in the shape of quasi-parallelograms and ellipticals were found that correspond to gross and partial slips, respectively. The experimental results showed that the dynamic behavior and damage processes depend strongly on the normal loads, angular displacement amplitudes, and cycles. In this paper, the debris and oxidation behaviors and detachment of particles in partial and gross slip regimes are also discussed. Debris and oxidation are shown to have important roles during the torsional fretting processes. The wear mechanism of torsional fretting was a combination of abrasive and oxidative wear and delamination before third-body bed formation. The mechanism was then transformed into third-body wear after a great amount of debris formed. [Copyright &y& Elsevier]

Abstract: Tests of LZ50 carbon steel against 52100 steel balls in ambient air (RH=60%) and in nitrogen were carried out on a controlled-atmosphere torsional fretting tribometer. The morphologies of worn scars were observed by a scanning electron microscopy (SEM), and the tribochemical behaviors of the contact zones were analyzed by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX). Curves of friction torques vs. torsional angular displacement amplitude (T–θ curves) were used to describe the kinetic behaviors of torsional fretting. According to the T–θ curves and damage morphologies, three fretting running regimes (partial slip regime, mixed regime, and gross slip regime) can be identified. Results indicated that the mixed and gross slip regimes shifted to higher angular displacement amplitudes in nitrogen, comparably to that in air. With an increase in the number of cycles, the curves of the friction torques can be divided into three stages: initial stage, climbing stage, and steady stage. The friction torque in nitrogen was much higher than in air, and the wear damage in nitrogen was also severer than that in air. The oxidative debris formed in air served as a lubricant and alleviated fretting wear. The torsional fretting wear mechanisms in the air were oxidative wear, delamination, and abrasive wear; however, the wear mechanisms in nitrogen were delamination and abrasive wear accompanied by a strong plastic flow due to the effect of tribo-oxidation being restrained. [Copyright &y& Elsevier]

• Effect of different copper graphite content ratio on the contact resistance was studied. • Relationship between surface atomic content and contact resistance was analysed. • The wear resistance and electrical contact endurance of different materials are compared. • The optimum proportion of copper/graphite materials is proposed. In this study, copper-graphite composites were prepared by powder sintering. The wear resistance and electrical contact endurance of composites with different copper-graphite ratios were investigated and are discussed. The results illuminate that the high electrical contact resistance evolution during fretting wear is related to the graphite content. With a decrease in the copper content, the interaction between graphite and copper increases, and the conductivity decreases. The graphite particles of the flat sample delaminate and form a graphite friction film between the contact surfaces; this friction film has excellent lubricating properties. Thus, the copper-graphite composites with the highest graphite content herein demonstrate good behavior against fretting wear and exhibit poor electrical contact performance. In other words, a relatively high copper content could maintain a decreased and stable contact resistance. The comprehensive performance of composite materials can be effectively developed by designing the copper-graphite ratio. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Various impact-sliding wear behaviors commonly occur among steam generator tubes and their supporters. The main purpose of this study is to investigate the effect of ultrasonic surface rolling process (USRP) on the impact-sliding wear behavior of Inconel 690 alloy tubes. A self-made two-dimensional cycling impact-sliding wear test rig was developed to realize multiple wear patterns by changing motion parameters in both impact and sliding directions. Tests were carried out under different impact and sliding velocities. Results indicated that USRP reduced the impact kinetic energy absorption rate, friction coefficient and increased the wear resistance of Inconel 690 alloy. These can be attributed to the USRP which decreased the grain size of 690 alloy, resulting in the increase of micro-hardness and compressive residual stress. Image 1 • USRP is capable to refine microstructure, improve micro-hardness and compressive residual stresses of 690 alloy tubes. • USRP treated samples showed better wear resistance and lower friction coefficient under impact-wear sliding condition. [ABSTRACT FROM AUTHOR]

Nuclear power plants, working in extremely harsh environment, primarily in the form of high-speed fluid flow, circulate through complex systems. Serious tribological problems can occur when a small amount of nuclear energy is converted into mechanical energy in the components (e.g., fuel-rod cladding, tube of the heat exchange systems). With the increase of the service life of nuclear power equipment, a considerable number of nuclear power equipment or structure failures occur one after another. Although the influencing factors are different, fretting damage is one of the important factors. Fretting damage has strong concealment and high risk, and it is often the main cause of component failure. Thus, improving the reliability of nuclear power equipment, extending their life, and optimizing their structure are important. In recent decades, many scholars have studied fretting wear, fretting fatigue, and fretting corrosion behavior in nuclear power equipment. Accordingly, they have solved many problems, accumulated a lot of experience, and put forward many criteria. In this article, the research status of fretting damage in key equipment and structures of nuclear power plant is reviewed. Typical positions of fretting wear in steam generator. Image 1 • The research status of fretting method, nuclear materials damage in key equipment and structures of nuclear power plant is reviewed. • Fretting research of heat exchange materials for steam generators and fuel cladding in nuclear power systems is reviewed. • The research status of fretting wear of fuel cladding is analyzed, including the latest coating and surface strengthening technologies. [ABSTRACT FROM AUTHOR]

Wear behaviors of materials in nuclear power stations are very complex, because they are rarely subject to just pure impact or sliding wear. This study uses a self-made impact-sliding wear test rig to study the influences of impact kinetic energy and sliding velocity on the energy absorption, mechanical response, interface deformation, and damage behavior of nuclear-grade 304 stainless steels (304SS). The results show that an increase in impact velocity causes an increase in absorbed energy, impact force, and friction force, while lowing the friction coefficient. The friction force and friction coefficient increase with an increase in the sliding velocity, whereas no obvious change is seen in impact force and absorbed energy. The dominant wear mechanism in test samples were delamination failure and friction oxidation. Furthermore, numerical study was performed to explain the effect of velocity on the mechanical response of 304SS. • The impact-sliding wear test rig is capable of testing the wear behaviors of different materials under various complex conditions. • Effect of different impact kinetic energies and sliding velocities on the impact-sliding wear behaviors of nuclear material was studied. • Effect of impact kinetic energies on the dynamic response of impact-sliding wear is more obvious than that of the sliding velocities. [ABSTRACT FROM AUTHOR]

Abstract: Bending fretting fatigue tests of 7075 aluminum alloy cylinders against 52100 steel cylinders orthogonally have been carried out under a same normal load and varied bending loads. The S–N curve of the bending fretting fatigue showed a characteristic of “C curve”. Based on the OM, SEM, and TEM, the fretting fatigue damages of 7075 alloy have been analyzed in detail. A physical model was set up to describe the surface damage and the crack formation process in MFR. The TEM analyses showed that the stress concentration at the wall of dislocation cells was the reason of the fatigue crack initiation. [Copyright &y& Elsevier]

• Surface morphology changes in the DD6 and TBC with various laser powers are studied. • The mechanism of fs laser on the DD6 and TBC is phase explosion and vaporization. • Laser spot regions includes ablation, melting, laser-induced, and irradiated regions. In recent years, single-crystal superalloy and thermal barrier coating (TBC) have attracted considerable attentions in femtosecond laser drilling. Surface morphology changes in DD6 single-crystal superalloy and TBC induced by incident laser pulses with a wide range of powers (2.28–11.18 W) at 50 kHz are studied. The ablation thresholds of DD6 single-crystal superalloy and TBC are calculated, and the ablation mechanisms of different femtosecond laser spot regions are discussed in details. Results show that the ablation threshold of DD6 single-crystal superalloy is 1.16 J/cm2, which is close to that of TBC (0.998 J/cm2). The femtosecond laser spot regions in the DD6 single-crystal superalloy and TBC can be divided into four (ablation, melting, laser-induced, and irradiated regions) on the basis of the energy distribution of the Gaussian laser beam. However, the physics behind femtosecond laser on single-crystal superalloy is laser-induced periodic surface structures (LIPSS), where is laser-induced cracks (LIC) on TBC. The dominant mechanism differs in different regions. The reason for cracks on the TBC may be the combined action of thermal stress and mechanism stress under high fluence and high repetition rate femtosecond laser. [ABSTRACT FROM AUTHOR]

The tribologically transformed structure of the white etching layer (WEL) always appears with some cracks accompanying microstructural evolution under friction. This work investigated crack behavior with the existence of WEL on pearlitic steel after rolling-sliding friction tests. The WEL microstructure was characterized using scanning electron microscopy, nano-indentation, focused ion beam, and transmission electron microscopy. According optical images, the WEL zone could be divided into white and yellowish zones; cracks existed at the boundary separating these two zones. The deformation degree of the cementite structure caused color differences in optical images and inhomogeneous chemical composition distributions in the same WEL zone. For cracks initiated and propagated at the WEL colony boundary, crack holes remained unconnected along the plastic deformation line. • Crack initiation and propagation in white etching layer (WEL) are investigated. • Under rolling–sliding friction, WEL of cementite appears on pearlitic steel. • WEL contains two "phases" of dissolved versus nanoscale cementite. • Cementite form determines color of WEL under optical microscopy. [ABSTRACT FROM AUTHOR]

Low energy laser shock peening (LE-LSP) with different energies was carried out at zirconium (Zr) alloy. Characterization and electrochemical corrosion behavior of Zr alloy after LE-LSP treatment were investigated. Results show that the surface profile of Zr alloy after LE-LSP treatment is rough due to the regular undulations on the surfaces. The hardness of Zr alloy increases after LE-LSP treatment because the grain size of Zr alloy is refined, and the plastic deformation generated on the surface induces the working hardening. A melting layer, plastic deformation layer, and transition layer are formed on Zr alloy after LE-LSP treatment. The dislocation entanglement is observed at the plastic deformation layer, which indicates that the dislocation slip is the main deformation mechanism of Zr alloy. The electrochemical corrosion resistance of Zr alloy after LE-LSP treatment is improved because of an increase in the grain boundary, which improves the activity of Zr alloy and is beneficial for forming passive films. • A melting layer, plastic deformation layer, and transition layer were formed on Zr alloy after LE-LSP treatment. • The dislocation slip is the main deformation mechanism of Zr alloy during LE-LSP process. • The increase in the grain boundary of Zr alloy after LE-LSP treatment is beneficial for forming passive films. [ABSTRACT FROM AUTHOR]

Abstract CoMoCrSi superalloy coatings were prepared on Mar-M247 Ni-based superalloy by high velocity oxygen fuel (HVOF) under various spraying parameters. Dense coatings with porosity < 0.8% were prepared, and the fretting wear properties of the coatings was investigated. The coatings showed good adaptability to the spraying parameters. As the temperature increased from R.T. to 400 °C, the friction coefficient of the coating decreased from 0.8 to 0.6, and the wear morphology gradually changed from pits to bulges. A large amount of material transfer occurred, and the main wear mechanisms at R.T. were abrasive wear and delamination; adhesive wear appeared slowly at elevated temperatures. The coating exhibited better wear resistance than the substrate during the experiments. Highlights • How the spraying parameters effect the fretting wear behavior of high velocity oxygen fuel (HVOF) coating was concerned. • The effect of temperature on the friction and wear properties of coatings has been studied. The friction coefficient decreases with increasing temperature, but the materials loss had the similar rule • The wear mechanism was abrasive wear and delamination in RT, and adhesive wear appeared slowly at elevated temperature. [ABSTRACT FROM AUTHOR]

• The effects of fretting parameter, environmental conditions, irradiation, fretting wear mode, and spacer grid on GTRF are reviewed, and the key influence factor of wear rate is discussed. • The accident tolerant fuel coating and its tribological behavior are investigated. • The highlighted points and research directions of GTRF are prospected. Fuel rods are the most important safety barrier in pressurized water reactors (PWR) and operates at high temperature, high pressure, high speed, and strong irradiation water condition. The grid-to-rod fretting (GTRF) induced by flow-induced vibration (FIV) is the main factor that causes failures in fuel rods. The effects of fretting parameter, environmental conditions, irradiation, fretting wear mode, and spacer grid on the GTRF are systematically reviewed, and the key influencing factor on GTRF is analyzed. The accident tolerant fuel (ATF) coating and its tribological behavior are investigated. Finally, key research guidance and popular topics consideration GTRF are proposed. [ABSTRACT FROM AUTHOR]

Cladding fuel rods supported in grids are important core components in pressurized water nuclear reactors. Small rod-to-grid misalignments can occur during the core manufacturing process. The presence of tilted contacts may promote fretting wear damage between claddings and grids by flow-induced vibrations (FIV). In this study, the influence of tilted contacts on the fretting wear between fuel rod cladding and a Zr-4 alloy grid, caused by deviations during assembly, was analyzed and discussed. A 3D finite element model was set up to obtain the stress state on the contact interface between the cladding and grid under different included angles. Results show that the wear morphology and profile presented evident dependence on the included angle. The change of the included angle between the cladding and grid changes the contact form of the two, leading to changes in the local stress and contact area in the interface. This process ultimately changes the thickness of the wear debris accumulation layer (WDL). [ABSTRACT FROM AUTHOR]

The impact wear test of 2.25Cr–1Mo steel against Gr5C12 alloy was performed at a controlled kinetic energy impact wear rig. The effect of temperatures (from 25 °C to 450 °C) on the impact wear damage mechanism was investigated. The contact force, energy absorption, and interface deformation during the impact process were recorded and analyzed in real time. Wear volume, morphology, and elemental distribution of the wear scars were used to characterize wear and tribo-chemistry behavior. Results demonstrate that at varied temperatures, the interface behavior of 2.25Cr–1Mo steel is different. With the rise in temperature, both the contact force, absorption energy, and wear volume first increase and then decrease. The explanation is that higher temperatures can modify the material's surface properties. Delamination, plastic deformation, and oxidative wear are the major mechanisms of impact wear, but the proportions of the three wear mechanisms differ at varied temperature. • The impact wear behavior of 2.25Cr–1Mo steel at elevated temperature was investigated. • The interface behavior of impact wear was analyzed. • The impact wear mechanism of 2.25Cr–1Mo steel at elevated temperature was discussed. [ABSTRACT FROM AUTHOR]