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Abstract In pressurized water reactor (PWR), fretting wear is one of the main causes of fuel assembly failure. Moreover, the operation condition of cladding is complex and harsh. A unique fretting damage test equipment was developed and tested to simulate the fretting damage evolution process of cladding in the PWR environment. It can simulate the fretting wear experiment of PWR under different temperatures (maximum temperature is 350 ℃), displacement amplitude, vibration frequency, and normal force. The fretting wear behavior of Zr-4 alloy under different temperature environments was tested. In addition, the evolution of wear scar morphology, profile, and wear volume was studied using an optical microscope (OM), scanning electron microscopy (SEM), and a 3D white light interferometer. Results show that higher water temperature evidently decreased the cladding wear volume, the wear mechanism of Zr-4 cladding changed from abrasive wear to adhesive wear and the formation of an oxide layer on the wear scar reduced the wear volume and maximum wear depth.

Abstract The current research of nuclear control rod drive mechanism (CRDM) movable latch only makes a simple measurement of wear mass. The wear volume and difference in various claw surfaces are ignored and the degradation mechanism of each claw surface is not clear. In this paper, a detailed degradation analysis was carried out on each claw surface of movable latch combined with wear result and worn morphology. Results indicate that the boundary of carbide is preferred for corrosion because carbide presents a nobler Volta potential compared to the metal matrix or boundary region. Due to the oscillation of drive shaft between the claw surfaces of movable latch, the dominant wear mechanism on the upper surface of claw (USC) and lower surface of claw (LSC) is plastic deformation caused by impact wear. Mechanical impact wear will cause the fragmentation of carbides because of the high hardness and low ductility of carbides. Corrosion promotes the broken carbides to fall off from the metal matrix. The generated fine carbides (abrasive particles) cause extra abrasive wear on USC when the movable brings the drive shaft upward or downward. As a result, USC has a higher wear volume than LSC. This research proposes a method to evaluate the wear on the whole movable latches using a 3D full-size scanner.

In this paper, we explore the optimal combination of femtosecond laser drilling parameters for micro-hole processing on DD6 single-crystal high-temperature alloy and analyze the significance of parameter variations on the microstructure characteristics of the holes. The L25(56) orthogonal test was performed by controlling six parameters during femtosecond laser ring processing: average power; overlap rate; defocus rate; feed amount; gas pressure; and end position. The significance of the influence of the factors was analyzed by ANOVA, and the parameters were optimized by genetic algorithm. Scanning electron microscopy was performed on the micropores and the salient features of the pores were analyzed. Finally, we calculated the extreme differences and conducted single-factor effect analysis. We conclude that the defocus rate has the most significant level on the hole drilling by femtosecond laser ring processing for DD6 single crystal high-temperature alloy; and the effect of the end position is smaller than others. The optimized parameters are power 6.73 W; overlap 99%, defocus 0 mm; pressure 0.2 MPa; feed 0.02 mm, and end −0.4 mm.

In a pressurized water reactor nuclear power plant, metal foreign matter in the rod–rod gap of the fuel assembly is constantly rubbed and collided with the fuel rod under continuous scouring of the coolant, resulting in wear to the fuel rod and even leakage of the perforation. In this work, the effects of different debris shapes and materials on the impact wear behavior of Zr−4 alloy tubes were studied through the dynamic response and damage of Zr−4 alloy tubes under cyclic impact. The results show that the sharper the shape of the impact block, the higher the wear rate of the Zr−4 alloy tube. Although the energy absorption rate of SA 508−A during the impact process is high, most of the energy is used for the wear of the impact block itself and the formation and peeling of the wear debris accumulation layer, and the damage to the Zr−4 alloy tube is small. The wear debris generated by the Zr−4 impact block is not easy to oxidize, and the wear caused by the cyclic impact is more serious. After the Zr−4 impact block cyclically impacts the Zr−4 alloy tube 200 w times, the Zr−4 alloy tube will be perforated due to wear. The oxidation and accumulation of wear debris and the wear mechanism in the impact process are mainly abrasive wear and surface peeling behavior. The occurrence of cutting and wear removal will promote the wear and thinning of the tube wall of the Zr−4 alloy tube, and the tube wall is easily perforated after thinning.

The viscoelastic materials exhibit different tribological responses when compared to the stiff materials, due to the intermediate mechanical properties between viscous liquid and elastic solid. In this work, the effect of damping materials viscoelasticity on sliding friction under dry condition was investigated. However, it was difficult to change its damping properties only while other properties (strength or surface hardness) remain unchanged, since viscoelasticity was one of its intrinsic properties. Therefore, the attention of interactions between the material components was closely paid. To achieve this, the experimental groups of damping materials with various viscoelasticity were established by adding various fillers and adjusting their surface properties. Additionally, a viscoelastic property determined friction coefficient model was obtained and validated by the molecular dynamic method. The results show that the test model is in good agreement with the experimental results. Meanwhile, tribo-pairs with higher proportion of viscous character had greater oscillations in friction. They also exhibited higher friction coefficient due to the increased contribution of viscoelastic hysteresis losses to friction.

Abstract In many industrial devices, impact-sliding wear is caused by a variety of complex vibrations between the contacted interfaces. Under actual conditions, impact and sliding motions do not occur in only one direction, and different complex impact-sliding motions exist on the tribology surfaces. In this study, an impact-sliding wear test rig is developed to investigate the wear effect of different complex motions. Using this rig, multi-type impact-sliding wear effects are realized and measured, such as those derived from unidirectional, reciprocating, and multi-mode combination motions. These three types of impact–sliding wear running behavior are tested and the wear damage mechanism is discussed.

Abstract This paper investigates the self-loosening of threaded fasteners subjected to dynamic shear load. Three kinds of typical coatings, PTFE, MoS2, and TiN applied to bolts and nuts, are tested in this investigation. The study experimentally examines the loosening mechanisms of fasteners and assesses the anti-loosening performance of the three tested coatings based on their tightening characteristics, loosening curves, and the damage of thread surface. Additionally, the anti-loosening performance of the three coatings is compared under different load forms. The results indicate that the PTFE and MoS2 coatings have significant anti-loosening effect, whereas the anti-loosening performance of TiN coating is not satisfactory. It is also found that an appropriate increase of the initial tightening torque can significantly improve the anti-loosening effect. In addition, the microscopic analyses of PTFE and MoS2 coating reveal that a reduced initial tightening torque leads to fretting wear on the thread contact surfaces of fasteners, thereby aggravating the damage.

The success of carbon nanotubes (CNTs) as fillers in improving the physicochemical and mechanical properties of polymer is attributed to their unique structure and performance characteristics. The interfacial interaction between fillers and matrix is of significant influence in agglomeration of fillers and mechanical/damping properties of as-prepared composites. Here, polydopamine (PDA), (3-Aminopropyl) triethoxysilane (KH550) and ionic liquid (1-aminoethyl-3methylimidazolium bis ((trifluoromethyl) sulfonyl) imide)) were used to not only functionalize CNTs for suppressing their agglomeration, but also regulate the interfacial interaction between CNTs and carboxylated butadiene nitrile rubber (XNBR) for achieving excellent mechanical properties and better damping properties. The storage modulus of composites rose by 80% (from 1392 to 2488 MPa) with the addition amount of 2.2 wt% CNTs-KH550 and the tensile strength rose by 110% (from 0.32 to 0.68 MPa) with 3.0 wt% CNTs-IL. In addition, the damping degradation of composites caused by the agglomeration of fillers was resolved. The results of molecular dynamics (MD) simulation show that the strong interfacial interaction of CNTs-PDA and CNTs-KH550 is mainly attributed to hydrogen bond interaction, while the interaction of CNTs-IL is determined by hydrogen bond interaction and van der Waals' (vdW) force. The functionalized CNTs with excellent interfacial interaction and dispersion have bright application prospects in the field of composite. Keywords: Functionalized carbon nanotubes, Composite, Molecular dynamics simulation, Mechanical/damping properties

MoS2/C nanocomposite coatings were deposited on a 304 stainless steel plate by unbalanced magnetron sputtering from carbon and molybdenum disulfide targets, and the target current of MoS2 was varied to prepare for coating with different carbon contents. The mechanical and tribological properties of the MoS2/C nanocomposite coating with different carbon contents were studied using a low-velocity impact wear machine based on kinetic energy control, and the substrate was used as the comparison material. The atomic content ratio of Mo to S in the MoS2/C coating prepared by unbalanced magnetron sputtering was approximately 1.3. The dynamic response and damage analysis revealed that the coating exhibited good impact wear resistance. Under the same experimental conditions, the wear depth of the MoS2/C coating was lower than that of the substrate, and the coating exhibited a different dynamic response process as the carbon content increased.

This paper investigates the self-loosening of threaded fasteners subjected to dynamic shear load. Three kinds of typical coatings, PTFE, MoS2, and TiN applied to bolts and nuts, are tested in this investigation. The study experimentally examines the loosening mechanisms of fasteners and assesses the anti-loosening performance of the three tested coatings based on their tightening characteristics, loosening curves, and the damage of thread surface. Additionally, the anti-loosening performance of the three coatings is compared under different load forms. The results indicate that the PTFE and MoS2 coatings have significant anti-loosening effect, whereas the anti-loosening performance of TiN coating is not satisfactory. It is also found that an appropriate increase of the initial tightening torque can significantly improve the anti-loosening effect. In addition, the microscopic analyses of PTFE and MoS2 coating reveal that a reduced initial tightening torque leads to fretting wear on the thread contact surfaces of fasteners, thereby aggravating the damage. [ABSTRACT FROM AUTHOR]