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As a fundamental component of aviation equipment, the gear has an essential effect on the service performance of the whole machine. Fine particle peening (FPP) technology is a good choice for the precision requirements of aviation gears. Therefore, a FPP model of aviation gears was constructed based on the discrete element‐finite element coupling method (DEM‐FEM) to simulate the evolution of surface roughness and residual compressive stress, and its results were verified by experiments. The effects of FPP intensity, coverage rate, and particle diameter on surface integrity were investigated. In addition, the importance degree of the intensity, coverage rate, and particle diameter of FPP on surface integrity was carried out by the random forest decision method. It demonstrates that the surface roughness Sa was mainly influenced by the FPP intensity and particle diameter. And the distribution state of the residual compressive stress was mainly affected by the particle diameter. Highlights: 1. The simulation model of FPP strengthening aviation gear based on DEM‐FEM was established. 2. The coefficient of restitution was taken into account in the damping force. 3. The importance degree of surface integrity was carried out by random forest method [ABSTRACT FROM AUTHOR]

Fine particle peening (FPP) technology offers an effective method to achieve outstanding surface integrity and fatigue performance in aviation gears. However, the lack of sufficient research on the correlation between process parameters, surface integrity parameters, and fatigue life undermines the full potential of FPP in strengthening aviation gears. Therefore, we have developed an elastic–plastic contact fatigue life model to predict the fatigue life of AISI 9310 gear steel after different strengthening processes. This model can consider surface integrity parameters such as surface micro‐topography, residual stress gradient, and hardness gradient. To validate the model, we conducted rolling contact fatigue tests and compared the results with the predictions from our model. The influence of process parameters on the rolling contact fatigue of AISI 9310 gear steel was further investigated. A process window for FPP was established, and an optimization method was proposed in order to provide guidance for selecting process parameters for FPP on high‐performance aviation gears. HIGHLIGHTS: 1. The rolling contact fatigue life of aviation gear after strengthening is predicted. 2. The simulation results are in good agreement with the rolling contact fatigue tests. 3. A process window for aviation gear steel after FPP is established. [ABSTRACT FROM AUTHOR]

• Peening with fine iron sulfide particles (FeS-peening) was introduced. • FeS-peening formed a layer of FeS particles without the use of aqueous Na 2 S 2 O 3. • FeS-peening increased the fatigue limit of steels by 125 MPa. • Improvement of fatigue limit (24 MPa) by residual stress was quantitatively investigated. • The fatigue limit of FeS-peened steels was 95 MPa higher than conventional processed one. Low alloy steels were subjected to peening with fine iron sulfide particles (FeS-peening) under ambient conditions to transfer a layer of such particles, which can improve seizure resistance and sliding properties, and thus enhance the fatigue characteristics of the steel. This process was performed without the use of aqueous Na 2 S 2 O 3 and the specimens were assessed using electron probe microanalysis and rotating bending fatigue tests. Treated specimens exhibited higher fatigue limits as a result of high degree of compressive residual stress generated on the steel surface. The effects of residual stress on the fatigue limit were quantitatively investigated using a modified Goodman diagram. Sample cross-sections were observed using electron backscattered diffraction, which confirmed that FeS-peening formed fine surface grains. Grain refinement was determined to be at least partly responsible for the improved fatigue properties of the steel following FeS-peening. [ABSTRACT FROM AUTHOR]

Fine particle peening (FPP) using hydroxyapatite (HAp) shot particles was performed to improve the fatigue strength and form a HAp transfer layer on a beta titanium alloy (Ti–22V–4Al). The surface microstructures of the FPP-treated specimen were characterized using scanning electron microscopy, micro-Vickers hardness testing, energy dispersive X-ray spectrometry, X-ray diffraction, and electron backscattered diffraction. A HAp transfer layer with a thickness of 5.5 μm was formed on the surface of the Ti–22V–4Al specimen by FPP. In addition, the surface hardness of the Ti–22V–4Al was increased, and high compressive residual stress was generated on the specimen surface by FPP. Rotating bending fatigue tests were performed at room temperature in laboratory air over a wide cycle-life region (103–109 cycles). In the long cycle-life regime, the fatigue strength at 107 cycles of the FPP-treated specimen became higher than that of the untreated specimen. This result is attributed to the formation of a work-hardened layer with high compressive residual stress by FPP. However, the fatigue strength was not improved by FPP in the short cycle-life regime, because fatigue cracks were initiated at surface defects formed during the FPP process. The fatigue fracture mode of the FPP-treated specimens shifted from surface-initiated fracture to subsurface-initiated fracture at a stress amplitude level of 600 MPa. [ABSTRACT FROM AUTHOR]

The effects of fine particle peening on the fatigue properties of a transformation-induced plasticity-aided martensitic steel with a chemical composition of 0.2% C, 1.5% Si, 1.5% Mn, 1.0% Cr, and 0.05% Nb (mass%) were investigated for applications in precision gears. When this steel was subjected to fine particle peening after heat treatment, higher fatigue limits and lower notch sensitivity were achieved compared with those of SNCM420 martensitic steel. The increased fatigue limits are principally associated with higher hardness and compressive residual stress on and just below the surface, as well as low surface roughness. Fine particle peening also increased the threshold stress intensity factor range in stage I, and decreased the crack propagation rate in stage II in this steel. The crack propagation behavior was mainly suppressed by (1) high hardness and high compressive residual stress, and (2) the strain-induced martensite transformation of retained austenite and high internal stress resulting from a difference in flow stress between the soft martensite matrix and the finely dispersed hard MA-like phase that developed during fatigue deformation. [ABSTRACT FROM AUTHOR]

High-performance precision gear drives such as harmonic gear have high requirements on tooth profile accuracy, surface quality, fatigue life and other service performance characteristics, which urgently needs an effective surface strengthening method. This work aims to examine the feasibility and effectiveness of fine particle peening (FPP) treatment on surface integrity of flexspline in harmonic drive precision transmission. To this end, FPP process experiments were carried out, and this process was simulated based on a coupling method of discrete element method and finite element method (DEM-FEM) considering the kinematic hardening behavior of the material. The simulation results were in good agreement with the test results. Effects of shot peening pressure, injection velocity, material properties and tooth profile on surface roughness and induced residual stress of the target flexspline were analyzed. The results reveal that after FPP, the amplitude of residual compressive stress of the flexspline can reach 470 MPa, and the surface roughness Sa becomes approximately 0.5 μm. For precision gears with low hardness such as flexspline in harmonic drive, it is suggested to adopt FPP with low air pressure to achieve both saturated residual compressive stress and lower surface roughness, thus benefitting enhanced fatigue life. • Considering the complex tooth geometry, the elastic-plastic model of FPP treating flexspline based on DEM-FEM is established. • The simulation results are in good agreement with the FPP experiments. • The FPP parameters for strengthening precision parts with low hardness such as flexspline are suggested. [ABSTRACT FROM AUTHOR]

• Fine particle peening was used to improve fatigue properties of high strength bolts under transverse loading. • Surface roughness, compressive residual stress and micro-hardness was measured. • A finite element analysis combined with equivalent stress method was performed. In order to avoid the fatigue failure of high strength bolt under cyclic transverse loading, fine particle peening (FPP) treatment was conducted to the bolt using steel beads. The surface roughness, residual stress and surface hardness of the treated bolts were examined. Fatigue tests were performed for bolts with or without FPP treatment under transverse loading. The test results show that FPP treatment effectively improves the fatigue resistance of high strength bolt through reducing the surface roughness, increasing the surface hardness and introducing high compressive residual stress in the surface layer. For the FPP treated bolts, failure location changes from the bolt head fillet to thread root as loading displacement decreases to 0.3 mm. A finite element analysis was performed to analyze the failure behavior before and after FPP treatment. [ABSTRACT FROM AUTHOR]