Functionally graded coatings are increasingly employed to alleviate interfacial stress concentrations and enhance surface durability. However, the elastic shakedown behavior of graded coating-substrate systems under lubricated conditions remains insufficiently understood, particularly when constrained by limited interfacial strength. To address this gap, a three-dimensional numerical model is developed for graded coatings in lubricated line contacts. The framework integrates a mixed-lubrication solver with a semi-analytical model based on the discrete convolution-fast Fourier transform algorithm and influence coefficients summation. The elastic shakedown limit is determined via Melan's static theorem coupled with a bisection iteration scheme. Numerical results indicate that increasing the coating stiffness and optimizing the gradient index effectively enhance the shakedown limit, whereas the improvement is strongly thickness-dependent. Conversely, weak interfacial adhesion significantly reduces the load-bearing capacity, acting as a primary failure trigger. Furthermore, higher entrainment speeds are found to decrease the shakedown limit and shift the critical failure location toward the surface. These findings offer theoretical guidance for the design of graded coatings in heavy-duty lubricated systems.

Surface coatings enhance tribological performance and extend service life. However, differences between coating and substrate properties make it challenging to design coatings that meet contact pair requirements. The study investigates the three-dimensional line contact problem of two cylindrical solids with an elastic coating using a semi-analytical method (SAM) and the conjugate gradient method (CGM). The pressure-displacement and pressure-stress influence coefficients (ICs) are obtained through a Frequency response functions (FRFs) using an FFT-based conversion method. Additionally, considering the axial direction is much longer than the contact width, the ICs summation method is introduced in the model to account for the effect of neighboring region pressures on the stress and displacement distributions within the computational domain. The validity and accuracy of the model are verified by comparing its solution with the analytical solution of Hertzian contact. The research further explores the effect of coating stiffness, coating thickness, and surface friction coefficient on the stress field distribution. The results provide theoretical support for optimizing coating designs and improving surface tribological performance, which could be applied in various engineering applications, such as gears and bearings.

Spline coupling widely used in aerospace drive devices suffers early tooth damage failure, resulting in power instability and shortened life cycle, etc. This problem is particularly significant in heavy-duty and high-power aero-engine and helicopter transmission with combined high and low cycle fatigue (CCF) conditions. To investigate the tooth damage behavior, this work presents a numerical method of tooth damage coupled wear and fatigue considering elastic-plasticity mechanics for spline coupling. Specifically, the modified tooth wear model based on energy model and the CCF damage criterion by combining HCF and LCF damage are established within the unified continuous damage mechanics (CDM) framework. The results show that the LCF damage considering plastic behavior is severely weakened by tooth wear, while the HCF damage considering elastic behavior is further developed by tooth wear. Tooth wear is regarded as the main failure mode of spline coupling under CCF load condition, instead of fatigue damage failure. The evolution of tooth wear is regulated by contact pressure, shear stress and tooth sliding parameters, and the tooth wear depth increases variously and unsteadily in different load cycles. These findings provide theoretical guidance for life prediction of spline coupling.

Investigating the flow-field characteristics of gears under various lubrication conditions, a fluid-solid multi-body dynamic model considering the coupling effect between lubricant and gear was established. Traditional models mainly consider lubrication effects by introducing a constant friction coefficient, making it difficult to accurately reflect the gear’s actual operating conditions under mixed lubrication. Therefore, to address the complexity of aircraft engine accessory gear conditions and insufficient studies on lubrication simulation, this study obtained oil pressures in the meshing region through flow-field simulations and integrated these data into a multi-body dynamic model, accounting for lubricant-induced impacts and loads during meshing, to examine the effects of lubrication conditions on dynamic responses. The results indicate that lubrication intensifies meshing force fluctuations, oil pressure increases with rotational speed, and vibration acceleration amplitudes become more pronounced under harsher operational conditions. Specifically, spray lubrication produces greater impacts on gears, whereas oil-churning lubrication is more significantly influenced by operational conditions.

A three-dimensional elastoplastic contact model is developed for a functionally graded coating/substrate system containing an interfacial bump defect. The graded coating/substrate system is represented by an equivalent homogeneous half-space with discretized inhomogeneities. The material mismatch caused by the graded property distribution is treated by the numerical equivalent inclusion method, and the plastic strain is updated by a return mapping algorithm. Surface tractions are solved iteratively by the conjugate gradient method, while the discrete convolution and fast Fourier transform method with summation of influence coefficients is used to account for pressure coupling from adjacent regions in three-dimensional line contact and to accelerate the computation. The model allows arbitrary spatial distributions of elastoplastic parameters within the computational domain through direct assignment on the computational grid. Based on this framework, the effects of bump geometry, defect position, friction, coating thickness, and the gradients of elastic modulus and yield strength on the elastoplastic contact response are investigated.

This review summarized the latest research progress on HEICs and HECs, with a focus on phase structure prediction criteria and strengthening/toughening strategies, in order to accelerate their engineering applications.

Abstract As a key process in the manufacturing of integrated circuit chips, the quality and effectiveness of wafer cutting directly affect the performance of the chip. Magnetorheological machining is a flexible machining technique that changes the rheological properties of polishing fluid through internal gradient electromagnetic fields, thereby achieving material removal and surface error correction. This article focuses on magnetorheological machining technology and conducts simulation and experimental research on wafers. By simulating the mechanical properties of the wafer surface under different polishing disc speeds, excitation gaps and particle sizes, the simulation obtained the optimal processing parameters through experiments and data analysis, and finally obtained a smooth wafer surface with a surface roughness of Ra 0.042 µm.

To improve the wear resistance of carburized 18CrNi4A steel used in aerospace transmission components with high-impact and heavy-duty conditions, DLC, TiAlN, and DLC/TiAlN coatings were deposited on carburized 18CrNi4A steel surfaces by magnetron sputtering. The surface and cross-sectional morphologies, chemical compositions, and mechanical properties of these coatings were characterized by SEM, XRD, nanoindentation, and micro-scratch tests. The tribological properties of carburized 18CrNi4A steel and these coatings with heavy-duty conditions of dry sliding, lubricant, and grease were investigated. In addition, TiAlN coatings were deposited on spline coupling teeth, and the anti-wear performance was investigated using a self-made spline coupling test rig. The results show that these coatings have lower coefficient of friction (CoF) and wear rate than carburized 18CrNi4A steel. DLC/TiAlN coating exhibits the lowest coefficient of friction and wear rate in aerospace synthetic lubricants (Mobil Jet Oil II) and molybdenum disulfide lithium grease (RIPP 7254), providing the best tribological properties. The wear mechanism of heavy-duty conditions with dry sliding, lubricant and grease were discussed. In addition, the TiAlN-coated spline coupling exhibited better wear resistance than the general spline coupling.

Premature wear, fatigue and other failures caused by non-linear vibration are one of the key problems of aerodynamic power transmission in spline coupling which maybe suffer from abnormal meshing effects due to misalignment between internal spline and external spline. A non-linear dynamic model of the misaligned spline coupling is established, which involves the calculation of dynamic meshing behavior of misaligned tooth pairs. The movement state of spline coupling can change from a periodic state to a chaotic state with the increase of speed. Under light load, the main resonance speed of system may be modified due to changes in the load. The existence of misalignment promotes the vibration intensity, advances the main resonance speed and increases the instability of spline coupling. In addition, a test bench for the misalignment spline coupling was developed to measure the vibration acceleration signal, and the effect of the misalignment on the dynamic behavior of spline coupling was discussed.

To improve the fretting wear performance of 18CrNi4A steel, DLC, TiAlN and DLC/TiAlN coatings were deposited on the surface of carburized 18CrNi4A steel, respectively. The microstructure morphologies, chemical compositions, and mechanical properties of these coatings were evaluated. The fretting tribological properties of pad/flat contact pairs for carburized 18CrNi4A steel, DLC, TiAlN and DLC/TiAlN coatings were investigated in different lubricant environments including dry sliding and #RIPP 7254 aviation grease. The results show that DLC, TiAlN and DLC/TiAlN coatings deposited on the carburized 18CrNi4A steel surface can improve surface roughness, hardness, fracture toughness and resistance to plastic deformation. DLC, TiAlN and DLC/TiAlN coatings deposited on the surface of carburized 18CrNi4A steel can make the surface of the substrate have excellent fretting wear properties. DLC and DLC/TiAlN coatings have lower coefficient of friction and better fretting wear resistance than TiAlN coatings in dry sliding condition, and DLC/TiAlN coatings have the lowest wear rate in #RIPP 7254 grease lubrication condition. In addition, the wear mechanisms of carburized 18CrNi4A steel, DLC, TiAlN and DLC/TiAlN coatings in dry sliding and #RIPP 7254 aviation grease conditions were analyzed.

In this paper, a multilayer body model in which material properties and wear coefficient change with node coordinates is proposed, so that the wear profile is not restricted by the singularity of the interface of the coated contact pairs. The conversion rate of the adhered particles was obtained to describe the growth and expansion of the debris at the fretting interface based on experiments, and the wear model of coated contact pair considering the dynamic evolution of the debris layer was established. By comparing the previous experimental and computational results, the wear calculation method proposed in this paper is more reasonable to predict the wear profile of the coated contact pair. In addition, the influence of the debris layer on the wear depth, friction width, and contact pressure in the fretting process is analyzed, indicating that the existence of the debris layer can delay the wear process. Finally, the fretting wear life of the SCMV steel contact pair deposited with the W-DLC coating is estimated.

In this paper, the ballistic damage mechanism and residual bearing capacity of ceramic/backing plate armor were investigated. First, a series of lightweight armors were prepared, consisting of ceramic and ultra-high molecular weight polyethylene fiber-reinforced resin matrix composite (UHMWPE) plates, and were wrapped in a high-strength fabric. Then, the ceramic/UHMWPE armors were hit by one or two bullets, and finally subjected to compression testing. The results showed that the main failure mode of integral ceramic/UHMWPE armors was ceramic brittle fracture. Many zigzag patterns on the compression curve indicated that the specimens had undergone the stages of crack propagation, ceramic fragment reorganization, plastic deformation of UHMWPE backing plate, interlaminar tearing, and overall fracture. The failure of spliced ceramic/UHMWPE armors was mainly due to the dislocation between ceramic sheets; the smooth compression curves indicated that there was no recombination of ceramic fragments and obvious interlayer debonding during the compression. Under the maximum load, each ceramic/UHMWPE armor with ballistic damage did not suddenly break and fail. The structure and thickness of ceramic plates all had an impact on residual strength: under the same structure, the greater the thickness, the greater the residual strength, but the relationship between them was not linear; under the same thickness, the residual strength of the spliced ceramic/UHMWPE armor was higher. The residual strength was also related to the number of shots: after two bullets hit, its value was only one-third of that after one bullet hit.

In this paper, a finite element model of the floating spline pair is first established, and the distribution of the contact pressure on the tooth surface of the spline with the axis and angular misalignment is analyzed. Then, the effects of axial misalignment and angular eccentricity on tooth fretting damage were evaluated, based on Ruiz fretting damage parameters. Finally, a floating spline wear fatigue damage model considering the wear effect is established based on the energy dissipation and critical plane SWT model, and the fretting fatigue cumulative damage distribution and life of the tooth surface under axial and angular misalignment are analyzed and evaluated. The results show that the misalignment of the axis makes the contact pressure distribution of each tooth uneven, and the RFFDP value of the most dangerous tooth is parabolic along the x direction, that is, serious fretting damage may occur at both ends of the tooth surface, and the crack initiation position on the tooth occurs near x/L=0. The angular misalignment makes the tooth contact only at one end edge, and the RFFDP value of the most dangerous tooth increases along the x direction, showing an exponential growth trend, reaching the maximum at x/L=1, and the crack initiation position occurs at near x/L=1. With the increase of axis or angular misalignment, the damage phenomenon of the floating spline tooth surface becomes more obvious, and the wear-fatigue life decreases sharply.

为探究不同磨损影响因素对浮动花键磨损的影响程度,基于能量耗散理论,建立了花键副微动磨损预测模型,分析了扭矩、载荷波动、花键材料、摩擦因数、轴向不对中以及角向偏心对浮动花键的磨损影响规律;同时建立熵权-模糊关联分析模型,客观分析了不同磨损影响因素对花键磨损的关联程度.结果显示:基于能量耗散的微动磨损模型所计算的花键齿顶、齿中以及齿根位置处最大磨损深度的计算误差分别低于6.9％、2.4％和14％.轴向不对中下部分花键磨损位置从齿根往齿中位置偏移;角向偏心使得花键两端接触不良,导致两端磨损分布不均.同时发现角向偏心、轴向不对中以及材料对花键副的磨损影响程度较大,为浮动渐开线花键抗磨损方法研究提供技术支撑.

Based on the bulletproof mechanism of ceramic composite armor, structural design and numerical simulation optimization of SiC/UHMWPE fiber composite armor were carried out to satisfy the protection requirements of vehicle. Penetration depth of bullet was taken as the evaluation standard, and the thickness, shape, size, and layout of SiC wood ceramic bullet proof sheet were considered as the research factors. An orthogonal simulation optimization scheme of four factors and three levels were designed, when the surface density of ceramic composite armor was 38 kg/m(2). Bulletproof performance was simulated by ANSYS/LS-DYNA finite element software. The optimized size parameters owing to the minimal penetration depth of bullet were selected. Accordingly, a SiC wood ceramic composite armor was prepared, and the bulletproof performance of designed ceramic composite armor was up to the protection standard of NATO AEP-55 STANAG 4569 level II as determined by the real bullet shooting test. Results show that the designed structure has 8 mm-thick SiC wood ceramic bulletproof panel and 13.7 mm-thick UHMWPE fiber bulletproof panel. The bulletproof panel is made of 4900 mm(2) hexagonal SiC wood ceramic bulletproof sheets. The influencing factors of SiC wood ceramic bulletproof sheet on the bulletproof performance is as follows: arrangement position>thickness>size>shape.

The teeth of misaligned spline couplings used in power transmission parts of helicopter and aeroengine often suffer serious abnormal wear faults during service. Through the self-made spline coupling test rig, the mechanism of misalignment on the spline coupling wear was explored. The tooth contact domain of the spline coupling with shaft misalignment is close to the addendum, and the tooth contact domain of the spline coupling with angle misalignment is mainly concentrated on the side of the tooth end. The edge contact effect becomes more serious as the amount of misalignment increases, resulting in abnormal wear at specific positions on the tooth surface. The presence of misalignment increases the vibration intensity of the spline coupling based vibration signal monitoring, which will increase the wear of the teeth. In addition, the difference in system vibration response of different misalignment types can be used to identify the misalignment failure mode of the spline coupling. It can be inferred from the characterization of wear debris that fretting wear is the cause of the failure of the misaligned spline coupling. Tooth modification, surface strengthening modification and lubrication design are necessary as potential solutions to improve the wear resistance of misaligned spline couplings.

In order to analyze the evolution of normal contact stiffness under loading and unloading, an accurate elastic-plastic contact finite element model between rigid plane and fractal surface is established by introducing the equivalent metal matrix deformation in terms of the modified Weierstrass-Mandelbrot function. The effects of the fractal dimension, scale parameter, material properties on the normal contact stiffness were discussed. A method for evaluating the normal contact stiffness was proposed to analyze the evolution of the normal contact stiffness. Numerical simulation shows that there is a positive power function relationship between the normal contact stiffness and the load of fractal surface. Under the same load, at the fractal dimensions ( D ) of 2.4-2.7 and scale parameters ( G ) of 1.36×10 -13 -1.36×10 -10 m, the loading normal contact stiffness increases with the increasing of fractal dimension and tangent modulus, but decreases with the increasing of scale parameter. The unloading normal contact stiffness increases with the material strengthening, and the variation amplitude is positively correlated with the fractal dimension, and negatively correlated with the scale parameters and tangent modulus.