Wear Analysis of a Low-Speed Diesel Engine Connecting Rod Based on Orthogonal Simulation Test

As con-rod is a critical component in an engine, its reliability overwhelmingly directly affects the performance of the whole diesel engine. The fretting wear of con-rod bushing mainly occurs on the contact surface with con-rod small end and con-rod small end cap. In the proposed study, the contact process of con-rod small end, con-rod small end cap and bushing under maximum combustion pressure condition was analyzed, and the distribution of contact pressure and friction stress was analyzed. Then the orthogonal simulation test was designed. According to the contact mechanics theory, the interference amount and friction coefficient of the contact surface were taken as the test factors, and the maximum contact pressure and friction stress under the maximum combustion pressure condition were taken as the objective functions. The influence of the test factors on the objective function was analyzed, and the most reasonable interference amount and friction coefficient were found, so as to slow down the fretting wear of the con-rod bushing.

Finite Element Investigation of Moment Effect on Fretting Fatigue

Fretting fatigue is a degrading process which is responsible for considerable amount of mechanical structure failure every year. In the present study, a finite element model is proposed to show the effect of a bending moment on a flat surface under fretting loading. The results show that the bending moment has a major effect on the friction stress distribution on the surface of the two solids under contact. Finite element analysis predicts an increased damage effect on the surface of solids when a load is applied as a pure moment. The results predict elevation in the relative slip between the surfaces after applying the bending moment.

Mechanical and Tribological Properties of Nitrile Rubber Reinforced by SiO2: Molecular Dynamics Simulation Mechanical and Tribological Properties of Nitrile Rubber Reinforced by SiO2: Molecular Dynamics Simulation

This paper investigated the mechanism of enhancing the mechanical and tribological properties of nitrile rubber (NBR) with SiO 2 on the molecular scale. Molecular dynamics (MD) simulations were performed on molecular structure models of pure NBR, NBR/SiO 2 and three-layer friction pairs. The results showed that the hydrogen bonds and interfacial interaction between SiO 2 and NBR molecular chains decreased the fractional free volume of NBR nanocomposites, and increased the shear modulus of NBR by 25% compared with that of pure NBR. During the friction process, SiO 2 decreased the radius of gyration of NBR molecular chains and effectively lowered the peak atomic velocity, the peak temperature and the peak friction stress at the interface between NBR and copper atoms. The average friction stress on NBR/SiO 2 was 34% lower than that on NBR, which meant the tribological properties of NBR were significantly improved by SiO 2 . The mechanism of SiO 2 reinforcing NBR on a molecular scale can lay a theoretical foundation for the design of water-lubricated rubber bearings.

Mechanical Performance and Microstructural Evolution of (NiCo)75Cr17Fe8Cx (x = 0~0.83) Medium Entropy Alloys at Room and Cryogenic Temperatures

We investigated the effects of the addition of Co and carbon on the deformation behavior of new medium-entropy alloys (MEAs) designed by increasing the entropy of the conventional NiCrFe-type Alloy 600. The strength/ductility combination of carbon-free (NiCo)75Cr17Fe8 MEA was found to be 729 MPa/81% at 298 K and it increased to a remarkable 1212 MPa/106% at 77 K. The excellent strength and ductility of (NiCo)75Cr17Fe8 at cryogenic temperature is attributed to the increased strain hardening rate caused by the interaction between dislocation slip and deformation twins. Strength/ductility combinations of carbon-doped (NiCo)75Cr17Fe8C0.34 and (NiCo)75Cr17Fe8C0.83 at cryogenic temperature were observed to be 1321 MPa/96% and 1398 MPa/66%, respectively, both of which are superior to those of other high-entropy alloys (HEAs). Strength/ductility combinations of (NiCo)75Cr17Fe8C0.34 and (NiCo)75Cr17Fe8C0.83 at room temperature were found to be 831 MPa/72% and 942 MPa/55%, respectively and both are far superior to 676 MPa/41% of the commercial Alloy 600. Yield strengths of carbon-free and carbon-doped alloys comprised strengthening components from the friction stress, grain size strengthening, carbide strengthening and interstitial strengthening and excellent agreement between the predictions and the experiments was obtained. A design strategy to develop new MEAs by increasing the entropy of the conventional alloys was found to be effective in enhancing the mechanical performance.

Mechanics of oscillations and waves in the ice of the Аrctic ocean during compression and ridging

One of the main scientific and practical problems in the Arctic is the study of the dynamic state of the sea ice cover. The main parameters in the general model of drifting ice are the drift velocity vector, friction stress at the air-ice and ice-water interfaces, and the forces of dynamic interaction of ice fields. Establishing the connection between the large-scale processes in the atmosphere-ice-ocean system is necessary for developing methods of forecasting ice compression and ridging and the formation of local and extended fractures and leads, which help improve the existing climate models. The main aim is to obtain results of full-scale instrumental measurements of parameters of ice large-scale mechanics and dynamics, which provide a physical basis for explaining the nature of observed large-scale ice processes and allow one to perform physical parametrization. To accomplish this aim and evaluate the physicomechanical condition of the drifting ice cover of the Arctic Ocean, the “Transarktika-2019” expedition performed a real-time ice monitoring in April 2019. The investigation was conducted using seismometers and tiltmeters installed on the ice such that they formed a triangle with the sides measuring up to two kilometers. Data has been obtained on the wave and oscillation processes of crack formation, compression and ridging of ice. The possibilities of deciphering the initial data on the physics of wave and oscillatory processes in the icewater system considerably increase when using the known methods of processing seismic signals. With use of spectral Fourier analysis wavelet-transformation of oscillations significanlty extending possibilities of the seismic method at revelation of prognostic signs of crack formation and compression was applied. It is shown that the dynamics of ice processes can be connected with oceanic swell and tidal events. A possibility is created for obtaining new results in the investigation of large-scale mechanics of sea ice.

Finite Element Analysis on Ultrasonic Drawing Process of Fine Titanium Wire

Ultrasonic drawing is a new technology to reduce the cross-section of a metallic tube, wire or rod by pulling through vibrating dies. The addition of ultrasound is beneficial for reducing the drawing force and enhancing the surface finish of the drawn wire, but the underlying mechanism has not been fully understood. In this paper, an axisymmetric finite element model of the single-pass ultrasonic drawing was established in commercial FEM software based on actual wire length. The multi-linear kinematic hardening (MKINH) model was used to define the elastic and plastic characteristics of titanium. Influences of ultrasonic vibration on the drawing process were investigated in terms of four factors: location of the die, ultrasonic amplitude, drawing velocity, and friction coefficient within the wire-die contact zone. Mises stresses, as well as contact and friction stress, in conventional and ultrasonic drawing conditions, were compared. The results show that larger ultrasonic amplitude and lower drawing velocity contribute to greater drawing force reduction, which agrees with former research. However, their effectiveness is further influenced by the location of the die. When ultrasonic amplitude and drawing speed remain unchanged, the drawing force is minimized when the die locates at the half-wavelength position, while maximized at the quarter-wavelength position.

Three-Dimensional Mathematical Model of the Liquid Film Downflow on a Vertical Surface

Film downflow from captured liquid without wave formation and its destruction is one of the most important aspects in the development of separation equipment. Consequently, it is necessary to create well-organized liquid draining in areas of captured liquid. Thus, the proposed 3D mathematical model of film downflow allows for the determination of the hydrodynamic parameters of the liquid film flow and the interfacial surface. As a result, it was discovered that the interfacial surface depends on the proposed dimensionless criterion, which includes internal friction stress, channel length, and fluid density. Additionally, equations for determining the averaged film thickness, the averaged velocity vectors over the film thickness, the longitudinal and vertical velocity components, and the initial angle of streamline deviation from the vertical axis were analytically obtained.