Running-in Stage Research Articles

The Conditions Necessary for the Formation of Dissipative Structures in Tribo-Films on Friction Surfaces That Decrease the Wear Rate.

Tribo-films form on surfaces as a result of friction and wear. The wear rate is dependent on the frictional processes, which develop within these tribo-films. Physical-chemical processes with negative entropy production enhance reduction in the wear rate. Such processes intensively develop once self-organization with dissipative structure formation is initiated. This process leads to significant wear rate reduction. Self-organization can only occur after the system loses thermodynamic stability. This article investigates the behavior of entropy production that results in the loss of thermodynamic stability in order to establish the prevalence of friction modes required for self-organization. Tribo-films with dissipative structures form on the friction surface as a consequence of a self-organization process, resulting in an overall wear rate reduction. It has been demonstrated that a tribo-system begins to lose its thermodynamic stability once it reaches the point of maximum entropy production during the running-in stage.

Metastable hybridized structure transformation in amorphous carbon films during friction—A study combining experiments and MD simulation

Amorphous carbon films have attracted substantial interest due to their exceptional mechanical and tribological properties. Previous studies revealed that the amorphous carbon films exhibited lower coefficient of friction (COF) because of the transformation in bond structure from sp3-C to sp2-C during friction processes. However, the mechanism for such a transformation during friction is not well understood. This study is conducted to get an insight into the metastable transformation in amorphous carbon film during friction by means of experiments and molecular dynamics (MD) simulation. Relevant wear tests showed that wear of the film changed from an abrasive wear mode to a mixture of abrasion and adhesive wear, resulting in a decrease in growth rate of the wear rate after the running-in stage. It is worth noting that the sp3-C atoms were increased during the running-in stage when the films contained lower sp3/sp2 ratios. However, the formed sp3-C atoms could only be short-lived and gradually transformed to sp2-C atoms with the graphitization generated on the wearing surface of the films. The radial distribution function and translational order parameter indicated that the films’ high sp3/sp2 ratio led to an increased sp2-C proportion on the wear scar after friction, which caused an increased structural ordering.

Research on the Coupling and Coordinated Development of the Tourism Industry and Regional Economy in the Economic Circle of the Sichuan–Chongqing Region in Southwest China

The construction of the Sichuan–Chongqing double-city economic circle represents a critical measure for high-quality development in China. The coordinated development of industry and economy is conducive to high-quality regional economic growth and the construction of a high-standard market system. This study selects 19 data indexes of the tourism industry and regional economy in the Sichuan–Chongqing region from 2000 to 2020 and analyzes the coupling coordination degree of them through a coupling coordination model. Such being the case, the gray correlation analysis method is used to explore the key factors affecting the coupling difference. It is found that the comprehensive development index of the tourism industry system and regional economic system of the Sichuan–Chongqing region witnesses a steady growth, but the overall performance of the regional economic system lags behind that of the tourism industry system. From the perspective of coupling coordination degree, the coupling coordination between the tourism industry and regional economy in the Sichuan–Chongqing region is increasingly strengthened, with the whole system being in the stage of running-in and high-level coupling. It has achieved the leap from unbalanced development to well-coordinated development. From the perspective of gray correlation analysis, the per capita consumption level of residents and regional GDP are the key factors affecting the coupling and coordination differences of the Sichuan–Chongqing circle.

Effect of the Graphitization Mechanism on the Friction and Wear Behavior of DLC Films Based on Molecular Dynamics Simulations.

Whether a graphitization mechanism can control the low-friction behavior of DLC films is still controversial. In this paper, we establish the molecular dynamics model of the DLC film with graphene (DLC-GR-DLC) by LAMMPS and study the influence of the graphitization mechanism on the friction and wear behavior of the DLC film. The friction force of the DLC-GR-DLC model in the running-in stage is significantly smaller than that of the DLC film and then gradually increases to the same size as that of the DLC film. Further analysis indicates that the graphitization mechanism could indeed reduce the shear stress of the friction interface when graphene remains intact. However, the curling and breaking of the graphene structure will lead to an increase in shear force at the friction interface.

Preparation and properties of TiP/Mg-RE composites through laser melt injection

Hardness and wear resistance of magnesium alloys should be improved without reducing mechanical properties to realize their widespread application. By adding metal particles into magnesium instead of ceramic particles can reducing the influence caused by large difference of thermophysical and mechanical properties between ceramics and Mg. The existing methods for Mg based composites are time-consuming, cause agglomeration, and not suitable for preparing complex surfaces. In this study, Ti particles were injected into Mg-RE alloy through laser melt injection. Results show that the prepared TiP/Mg-RE composites with large surface area have no obvious welding defects in microstructure. Ti particles have good metallurgical bonding with the Mg-RE matrix. Microhardness of the TiP/Mg-RE composites is 100% higher than that of the Mg-RE matrix, at a cost of reducing partial mechanical properties. Moreover, the composites showed a stable friction coefficient and running-in stage. The TiP/Mg-RE composites show excellent comprehensive properties in a summary.

Improvement of impact wear properties of seat insert by laser cladding cobalt-based alloy

The impact wear properties of two different contact pairs, N80A valve-cast iron seat insert (cast iron group) and N80A valve-clad seat insert (cladding group), were studied in this work. In this paper, an independently designed tribo-tester combined with a depth gauge and corresponding auxiliary devices can record the axial subsidence of the contact pairs during the entire worn process. The results showed that during the 5 × 106 impact test, cast iron groups and cladding groups followed the worn process curve, and all went through the running-in stage and the stable worn stage. However, at each stage, the subsidence of cladding groups was smaller than that of cast iron groups. The roughness meter not only recorded the roughness of all samples before and after the test, but also can obtain the respective subsidence of the samples through the difference between the profiles before and after the test. The results can be mutually corroborated with the axial subsidence measured by the depth gauge. As a result, the roughness of the sealing surfaces of all valve-seat inserts increased significantly after the impact test. The total worn subsidence of the cast iron groups was about 1.61 times that of the cladding groups. The worn morphology was further studied by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The cast iron group mainly experienced serious adhesive wear and oxidation wear, while the cladding group mainly experienced fatigue wear, oxidative wear and abrasive wear.

Numerical model to predict wear of dynamically loaded plain bearings

Wear resistance of dynamic system components is a major challenge in aeronautics. According the usage of the aircraft, off-centred dynamic loads can appear on shafts when rotating bodies are unbalanced. In literature, most of the wear studies applied to plain bearing consider static loads centred in the contact area. This article presents a study on the wear of a plain bearing submitted to off-centred dynamic loads in order to look for a better mastering of service life of plain bearing for their usage in severe aeronautic conditions. Boussinesq's equations were used to compute the pressure distribution and Archard's law was used to calculate the wear. The wear coefficients of the running-in and stable wear stages were defined experimentally. The evolution over time of the maximum wear depth and the size of the contact zone were validated with experimental results. The perspective of this work is to feed digital twins of dynamic systems in order to predict wear according aircraft usage.

The Characterization of Running-In Coatings on the Surface of Tin Bronze by Electro-Spark Deposition

Antifriction materials, such as silver, copper, Babbitt B83, and graphene oxide (GO), were used to prepare running-in coatings on the surface of bronze QSn10-1 by electro-spark deposition (ESD). The analyses of mass transfer, roughness, thickness, morphology, composition, nanoindentation, and tribological properties of the coatings were investigated. The results showed that the running-in coatings were dense with refined grains that were uniformly distributed and in a metallurgical bond state with the tin bronze substrate. At optimum process parameters, the mass transfer was 244.2 mg, the surface roughness was 15.9 μm, and the thickness of the layers was 160 μm. The diffraction peaks clearly indicated the phases corresponding to α-Sn, SbSn, Cu6Sn5, and Cu, and a phase of Ag3Sn appeared. The modulus and the hardness of the running-in coatings were 24.9% and 14.2% of the substrate, and the deformation ratio of the coatings was 10.2% higher than that of the substrate. The friction coefficient of the running-in coatings was about 0.210 after the running-in stage, which was 64.8% of that of the substrate (0.324). The main wear mechanism of the running-in coatings under optimal process parameters is plastic deformation, scratching, and slight polishing. The running-in coating deformation under the action of high specific loads provides the automatic adjustment of parts and compensation for manufacturing errors.

Effect of Variation of Martensite with a Constant Carbon Content on Mechanical Behavior and Sliding Wear of Dual Phase Steels

In a dual phase steel, an increase in the martensite volume fraction leads to a decrease in its carbon content, and hence, elucidating the effect of martensite content on the mechanical and tribological behaviors has not been possible. For the first time, the present work dealt with this subject by maintaining a constant amount of carbon in different volume fractions of martensite. Tribological properties was evaluated via a pin-on-disk sliding tribometer. The study of wear tracks and debris revealed oxidative wear as the dominant wear mechanism. Increasing normal load from 10 to 30 N resulted in a decrease in the specific wear rate, which was related to the high work-hardening capacity. This resulted in higher surface hardness, accommodating the formation of a more durable tribofilm on the surface, and a lower coefficient of friction. However, the increase in normal load from 30 to 60 N resulted in an increase in the specific wear rate and reduction of oxide coverage on the sliding surface due to high surface stresses. The worn debris were mainly identified as metallic in the running-in stage and Fe3O4 oxide in the steady-state stage.Graphical Abstract

Effect of the cycle number on fretting wear behavior of alloy 690TT tube in high-temperature pressurized water

In high temperature water, the fretting wear behavior of Alloy 690TT against Type 405 stainless steel were investigated under different cycle numbers. Results indicated that the change of wear coefficient strongly depended on wear stage and oxide type of compact third body layer (TBL). Within 100000 cycles, the wear gradually entered the stable wear stage from the running-in stage, and the wear coefficient changed conformed to power law distribution. When the number of cycles exceeded 100000, a smooth and compact TBL composing of Fe2O3 and spinel oxide was formed on the surface of the wear scar, the wear coefficient changed slowly. With the increase of cycle number, the percentage of NiCr2O4 and NiFe2O4 in the surface oxide gradually decreased, while that of Fe2O3 gradually increased. The formation of cracks parallel to the surface was related to the surface stress field distribution. During the fretting process, the state of the stress component parallel to the surface changed from tension to compression, prevented cracks from moving to the matrix deep expansion, resulting in the crack propagation direction parallel to the wear surface in the TBL. Finally, the relationship between stable wear life and critical wear depth was established, and the stable wear life was related to running-in wear volume (V0) and stable wear rate (γa).

Оценка надежности трибосистем на неустановившихся режимах работы

The issue of determining the wear rate in unsteady operating modes (during running-in period) and in stationary modes (after running-in is completed) during bench tests of vessel technical equipment is considered. The availability of such information will reduce the time for finishing prototypes. Moreover, it will help to identify ways to improve the reliability of technical equipment during operation. There have been carried out the experimental studies that showed the reliability of the kinetics of the surface destruction processes at the stage of tribosystems running-in. Experimental studies were carried out in two stages and determined the correlation between the rate of volumetric wear and acoustic emission parameters: the variance of signal amplitudes and the spectral power of radiation. The presented graphic dependences demonstrate that the spectral power has the optimal functional relationship with the friction parameters: friction torque and temperature. The analysis of the dependences obtained showed that the variance of the amplitudes and the spectral power of the acoustic emission signals reflects sufficiently complete the wear process. Thus, it is in a functional relationship with the rate of volumetric wear. It has been experimentally confirmed on various tribosystems that the spectral power of acoustic emission signals has a better correlation coefficient with the wear rate than variance. Therefore, it can serve as a parameter for estimating the wear rate in unsteady operating modes. A technique for evaluating the tribosystems wear rate during running-in is proposed. The technique is based on the recording of acoustic radiation from the friction zone. The spectral power of acoustic radiation correlates with the wear rate with a correlation coefficient R = 0.82.

Short communication: Running-in behavior on single-mobility total hip arthroplasty

Total hip arthroplasty is a short-term solution for replacing a damaged hip joint with synthetic biomaterials. Total hip arthroplasty comes in two flavors: single and dual mobility. Mechanical and biological factors may degrade the quality of biomaterials over time. This may lead to implant failure and second surgical treatment. Wear is the crucial element leading to damaged bone and debris release throughout the body over time. Running-in is the initial wear phase between two surfaces before the steady-state phase. The stage of running-in is critical for understanding hip joint wear. Running-in and wear behavior have been extensively studied in single-mobility total hip arthroplasty, but aseptic loosening is the leading reason for restoration in arthroplasty registries. This paper seeks to summarize running-in behavior on single mobility hip implants, emphasizing its key aspects and recent developments.

A new two-stage degradation model for the preload of ball screws considering geometric errors

Owing to the geometric errors, preload of ball screws usually exhibits a two-stage degrading characteristic during operation, which is taken as the running-in stage (the first stage) and steady wear stage (the second stage), respectively. While existing researches were mainly focused on the steady wear stage, no references can be found in modelling the preload degradation during the running-in stage. Therefore, we proposed a two-stage model to compute the wear volume and preload degradation of ball screws. In the first stage, a new model considering macroscopic, geometric errors (the pitch errors, profile errors, ball radius errors, and waviness) was constructed to compute the wear volume. In the second stage, fractal theory was utilized to depict the wear volume from the microscopic perspective, in which both the adhesive wear and abrasive wear were considered. The predicted preload of the proposed model coincides well with the experimental results. Simulation results show that when the axial load increases from 5000 N to 7000 N, the first stage can be shortened as much as 50%. When the rotational speed increases from 600 rpm to 1000 rpm, the degradation rate of the first stage increases by 178%, and the first stage decreases by more than 50%. When the peak value of geometric errors increases from 1 μm to 1.8 μm, the first stage can be extended as much as 416%.

Research on the Coupling Relationship between Marine Resources and Environmental Carrying Capacity and Marine Economy in Jiangsu Province

This paper takes the coastal area of Jiangsu Province as the research area, collects the relevant statistical data of the coastal area from 2010 to 2020, and uses the coupling degree and coupling coordination degree model to analyze the degree of marine economy-marine environment coupling in Jiangsu Province in the past 10 years and its correlation. The coordination type is analyzed and evaluated. The research results show that the coupling index of marine resources and environmental carrying capacity and marine economy in Jiangsu Province fluctuates up and down in the interval of 2010-2020. trend. From 2010 to 2020, the coupling index of marine resources and environmental carrying capacity and economic development level in the coastal areas of Jiangsu Province showed an inverted "U"-shaped change, which is in line with the environmental Kuznets curve. The coupling coordination index fluctuates repeatedly, and the value is between 0.4 and 0.8. The coupling stage is from the antagonistic stage to the running-in stage. The coupling coordination type is mainly based on the coordinated development type, and the coupling level roughly develops from a mild imbalance to a low-level coordinated development to a well-coordinated development. It began to rise rapidly, and the coupling status is good. The coupling status of Lianyungang and Yancheng needs to be further improved.

Mechanical behaviors of pipeline inspection gauge (pig) in launching process based on Coupled Eulerian-Lagrangian (CEL) method

Successful launching of the pig is the premise for ensuring the efficiency and accuracy of the pigging operation. This study investigates the effect of the flow field on pig launching by the three-dimensional (3D) fluid-structure interaction (FSI) model based on the Coupled Eulerian-Lagrangian (CEL) method for the first time. Besides, the flow field experiment and the dragging experiment are conducted to verify the reliability of the simulation results. Four parameters as friction force, mandrel flip angle, pig velocity, cup deformation are selected to describe the mechanical behaviors of the pig. Research results indicate that the flow field has a significant effect on contact behaviors between the pig and the pipeline in the pig running-in stage but less effect on that in the steady stage, which presents the necessity of the FSI simulation for investigating the pig launching process.

Influence of compositions ABRO GT-409 and POLYTRONMTC in transmission oil on tribological contact in material systems "CuCrNiZrTi - KCh50", "CuCrNiZrTi – 40X"

The work carried out definitive tribotechnical tests of the systems of materials "CuCrNiZrTi - 85W90 - 40X", "CuCrNiZrTi - 85W90 - KCh50" to assess the nature of the manifestation of the effect of additive compositions (AC) ABRO GT-409 and POLYTRONTMC on adaptability to loading and lubrication modes parameters of adhesion properties when modeling shear on small samples. It was found that at the stage of running-in, the systems of materials operate stably with clearly pronounced tendencies to reduce the sliding resistance to a certain minimum, followed by its increase due to the influence of the AC components. ACs do not determine the effect of reducing the wear intensity in the investigated range of contact pressures, and a decrease in friction is caused by a decrease in shear resistance in the zones of contact interaction of protrusions and depressions of surface irregularities. A more significant effect on the decrease in the parameters of adhesion properties is exerted by the POLYTRONMTC 10% AC components, which cause the formation of secondary lubricant formations with denser structures at the interface of adhesion with metal surfaces and reduced resistance to movement within the formed cohesive bonds between them.

The Wear Mechanism of Coated Cutting Tools During Machining Process under the Thermal Effect

To figure out the wear process of ZrN-coated cutting tools under the thermal effect, this study performed wear experiments on ZrN-coated cutting tools during the machining process and tested on their hardness, elastic modulus, and microstructures under the thermal effect; then, the paper analyzed the internal laws and mechanisms of factors that cause wear to the ZrN-coated cutting tools under high temperature conditions, and determined their damaged state under certain load and speed conditions. After that, this paper summarized that the wear of ZrN-coated cutting tools during use can be divided into three stages: the running-in stage, the normal wear stage, and the acute wear stage. Through experiments, it’s found that the friction coefficient and wear rate of uncoated cutting tools were significantly higher than those of coated cutting tools; with the increase of load and rotate speed, the friction coefficient showed a decline trend; as the load increased, the wear rate showed an increase trend; as the rotate speed grew, the wear rate decreased; under the condition of a same kind of substrate, the friction reduction and anti-wear effect of cutting tools with a transition layer was better than those of cutting tools without a transition layer.

Effect of Surface Topography on ZDDP Tribofilm Formation During Running-in Stage Subject to Boundary Lubrication

Experimental investigations have been conducted to study the effects of surface topography on ZDDP (zinc dialkyldithiophosphate) chemical tribofilm formation during running-in stage under boundary lubrication conditions. The scope of presented work has been limited and focused on reciprocating motion under boundary lubrication to simulate the upper and lower dead centre of piston ring movement, which is prone to adhesive wear failure. Several surface topographies were designed and fabricated to measure, compare coefficient of friction and ZDDP critical time of tribofilm formation. Rubbing surfaces and their corresponding tribofilms were characterized by SEM and EDX. Mechanisms of surface topography effects on the critical time of ZDDP tribofilm formation is presented and discussed. Results from this study have demonstrated that the surface topography has a significant influence on the critical time of ZDDP tribofilm formation during running-in process and corresponding wear performance. This research provides an opportunity to augment anti-wear performance under boundary lubrication condition. This can be achieved by optimizing surface morphology design to influence the formation of anti-wear tribofilms during the running-in stage. In turn, this will result in interacting component’s service life enhancement and significant cost savings from mitigated wear.

Improving early running-in wear characteristics for dental lithium disilicate glass-ceramics by ion-exchange

ObjectivesThis study examined the effects of Li+→Na+ ion-exchange on the early wear performance of dental lithium disilicate (LD) glass-ceramics. MethodsSpecimens with different shapes were prepared using IPS e.max Press as the LD glass-ceramics. Ion-exchange was conducted by placing polished specimens in molten salt containing 25% NaNO3 and 75% KNO3 at 385 °C for 16 or 64 h. The ion-exchanged specimens were analyzed using X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) to investigate the structure and the elemental distribution. Thereafter, the specimens were tested for flexural strength, Vickers hardness, and fracture resistance. A portion of the specimens were tested with a pin-on-disk tribometer with 10 N for 40 × 104 wear cycles in artificial saliva. Wear analysis of the specimens was performed using a 3D profilometer and analyzed with one-way analyses of variance and Tukey's post hoc pairwise comparisons. Worn surfaces were examined with scanning electron microscopy. ResultsThe LD glass-ceramics exhibited strong time-dependent wear behavior, with typical running-in and steady wear stages. Ion-exchange treatments at 385 °C for 16 h and 64 h both enhanced the mechanical properties and decreased the wear rates of early running-in wear stage. The early wear performance of specimens treated with ion-exchange for long time (64 h) was improved significantly. ConclusionA thicker ion-exchange layer may be obtained by processing ion-exchange for a long time. This protocol improves the early wear performance of the glass-ceramics effectively. Clinical significanceDental restorations may fail prematurely due to excessive wear. It is important to improve the early wear performance of the glass-ceramics. Ion-exchange has the potential to strengthen dental LD glass-ceramics. Understanding the effect of ion-exchange on the early wear performance of glass-ceramics provides insight improving the early wear performance of these restorations.

Experimental Investigation on the Friction-Induced Vibration with Periodic Characteristics in a Running-In Process under Lubrication

This paper investigated the friction-induced vibration (FIV) behavior under the running-in process with oil lubrication. The FIV signal with periodic characteristics under lubrication was identified with the help of the squeal signal induced in an oil-free wear experiment and then extracted by the harmonic wavelet packet transform (HWPT). The variation of the FIV signal from running-in wear stage to steady wear stage was studied by its root mean square (RMS) values. The result indicates that the time-frequency characteristics of the FIV signals evolve with the wear process and can reflect the wear stages of the friction pairs. The RMS evolution of the FIV signal is in the same trend to the composite surface roughness and demonstrates that the friction pair goes through the running-in wear stage and the steady wear stage. Therefore, the FIV signal with periodic characteristics can describe the evolution of the running-in process and distinguish the running-in wear stage and the stable wear stage of the friction pair.