Unexpected Wear Research Articles

Machine learning assisted design of Fe-Ni-Cr-Al based multi-principal elements alloys with ultra-high microhardness and unexpected wear resistance

In this work, machine learning (ML) technique was used to discovery new multi-principal elements alloys (MPEAs) with desirable properties. Generalized Regression Neural Network (GRNN) showed high accuracy to construct the composition-microhardness model and was used for microhardness prediction and composition optimization. Based on ML results, Fe0.6Ni0.7CrAl MPEAs were designed and prepared. The proposed GRNN model aligns well with experimental data, Fe0.6Ni0.7CrAl MPEAs exhibit ultra-high microhardness (∼700 HV) and unexpected wear resistance in the as-cast bulk state. Nano-indentation test showed that an average nano-hardness of 8.69 GPa and an average elastic modulus of 242.8 GPa were derived for the Fe0.6Ni0.7CrAl MPEAs. The hardening increment originates from the synergistic effect of disordered BCC phase and B2 phase. Moreover, Fe0.6Ni0.7CrAl MPEAs showed good wear resistances with friction coefficient of ∼0.41, as well as wear rate of 4.5×10−6mm3/(Nm). Abrasive wear and oxidative wear occurred during repetitive dry sliding, abrasive wear is the main wear mechanism. MD simulation explains the atomic structure evolution during the nanoscratch process, further revealing the wear mechanism at the atomic scale. This high-performance alloy shows potential for engineering applications.

Multi‐Scenario Applications of Fluoro‐Free Super Liquid‐Repellent Particles Prepared Through Excluded Volume Effect

AbstractSuperhydrophobic surfaces garner tremendous research attention due to their potential applications in the fields of oil–water separation membrane, self‐cleaning, and anti‐icing systems. However, the reported superhydrophobic materials that achieve low‐surface‐tension (<60 mN m−1) liquid repellency are typically prepared using perfluorinated compounds (PFCs), which pose significant risks to the natural environment and human health. Here a concept based on the excluded volume effect in polymer dilute solutions is explored to achieve a hydrophobic flexible polymer‐chain wrapping of multidimensional particles, which forms a nonadherent soft‐shell‐hard‐core structure and maintains the original structural integrity of particles. The prepared fluoro‐free super‐repellent multidimensional particles can be spray‐coated and dip‐coated on different substrates to prepare large‐scale superhydrophobic coatings, which exhibit excellent low‐surface‐tension (42.6−50 mN m−1) liquid repellency superior to the reported fluoro‐free superhydrophobic materials. Benefiting from the strong interaction of super‐repellent particles with flexible polymer chains, the superhydrophobic coatings show unexpected wear resistance and durability. This first demonstration of hydrophobic polymer‐wrapped particles for repelling low‐surface‐tension liquids provides insights into next‐generation fluoro‐free superhydrophobic materials.

Equivalent linearization of hyperelastic rubber rings in dynamic vibration absorber boring bar and simulation of its dynamic properties

A slight perturbation in high-speed precision cutting could cause violent vibration of boring bars, resulting in unexpected wear and failure of the structures. In this paper, the dynamical characteristic of a boring bar with a dynamic vibration absorber (DVA) is investigated. Considering that the nonlinear characteristics of the rubber ring play a significant role in improving the capacity of DVA, we proposed an equivalent linearization method for modeling hyperelastic rubber rings based on the experimental data of uniaxial tensile test. The relationship between the stiffness of rubber rings and the precompression parameter δ is established for two types of rubber. The equivalent linearization model shows good accuracy and calculation efficiency while the mass of the DVA is confined to a narrow space and the assumption of small strain is inherently satisfied. Numerical results show that the time cost of the equivalent linearization model is only 5% of the full hyperelastic model. Furthermore, the effect of different spring stiffnesses and damping on the dynamic characteristics of the boring bar is compared by using the equivalent linearization model, and the vibration peak of the DVA boring bar is found to be reduced about 45%. Our findings establish a simplified modeling scheme for choosing rubber rings in design of dynamic vibration absorbers with acceptable accuracy and little time cost, which could also give some reference for modeling of metal rubber and gel-like materials.

Unexpected Wear of a Uniquely Designed Moderately Cross-Linked Polyethylene in Total Hip Arthroplasty.

A uniquely designed, non-heat-treated moderately cross-linked acetabular polyethylene liner used in total hip arthroplasty (THA) demonstrated excessive wear during routine follow-up, prompting an evaluation of the linear wear rate. All THAs were performed by the senior author. The study group included 38 THAs using the uniquely designed polyethylene in question, compared to a control group of 21 THAs using another moderately cross-linked polyethylene with good 10-year outcomes. Two-dimensional linear head penetration wear measurements were obtained using the Martell Hip Analysis Suite, and retrieval analysis was performed on two liners. The study group had a significantly higher average penetration rate of 0.089 mm/y than the control group average rate of 0.047 mm/y (P= .04). Forty-five percent of the study group had a wear rate above the osteolysis threshold (0.1 mm/y), compared to 24% in the control group. Macroscopic analysis of two retrieved liners validated the radiographic findings. The data suggest unexpectedly higher wear rates for a moderately cross-linked polyethylene design, with nearly half of the study group at risk for osteolysis. Further registry or database analyses of this particular moderately cross-linked polyethylene are warranted.

Mechanisms of oxide dependent tribological behavior in Ti / Steel sliding and influence of nanostructured surfaces

The tribological behavior of pure titanium having coarse-grained or nanostructured surfaces has been investigated against a steel ball moved with an alternative motion. The nanostructures were obtained by Surface Mechanical Attrition Treatment (SMAT) both at room and at cryogenic temperatures. An unexpected wear behavior was revealed: the hard steel ball was abraded for all cases even if it was several times harder compared to the Ti surface. This was due to the formation of a third body consisting of hard Ti oxides. Interestingly, important variations of the coefficient of friction were also revealed during the rubbing process. These variations could be separated into three successive stages, each with its specific wear mechanisms. The wear regimes were related to changes in the third body layer formed between the Ti and steel surfaces. SMAT changed the formation kinetics of the third body. The temperature at which the SMAT was conducted also introduced different third body formation kinetics. Important variations in the wear resistance were consequently observed between each surface condition.

Performance evaluation of a novel single-screw compressor and expander design

Single-screw machines have seen significant development and improvement over the last decades and they are currently employed as both compressors and expanders in several applications. The correct functioning of the machine heavily relies on the meshing between the gate rotors and the central rotor which is directly linked to the precision of the manufacturing process to avoid unexpected wear of the tooth profiles. It is well known that the wear of the gate rotor tooth profiles over time is one of the limiting factors with respect to twin-screw machines. To this end, a number of studies have been reported in the literature about improved tooth profiles. For instance, the conventional straight-line profile has been replaced by multi-column tooth flank designs to enlarge the contact surface. However, the manufacturing process is still based on CNC machines with associated challenges.In a previous study, the authors proposed and modeled a new tooth profile design to overcome the aforementioned limitations. In particular, 3D printing technique was utilized to manufacture the non-conventional tooth design. A geometry model has also been developed to calculate the sealing lines, groove volume curves, and surface areas of the new design.In this work, a detailed mechanistic model of the single-screw machine is exercised to compare the conventional straight-line profile with the newly proposed tooth profile. Particular emphasis is given to the effect of seal lines on the leakage flows. Furthermore, the design implications of the new tooth profile on internal volume ratio, porting, and displacement are also discussed.

Vibration analysis of open TBM gripping-thrusting-regripping mechanism

The gripping-thrusting-regripping mechanism in the open tunnel boring machine is inevitably excited by strong impacts during tunnelling operations, leading to severe vibrations and unexpected wear in the joints and/or damage to the other machine components. Therefore, it is crucial to gain deep insight into the dynamic behaviours of equipment in tunnelling operations. This paper presents an approach for the elasto-dynamic modelling of the mechanism, by considering the surrounding rocky boundary conditions and configuration-dependent rigidities of the actuators, joints and key components, allowing for the dynamic response and vibration energy distribution to be predicted theoretically. The agreement between the analytical model and finite element model at frequencies and mode shapes proves the effectiveness of the modelling method. The simulation results demonstrate that the first four mode shapes dominate the dynamic system behaviours as a whole during tunnelling operations. The outcomes are helpful in predicting the dynamic behaviours of the mechanism so that weak links can be identified and subsequently improved during the design stage.

Thermo-Mechanical Modeling of Abradable Coating Wear in Aircraft Engines

In modern turbomachine designs, the nominal clearances between rotating bladed-disks and their surrounding casing are reduced to improve aerodynamic performances of the engine. This clearance reduction increases the risk of contacts between components and may lead to hazardous interaction phenomena. A common technical solution to mitigate such interactions consists in the deposition of an abradable coating along the casing inner surface. This enhances the engine efficiency while ensuring operational safety. However, contact interactions between blade tips and an abradable layer may yield unexpected wear removal phenomena. The aim of this work is to investigate the numerical modeling of thermal effects within the abradable layer during contact interactions and compare it with experimental data. A dedicated thermal finite element mesh is employed. At each time-step, a weak thermo-mechanical coupling is assumed: thermal effects affect the mechanics of the system, but the mechanical deformation of the elements has no effect on temperatures. Weak coupling is well appropriated in the case of rapid dynamics using small time-step and explicit resolution schemes. Moreover, only heat transfer by conduction is considered in this work. To reduce computational times, a coarser spatial discretization is used for the thermal mesh comparing to the mechanical one. The time-step used to compute the temperature evolution is larger than the one used for the mechanical iterations since the time constant of thermal effect is larger than contact events. The proposed numerical modeling strategy is applied on an industrial blade to analyze the impact of thermal effects on the blade's dynamics.

Contact stress analysis of the anterior tibial post in bi-cruciate stabilized and mobile-bearing posterior stabilized total knee arthroplasty designs

In posterior-stabilized (PS) total knee arthroplasty (TKA), unexpected wear and fracture of the tibial post due to anterior post impingement have been reported. The purpose of this study was to determine the contact stress on the anterior aspect of the tibial post in four contemporary TKA designs. We evaluated one bi-cruciate stabilized design (Journey II) and three mobile-bearing PS designs (Vanguard RP, PFC Sigma RP, and NexGen LPS Mobile). The contact conditions at the anterior aspect of the tibial post were determined upon application of a posterior force of 100N to individual implants. Each measurement was sequentially performed five times, and the data were compared within and across designs using analysis of variance and a post-hoc test. The contact stress of the Journey II and Vanguard RP was less than the compressive yield stress for polyethylene (10MPa) at all tested flexion angles and degrees of rotation. The PFC Sigma RP did not show anterior tibial post impingement under any experimental conditions. The NexGen LPS Mobile demonstrated bilateral edge loading at the anterior tibial post and exceeded 10MPa of contact stress in some test conditions. Thus, the differences among implants in terms of the dimensions of the femoral anterior cam or intercondylar notch and the anterior aspect of the tibial post in the axial and sagittal planes led to significant differences in contact conditions. The present study helps the surgeon to be more aware that various contact conditions of the anterior aspect of the tibial post can occur in individual TKA designs.

Investigation on the phase transformation of electroless Ni–B coating after dry sliding against alumina ball

The purpose of the work was to evaluate the possibility of tribochemical reactions during dry sliding of electroless Ni–B coating against an alumina ball. The effect of probable tribochemical products on the tribological behavior of Ni–B/Al2O3 tribosystem was investigated. Wear experiments were performed in a ball-on-disc configuration pressing alumina balls towards rotating disc specimens. Wear tests were carried out at normal loads of 5, 20, 40 and 60 N at the sliding distance of 100 m. Electroless Ni–B coatings with a mean thickness of 50–60 μm were applied on the mild carbon steel substrates. The worn surfaces of Ni–B coatings were studied with Scanning Electron Microscope (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), X-Ray Diffractometer (XRD) and X-ray Photoelectron Spectrometer (XPS). The results showed that the structure of the worn surfaces of the coatings changed from amorphous to the crystalline. The dominant wear mechanism in the present tribosystem was combination of adhesive and abrasive wear. As the load was increased the friction coefficient and its fluctuations were decreased. The wear rate of alumina balls changed from increasing to decreasing at the load of 40 N. XPS and XRD analysis revealed the phase transformation and production of Ni–Al compounds on the worn surface of electroless Ni–B coating. It was elucidated that tribochemical reactions between the mating surfaces were responsible for tribological behavior of Ni–B coating and unexpected wear behavior of alumina balls.

Does the Use of Diamond‐Like Carbon Coating and Organophosphate Lubricant Additive Together Cause Excessive Tribochemical Material Removal?

We observe unexpected wear increase on a steel surface that rubbed against diamond-like carbon (DLC) coatings only when lubricated by phosphate-based antiwear additives. Contrary to the literature hypothesis of a competition between zinc dialkyldithiophosphate produced tribofilms and DLC-induced carbon transfer, here a new wear mechanism based on carbon-catalyzed tribochemical interactions supported by surface characterization is proposed

Study of Microparticle Rebound Characteristics Under High Temperature Conditions

Large amounts of tiny microparticles are ingested into gas turbines over their operating life, resulting in unexpected wear and tear. Knowledge of such microparticle behavior at gas turbine operating temperatures is limited in published literature. In this study, Arizona road dust (ARD) is injected into a hot flow field to measure the effects of high temperature and velocity on particle rebound from a polished 304 stainless steel (SS) coupon. The results are compared with baseline (27 m/s) measurements at ambient (300 K) temperature made in the Virginia Tech Aerothermal Rig, as well as previously published literature. Mean coefficient of restitution (COR) was shown to decrease with the increased temperature/velocity conditions in the VT Aerothermal Rig. The effects of increasing temperature and velocity led to a 12% average reduction in COR at 533 K (47 m/s), 15% average reduction in COR at 866 K (77 m/s), and 16% average reduction in COR at 1073 K (102 m/s) compared with ambient results. The decrease in COR appeared to be almost entirely a result of increased velocity that resulted from heating the flow. Trends show that temperature plays a minor role in energy transfer between particle and impact surface below a critical temperature.

Tribological properties of the two-step thermally deposited chromium films

Chromium thin films were prepared on glass substrate via a two-step thermal deposition and their structural, chemical and tribological properties were determined. The X-ray diffraction pattern of the two-step thermally deposited chromium film showed the presence of well-defined body-centered cubic Cr metal structure with a prominent (110) plane. X-ray photoelectron spectroscopy depth profile showed a presence of ∼2% of oxygen in the film within the first five etching cycles showing oxygen incorporation. Dry sliding wear experiments at temperatures ranging from 20 to 200°C were conducted. The thin films were worn with either 100Cr6 or 440C bearing balls using a ball-on-disk sliding configuration at a contact load of 1N. Friction coefficient and coating wear rates were measured and wear tracks were analyzed using optical microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Thin films exhibited low wear rates at room temperature and an unexpected wear behavior at the elevated temperatures. Only the first half of the metallic chromium film was worn out after ∼18m of dry sliding at room temperature, whereas increase in temperature resulted in a decrease in wear resistance of the film.

Utilizing Validated Computational Models to Predict Tibial Insert Abrasion in Mobile Bearing Knees: A Design Performance Standard

Abstract Validated computational models that successfully predict clinically observed outcomes, such as damage occurring in the polymer insert component of a Mobile Bearing Knee (MBK) replacement design, are powerful predictive tools. This paper demonstrates the long term use of a validated computational model that uses the finite element method to visualize the magnitude and location of stresses on the polymer insert associated with abrasive wear damage that occurs in vivo. The use of component geometries generated from three-dimensional laser scans of sterilized, implantable quality components allows detection of poor fit between manufactured component articulations, which is key to successful prediction of observed clinical wear patterns in tibial inserts. The robustness of the model is demonstrated by its ability to predict expected and unexpected wear simulator and clinical retrieval outcomes for a wide variety of MBK designs. It can then be used with some confidence to determine the effect that new, innovative component design changes will have on polymer damage. Validated computational models provide rapid evaluations of anticipated design and material performance at a lower cost than other methods, with results that are predictive of clinical outcomes and allow direct comparison between devices. These methods should be accepted as an a priori evaluative tool by standards and regulatory bodies.

The John Insall Award: No Functional Advantage of a Mobile Bearing Posterior Stabilized TKA

Mobile bearing (MB) total knee design has been advocated as a means to enhance the functional characteristics and decrease the wear rates of condylar total knee arthroplasty (TKA). However, it is unclear if these designs achieve these goals. We asked whether function of patients or survivorship would be greater or complications would be lesser in groups of patients with MB compared with fixed bearing (FB) TKA. We also sought to describe retrieval findings. We randomized 507 primary TKAs in 416 eligible patients to receive MB (n = 252) or FB (n = 255) devices from November 2001 to August 2007 (Investigational Device Exemption G000180, ClinicalTrials.gov registration number NCT00946075). Patients were blinded to treatment allocation. WOMAC Index, SF-12 Health Survey, knee range of motion, and Knee Society scores were collected and compared preoperatively and at 6, 12, and 24 months postoperatively. We recorded device failures and complications until October 2009. Kaplan-Meier survivorship was compared using the log rank test. Twelve retrieved MB devices underwent pathologic analysis. The minimum postoperative time was 2.2 years (mean, 5.9 years; range, 2.2-7.9 years). We found no differences in mean clinical assessment scores or mean score changes from baseline at any postoperative interval through 2 postoperative years. Nineteen of the 252 MB and 13 of the 255 FB knees had undergone revision of any component. Estimated survival at 6 postoperative years was similar for the two devices: 90.1% (95% confidence interval [CI], 84.1-93.9) for MB and 94.2% (95% CI, 90.1-96.6) for FB. Two MB and no FB tibial components were revised for loosening. There was one case of MB insert dislocation. Retrieved MB devices demonstrated no unexpected wear or mechanical device failures. We found no evidence of functional advantage of the MB design. Survivorship was similar, although the study is limited by short duration of followup.

Unexpected wear may yield new plasma rockets

Unexpected wear may yield new plasma rockets

Unexpected wear may yield new plasma rockets

Unexpected wear may yield new plasma rockets

ESTUDO DA VARIAÇÃO DA CARGA DE CONTATO ENTRE OS CILINDROS EM LAMINADORES QUÁDRUOS EM FUNÇÃO DE SUA COROA, CHANFRO E DESGASTE

The author has developed a mathematical-numerical model for simulation of 4-high rolling mills. With this computer model it is possible to calculate the strip profile, the rolling loads and contact loads between the rolls and the flatness quality of the strip rolled. It is shown that depending on the form of grinding the roll, load peaks may appear on the edges of the rolls that can produce unexpected wear and strips out of customer’s specification. These rolls can break, causing financial prejudice for the industry. It is studied, also, the effects on these load peaks when the rolls were chamfered. When the wear of the work-rolls is taken into account, it is shown that the rolling load becomes larger, the

Slurry wear behavior of zinc-based alloys: influence of some material and test parameters

This investigation pertains to the analysis of slurry wear behavior of a zinc-based alloy. The effects of material composition/microstructure, slurry composition and traversal distance and speed on the response of the alloy system have been studied. Sample rotation method was adopted for testing the samples. In some cases, unexpected wear response (from conventional understanding) was observed. For example, presence of a less corroding phase like Si particles in the alloy system caused inferior wear response while increasing traversal speed led to improved wear behavior (in the liquid-only medium). Further, hard sand particles suspended in the test environment offered superior wear characteristics despite their additional erosive and abrasive damage to the samples. In the tested range (20–60 wt%) of sand concentrations in the slurry medium, the wear rate increased initially with increasing sand concentration, attained the maximum (although less than the liquid-only medium) at 40% sand and then finally followed a reversal in the trend at a still higher sand concentration of 60%. Increasing traversal speed from 4.71 to 7.02 m/s led to inferior response while the silicon containing alloy performed better than the one without the element in general in liquid plus sand slurries. The wear rate increased with traversal distance initially, attained the maximum and then decreased once again at still larger distances. The sensitivity of the rate of increase/decrease in wear rate with distance became less in the presence of suspended sand particles in the medium (electrolyte). The observed wear response of the samples has been substantiated through specific characteristics of affected surfaces. The latter also helped to understand the operating material removal mechanisms.

Anomalous wear behavior of MoS2 films in moderate vacuum and dry nitrogen

440C steel thrust ball bearing races lubricated with 1 μm thick sputtered films of MoS2 were tested in the unidirectional and oscillatory modes against bare steel balls in moderate (10−4−10−5 Pa ≈ 10−6−10−7 Torr) vacuum and in 1 atmosphere of 99.999% pure (⩽ 1 ppm water) N2 in the same unbaked environmental chamber. Over 90% of the residual gases in the chamber vacuum consisted of H2O vapor. The bearings operated in N2 showed substantially longer lives compared to the specimens tested in vacuum. Scanning electron microscope (SEM) tribometry was also performed on an MoS2 film powder-burnished onto a 440C flat. This flat was repeatedly oscillated against bare, hemispherical-tipped 440C pins on fresh wear tracks in the same type of N2 and column vacuum of ~10−3 Pa ≈ 10−5 Torr itself containing over 90% residual H2O. The SEM-generated results on the burnished film confirmed the same, atmosphere-dependent difference in wear life observed with the sputtered layers. Varying the moisture content of the burnished flat and its immediate environment by cryosorption predictably manipulated the coefficient of friction and wear life of MoS2. The various possible causes of this perplexing phenomenon are reviewed, and a plausible hypothesis is offered attributing the unexpected wear life reduction to the physico-chemical consequences of residual H2O hydrogen-bonding to the oxidized and/or hydrated edge and basal plane sites of MoS2 in moderate vacuum. The site-specific sorption of water is severely hindered in 1 atm N2 by the gas molecules disrupting the H-bonding mechanism.