Thermal,corrosion and wear analysis of copper based metal matrix composites reinforced with alumina and graphite

The wear and corrosion resistances are important in marine applications, especially when it comes to structural support components like bearings, bushes and blocks. The copper hybrid metal matrix components are the new avenues explored in this front. A novel combination of alumina and graphite were considered as the reinforcements in a copper base for the development of a metal matrix composite.Power metallurgical techniques were used for the development of the MMC. The Vickers' s hardness value of 64.9 Hv has been observed by increasing the volume of alumina. Thermogravimetric analyses were carried out on material samples to estimate the exact sintering temperature and identified that 450-700℃ would be conducive. The TGA curves shows two step decomposition exists between 430 ℃-460 ℃. FT-IR analysis was done to confirm the peak values of the materials. FTIR exposed the peak value of 1600 cm^(-1) for alumina where as for Copper and graphite peak values have been 2840 cm^(-1) and 17260 cm^(-1) respectively. The potentio dynamic analysis was done to estimate the rate of corrosion on the samples. The sample with nano and micro reinforcements offered intensive resistance to corrosion. The presence of graphite minimized the weight loss of the samples during the corrosion test. Finally the wear rates of the samples were estimated using the Pin On Disc experimental setup. The samples with nano material reinforcement and with a maximum proportion of graphite exhibited a better wear rate of 1.52×10^(-12) m^2/kg under maximum load conditions.

Investigation of the friction coefficient evolution and lubricant breakdown behaviour of AA7075 aluminium alloy forming processes at elevated temperatures

The lubricant behaviour at elevated temperatures was investigated by conducting pin-on-disc tests between P20 tool steel and AA7075 aluminium alloy. The effects of temperature, initial lubricant volume, contact pressure and sliding speed on the lubricant behaviour(i.e. evolutions of the coefficient of friction(COF) and the breakdown phenomenon) were experimentally studied. The evolutions of COF at elevated temperatures consisted of three distinct stages with different friction mechanisms. The first stage(stage Ⅰ) occurred with low friction when the boundary lubrication was present. The second stage(stage Ⅱ) was the transition process in which the COF rapidly increased as the lubricant film thickness decreased to a critical value. In the final plateau stage(stage Ⅲ), lubricant breakdown occurred and intimate contact at the interface led to high friction values. At the low friction stage(stage Ⅰ), the value of COF increased with increasing temperature. The increase in temperature, contact pressure and sliding speed as well as the decrease in initial lubricant volume accelerated the lubricant breakdown.

Tribological and vibrational characteristics of AISI 316L tested at elevated temperature and 600 Torr vacuum

Friction and wear studies enable the investigation of material interaction between two sliding surfaces in contact. In the present investigation, the coefficient of friction and the wear resistance of AISI 316 L parts were studied under self-mating, dry sliding conditions using a pin-on-disc type configuration. The experiments were conducted at vacuum based high temperature pin-on-disc tribometer. The 4 mm diameter pin and 180 mm diameter disc were subjected to varying sliding velocities(0.5, 0.75 and 1.5 m/s) and were operated in 200, 400, 500 and 580 ℃ temperature at 600 Torr vacuum. The variation of specific wear rates with sliding velocities and different environmental conditions was studied. The morphology of sliding/rubbed surfaces was observed using Scanning Electron Microscope. In summary, it was found that a severe to mild wear transition occurred in sliding under operating conditions. Increased wear rates have been observed for 500 and 580 ℃ with increasing sliding velocity. Adhesive wear has been found to be predominant at 500 and 580 ℃ where as de-lamination has been observed at ambient temperature,200 and 400 ℃ in vacuum. The present paper also carried out the numerical analysis of the vibration behavior of AISI 316 L under thermal environment. Results revealed that at high temperature vibrational amplitude and natural frequency is significantly reduced. This can be attributed to the reduction in stiffness of the material at elevated temperatures. This high amplitude vibration during service can lead to high wear rate.

Influences of TiC Impurities on Dry-sliding Wear of Polycrystalline Ceramic

The wear behavior of titanium silicon carbide MAX phase was investigated.Samples of highly pure TiSiCand containing 8% of TiC,sliding dryly against Corundum counterpart,were tested at various speeds increasing from 5 to 60 m/s and under applied pressure of 0.1-0.8 MPa.The sliding-wear tests were performed on Tribometer,at room temperature of 15℃ with a relative humidity of 10%.The expermental results show that the presence of TiC particles can be beneficial to reducing the wear rate for certain ranges of sliding speed and applied pressure.The sliding-wear performances were expressed as a mathematical model,obtained through a modelling by the method of design of experiment.The influence of TiC impurities on the wear behaviors was also investigated.It is concluded that the wear mechanisms of samples are more affected by the presence of TiC under the effect of applied pressure compared with that of the sliding speed.

On the experimental characterization of the fluid volume influence on the friction between rough surfaces

The load-bearing behaviour of lubricated contacts depends primarily on the normal force,the relative velocity,and the geometry.Thus,with the aid of the Stribeck curve,it is usually well possible to characterize whether hydrodynamics,mixed friction,or boundary friction is more likely to be present.The fact that the load regime can also depend on the fluid quantity is obvious,but has hardly been systematically investigated so far.Especially for contacts with microscopic roughness,the defined application of a very small amount of fluid is a very challenging requirement.In this paper,a very fundamental study shows how a pin-on-disc tribometer can be used to achieve the transition from dry friction via mixed friction to predominant hydrodynamics by the amount of supplied fluid.The experiments are carried out on samples filed with different coarseness.In addition,the simultaneous influence of partial filling and normal force as well as relative velocity is also shown.Very good reproducibility has been practically reached over the entire range of the tests.Regarding the quantities for the coefficient of friction(COF),it was concluded that close to full filling,a reduction of the fluid quantity has a similar effect on the COF as the reduction of the velocity.This property goes along with the common theory of starved lubricated systems.Such behaviour was not observed to the same extent for the normal force.In the vicinity of smaller fluid quantities,the COF increases very rapidly with further reduction in fluid quantity,far more disproportionately than that with reduction in velocity.With a deeper understanding of this problem,various practical issues such as idling or the run-up process in bearings can also be studied in a more focused manner.

A finite element analysis(FEA)approach to simulate the coefficient of friction of a brake system starting from material friction characterization

The coefficient of friction(COF)is one of the most important parameters to evaluate the performance of a brake system.To design proper brake systems,it is important to know the COF when estimating the brake force and resulting torque.It is challenging to simulate the COF since friction in disc brakes is a complex phenomenon that depends on several parameters such as sliding velocity,contact pressure,materials,and temperatures,etc.There is a lack of studies found in the literature focusing on simulation of the COF for a full brake system based on tribometer material characterization.The aim of this work is therefore to investigate the possibility to use a finite element analysis(FEA)approach combined with a COF pv-map to compute the global COF of a disc brake system.The local COF is determined from a pv-map for each local sliding velocity and contact pressure determined by the FEA.Knowing the local COF,the braking force of the entire brake system and the global COF can be evaluated.Results obtained by the simulation are compared with dyno bench test of the same brake system to investigate the validity of the simulation approach.Results show that the simulation is perfectly in line with the experimental measurements in terms of in-stop COF development,but slightly higher with a positive offset for every braking.

Contact Stress and Wear Analysis of Zirconia Against Alumina for Normal and Physically Demanding Loads in Hip Prosthesis

Risky gait activities lead to severe wear in orthopaedic implants during postoperative periods.The aim of the present study is to predict the linear and volumetric wear of zirconia(ZrO2)vs alumina(Al2O3)hip implants subject to risky and normal gait activities.Initially,the gait loads pertaining to risky gait activities were converted to equivalent normal loads.Then using the computed normal loads,friction and wear coefficients of ZrO2 ball against Al2O3 disc were calculated from Pin-on-Disc(POD)tribometer under dry and lubricating conditions.Saline solution,a bio-lubricant was utilized for lubrication purpose to mimic synovial fluid properties.Nineteen gait activities stair ascending or descending,carrying load,lifting load and ladder up or down etc.,grouped as A,B,C and D were used to determine friction and wear coefficients.Finite Element Method(FEM)was employed to predict the wear of the bearing couple.The developed contact pressure for these gait activities was then utilized to compute linear and volumetric wear for 2 million cycles.Our findings suggests that,patients regularly involved in group C and D type gait activities were likely to cause more wear which may accelerate early implant failure.

Comprehensive review of tribometer dynamics-Cycle-based data analysis and visualization

Tribologists often rely on triboexperiments to investigate factors that affect a tribosystem.The inherent dynamic behavior of the respective tribometer setups and its effect on data interpretation remain often unknown.In this study,a comprehensive analysis of sensor data obtained from lubricated and dry triboexperiments is performed.Data are generated on a pin-on-disc test rig with a silicon nitride ball on a steel disc contact with a rotation frequency of~3 Hz.High-speed acquisition of sensor data up to 5 kHz is performed to resolve changes in the data within individual cycles.The characteristic frequencies of the system and their temporal evolution are determined via time--frequency analysis,which reveals periodic patterns in the sensor data.Cycle-based data evaluation allows the detection of localized events and changes during an operation and considerably reduces the apparent measurement uncertainty,as compared with an unreduced dataset.The data analysis and visualization routines presented herein may serve as a prototype for further application to tribometer setups.