Research On Application Of Photoelasticity Technique To Tribology Experiment

Tribology is an interdiscipline composed of many different fields,such as mechanics,materials,physics and chemics.More and more researchers have great interest on it and have found and obtained many benifitful results.Some tribology problems have not yet clearly analyzed through.Experimental research is essential for tribology research.Reseachers put forward different real-time online measurement technology to analysis problems in tribology.In this thesis,photoelastic technique was proposed to study tribology experiment,conbined with numerical calculation method to further analyze the mechanism of problems.Photoelastic technology is an experimental stress analysis method.In this paper,the basic principle of photoelastic stress analysis and the method of RGB photoelastic stress measurement were introduced.Based on the analysis of the characteristics of several problems in tribology,the relative optical intensity method was proposed to measure the principal stress difference in the photoelastic interference image.A calculation formula of the principal stress difference was deduced from photoelastic interference fringes.This method could be easily analyzed to the principal stress difference under the contact subsurface.According to the principle of photoelasticity,the photoelastic line contact motion platform was built up,which is contained with its mechanical device,optical elements and image acquisition system to provide a stable and reliable analysis platform for the test.Some problems in tribology were studied by photoelastic experiment platform combined with numerical analysis.Firstly,stress distributions under the subsurface of the coating substate were analyzed by photoelastic technique.The preparation of photoelastic coating substrate samples was in detail described.The samples contacted with cylinder were carried out in the developed photoelastic platform.The principal stress difference could be determined by RGB photoelastic method.The finite element model was established to analyze the stress distribution under experiment conditions.The experimental and numerical results showed that the pricipal stress difference had obviously changed at the coating interface.In the coating substract,stress change would affect the coating strength.Then,soft Elastohydrodynamic lubrication(soft-EHL)in line contact was analyzed based on photoelasitic technology.In the experiment method,the stress distribution of soft-EHL under different speeds and loads were conducted.Photoelastic interference image were real-time observed and analysed.The oil film thickness,pressure and contact stress distribution under EHL were calculated by numerical modeling.It is found that the elastic modulus of the material was relative low,the lubrication contact state changes soft EHL,and the subsurface stress distribution was shifted from the oil film outlet area with the velocity increase.Finally,stress distributions under subsurface in wear process were studied by photoelastic technique.Using the photoelastic line contact movment platform,the real-time photoelastic interferenc images were recorded under wear experiment conditions.The wear surfaces were analyzed to diteremine wear rate of the polymer on metal.At the same time,the wear calculation model was established on the numerical method.The contact pressures were solved by the fast Fourier transformation and conjugate gradient method.According to the Archard model,the change of wear profiles during the run-in process could be obtained.Furthermore,photoelasitic experiment of the reciprocating wear process was carried out.The phoelasitc stress distribution and surface profiles were analysed to explore the mechanism of wear.