Abstract
The requirements for improved fuel economy and reduced vehicle emission have driven the lubricant industry to develop new lubricants for engines and other dynamic systems. The selection of appropriate lubricant formulation is a complicated process involving extensive and costly bench and field tests. Thus, there is a demand for developing quick, effective and less costly methods to evaluate and rank lubricants. The authors previously proposed a statistical technique for evaluating and ranking lubricants through examining spatial variations in local mechanical properties of a worn surface after lubricated sliding testing using a micromechanical probe. Examination of the mechanical heterogeneity of worn surface has been turned out a promising approach for prescreening lubricants before further bench and field tests. Research was conducted to further investigate the suitability of such a method to evaluate lubricant performance during lubricated wear tests for a number of engineering materials and in particular, to identify which mechanical property (e.g. hardness, Young's modulus, creep behaviour) was the most sensitive and reliable indicator of the surface mechanical heterogeneity. Efforts were also made to identify the optimum indentation load range for evaluating the mechanical heterogeneity. It was demonstrated that the statistical method based on the heterogeneity of worn surfaces was effective for evaluating and ranking lubricants. Microhardness was proven to be the most suitable parameter for evaluation of the mechanical heterogeneity of worn surfaces, especially for harder materials.
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