Alessandro Godi

A new procedure for characterizing textured surfaces with a deterministic pattern of valley features

In recent years there has been the development of a high number of manufacturing methods for creating textured surfaces which often present deterministic patterns of valley features. Unfortunately, suitable methodologies for characterizing them are lacking. Existing standards cannot in fact properly characterize such surfaces, providing at times unreasonable values. In this paper, a new procedure for characterizing such surfaces is proposed, relying on advanced filtering and feature recognition and separation. Existing advanced filtering methods do not always eliminate all distortions, therefore some modifications are investigated. In particular the robust Gaussian regression filter has been modified providing an envelope first-guess in order to always fit the mean line through the plateau region. Starting from a filtered and aligned profile, the feature thresholds recognition and separation is therefore made possible. In particular the plateau and valley regions can be detected, separated and independently analyzed according to their function. The example of a multifunctional profile is presented. The profile is analyzed using the new procedure, which demonstrates outputting a correctly aligned roughness profile and permitting comprehensive feature analyses.

A New Rig for Testing Textured Surfaces in Pure Sliding Conditions

Throughout the years, it has become more and more important to find new methods for reducing friction and wear occurrence in machine elements. A possible solution is found in texturing the surfaces under tribological contact, as demonstrated by the development and spread of plateau-honed surface for cylinder liners. To prove the efficacy of a particular textured surface, it is paramount to perform experimental tests under controlled laboratory conditions. In this paper, a new test rig simulating pure sliding conditions is presented, dubbed axial sliding test. It presents four major components: a rod, a sleeve, a housing and a stripwound container. The rod and the sleeve are the two surfaces in relative sliding motion; the stripwound container maintains a constant, but adjustable normal pressure, and the housing serves as interface between the sleeve and the container. For carrying out the test, two machineries are necessary: a press to provide the normal pressure and a tensile machine to perform the axial movements. The test is calibrated so that the correspondence between the normal pressure and the container advancement is found. Preliminary tests are carried out involving a multifunctional and a fine-turned rod against a mirror-polished sleeve. Qualitatively, the multifunctional surfaces improve the friction conditions, but a more structured test campaign is required. It is furthermore assessed the repeatability of the test device, in order to rely on the results obtained. Ten repetitions made at the same pressure using the fine-turned rod displayed good repeatability of the force results both in terms of average values and trends.