Finite-element analysis of the initial stage of the indentation-rotation test for phosphate and stearate coatings

• Published in: Journal of materials processing technology 1994-02, Vol.41 (2), p.171-185
• Main Authors: Wierre, C., Guerin, J.D., Oudin, J., Bricout, J.P.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Mechanical and acoustical properties; Physical properties of thin films, nonelectronic; Physics; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 0924-0136
• DOI: 10.1016/0924-0136(94)90059-0

Well fitted to determine the behaviour and seizure of thin coatings, the test involves a rotating cylindrical specimen on which a small profiled indentor exerts a non-uniform normal pressure. The normal load remains constant as the time of rotation increases. The friction-force values are related to the behaviour of the coatings and when the interface become damaged generally, the friction force increases strongly. The rotating time required for these observations is related to the initial stress and strain distribution in the vicinity of the contact surface when the normal load is applied on the indenter, the spcimen being motionless. For this identatition phase, the distribution of stress and strain are obtained by means of a refined localised finite-element model which takes into account the mean thickness and the mechanical properties of a typical zinc-phosphate coating first, and then of a typical bilayered zinc-phosphate and zinc-stearate coating second. It is found that the slider-specimen contact area and the stress and strain maps in the contact vicinity change significantly from the virgin steel specimens to the bi-layered specimens. The effective stress decreases whilst the effective strain increases, the strain maps being more perturbed by the coatings than the stress map. Particular attention is focused on the local shear stress which is related to the performance of the adhesion coating.