Numerical analysis of the influence of film thickness and properties on the stress state of thin film-coated piston rings under contact loads

In this work, a series of finite element analyses was conducted to analyze the stresses in thin film-coated piston rings under contact loads. The actual normal and tangential pressure observed during a complete four-stroke gasoline engine cycle (720°) was used as input to load an axisymmetric film/substrate mesh. Four values of coating thickness were analyzed (from 20 to 100 μm) and, for each one, five values of elastic modulus (from 144 to 578 GPa) were considered. The systems were compared based on the stress distribution, particularly in terms of the intensity and position of the peak stresses in the film and at the film/substrate interface. Results show that (a) in terms of radial stresses in the ring, the stiffer (or thicker) the film, the lower the compressive stresses at the interface immediately under the film-sleeve contact, and the higher the tensile stresses deeper at the ring, while (b) in the coating, the more compliant the material, the more compressive the axial stresses observed.