Application of undercut and FGM to mitigate stress gradients in cylindrical contacts

The presence of high longitudinal stresses near the contact interface leads to the initiation and propagation of cracks. This work investigates the mitigating effects of undercuts and surface coatings of functionally graded materials (FGM) on the peak stresses in cylindrical contacts using finite element analysis. A rigid indenter of a cylindrical profile in contact with a flat half-space with undercuts on both sides of the contact region is considered for contact analysis. The effect of the presence of undercuts is studied, with its size and location from the contact edge being the parameters. An undercut of larger radius decreases the peak longitudinal stress in the contact region when only normal loading as well as combined normal and tangential loading is applied. While contact pressure increases with an increase in undercut radius under normal loading only, undercut radius and position have negligible effect under combined loading. The peak stresses in the contact region are found to decrease with a decrease in modulus ratio and an increase in the thickness of FGM coating. The combined effect of undercut and FGM coating reduces the peak longitudinal stress significantly for an optimum combination of undercut radius, undercut position, and modulus ratio.