Yield inception of a soft coating on a flat substrate indented by a rigid sphere

The yield inception of a deformable half space covered by a soft coating and indented by a rigid sphere is studied using the finite element method. A soft coating parameter, which controls the yield behavior of this problem, is defined. Dimensionless empirical expressions for the critical load, critical contact area and critical interference at yield inception are derived as functions of the dimensionless soft coating parameter. Three different locations of the yield inception of the coated system are observed. A comparison of yield inception behavior for an uncoated substrate and substrates with soft and hard coatings is made. A minimum value of dimensionless coating thickness, which is required to protect the substrate from yielding, is proposed. It is shown that a coating with low Young's modulus and high yield strength is most desirable for protecting the substrate against yielding.