Hardness of Thin-Film Media: Scratch Experiments and Finite Element Simulations

Experiments and finite element simulations are presented pertaining to the effective hardness and the mechanics of indentation and sliding contact on elastic-plastic layered media. Hardness measurements obtained from scratch experiments are presented for thin-film rigid disks with 30 nm carbon overcoats. Reproducible results are obtained for residual scratch depths greater than approximately 8 nm. A simple force balance model is used to calculate the effective hardness of the layered medium. Hardness values for the surface layer are calculated by fitting a relationship between the hardness, scratch geometry, and layer thickness to the experimental data. The experimental results are compared with three-dimensional finite element simulations of a rigid spherical indenter sliding over a half-space with a stiffer and harder surface layer. The finite element results are used to verify the hardness model applied to the experimental data and to provide insight into the observed experimental behavior in the context of the associated elastic-plastic deformation characteristics of the layered medium.

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Three-Dimensional Finite Element Analysis of Elastic-Plastic Layered Media Under Thermomechanical Surface Loading

Journal of Tribology ◽

10.1115/1.1497360 ◽

2002 ◽

Vol 125 (1) ◽

pp. 52-59 ◽

Cited By ~ 50

Author(s):

N. Ye ◽

K. Komvopoulos

Keyword(s):

Finite Element ◽

Layered Medium ◽

Numerical Solutions ◽

Equivalent Stress ◽

Three Dimensional ◽

Layered Media ◽

Thin Layers ◽

Surface Loading ◽

Elastic Plastic ◽

Thermomechanical Surface

The simultaneous effects of mechanical and thermal surface loadings on the deformation of layered media were analyzed with the finite element method. A three-dimensional model of an elastic sphere sliding over an elastic-plastic layered medium was developed and validated by comparing finite element results with analytical and numerical solutions for the stresses and temperature distribution at the surface of an elastic homogeneous half-space. The evolution of deformation in the layered medium due to thermomechanical surface loading is interpreted in light of the dependence of temperature, von Mises equivalent stress, first principal stress, and equivalent plastic strain on the layer thickness, Peclet number, and sliding distance. The propensity for plastic flow and microcracking in the layered medium is discussed in terms of the thickness and thermal properties of the layer, sliding speed, medium compliance, and normal load. It is shown that frictional shear traction and thermal loading promote stress intensification and plasticity, especially in the case of relatively thin layers exhibiting low thermal conductivity.

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Effect of Residual Stress in Surface Layer on Contact Deformation of Elastic-Plastic Layered Media

Journal of Tribology ◽

10.1115/1.1572516 ◽

2003 ◽

Vol 125 (4) ◽

pp. 692-699 ◽

Cited By ~ 29

Author(s):

N. Ye ◽

K. Komvopoulos

Keyword(s):

Residual Stress ◽

Finite Element ◽

Surface Layer ◽

Coefficient Of Friction ◽

Layered Medium ◽

Equivalent Stress ◽

Equivalent Plastic Strain ◽

Layered Media ◽

Contact Loading ◽

Elastic Plastic

The effect of residual stress in the surface layer on the deformation of elastic-plastic layered media due to indentation and sliding contact loading and unloading was analyzed with the finite element method. A three-dimensional finite element model of a rigid sphere interacting with a deformable layered medium was developed, and its accuracy was evaluated by contrasting finite element results with analytical solutions for the surface stresses of an elastic homogeneous half-space subjected to normal and friction surface traction. Deformation of the layered medium is interpreted in terms of the dependence of the von Mises equivalent stress, first principal stress, and equivalent plastic strain on the magnitudes of residual stress and coefficient of friction. The effect of residual stress on the propensity for yielding and cracking in the layered medium is discussed in the context of results for the maximum Mises and tensile stresses and the evolution of plasticity in the subsurface. It is shown that the optimum residual stress in the surface layer depends on the type of contact loading (indentation or sliding), coefficient of friction, and dominant deformation mode in the layer (i.e., plastic deformation or cracking).

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