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A friction model of microbearings with thin metallic compliant coatings

Stiharu I., Bhat R., Hong H.

International Journal of Applied Mechanics and Engineering

2003

Vol. 8, no 2

317-329

The paper presents experimental results of the investigation on the micro-tribological properties of Ti thin film layers deposited on metallic substrates of various hardness. The tests were carried out under standard dry friction conditions using a miniature pin on disk apparatus. The experimental results found for the friction coefficient developed between 52100 steel pin and Ti as a compliant layer deposited on various hardness substrates from soft to hard are consistent with other results presented in literature for the pair steel/Ti. A friction model that assumes the plowing of microasperities into the soft thin film layer supported by the elastic substrate as the main factor in the originating friction is further proposed. A simplified one-asperity model is assessed against the compliant layer assumed deposited on a rigid substrate. The analysis of the influence of the stress developed at the interface substrate-film is assumed in this model. Tests carried out qualitatively confirmed that the influence of the inter-laminar stress is significant to friction. Given the simplification assumptions, the proposed model exhibits reasonable agreement with the experimental results. It is further suggested that the lubrication of the hard surfaces with thin compliant metallic layers of Ti represents an alternative for the friction improvement in the small bearings belonging to miniature mechanical systems and the Micro-Electro-Mechanical Systems (MEMS).

Vibration of annular elliptic orthotropic plates using two dimensional orthogonal polynomials

Chakraverty S., Bhat R. B., Stiharu I.

Applied Mechanics and Engineering

2000

Vol. 5, no 4

843-866

The free vibration natural frequencies of specially orthotropic annular elliptic and circular plates are analyzed by the Rayleigh-Ritz method, using two-dimensional boundary characteristic orthogonal polynomials generated following a recurrence scheme as assumed shape functions. The first eight natural frequencies are reported here for various values of aspect ratios of the outer and inner ellipse. Results are given for various boundary conditions at the inner and outer edges of the annular plate. The influence of the material property as it changes from isotropic to orthotropic on the natural frequencies is presented graphically. When the inner hole of the annular plate becomes zero i.e. for rectangular orthotropic full circular and elliptic plates, the results are compared with those that are available in the existing literature, and are found to be in good agreement. Presented results may be used as bench marks for validating those obtained by approximate methods such as the finite element method.