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This paper is a review of ceramic tribological characteristics and application of silicon-based ceramics as engine valves and seat inserts. This review has shown that wear of ceramics is not an intrinsic material property or a constant, rather it depends on the operating conditions as well as on microstructure, environment, measurement techniques and material properties. The review also found that the dominant ceramic wear mechanism is a fracture/crack controlled process. There have been many models developed to describe the wear of ceramics, however, the complexity of the wear and the existence of wear transitions suggest that satisfactory results can be obtained for each wear model/equation only for the operating conditions for which it was derived. The application of silicon-based ceramics for engine valves and seat inserts is also reviewed and field engine test results are presented. The advantages and disadvantages of ceramics for engine valves and seat inserts are discussed.

In this investigation, worn valve seats and inserts have been examined to obtain a fundamental understanding of the primary wear mechanisms. Seats and inserts from a wide variety of engines were studied using optical and electron microscopy. The recessed region on seats and inserts displayed a common feature which can be described as a series of ridges and valleys formed circumferentially around the seat axis. These ridges and valleys were found to be due to either a relatively severe gouging process or to a milder deformation and wearing process. These processes were related to assembly and product geometry factors which caused misalignment between the seats and inserts.

Factorial analyses of stress concentrations at the bolt thread root based on finite element models are presented in this paper. A full bolted joint including a bolt, a nut, and fastened members were modeled using solid elements. Bolt and bolt threads were meshed in detail in 3-dimensional mode, with their interaction being only the direct load transfer between the bolt and nut. Statistical design of experiments was conducted to identify the factors and two-factor interactions, which may have impact on the stress concentration at the bolt thread root.