Stress analysis of marine gears considering 3D mixed lubrication-contact state

Abstract

Marine transmission gears usually have large size, and often experience severe working conditions, such as heavy load, large transmission power and high speed ratio, together with the effect of surface asperities, which cause coexisting lubrication-contact state and seriously stress concentration, and further may lead to micro-pitting and fatigue failure. In this paper, the subsurface stress prediction model of the timing transmission spur gears of marine engine is developed, together with considering real 3D machined surface roughness and mixed lubrication-contact state. Results show, when the contact bodies with perfect elastic behavior,the maximum von Mises stress appears on the surface and no longer shows regular distributions along the line of action because of the 3D roughness.The transverse turned surface can reduce the subsurface stress greatly, the shaved and ground surfaces cause large subsurface stress and high-pressure area on the surface. The influence of surface roughness on the stress state is increased under the special conditions of low velocity and high power density, and the contact state is greatly improved by optimizing the parameters of tooth width. Effects of different materials indicate nylon-nylon contact surfaces has the smallest maximum stress compared with that in other four pairs. However, nylon-nylon contact surfaces have the highest friction coefficients, which can easily lead to severe wear or scuffing failures.

Modeling and analysis of 3D mixed lubrication in marine cam–tappet pair

“…The total friction is determined by integrating shear stress of the entire region, including both the hydrodynamic and contact region, as described in Sun et al and Zhang et al's study. 35,36…”

“…The total friction is determined by integrating shear stress of the entire region, including both the hydrodynamic and contact region, as described in Sun et al and Zhang et al’s study. 35,36 Based on the moving heat source model, the flash temperature model for the cam–tappet interface is establish. 37 In addition, the subsurface stress can be calculated by the integration of the surface normal pressure and the shear stress. where Tijn and Tijt ( i = x , y , z and j = x , y , z ) are the stress components from normal and tangential unit forces, respectively.…”

Predictions of friction and temperature at marine cam-tappet interface based on mixed lubrication analysis with real surface roughness

“…It is assumed that the contact load on the surface is evenly distributed, so the contact load at any position is equal to F. After obtaining the film shear stress in the lubrication region, the friction force of the cam-tappet is calculated by integrating the shear stress, thus the friction coefficient is obtained from, 37,38…”

“…35,36 The shear stress is obtained by multiplying the friction coefficient and the corresponding pressure, and then the asperity contact friction is obtained by integrating the shear stress. It is assumed that the contact load on the surface is evenly distributed, so the contact load at any position is equal to F . After obtaining the film shear stress in the lubrication region, the friction force of the cam-tappet is calculated by integrating the shear stress, thus the friction coefficient is obtained from, 37,38 The flash temperature at the cam-tappet interface can be evaluated by using the heat transfer theory based on a fast moving point heat source. Therefore, the following Volterra integral equations of the second kind can be utilized, and the flash temperature of the cam-tappet pair is then obtained.…”