Kazunori Ichimaru

Three-Dimensional Fracture Mechanics Analysis of Pit ormation Mechanism Under Lubricated Rolling-Sliding Contact Loading

The mechanism of so-called arrow headed pit formation on contact surfaces under lubricated rolling-sliding cyclic contact loading was analyzed by fracture mechanics. The stress intensity factors of Modes I, II and III for an arrow-headed crack were calculated by three-dimensional numerical analysis. The analytical results support the hypothesis that an arrow headed crack in pitting phenomenon first propagates in shear mode, and that crack growth by tensile mode follows due to a hydraulic effect on crack faces by the oil that has penetrated into the crack. The analysis predicts that the values of contact pressure and frictional force dominantly determine the final surf ace apex angle of an arrow headed crack. The shape of an arrow headed crack observed under service loading is considered to be useful to estimate the operating conditions in the service loading.

Experimental and Fracture Mechanics Study of the Pit Formation Mechanism Under Repeated Lubricated Rolling-Sliding Contact: Effects of Reversal of Rotation and Change of the Driving Roller

Five rolling contact fatigue tests, Tests (1)-(5) have been conducted. In Tests (1)-(3), when a fatigue crack was initiated on the surface of a follower, the test was halted. Then, in Test (1) the rotating direction was reversed. In Test (2) the follower and driver were interchanged, and in Test (3) the test was continued unchanged. In Test (3) the original crack grew to a pit. In Tests (1) and (2) the original crack immediately stopped propagating. In Tests (4) and (5), mating with a harder roller, a softer roller was used as the follower in Test (4) and as the driver in Test (5). A typical pit occurred in Test (4). In Test (5), surface damage substantially different from a typical pit was generated. Based on these experimental results, a 3-D crack analysis including the effect of frictional force on the contact surface and oil hydraulic pressure on crack surfaces, was conducted to elucidate the mechanisms of pit formation and surface damage in contact fatigue.

Observation and numerical simulation of oil-film formation under reciprocating rolling point contact

A basic study on oil-film formation in reciprocating pure rolling point contact was conducted by optical interferometry observation and numerical analysis. In the analysis the program code published by Venner and Lubrecht was extended for time dependent and starved problems. The observations showed that the oil-film thickness in reciprocating rolling was less than that in unidirectional rolling; this because of the starved condition that was induced by cavitation generated in the previous passing of the contacting region and which survived in the inlet region for a while after reversal. The Elrod algorithm was used in the numerical analysis, and the amount of oil on the trailing edge of the calculation domain was stored and used on the leading edge of the calculation domain when it returned after reversal. In this calculation model, the oil-film thickness decreased with cycle repetition, while in the fully flooded condition the oil-film almost recovered when the contacting area returned to the stroke center, and nearly the same oil-film thickness trajectory was traced along with changes of the entrainment velocity.

Numerical simulation of oil-film behavior on cylinder liners in sliding contacts with piston rings

Marine diesel engines, which have large strokes and large cylinder diameters, need to be supplied with cylinder oil to maintain good lubrication. However, the consumption of cylinder oil needs to be reduced to improve cost efficiency. This study proposes a new simulation model, which can be used to calculate oil conservation over the whole of cylinder liners, solving the transport equation. We present some results of the oil mass distribution and discuss the optimal settings for the quantity and timing of the oil supply, the rate of oil quantity (1) scraped by the top or the bottom ring, (2) that remaining on the cylinder liner and (3) that retained between the rings. The formation of a thick oil film is explained by these results.

A deterministic model of mixed EHL in line contact considering the three-dimensional surface roughness

In mixed elastohydrodynamic lubrication, it is supposed that asperity conjunctions should interrupt oil flow in advance of the occurrence of a direct contact. The local transient Reynolds equation, which is expressed in the coordinate system travelling with a rough surface, will serve to simulate the interruption process of oil flow. In this paper, we propose a new model for mixed EHL for the rolling-sliding contact of cylindrical bodies with 3-dimensional single-sided roughness considering a periodical boundary condition and oil mass conservation. Under the conditions of pure rolling, as the local Reynolds equation does not include the wedge-film term, direct contact is predicted to occur easily, especially in the case of a single bump. On the other hand, in the case of a sinusoidal wavy surface, oil entrapped in the space between asperities at the entrance of the Hertz conjunction will be compressed up to a considerable pressure in the Hertz region so that direct contact will be prevented unless there is a large amplitude of roughness.