Oil film variation and surface damage in the process of reciprocation-oscillation transformation

Evolution of grease lubrication regimes and surface damage during reciprocation-oscillation transformation

“…As for oil lubrication, as suggest with Han et al, 13 the low film thickness is formed at the startup of the motion since the load is applied and the surface speeds are zero. Moreover, the critical radius stroke ratio of the oil lubricated reciprocating motion is 0.5 for the occurrence of the BL region.…”

“…At this stage, with the removal of the thickener lumps, the film shapes somewhat resemble those in the 1 st cycle of PAO100 lubricated simple sliding results by the authors. 13 The oil lubrication can be maintained up to 1000 working cycles. But for grease lubrication, surface spalling of the glass disk has happened in the 40 th cycle, as shown inside the white circle in Figure 13(d) for λ = 0.5.…”

“…Now, the film shapes at the left and the right stroke ends are the same but only in opposite directions, just like what happened in oil lubricated reciprocating motion. 13,42,43 Because the disturbance on the film thickness due to the thickener lumps has disappeared, the squeeze effect becomes prominent at the stroke end so that a lunular entrapment is seen. With the increase of the λ , the dark green region increases at the stroke ends.…”

“…The authors found that 25 after thousands of working cycles, only a very thin grease layer is remained on the running track, so that the central and minimum film thickness hardly change over one working stroke. As an extension of the previous work, 13 the performance of greases over a large number of working cycles during the reciprocation-oscillation transformation needs to be clarified.…”

“…In oscillating motion, wear and lubrication phenomena are greatly different compared with the general reciprocating motion. 4,[11][12][13] For rolling/sliding motion, insufficient lubrication under the oscillating motion often results in the so-called tangential fretting, which is detrimental to the mechanical components but often is ignored. Recently, the authors 13 found that with oil lubrication, that the ratio of the Hertzian contact radius over the stroke length is 0.5 should be the threshold of the existence of boundary lubrication (BL) region for a long run.…”