Lubricant influence on fatigue crack initiation and propagation.

Lubricant action during two stages of wear development by fatigue of surfaces in contact was examined:- for initiation, on a four-ball fatigue machine, the use of anti-wear and extreme-pressure additives discloses two types of lubricant beahviour, according to the product and its concentration. As for crack propagation on fracture mechanics samples, the presence of a lubricant gives rise to higher cracking speeds than in air. This increase in speed is a function of temperature and shows a maximum around 60 to 70SUPC. This temperature effect is also observed with oil containing an adition of chlorinated parafin. In other respects, at 80SUPC, no pronounced features are observed with different products added to the basic oil when compared to the behaviour of the basic oil alone. (A)