Reply to comments on “oxidational wear”

LETTERS TO THE EDITOR

501

Reply to comments on “Oxidational wear” I am pleased that Mr. Berry has shown such an interest in my paper. Regarding his first point, I agree that, according to the theoretical equation proposed by Archard, a graph of wear rate (w) versus the real area of contact (A) should be a straight line of slope K, passing through the origin. However, it must be pointed out that the abscissae in Fig. 1 were values of the ratio of the load (W) divided by the initial hardnesses of the steel specimens (p,). Only in the case of severe wear has it been universally accepted that (W/p,) is equal to the real area of contact (A). Under the conditions of mild wear which occurred during the experiments covered by Fig. 1, it is quite possible that only for the lower loads was the real area of contact given by this ratio. For higher loads, one might expect a change in hardness at the contacting asperities. For instance, if some softening occurred, then the real area of contact would actually be larger than indicated by the ratio of load to initial hardness, (i.e. W/p,). Hence a graph of w versus W/p, would appear to have an increase in slope at a certain critical area ofcontact i.e. at about 10V4 cm2. Thus I would agree with Mr. Berry in taking the initial slope as being the relevant one for calculating K. I would suggest, however, that the difference between the initial and final slopes is a secondorder factor compared with the large differences between the slopes of mild and severe wear rates when plotted against (W/p,). This brings me to Mr. Berry’s second point regarding the interpretation of the K-factor. Mr. Berry interprets K as the probability that a wear particle will be produced at any given time. I introduce the K-factor by assuming that l/K encounters are necessary to produce a critical oxide thickness at a given asperity contact. This latter assumption allows us to neglect the shape of the wear particles. We are only interested in thickness of oxide formed whilst still in contact. Quite clearly, the wear particles will initially be flakes, which then degenerate into spherical particles with diameters about the same as the flake thickness. This has been confirmed by electron microscopy. In the paper, the approach to the derivation of a wear equation makes no effort to equate wear volumes with oxide volumes. It is concerned only with oxide thickness. Hence, I cannot accept Mr. Berry’s modification ofmy wear formula. Nevertheless, I do think that the situation still requires much further clarification. We need to know much more about the real areas of contact between wearing surfaces, more about the heat flow distribution between the surfaces, more about the actual temperatures at which the surfaces oxidize during wear, and more about the dependence of oxide growth upon time during asperity contacts. In fact, we need to know more about the whole “micro-activity” between sliding surfaces. When we have obtained some more hard facts about these unknowns, then will come the time to consider further refinements of the Oxidational Wear Hypothesis! T. F. J. Quinn Department of Physics, The University of Aston Gostu Green, Birmingham 4 (Gt. Britain)

Received August 2, 1971 Wear, 18 (1971) 501

502

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NOTES ON CONTRIBUTORS

R. T. Aird:

(for biographic

A. Beerbower:

note see Wear, 18 (1971) 427).

(for biographic

A. W. J. De Gee: S. W. Earles:

note see Wear, 18 (1971) 427).

(for biographic

note see Wear, 18 (1971) 427).

(for biographic

S. L. Forgham:

note see Wear, 17 (1971) 88).

note see Wear, 18 (1971) 427).

(for biographic

[See p. 4911 [See p. 4931 [See p. 4961 [See p. 4981 [See p. 4911

Tedric A. Harris : a graduate of Pennsylvania State University; obtained his B.S. in mechanical engineering in 1,953, his M.S. in 1954 and was a postgraduate student at University of Pittsburgh 1955-1959; had considerable experience of industrial &search design, development work, production and administration with various companies before joining SKF in 1960; is now Manager, Analytical Services Department, dealing with bearing analysis and development of computer programmes to simulate bearing performance; is member of the American Society of Mechanical Engineers and A.S.L.E. and has been Chairman or several committees; is author of 32 publications principally on ball and roller bearing technology, a book on rolling [See p. 4291 bearing analysis and holds three U.S. patents. D. W. Morecroft T. F. J. Quinn: S. K. Rhee: J. M. Senior:

(for biographic

(for biographic (for biographic

G. H. G_ Vaessen: G. H. West:

: (for biographic

note see Wear, 18 (1971) 427).

note see Wear, 16 (1970) 468). note see Wear, 18 (1971) 360).

(for biographic

(for biographic

note see Wear, 18 (1971) 360).

note see Wear, 18 (1971) 427).

note see Wear. 18 (1971) 427).

[See p. 4801 [See p. Sol] [See p. 4711 [See p. 4871 [See p. 4961 [See p. 4871

Hai Wu: graduated f;om Cheng Kung University, Taiwan, China with B.S. in mechanical engineering in 1958; came to the United States of America in September 1961; received his MS. from the University of Iowa in 1963, majoring in gas dynamics and his Ph.D. from Case Institute ofTechnology in 1969, majoring in fluid mechanics and heat transfer; joined the Scientific Research Staff, Ford Motor Company in February [See p. 4611 1969 as Senior Research Engineer. N. Tenwick:

(for biographic

Wear, 18 (1971) 502

note see Wear, 18 (1971) 427).

[See p. 4981