Component Hardness Differences and Their Effect on Bearing Fatigue

Abstract

IT h e ' f i v e -b a l l f a t i g u e t e s t e r and f u l l -s c a l e rolling-element bearings were used t o determine t h e \ e f f e c t of component hardness d i f f e r e n c e s of SAE 52100 s t e e l on bearing f a t i g u e and load capacity.Maximum f a t i g u e l i f e and load capacity a r e achieved when t h e r o l l i n g elements of a bearing a r e one t o two p o i n t s (Rockwell C) harder t h a n t h e races. r e s i d u a l s t r e s s e s induced i n t h e races during operation, d i f f e r e n c e s i n component hardness, and f a t i g u e l i f e . Differences i n contact temperature and p l a s t i c a l l y deformed p r o f i l e r a d i i could not account There appears t o be an i n t e r r e l a t i o n among compressive f o r d i f f e r e n c e s i n f a t i g u e l i f e ..4 X-52087'ry W NOMENCLATURE deformation and wear a r e a from s u r f a c e t r a c e , sq. in.( a = D + W) load capacity, t h e load a t which 90 percent of a group of bearings can endure 1,000,000 i n n e r r a c e revolutions, or for b a l l specimens, 1,000,000 s t r e s s cycles, 1%( C = P&) deformation a r e a from surface t r a c e , sq in. i n n e r race conformity, percent o u t e r r a c e conformity, percent depth of running t r a c k from s u r f a c e t r a c e , in.hardness of r o l l i n g element minus race hardness f o r f u l ls c a l e bearings or f o r f i v e -b a l l t e s t system, t h e hardness of t h e lower t e s t b a l l s minus t h e hardness of t h e upper t e s t ball, Rockwell C 10-percent f a t i g u e l i f e , m i l l i o n s of revolutions or s t r e s s cycles bearing o r t e s t system r a d i a l or t h r u s t load, l b normal b a l l load, 1%

NASA Five-Ball Fatigue Tester—Over 20 Years of Research

“…The reanalyzed data not only indicated the opuimum aH relation, but also exhibited relative life values of approximately the sane magnitude with varying aH as those shown for the 207-size bearings in [18].…”

“…Based upon the above results, the data of [12], which were among the earliest data to show an effect of hardness on life, were reanalyzed considering hardness differences between the balls and race [18]. The reanalyzed data not only indicated the opuimum aH relation, but also exhibited relative life values of approximately the sane magnitude with varying aH as those shown for the 207-size bearings in [18].…”

“…While it may be difficult, although not impossible, to predict actual bearing life [59] from them, or based on them, bench-type fatigue tests, such as those run in the NASA five-ball fatigue tester, can rank material, lubricant, or operating variables on a relative life basis [5,[14][15][16][17][18]36]. This is illustrated in Fig.…”

“…Therefore, where plastic deformation does occur under rolling contact, the calculated Hertz stress may only be approximate [14,16] [17,18] and summarized in Fig. 3.…”

“…To illustrate the effect of hardness differential, eH, on bearing fatigue and load capacity, four lots of AISI 52100, 207-size, deep-groove ball bearings, each with balls of a specific hardness and races of Rockwell C hardness 63, were fatigue tested at a radial load of 5870 N (1320 pounds), a speed of 2750 rpm with a mineral oil lubricant, and with no heat added [18,19]. The relative bearing load capacity is shown as a function of off in Fig.…”