The paper reviews, from both a technical and historic perspective, the results of research conducted using the NASA Five-Ball Fatigue Tester. The

Response to caloric stimulation was examined in two subjects in the weightless environment of orbital flight. Using air insufflation, a binaural temperature stimulus profile was performed twice on each subject during flight. In all but one test, which was carried out on the first mission day, a caloric nystagmus was registered. This zero-g nystagmus was similar to ground-based pre- and postflight responses with regard to its intensity, its temporal correlation with the stimulus profile (nystagmus was always directed towards the warmer ear) and the subjective sensations reported by the tested subjects. These findings demonstrate that mechanisms other than thermoconvection are involved in the elicitation of the caloric nystagmus response. At each stage of the temperature stimulus profile, linear acceleratory stimulation was presented in the form of oscillations in the X-axis. Some differences were found between one-g and zero-g conditions in the resultant modification of the nystagmus response.

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%

Lubricated and unlubricated tests were conducted in the NASA spinning friction apparatus with SAE 52100 steel specimens with ball-race conformities of infinity (a ball on a flat), 60, 55, and 51-percent. For a constant conformity under lubricated conditions, the coefficient of spinning friction decreased from approximately 0.5 to 0.05 with increasing load and stress. At a constant stress, the coefficient of spinning friction increased with decreasing conformity (increasing percent conformity). Under unlubricated conditions, the coefficient of spinning friction remained relatively constant regardless of load, stress, or conformity, having values within a scatter band of 2.5 to 6.0. For a constant stress under both lubricated and unlubricated conditions, the greater the conformity (the smaller the percent conformity), the higher the torque.