NASA 

TP 

1511 

c .1 

NASA Technical Paper 1511 

I 

Ferrographic Analysis of Wear 

Debris From Full-Scale 

Bearing Fatigue Tests 

William R. Jones, Jr., and Stuart H. Loewenthal 

SEPTEMBER 1979 
TECH LIBRARY KAFB, NM 

.. 

0334733 

NASA Technical Paper 1511 

Ferrographic Analysis of Wear 

Debris From Full-Scale 

Bearing Fatigue Tests 

William R. Jones, Jr., and Stuart H. Loewenthal 

Lewis Research Center 

Clevelaud, Ohio 

NASA 

National Aeronautics 

and Space Administration 

Scientific and Technical 

Information Branch 

1979 
SUMMARY 

The Ferrograph was used to determine the types and quantitites of wear particles 

generated during full-scale bearing fatigue tests. Deep-groove ball bearings (65-mm 

bore diameter) made from AIS1 52100 steel were used. A MIL-L-23699 tetraester 

lubricant was used in a recirculating lubrication system containing a 49-micrometer 

absolute full flow filter. Test conditions included a maximum Hertz stress of 2.4 gigapascals (at innerrace), a shaft speed of 15 000 rpm, and a lubricant supply temperature 

of '74' C (165' F). 

Four fatigue failures were detected by accelerometers in this test set. In general, 

the Ferrograph was more sensitive (up to 23 hr) in detecting spall initiation than either 

accelerometers or the normal spectrographic oil analysis (SOAP). For three of the 

failures, increases were observed in the number of spheres, in the wear severity index, 

and in the composite Ferrogram density prior to failure detection by accelerometers. 

For the fourth failure, similar increases were observed but only in the lubricant sample 

taken at test shutdown. In general, lubricant samples contained few particles. Four 

particle types were observed: normal rubbing wear particles, spheres, nonferrous particles, and severe wear (spall) fragments. 

INTROD UC TION 

The goals of oil analysis are to diagnose the current condition of operating machines 

and to be able to predict any future problems. A variety of different techniques (ref. 1) 

are being employed to effect these goals. These include spectrographic oil analysis 

(SOAP), magnetic chip detectors, vibration sensors, and particle counters. Although 

each of these techniques has certain advantages, most of the techniques suffer from not 

being able to distinguish among the various wear modes that can occur. 

The Ferrograph has been developed to magnetically precipitate wear debris from 

used lubricants onto a glass slide to yield a Ferrogram (refs. 2 to 4). The precipitated 

particles range from approximately 0.02 to a few micrometers and are arranged according to size on the slide. Individual particles may be observed with a unique bichromatic 

microscope, the Ferroscope, or with a conventional scanning electron microscope. 

particles associated with the various wear mechanisms. In particular, three particle 

types have been observed during rolling-element fatigue: spheres, spall particles, and 

A number of investigators (refs. 5 to 10) have identified the characteristic wear 
laminar particles (ref. 10). In fact, the occurrence of spherical particles in oil samples has been suggested to be a precursor of bearing fatigue in some cases (refs. 9 to 

11). Recently, the Ferrograph was used to characterize the wear debris generated in 

accelerated rolling-element fatigue tests (ref. 12). Although spheres and microspall 

particles were observed in that study, their detection as a function of time was of limited 

use in predicting fatigue failures. It was felt that this result may have been related to 

the accelerated nature of those tests (high maximum Hertz stress levels of 5.5X10 Pa 

were employed). 

wear particles generated in full-scale bearing fatigue tests by Ferrographic analysis 

and (2) determine the relative sensitivity of the Ferrograph compared to an accelerometer system in detecting spa11 initiation. Tests were conducted on a multiple bearing 

fatigue test machine with 65-millimeter-bore-diameter, deep-groove ball bearings lubricated with Mil-L-23699 qualified tetraester oil. Test conditions consisted of a shaft 

speed of 15 000 rpm, a radial load of 4580 newtons (1030 lb), and an oil inlet temperature of '74' C (165' F). 

9 

The objectives of this investigation were to (1) determine the types and quantities of 

APPARATUS 

Bearing Fatigue Tester 

A cross section of the bearing fatigue tester used in this investigation is shown in 

figure 1. This tester is described in detail in reference 13. Two identical bearing 

fatigue testers, each containing four test bearings, were operated concurrently. Each 

bearing tester is driven by a quill shaft system connected to the 37.3-kilowatt (50 hp) 

variable speed drive system (not shown in the illustration). The bearings are loaded 

only in a radial direction by a hydraulic cylinder. The radial load is transmitted equally 

to the two center bearings through a wiffletree and is transmitted to the two outboard 

bearings as shown. Thermocouples were attached to the outer race of each test bearing. 

The lubrication supply system, shown schematically in figure 2, delivers a total of 

1090 kilograms per hour (2400 lb/hr) of oil through the test filter to the eight test bearings. The flow is equally divided among the test bearings by a calibrated orifice at an 

oil supply pressure of 0.28 megapascals (40 psi). Each test bearing was lubricated by 

its own calibrated oil jet. A total of 3X10-2 (8 gallons) of lubricant was contained in the 

lubrication system. About 6X10m3 cubic meter (1.6 gallons) was removed from the system daily and replenished with fresh lubricant. 

The oil drains from the test bearings by gravity into a collector pan and is returned 

to the oil supply tank by a scavenge pump. On this return line is an oil-water heat exchanger that regulates the oil inlet temperature to the bearings at the required 74' C 

2 
(165' F). An automatic oil sampler is located in this return line. The sampler uses a 

plunger containing about a 4X10-6 cubic meter (4 ml) cavity which sweeps across the oil 

line cross section when actuated. The sampler was cycled for about 50 seconds to fill a 

lX10-4 cubic meter (100 ml) bottle. 

The test stand instrumentation included an acceleromder system which detected 

bearing failures as well as protective circuits which shut down the drive system if any 

of the test parameters deviated from the programmed conditions. Parameters monitored and recorded during the test included bearing inner race speed, oil flow to each 

tester, test bearing outer race temperature, lubricant supply and scavenge temperature, 

and bearing vibration level. 

filter. It had a mean particle removed rating of 40 micrometers and an absolute rating 

of 49 micrometers (Mil-F-27656). It was of the porous depth-media type, composed of 

resin impregnated organic/inorganic fibers. 

The lubricant used was a prefiltered neopentyl polyolester (tetraester) meeting the 

Mil-L-23699 specification. Table I lists some of its typical properties. 

The filter used in this study was a 30-micrometer nominal (Mil-F-5504) full-flow 

Bearings 

The bearings used in this study were ABEC-3 grade, deep-groove ball bearings with 

a 65-millimeter bore diameter containing 18 balls, each having a 7.94-millimeter diameter. The races and balls were manufactured from a single heat of carbon vacuumdegassed (CVD) AIS1 E-52100 steel. The nominal hardness of the races was Rockwell 

C 62+1.0. The retainer was a machined two-piece inner-land riding cage made from 

iron silicon bronze. The raceways were ground to a nominal surface finish of 0.1 

micrometer rms and the balls to 0.05 micrometer rms. An overall view of a test bearing is shown in figure 3. 

WEAR DEBRIS ANALYSIS 

Ferrograph 

The Ferrograph (refs. 2 to 4) was used to magnetically precipitate wear particles 

from the used oil onto a specially prepared glass slide. The oil sample was heated to 

70' C for a minimum of 10 minutes and then shaken vigorously. A mixture of 3X10-6 

cubic meter (3 ml) of used oil and 1X10'6 cubic meter (1 ml) of solvent is then prepared. 

This mixture is slowly pumped over the slide as shown in figure 4. A solvent wash and 

3 
fixing cycle follows which removes residual oil and permanently attaches the particles 

to the slide. The resulting slide with its associated particles is called a Ferrogram. 

cal density (percent area covered) of the deposit at seven'positions along the slide - 

entry (55-56), 54, 50, 40, 30, 20, and 10 millimeters from the end of the slide. A composite Ferrogram density was determined for each slide by averaging the seven readings. 

The amount of wear debris on a Ferrogram was determined by measuring the optiEnergy Dispersive X-ray Analysis 

The elemental composition of the different types of wear debris was determined by 

using an energy dispersive X-ray analysis (EDAX). In order to prevent charging in the 

scanning electron microscope, the Ferrogram slides were coated with either a thin 

layer (2X10-8 m, 200 8) of carbon or gold. 

RESULTS AND DISCUSSION 

The lubricant samples analyzed in this study were selected from the larger fatigue 

test program reported in reference 13. Samples were taken at approximately 6- and 

12-hour intervals from the lubrication line downstream of the bearings between the 

scavenge pump and supply tank as shown in figure 2. These samples were from a test 

set which resulted in four fatigue failures at 443, 526, 1013, and 1096 hours, respectively. The exact time of failure initiation is uncertain. However, the length of the 

spall is somewhat indicative of the time interval between spall initiation and dectection 

due to high vibration levels. Table 11 contains the sizes of the spalls and the weight loss 

for each bearing. 

The fatigue spall which was detected at 526 hours is illustrated in figure 5(a). A 

scanning electron micrograph of this spall is shown in figure 5(b) at low magnification 

and in 5(c) at higher magnification. This failure, which is typical of the failures in this 

test series, appears to be of the classical subsurface originated type. 

Types of Wear Debris 

Essentially four types of wear debris were observed during this study. These types 

were normal rubbing wear particles, spherical particles, nonferrous particles, and 

severe fragments. Fatigue microspall particles and laminar particles sometimes reported during fatigue tests (ref. 10) were not observed in this study. 

4 
Almost all of the oil samples of this study were exceptionally clean (i. e., they contained very few particles). Typically, Ferrogram composite density measurements 

were less than 1 percent (for a 3X10’6 m3 (3 ml) sample). 

served in almost all oil samples from lubrication systems. This study was no exception 

as most samples yielded at least a few such particles. Typically, these particles are 

small asymmetrical metallic flakes (<15 pm in major dimension and <1 pm thick). 

They are produced anytime that sliding wear takes place. Electron micrographs of 

some normal rubbing wear particles appear in figures 6(a) and (b). An X-ray energy 

map for iron appears in figure 6(c) and indicates that most of the particles are predominately iron. 

bing wear particles were observed in the samples taken at test startup and at 2 and 5 

hours. This is related to the wear-in process and possible startup contamination. 

Throughout the rest of the test few rubbing wear particles were observed. One possible 

source for these particles is the gear-type scavenge pump (fig. 2) located upstream of 

the automatic sampler. 

samples. An 8-micrometer sphere is shown in figure 6(a). Although most of the 

spheres appeared metallic when observed in the bichromatic microscope, an X-ray 

energy analysis indicated that there were two types present. These types are illustrated 

in figure 7 where two different 4-micrometer-diameter spheres are shown. An iron 

X-ray energy map for the sphere of figure 7(a) appears in figure 7(b). This is the normal iron map one would obtain from a solid iron or steel microsphere. However, the 

4-micrometer-diameter sphere of figure 7(c) indicates a much lower concentration of 

iron. This type of sphere may contain a large amount of organic material (ref. 14) that 

may be a compound of iron (an inclusion) (ref. 15) or perhaps even be hollow (ref. 16). 

Although an analysis of all the spheres observed during this study was not possible, 

measurements on a number of Ferrograms indicated about half of them contained a high 

concentration of iron and the remaining half a much lower concentration. 

Nonferrous particles. - Several samples contained metallic nonferrous particles. 

In particular, two of the oil samples (429 to 435 hr) prior to the 443-hour failure contained this particle type. An optical micrograph of one such particle appears in figure 

8(a); its accompanying electron micrograph is shown in figure 8(b). 

pear bronzelike in reflected white light and an X-ray energy analysis confirms this. 

X-ray energy maps for copper and zinc appear in figures 8(c) and (a), respectively. 

An analysis of the iron-silicon bronze bearing retainer closely resembles that of these 

particles. Therefore, it seems likely that the retainer is the source of these particles. 

Severe wear particles. - Severe wear particles refer to large metallic (>2O pm in 

major dimension) wear fragments which are the result of some catastrophic wear mode. 

Normal rubbing wear particles. - Normal rubbing wear particles (ref. 10) are obThis particle type is not related to the fatigue process. Moderate amounts of rubSpherical __ particles. - Microspheres (1- to 10-pm diam) were observed in many 

These particles ap5 
Most of the severe particles observed in this study appeared to be spall fragments, 

since they were usually observed just prior to or after a fatigue failure. However, considering the rather large spalls that occurred, it is surprising that so few were observed. Either the spalling occurred very rapidly or the filtration system was efficient 

enough to greatly limit their concentration. Another possibility is that the large particles may have been comminuted in passing through the scavenge pump. After the test 

rig was shut down following each failure, the test head was completely cleaned and 

flushed out. Therefore, one would not expect to observe a large number of these particles after failure. 

Correlation of Ferrogram Results with Fatigue Failure 

AS previously mentioned, composite Ferrogram densities were determined for each 

sample. This parameter yields the average particle density for each sample. A second 

parameter, the wear severity index, has been advocated by Bowen and Westcott (ref. 10). 

This parameter is calculated from optical density measurements made at the entry position of the Ferrogram (AL) and at the 50-millimeter position (AS). These are the areas 

covered by the large and small particles. Their sum (AL + As) yields the general level 

of wear, while their difference (AL - As) gives an indication of abnormality. These two 

quantities multiplied together (AL + As) (AL - As) yield the wear severity index 

Ai - AS, usually abbreviated Is. In this study, increases in Is are generally related 

to increases in the number of spall fragments. 

The progression of the fatigue process has been studied by other investigators 

(refs. 6 to 11). In those studies, a precursor to fatigue failure has been the appearance 

of metallic microspheres in the lubricant. In addition, microspall particles and laminar 

particles sometimes appear in the oil prior to failure . 

were observed in some accelerated rolling-element fatigue tests but not in all tests. In 

these tests of reference 12, optical density measurements were of little use in following 

fatigue progression because of contaminating friction polymer deposits. 

In the present study, three parameters were followed as a function of test duration. 

These were the composite Ferrogram density, the wear severity index, and the number 

of microspheres. These parameters appear in figure 9 as a function of test time. 

As can be seen, all three parameters yielded relatively high values during the first 

few hours of the fatigue test. The appearance of a large amount of debris during run-in 

is not unusual. However, the high initial sphere count in the 3-hour sample is not 

understood. As the test progressed, average background levels of about 2 for the number of spheres, less than 8 for the wear severity index, and less than 1 for the composite density were observed. 

2 

In a previous paper by the author (ref. 12) microspheres and microspall particles 

6 
First fatigue failure (443 hr). - Discounting the run-in period, there were only a 

few samples that yielded values greater than the background levels for the wear severity 

index Is and composite density during the first 400 hours (fig. 9). An examination of 

the particles present in these samples indicated a general increase in the amount of debris, but no particles were observed which would be related to fatigue. 

hours before the first fatigue failure was detected, a few spall fragments were observed 

(423-hr sample). In the next sample (429 hr) there was a dramatic increase in the number of spheres (2 to 49), more spall fragments were noted, and a few bronzelike particles were observed. Similar results were obtained with the next sample (435 hr) but the 

sphere count had decreased to 10. Normal background levels were then observed in the 

441-hour sample. Two hours later (443 hr) the accelerometer detected the first spall. 

(503 hr) a sphere count of 12 was noted and spall particles were observed. The next 

sample (515 hr) yielded a similar sphere count, more spall fragments, and a large increase in Is. Eleven hours later (526 hr) this failure was detected. After the failed 

bearing was replaced and the test was restarted, spall particles were observed in the 

next three samples (530, 542, and 554 hr), and a higher than normal sphere count (14) 

was observed in the 530-hour sample. 

~~~ Third (1013 hr) and fourth failure (1096 hr). - Fewer samples were analyzed after 

the second failure because of time limitations. Samples returned to background levels 

until the 897-hour sample, which yielded a few brongelike particles and an accompanying increase in Is. Two samples later, Is increased again but no abnormal particles 

were observed. The 1005-hour sample appeared normal but had a sphere count of 13. 

Eight hours later the fatigue failure was detected. The sample taken at shutdown was 

normal except for a few spall fragments. However, the next sample (1021 hr) yielded 

more spall particles, a sphere count of 16, and a very-large increase in Is. A few 

spall particles were observed at 1032, 1044, and 1073 hours, but other parameters were 

normal. The final failure was detected at 1096 hours. The sample taken at that time 

yielded a sphere count of 12, a few spall particles, and a high Is value. 

In analyzing these results, it appears that spall initiation occurred more than 20 

hours before accelerometer detection for the first failure, 23 hours before the second, 

and 8 hours before the third. It is not clear when spall initiation occurred in the fourth 

failure. 

aftermath of the 1013-hour failure. The final spall was probably initiated sometime 

after the 1085-hour sample, propagated rapidly, and was detected by the accelerometers 

before the next routine sample was to be taken. 

It should be noted that the accelerometer sensitivity was not optimized in this study. 

It is likely that a more sensitive accelerometer setting would have allowed for earlier 

failure detection. However, this would also increase the chance of spurious signals 

stopping the test before a failure occurred. 

However, 20 

Second failure (526 hr). - Twenty-three hours before this failure was detected 

The large increase in parameters in the 1021-hour sample is most likely an 

7 
Spectrographic Oil Analysis 

One other parameter was studied for possible failure correlation. This parameter 

was the change in concentration of iron in the oil samples measured by ordinary spectropgrahic analysis (SOAP). Measurements were only made on selected oil samples 

from test startup to 566 hours, thus encompassing the first two fatigue failures. The 

iron concentration in parts per million appears as a function of test time in figure 10. 

Rather low values were observed (0 to 3 ppm), and there was no correlation with the two 

failures . 

CONCLUDING REMARKS 

In general, the Ferrograph proved to be more sensitive in detecting spall initiation 

than the accelerometers or normal spectrographic oil analysis. Particles normally 

associated with fatigue were observed in the lubricant from 8 to 23 hours before accelerometer detection for three of the failures. For the fourth failure, these particles were 

observed only in the lubricant sample taken at test shutdown. 

SUMMARY OF RESULTS 

The Ferrograph was used to characterize wear debris from full-scale bearing 

fatigue tests. Four fatigue failures were detected by accelerometers at 443, 526, 1013, 

and 1096 hours. The results are summarized as follows: 

1. In three of the four failures, there were increases in the number of spheres, the 

wear severity index, and the composite Ferrogram density prior to failure detection by 

accelerometers. 

2. There was no correlation between the fatigue failures and iron concentrations in 

the lubricant as measured by ordinary spectrometer techniques (SOAP). 

3. In general, lubricant samples contained very few particles. 

gram densities were typically less than 1 percent. 

4. Basically, four types of wear particles were observed: normal rubbing wear 

particles, spheres, nonferrous particles, and severe wear (spall) fragments. Fatigue 

microspall and laminar particles were not observed. 

Composite FerroLewis Research Center, 

National Aeronautics and Space Administration, 

Cleveland, Ohio, July 10, 1979, 

505-04. 

8 
REFERENCES 

1. Beerbower, A. : Spectrometry and Other Analysis Tools for Failure Prognosis. 

Lubr. Eng., vol. 32, no. 6, June 1976, pp. 285-293. 

2. Seifert, W. W. ; and Westcott, V. C. : A Method for the Study of Wear Particles in 

Lubricating Oil. Wear, vol. 21, Aug. 1972, pp. 27-42. 

3. Westcott, V. C.; and Seifert, W. W. : Investigation of Iron Content of Lubricating 

Oil Using Ferrograph and an Emission Spectrometer. Wear, vol. 23, Feb. 1973, 

pp. 239-249. 

4. Scott, D. ; Seifert, W. W. ; and Westcott, V. C. : Ferrography - An Advanced Design Aid for the 80's. Wear, vol. 34, 1975, pp. 251-260. 

5. Reda, A. A. ; Bowen, R. ; and Westcott, V. C. : Characteristics of Particles Generated at the Interface Between Sliding Steel Surfaces. Wear, vol. 34, 1975, 

pp. 261-273. 

6. Scott, Douglas; Seifert, William W.; and Westcott, Vernon C. : The Particles of 

Wear. Sci. Am., vol. 230, no. 5, May 1974, pp. 88-97. 

7. Westcott, V. C.; and Middleton, J. L. : The Investigation and Interpretation of the 

Nature of Wear Particles. Final Rep. 10 May 1973 - 9 Mar. 1974, Trans-Sonics, 

Inc., 1974. (Available from NTIS as AD-A003553.) 

8. Scott, D.; and Mills, G. H. : Debris Examination in the SEM: A Prognostic Approach to Failure Prevention. 

Electron Microscopy, A Workshop on Failure Analysis and SEM (Chicago, Ill.), 

Apr. 8-11, 1974, pp. 883-888. 

Presented at the 7th Annual Symposium on Scanning 

9. Scott, D.; and Mills, G. H. : Spherical Debris - Its Occurrence, Formation and 

Significance in Rolling Contact Fatigue. Wear, vol. 24, May 1973, pp. 235-242. 

10. Bowen, E. Roderic; and Westcott, Vernon C. : Wear Particle Atlas. Naval Air 

Engineering Center, July 1976. 

11. Middleton, J. L.; Westcott, V. C.; and Wright, R. W. : The Number of Spherical 

Particles Emitted by Propagating Fatigue Cracks in Rolling Bearings. Wear, vol. 

30, 1974, pp. 275-277. 

12. Jones, William R., Jr. ; and Parker, Richard J. : Ferrographic Analysis of Wear 

Debris Generated in Accelerated Rolling-Element Fatigue Tests. ASLE Trans. , 

vol. 22, no. 1, Jan. 1979, pp. 37-45. 

13. Loewenthal, S. H. ; and Moyer, D. W. : Filtration Effects of Ball Bearing Life and 

Condition in a Contaminated Lubricant. ASME Paper 78-Lub-34, Oct. 1978. 

9 
14. Ruff, A. W. : Metallurgical Analysis of Wear Particles and Wearing Surfaces, 

NBSIR 74-474, National Bureau of Standards, 1974. (Available as AD-778340.) 

15. Christensen, C. : On the Origin of Spherical Particles Found on Fatigue Fracture 

Surface and Ferrograms. Wear, vol. 53, Mar. 1979, pp. 189-193. 

16. Jones, W. R., Jr. : Spherical Artifacts on Ferrograms. Wear, vol. 37, Apr. 1976, 

pp. 193-195. 

10 
111 ~ I1 11111 I I .I 

TABLE I. - PROPERTIES OF TETRAESTER LUBRIC~NT 

Additives 

Kinematic viscosity, cS, at - 

311 K (100' F) 

372 K (210' F) 

477 K (400' F) 

Flash point, K (OF) 

Fire point, K (OF) 

Autoignition temperature, K (OF) 

Pour point, K (OF) 

Volatility (6.5 hr at 477 K 

(400°F)), wt. % 

Specific heat at 477 K (400' F), 

Thermal conductivity at 477 K 

J/(kg) (K) (@tu/&) (OF) 1 

(400' F), J/(m)(sec)(K) 

((Btu/hr) (ft) (OF)) 

Specific gravity at 477 K (400' F) 

Antiwear, oxidatior 

inhibitor, antifoam 

28. 5 

5.22 

1.31 

533(500) 

Unknown 

694( 800) 

2 14( -75) 

3.2 

2340(0.54) 

0.13(0.075) 

0.850 

TABLE II. - SUMMARY OF BEARING FAILURES 

Description of failure 

accelerometer, 

443 

526 

1013 

1096 

118 

62 

--- 

75 

One inner race spall 12.7 mm long; 

one ball with spall 

One inner race spall 1 mm long by 

2.5 mm wide; one outer race 

spal16.4 mm long 

One inner race spall 

One outer race spall 5.6 mm long 

by 3.2 mm wide 

11 
r----------- 1 

f&&v,rHydraulic loader 

NL 

Thermocouple 

,-Spherical load 

// bearing 

;Thermocouple port 

f 

+- 

9" I L \., Carbon face I\ ' 

"Ther mocbuple 1 

ports 

Figure 1. - Bearing fatigue tester. 

valve I 

r------- e-----_I I 

Instrument sensors 

0 Temperature 

in controller g- Filter 

Pressure I$] Pressure 

reducing ,, 

valve - ,- Flowmeter , \ 

,- 

W 

Scavenge Tpmp 

:iY:Oa:::r 

Figure 2. - Lubricant supply system. 
Figure 3. -Test bearing with 65-millimeter bore diameter. 

Oilinlet, / 

Figure 4. - Ferrograph analyzer. 

13 
in- I 

[a) Fatigue failure on inner race 

(b) Fatigue Spall under low magnlflcation. (C) Leading edge of spall under medium magnificatloo 

Figure 5. - Apparent subsurface Initiated fatigue spall on inner lace of test bearing (526-hr fadure) 

(a) String of wear particles (b) Area (a) at higher magnifi- (c) X-ray energy maps of (b) for 

and 8-micrometer-diameter cation. iron. 

sphere from 530-hour sample. 

Figure 6. - Scanning electron micrographs. 

14 
(C) 

(a) Bronze particle. 

(c) Of (b) for copper. 

(b) Same particle. 

(d) Of (b) for zinc. 

Figure 8. - Optical micrograph (a) and scanning electron micrograph (b) of same 

particle and their corresponding X-ray energy maps ((c) and (dl). 

Figure 7. - Scanning electron micrographs of two sperical particles ((a) and (c)) and 

their corresponding iron X-ray energy maps ((b) and (d)). 530-Hour sample. 
60 L 

om 

n c 

z 

&$ 40 

5% 20 

0 

200 Accelerometer- I 

d 

p 100 

& 2 

s 

5- 

s<;s 4 .s .z E 

-5, 2 E= 

-0 c 

.- 

> al v) 

L m 

0 

8 

g$E 6 

Le 

Y 

u 

0 100 300 400 450 400 450 500 600 800 900 1100 

Test time, hr 

Figure 9. - Composite Ferrqram density, wear severity index, and number of spheres as functions of test time. 

El0[ n~ 

I I 

Accelerometer- I ! 0 

cz6 L 

$4 

0 

._ 

- 

c 

c 0 u 

L E2 - 

0 100 200 400 500 600 

Test time, hr 

Figure 10. - Iron concentration in oil in ppm as function of time from spectrographic 

oil analysis (SOAP). 

16 

..... I 11.1 I, 1-1 111.1.1111.-11111. I I I I 111 I1111111111111 I1 I 111 I111 
r 

17. Key Words (Suggested by Authorls) ) 

Ferrographic analysis; Spectrographic oil 

analysis; Rolling-element fatigue; Wear 

mechanisms; Lubrication 

1. Report No. 2. Government Accession No. 

-. I .__-. NASA TP-1511 

4. Title and Subtitle 

FERROGRAPHIC ANALYSIS OF WEAR DEBRIS FROM FULLSCALE BEARING FATIGUE TESTS 

.. ~ ~ .- . -. 

7. Author(s1 

William R. Jones, Jr., and Stuart H. Loewenthal 

. ~~ . . . .. . . .- . . - .. .~ ~... 

9. Performing Organization Name and Address 

National Aeronautics and Space Administration 

Lewis Research Center 

Cleveland, Ohio 44135 

National Aeronautics and Space Administration 

Washington, D. C. 20546 

- . 

12. Sponsoring Agency Name and Address 

__.~___ 

18. Distribution Statement 

Unclassified - unlimited 

STAR Category 37 

3. Recipient's Catalog No. 

-~ . . -- 

5. Report Date 

September 1979 ____. . 

6. Performing Organization Code 

~ ~. 

8. Performing Organization Report No. 

E-9827 

10. Work Unit No. 

505-04 

.- 

- .. 

11. Contract or Grant No. 

13. Type of Report and Period Covered 

Technical Paper 

~ -- - 

14. Sponsoring Agency Code 

- _ 

16 Abstract 

The Ferrograph was used to determine the types and quantities of wear particles generated during full-scale bearing fatigue tests. Deep-groove ball bearings made from AIS1 52100 steel were 

used. A MIL-L-23699 tetraester lubricant was used in a recirculating lubricant system containing a 49-pm absolute filter. Test conditions included a maximum Hertz stress of 2. 4 GPa, a 

shaft speed of 15 000 rpm, and a lubricant supply temperature of 74' C (165' F). Four fatigue 

failures were detected by accelerometers in this test set. In general, the Ferrograph was more 

sensitive (up to 23 hr) in detecting spall initiation than either accelerometers or the normal 

spectrographic oil analysis (SOAP). Four particle types were observed: normal rubbing wear 

particles, spheres, nonferrous particles, and severe wear (spall) fragments. 

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