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The crack growth rate in rolling contact fatigue process is very fast
291
Wear, 113 (1986) 291- 294
Research Report The crack growth rate in rolling contact fatigue process is very fast TAKE0 YOSHIOKA and TAKASHI FUJIWARA Mechanical
Engineering
(Received June 9,1986;
Laboratory,
Namiki
1 - 2, Sakura, Niihari, Ibaraki 305 (Japan)
accepted June 26,1986)
When does a crack begin to propagate during the rolling contact fatigue process? How long does it take from the time that a crack begins to propagate to the time when flaking occurs? These questions about rolling contact fatigue are very interesting. There are many papers in which the appearance and propagation of a fatigue crack at the surface have been reported and, although unknown, the propagating time was thought to be very short. However, the initiation time of the crack propagation and the propagating time were not measured experimentally. In this report, we describe our experimental results obtained using the detection of acoustic emission and vibration. We have already reported that during rolling contact fatigue the position of the source of acoustic emissions coincides with the position of fatigue failure [l, 21. It was also shown that vibration signals contain useful information concerning the condition of the contact surfaces. Here we define the initiation time T, of crack propagation, the propagating time TV - T,, and the life L as follows: T, is the time at which acoustic emissions increase at the position of failure on the raceway of a sample; T” - T, is the period from the initiation time to the time when vibration acceleration increases; L is the running time until a test is automatically stopped by a vibrometer. The test bearing simulated a thrust ball-bearing 51105 (with a bore diameter of 25 mm, an outer diameter of 42 mm and a height of 11 mm) and consisted of an inner race, three balls, a retainer and an outer race (sample). Balls in the test bearing were in contact with a plane on the side of the outer race to accelerate the fatigue test. The bearing testing machine used in the rolling contact fatigue test is shown in Fig. 1. The test bearing was attached to the bottom end of a spindle. The vertical and downward thrust load was statically applied to the bearing by a lever and a dead-weight system. The test bearing was run under an axial load of 3.14 kN at a rotational speed of 660 rev mine1 in a mineral oil bath. The maximum contact pressure induced in the outer race was 5.64 GPa. The ratio of the minimum film thickness Ho to the composite surface roughness R was 0.13 - 0.17. The minimum 0043-1646/86/$3.60
0 Elsevier Sequoia/Printed in The Netherlands
292 KNIFE EDGE.
,
SUPPORT BEARING ITHRUST BALL BEARING) SUPWRT BEARINGS (ROLLER BEARINGS) SPINDLE TEST BEARING WEIGHT HOUSING ’
/n/
Fig. 1. Bearing testing machine for the invocation
TEST BEARING
of rating contact fatigue.
NOISE DISCRIMINATOf+
HOUSING
-+~UNTE~_(RECODER] ~ELIMINATOR I
BEARING TESTING
MACHINE
2. Block diagram of the acoustic em&&on source locater. Fig.
emission measuring system,
including
the acoustic
film thickness Ho was calculated according to the equation derived by Hamrock and Dowson [3]. The block diagram in Fig, 2 shows our acoustic emission measuring system including an acoustic emission source locater. The system has been described in refs. 1 and 2 in detail. The measuring conditions of the acoustic emissions were as follows: the bandwidth was from 200 to 400 kHz, the amplification degree was 80 dB and the threshold level was 0.8 - 2.5 V. Vibration accel~tion from 0.01 to 20 kHz was detected and the fatigue test was au~rna~c~y stopped as soon as its r.m.s. value exceeded a preset level at the occurrence of flaking. The preset level was set in the range 4.9 - 9.8 m S-2.
Figures 3 and 4 give examples of results. Figure 3(a) is the record of the event rate and Fig. 3(b) shows the vibration acceleration. In this case the threshold level of 1.5 V was preset for the event rate and an acceleration of 8.0 m se2 was attained at shutdown. The outer race failed after 16.01 h. It can be seen in Fig. 3(a) that many acoustic signals were emitted in the several minutes before the shut-down. However, it is clear from Fig. 3(b) that the minimal values of acceleration variation increased after the event rate did. The acoustic ‘emission location results obtained from this test are shown in Fig, 4. The x axis indicates the positions on the raceway track and the y
293
1000
A E EVENT RATE
FLAKING
z
100 01, 100 01,
1
1
TIME&“RS, 1 : PI P2
16 P,
H 6
PZ PI 1
, I /
0.5
0.0 POSITION
1.0
ON THE RACEWAY TRACK
Fig. 3. Acoustic emission event rate and vibration acceleration. Fig. 4. Location of the acoustic emission sources.
axis the number of acoustic emissions. On the LXaxis the whole raceway track is measured on a scale from 0.0 to 1.0. The figure shows the locations from period Pi to Pq; these correspond to those in Fig. 3. The locating time of P4 was 3 min before failure. However, the time was 30 min in other periods. There were few acoustic emissions from period Pi to period Pz; on the contrary, for periods P3 and Pq. three conspicuous peaks can be seen. It seems that many acoustic emissions are generated at three particular positions on the raceway track. The positions emitted for period P4 are the same as those for Ps. After the test, the outer race was removed and its raceway track was inspected; flaking was found at the position corresponding to the middle peak in Fig. 4. Although there was one flaking site, it can be seen in Fig. 4 that the three peaks are placed at equal intervals. The reason is that three balls were implanted at the same intervals in the test bearing. This shows that the failure point on the raceway generated the acoustic emission when each ball passed that point. It becomes clear from Fig. 3(a) and Fig. 4 that acoustic emissions at the failure position began at ‘I’,, = 15.86 h, i.e. the fatigue crack started to propagate at T,. Figure 3(b) shows that the fatigue failure appeared on the surface at !I’,. Therefore, 2’” - l’,, the propagating time in this case, was 6 min. The ratio T,/L of the initiation time of crack propagation to the life was 98.9%. The propagating times obtained from 18 tests are shown with their corresponding lives in Fig. 5. The lives were distributed from 11.47 to 112.02 h and the propagating times were from 1 to 25.2 min. The ratios (TV - T,)/L were 0.07% - 1.04%. Therefore the propagating times were equal to or shorter than one-hundredth of the lives.
294
WEIBULL PAPER
TIME(HOURS) 1
20
2
TIME(ih$ES)
Fig. 5. The propagating time TV - T, (0) and the life L (0).
This fact also shows that a fatigue crack begins to propagate immediately before failure and it develops into flaking within a brief period. We think that L - TV is the period of the development of flaking. T. Yoshioka and T. Fujiwara, A new acoustic emission source locating system for the study of rolling contact fatigue, Wear, 81 (1982) 183 - 186. T. Yoshioka and T. Fujiwara, Application of acoustic emi&on technique to detection of rolling bearing failure, Acoustic Emission Monitoring and Analysis in Manufacturing, Vol. 14, American Society of Mechanical Engineers, New York, 1984, pp. 55 * 75. J. Hamrock and D. Dowson, Ball Bearing Lubrication, Wiley, New York, 1981.
Wear, 113 (1986) 291- 294
Research Report The crack growth rate in rolling contact fatigue process is very fast TAKE0 YOSHIOKA and TAKASHI FUJIWARA Mechanical
Engineering
(Received June 9,1986;
Laboratory,
Namiki
1 - 2, Sakura, Niihari, Ibaraki 305 (Japan)
accepted June 26,1986)
When does a crack begin to propagate during the rolling contact fatigue process? How long does it take from the time that a crack begins to propagate to the time when flaking occurs? These questions about rolling contact fatigue are very interesting. There are many papers in which the appearance and propagation of a fatigue crack at the surface have been reported and, although unknown, the propagating time was thought to be very short. However, the initiation time of the crack propagation and the propagating time were not measured experimentally. In this report, we describe our experimental results obtained using the detection of acoustic emission and vibration. We have already reported that during rolling contact fatigue the position of the source of acoustic emissions coincides with the position of fatigue failure [l, 21. It was also shown that vibration signals contain useful information concerning the condition of the contact surfaces. Here we define the initiation time T, of crack propagation, the propagating time TV - T,, and the life L as follows: T, is the time at which acoustic emissions increase at the position of failure on the raceway of a sample; T” - T, is the period from the initiation time to the time when vibration acceleration increases; L is the running time until a test is automatically stopped by a vibrometer. The test bearing simulated a thrust ball-bearing 51105 (with a bore diameter of 25 mm, an outer diameter of 42 mm and a height of 11 mm) and consisted of an inner race, three balls, a retainer and an outer race (sample). Balls in the test bearing were in contact with a plane on the side of the outer race to accelerate the fatigue test. The bearing testing machine used in the rolling contact fatigue test is shown in Fig. 1. The test bearing was attached to the bottom end of a spindle. The vertical and downward thrust load was statically applied to the bearing by a lever and a dead-weight system. The test bearing was run under an axial load of 3.14 kN at a rotational speed of 660 rev mine1 in a mineral oil bath. The maximum contact pressure induced in the outer race was 5.64 GPa. The ratio of the minimum film thickness Ho to the composite surface roughness R was 0.13 - 0.17. The minimum 0043-1646/86/$3.60
0 Elsevier Sequoia/Printed in The Netherlands
292 KNIFE EDGE.
,
SUPPORT BEARING ITHRUST BALL BEARING) SUPWRT BEARINGS (ROLLER BEARINGS) SPINDLE TEST BEARING WEIGHT HOUSING ’
/n/
Fig. 1. Bearing testing machine for the invocation
TEST BEARING
of rating contact fatigue.
NOISE DISCRIMINATOf+
HOUSING
-+~UNTE~_(RECODER] ~ELIMINATOR I
BEARING TESTING
MACHINE
2. Block diagram of the acoustic em&&on source locater. Fig.
emission measuring system,
including
the acoustic
film thickness Ho was calculated according to the equation derived by Hamrock and Dowson [3]. The block diagram in Fig, 2 shows our acoustic emission measuring system including an acoustic emission source locater. The system has been described in refs. 1 and 2 in detail. The measuring conditions of the acoustic emissions were as follows: the bandwidth was from 200 to 400 kHz, the amplification degree was 80 dB and the threshold level was 0.8 - 2.5 V. Vibration accel~tion from 0.01 to 20 kHz was detected and the fatigue test was au~rna~c~y stopped as soon as its r.m.s. value exceeded a preset level at the occurrence of flaking. The preset level was set in the range 4.9 - 9.8 m S-2.
Figures 3 and 4 give examples of results. Figure 3(a) is the record of the event rate and Fig. 3(b) shows the vibration acceleration. In this case the threshold level of 1.5 V was preset for the event rate and an acceleration of 8.0 m se2 was attained at shutdown. The outer race failed after 16.01 h. It can be seen in Fig. 3(a) that many acoustic signals were emitted in the several minutes before the shut-down. However, it is clear from Fig. 3(b) that the minimal values of acceleration variation increased after the event rate did. The acoustic ‘emission location results obtained from this test are shown in Fig, 4. The x axis indicates the positions on the raceway track and the y
293
1000
A E EVENT RATE
FLAKING
z
100 01, 100 01,
1
1
TIME&“RS, 1 : PI P2
16 P,
H 6
PZ PI 1
, I /
0.5
0.0 POSITION
1.0
ON THE RACEWAY TRACK
Fig. 3. Acoustic emission event rate and vibration acceleration. Fig. 4. Location of the acoustic emission sources.
axis the number of acoustic emissions. On the LXaxis the whole raceway track is measured on a scale from 0.0 to 1.0. The figure shows the locations from period Pi to Pq; these correspond to those in Fig. 3. The locating time of P4 was 3 min before failure. However, the time was 30 min in other periods. There were few acoustic emissions from period Pi to period Pz; on the contrary, for periods P3 and Pq. three conspicuous peaks can be seen. It seems that many acoustic emissions are generated at three particular positions on the raceway track. The positions emitted for period P4 are the same as those for Ps. After the test, the outer race was removed and its raceway track was inspected; flaking was found at the position corresponding to the middle peak in Fig. 4. Although there was one flaking site, it can be seen in Fig. 4 that the three peaks are placed at equal intervals. The reason is that three balls were implanted at the same intervals in the test bearing. This shows that the failure point on the raceway generated the acoustic emission when each ball passed that point. It becomes clear from Fig. 3(a) and Fig. 4 that acoustic emissions at the failure position began at ‘I’,, = 15.86 h, i.e. the fatigue crack started to propagate at T,. Figure 3(b) shows that the fatigue failure appeared on the surface at !I’,. Therefore, 2’” - l’,, the propagating time in this case, was 6 min. The ratio T,/L of the initiation time of crack propagation to the life was 98.9%. The propagating times obtained from 18 tests are shown with their corresponding lives in Fig. 5. The lives were distributed from 11.47 to 112.02 h and the propagating times were from 1 to 25.2 min. The ratios (TV - T,)/L were 0.07% - 1.04%. Therefore the propagating times were equal to or shorter than one-hundredth of the lives.
294
WEIBULL PAPER
TIME(HOURS) 1
20
2
TIME(ih$ES)
Fig. 5. The propagating time TV - T, (0) and the life L (0).
This fact also shows that a fatigue crack begins to propagate immediately before failure and it develops into flaking within a brief period. We think that L - TV is the period of the development of flaking. T. Yoshioka and T. Fujiwara, A new acoustic emission source locating system for the study of rolling contact fatigue, Wear, 81 (1982) 183 - 186. T. Yoshioka and T. Fujiwara, Application of acoustic emi&on technique to detection of rolling bearing failure, Acoustic Emission Monitoring and Analysis in Manufacturing, Vol. 14, American Society of Mechanical Engineers, New York, 1984, pp. 55 * 75. J. Hamrock and D. Dowson, Ball Bearing Lubrication, Wiley, New York, 1981.