Pivot Shaft 의 파손 분석
Failure analysis of Pivot Shaft
Report No. RB-FA-C016
R&B INC.
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File name: RB-FA-C016 Pivot Shaft 의 파손 분석
LIST OF CONTENTS
LIST OF TABLE
LIST OF FIGURES
1. Background, Specimen and Crack Type
1.1 Background
1.2 Specimen and Crack Type
2. Block Loading Spectrum
2.1 Random Spectrum Loading Data
2.2 Spectrum Analysis
3. SEM Fractographic Analysis
4. Conclusions
LIST OF TABLE
Table 1: Stress values (9000~10100psi) as functions of load points for each block for the present fractographic
analysis
Table 2. The crack length versus the number of blocks
LIST OF FIGURES
Figure 1. The pivot shaft received for fractographic analysis
Figure 2. The specmen prepared from the fatigued pivot shaft for the SEM fractographic analysis
Figure 3. Low magnification (x50) SEM fractograph of pivot shaft showing the area where the high magnification SEM
fractographic analysis was conducted
Figure 4 Random spectrum loading data of each block
Figure 5 Distribution of stress (9000~10100psi)
Figure 6 High magnification (x500) SEM fractographs was documented along the crack propagation direction in
Figure 3. This figure shows the change in crack length from the 36th block to the 21st block, the measurement
of which was based on the recurring striation patterns
Figure 7 High magnification (x500) SEM fractographs showing the matching striations associated with the cycles
#6,#1,#7 and #4 on the (a) 21st bl., (b) 22nd bl., (c) 23rd bl., (d) 24th bl., (e)25th bl., (f)26th bl., (g)27th bl., (h) 28th
bl., (i) 29th bl., (j) 30th bl., (k) 31st bl., (l) 32nd bl.. (m) 33rd bl., (n) 34th bl., (o)35th bl. and (p)36th bl.,
respectively,
as marked in figure 6
Figure 8 High magnification (x500) SEM fractographs of pivot shaft as marked in Figure 2···17
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1. Background, Specimen and Crack Type
1.1 Background
a. The fatigue test was conducted on pivot shaft with a pre-flaw for development purpose.
b. The fatigue test was stopped after the 36th block.
c. The fractographic analysis was requested for crack length vs. no. of block data.
1.2 Specimen and Crack Type
Figure 1: The pivot shaft received for fractographic analysis.
a. The cracked specimen was tensile fractured and the SEM fractographic analysis was conducted.
Figure 2. The specimen prepared from the fatigued pivot shaft for the SEM fractographic analysis.
a. The low magnification SEM fractograph in Figure 3 shows that fracture surface was contaminated during fatigue (as
indicated by arrows).
b. For the fractographic analysis, the area marked in Figure 3 was examined by using SEM along the crack
propagation direction.
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Figure 3: Low magnification (x50) SEM fractograph of pivot shaft showing the area where the high magnification SEM
fractographic analysis was conducted
2. Block Loading Spectrum
2.1 Random Spectrum Loading Data
Figure 4: Random spectrum loading data of each block.
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2.2 Spectrum Analysis
Figure 5: Distribution of stress (9000~10100psi).
Table 1: Stress values (9000~10100psi) as functions of load points for each block for the present fractographic
analysis.
No.
% Maximum Spectrum Load
Stress Value
Load Point
1
100%
9934
10395
2
98%
9753
3839
3
98%
9753
20867
4
97%
9653
11859
5
97%
9653
20835
6
97%
9616
3618
7
97%
9616
9568
8
97%
9616
11321
9
97%
9616
12289
10
97%
9616
13154
11
97%
9616
18656
a. In order to analyze the number of spectrum loading blocks as a function of crack length observed in the pivot shaft
during fatigue test, 11 most prominent loading cycles, #1 to #11, were designated as shown in figures 4 and 5.
b. Since there was no surface measurement acquired during the fatigue test, high magnification (x500) SEM
measurements were conducted to find the matching striations to the loading points #1 to #11 from the final fractured
area back to the crack origin.
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3. SEM Fractographic Analysis
a. From the high magnification (x500) SEM fractographs, the crack length for each block was counted using the
recurring striation patterns.
Figure 6: High magnification (x500) SEM fractographs was documented along the crack propagation direction in
Figure 3. This figure shows the change in crack length from the 36th block to the 21st block, the measurement
of which was based on the recurring striation patterns.
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Figure 7: High magnification (x500) SEM fractographs showing the matching striations associated with the cycles #6,
#1,#7 and #4 for the (a) 21st bl., (b) 22nd bl., (c) 23rd bl., (d) 24th bl., (e) 25th bl., (f) 26th bl., (g) 27th bl., (h) 28th bl.,
(i) 29th bl., (j) 30th bl., (k) 31st bl., (l) 32nd bl., (m) 33rd bl., (n) 34th bl., (o) 35th bl. and (p) 36th bl., respectively, as
marked in Figure 5.
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Figure 7: Continued.
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Figure 7: Continued
a. The striations associated with the cycles #6, #1, #7 and #4 were discernable only beyond the 21st block.
a. The crack length information for each block measured from the fractographs is summarized in Figure 8.
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Figure 8: The length of fatigue area as a function of number of blocks.
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4. Conclusions
a. The high magnification SEM fractographic analysis was conducted to find the matching striations to load points #1
through #11 in Figure 4 from the final fracture area back to the crack origin.
b. The striations associated with the cycles #6, #1, #7 and #4 were discernable only beyond the 21st block in pivot
shaft.
c. The crack length measurement from the present fractographic analysis is summarized in the following table.
Table 2: The crack length versus the number of blocks
No. of blocks
Crack length (inches)
21
0.078
22
0.082
23
0.087
24
0.091
25
0.096
26
0.100
27
0.111
28
0.12
29
30
0.128
0.136
31
0.145
32
0.155
33
0.165
34
0.177
35
0.190
36
0.203
End of 36
0.216
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