Application
News
Fig. 5 S-N Diagram
Fatigue Test
Based on the maximum test force measured in the static test,
the maximum load test force during the fatigue test was set.
The fatigue test conditions are shown in Table 2. The obtained
S-N Curve is shown in Fig. 5.
Table 2 Fatigue Test Conditions
Maximum Load Test
Force:
195, 243, 292, 341, 389, 438 N
(40 % to 90 % of the Static Maximum Test Force)
Stress Ratio: 0.1
Maximum Number of
Cycles:
1.0 × 10
6
Frequency: 10 Hz
Number of Tests: N = 2
0
50
100
150
200
250
300
350
400
450
500
1,000 10,000 100,000 1,000,000 10,000,000
Maximum Load Test Force [N]
Number of Cycles to Failure [Cycles]
Observation of Cracks by the Air-Servo
Microfocus X-Ray CT System
Using the Air-Servo Microfocus X-Ray CT System, the status of
cracks propagating during the test was observed.
The system is designed to be compact with light weight,
making it easy to transport. After fatigue tests, the specimens
can be transported inside the X-ray CT system while still
attached. Furthermore, by applying static loading inside the CT
system, imaging can be performed with the crack held open,
allowing the crack tip to be observed more clearly.
Measurement System
Table 3 shows the equipment configuration of the Air-Servo
Microfocus X-Ray CT System. Fig. 6 shows the test and imaging
setup, and Fig. 7 shows the test force-time waveform. From
Fig. 5, the condition was set so that the maximum test load test
force was 70 % of the static maximum test force. Fig. 7 shows
that control with a good sine wave was achieved.
Table 3 Equipment Configuration of
the Air-Servo Microfocus X-Ray ST System
Fatigue Testing Machine: Air-Servo Mini
X-Ray CT: inspeXio SMX-225CTS
Load Cell: 1 kN
Controller: Servo Controller 4830
Software: Windows Software for 4830
0
50
100
150
200
250
300
350
400
0 0.1 0.2 0.3 0.4 0.5
Test Force [N]
Time [s]
Fig. 7 Control Waveform
Crack Observation
Under the condition in which 70 % of the static maximum test
force was used as the maximum load test force for obtaining the
S-N diagram, the displacement increased sharply after 30,000
cycles. Therefore, during X-ray CT imaging, imaging was
performed every 1,000 cycles after 30,000 cycles, and after
35,000 cycles, imaging was performed when the displacement
increased sharply. Fig. 8 shows cross-sectional images of the
notch region of the specimen obtained by X-ray CT, and Fig. 9
shows the average amplitude of displacement at each cycle. In
Fig. 8(1), no crack can be confirmed up to 30,000 cycles, but in
Fig. 8(2), a crack was observed for the first time at 31,000 cycles.
After that, the crack gradually propagated and led to fracture at
36,392 cycles in Fig. 8(6).
Fig. 10 shows a three-dimensional representation of the cross-
section at fracture in Fig. 8(6). It was found that crack
propagation in the width direction was greater on the left side
than on the right side.
(1) 30,000 cycles (2) 31,000 cycles (3) 32,000 cycles
(4) 34,000 cycles (5) 35,650 cycles (6) 36,392 cycles
Cracks
Fig. 8 Continuous Cross-Sectional Images of the Notch Region
Fig. 6 Test and Imaging Setup
