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Abstract
The lock-in infrared thermography has been applied to an estimation of fatigue limits at several stress ratios, i.e., R=-1, 0.05, and 0.5, for commercially pure titanium (CP-Ti JIS grade 2) at room temperature. In the present study, frequencies were1 Hz and 4 Hz at R=-1, and 7 Hz at R=0.05 and 0.5. Tests at R=-1 showed a negligible frequency dependency of a fatigue limit of 250 MPa. Other tests at R=0.05 and 0.5 showed respective fatigue limits of 123 MPa and 48 MPa. Tensile tests were performed to obtain a tensile strength and a proof stress. A fatigue limit diagram of the sample was plotted using the above values, showing a violation of the mod. Goodman line and the Soderberg line. Next, the diagram was revised using a stress starting plastic deformation shown by creep tests. It revealed a safety area of the new diagram is 35% smaller than that of the conventional safety standards.
Highlights
Development periods of new aircrafts become more than 10 years
The lock-in infrared thermography was applied for the safety evaluation of CP-Ti JIS grade 2 at room temperature
The fatigue limits were estimated by the new method to modify the fatigue limit diagram of the material
Summary
Because an evaluation of a safety standard of a new material needs more than a year by standard mechanical tests, it occupies the large part of the development period. A new method, i.e., a lock-in infrared thermography [1-4], is considered for an estimation of a fatigue limit at a stress ratio (R). The lock-in infrared thermography is expected to estimate a fatigue limit. An infrared camera detects an irreversible temperature change including a thermo-elastic effect and an energy dissipation (TE[K]) during cyclic loading with a frequency (f). The effects can separate by Fourier analysis because the frequency of energy dissipation is double, i.e., 2f, comparing with the cyclic loading and the temperature change by the thermo-elastic effect [4]. The fatigue limit estimated by the thermography compared to that obtained by standard fatigue tests to confirm the utility of the new estimation method of fatigue limit for CP-Ti at room temperature
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