Safety Evaluation for Pure Titanium by Lock-in Infrared Thermography

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.