PSI - Issue 57

Mathilde Renault et al. / Procedia Structural Integrity 57 (2024) 22–31 Mathilde RENAULT/ Structural Integrity Procedia 00 (2019) 000 – 000

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3. Test protocol The tests were interrupted with thermal marking of the fatigue crack fronts, and the mechanical stress was a 4-point bending stress to promote initiation on the rough surface. The tests were carried out at a loading ratio of = = 0.1 and a mechanical frequency =5 Hz on a 200kN capacity servo-hydraulic testing machine. The test stopping criterion is a 50% increase in machine displacement. The nominal stress amplitude ( , ) is given by the following relation = 3 4 (1 − )( − ) . 2 Eq 3 with the maximum force applied by the hydraulic actuator, the distance between the two support points, the distance between the two load application points, and the width of the specimen. The test was instrumented by an INFRATECH infrared camera with a 1280x1024 pixels sensor at a sampling frequency of 100Hz and an infrared mirror (with a reflectivity coefficient of 98%). To improve measurement accuracy, the raw surface was coated with black high-emissivity paint. As the tests were interrupted to allow thermal marking of the crack face, a shim device was added to the 4-point bending device to allow the specimen to be repositioned, as shown in Figure3.

Figure3: 4-point bending fixture with infrared mirror for rough surface monitoring