Page 461 - Biaxial Multiaxial Fatigue and Fracture

Microcrack Propagation Under Non-Proportional Multiaxial Alternating Loading 445

Measurement instrumentation

The measurement of the axial strain was performed by a conventional clip extensometer (s.
Fig. 3). To determine the circumferential strain, six radial extensometers were distributed at the
circumference of the specimen. From the average value of the radial displacement, the
circumferential strain was calculated. With this, a more precise registration of the
circumferential strain compared to a diametrical layout was possible.
To obtain information about the sonic emissions transmitted during the experiment, two
sonic emission sensors were mounted outside the pressure vessel. These two sensors have a
registration spectrum from 600 kHz up to 1200 kHz. In this frequency range, most signals due
to crack nucleation and crack propagation are recorded. Signals induced by plastic
deformations have frequencies lying below this spectrum.

1. Specimen
2. Axial strain extensometer
3. Radial displacement extensometers +circumferential strain
4. Sonic emission sensors

Fig. 3. Measurement of the experimental parameters.