Fatigue Crack Paths 2003

E X P E R I M E N T A L

The experimental analysis was carried out in two different steps: the first one was the

characterisation of the material investigated, a C40 steel, the second was the study of

crack propagation in notched specimen.

All the tests in this work have been carried out with a 250 kN servohydraulic test

machine under displacement control in fully reversed tension-compression loading. A

frequency of 1 Hz has been used. The waveform of a dynamic load cycle has been set

sinusoidal. Displacement control has been achieved using an extensometer.

Material Testing

The specimens to determine material static and cyclic constants, have been built

according to the A S T ME606-92 standard [7]. Starting from a 20 m mdiameter round

bar, a smooth hourglass specimen, having the aspect of Fig. 3, with a minimumsection

diameter of 10 m mhas been obtained (see Fig. 2 drawing for details). Prescribed shape

guarantees a buckling stability of the specimen during compression.

Figure 2. Drawing of specimen adopted for material testing.

Figure 3. Actual specimen adopted for material testing.

Traction tests to find σsn , σr and E, and fatigue tests to find the coefficients of Coffin

Manson equation (Eq. 3) and of Ramberg-Osgood curve (Eq.4) have been performed.

The results are reported in Table 1.