PSI - Issue 16

Eugene Kondryakov et al. / Procedia Structural Integrity 16 (2019) 43–50 Eugene Kondryakov et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 6. Macrofracture of standard Charpy specimen (а) and side -grooved specimen (b).

For each specific zone of fracture it is possible to determine the average velocity of the crack propagation using the length of the given zone and time of the crack propagation in it by the following formula:

L

V



.

i

t

i

The average velocities of the crack propagation within each specific zone were determined for all the types of the specimens under investigation. Fig. 7 illustrates the temperature dependencies of the average velocities of the crack propagation for the specimens of three types. It was established that the average velocity of the main crack varies in very large ranges of 1-400 m/s. The velocity of the unstable crack propagation in the zone of brittle fracture varies in the range of 100-900 m/s. The velocity of the crack propagation within the zone of ductile fracture varies in the range of 1-15 m/s. The velocities of the crack propagation for standard Charpy specimens and side-grooved specimens are close, while the velocities of the crack propagation of sub-sized specimens are significantly lower. Here the character of the variation of the average velocity of the crack propagation practically coincides for the specimens of all three types depending on the test temperature.

Fig. 7. Temperature dependencies of the average velocities of the crack propagation for the specimens of three types: main cr ack (а), brittle crack (b).

A special experimental procedure was developed to determine the instantaneous velocity of the crack propagation in standard Charpy specimen. The fracture gauges were applied to monitor the process of propagation, which were pasted on the lateral surface of the specimen on the way of the assumed crack propagation. The gauges consist of 50 parallel paths made of conductive brittle material, which are connected at the edges. These paths undergo rupture during the crack propagation under them. In the process of rupture of each of the paths, the gauge demonstrates the variation of its general resistance, which is measured by the high-sensitive system of registration. Here the time interval between the rupture of each gauge paths is measured with high accuracy. The distance between the paths