PSI - Issue 18

Andrzej Katunin et al. / Procedia Structural Integrity 18 (2019) 20–27 Author name / Structural Integrity Procedia 00 (2019) 000–000

25

6

Fig. 5. Hit-cascade envelopes of the AE response for the considered cases.

The obtaining preliminary results allow for posing a conjecture that the air cooling can be a good tool for extending residual life of structures as well as can be helpful during fatigue tests. However, in order to apply this technique in practice the exact mechanisms standing behind this phenomenon need to be investigated. In particular, in order to obtain the most effective cooling other possible scenarios are considered. 4. Alternative air cooling scenarios Taking into account the approach of fatigue testing of polymer composites (see section 3), two alternative cooling scenarios can be considered during these tests (see the schemes in Fig.6). Both scenarios are based on the Newton’s equation (4) for the change in the heat transfer coefficient  (scenario no. 1) or the change in the ambient temperature  0 (scenario no. 2).

(a)

(b)

Fig. 6. Alternative air cooling scenarios: (a) forced cooling, (b) ambient temperature change.

The first of the considered scenarios concerns the use of forced convection, but it is assumed that the temperature of the produced air stream reaching the tested specimen is constant and equal to the ambient temperature  0 . The forced air flow around the specimen causes an increase in the heat transfer coefficient  , which can be estimated by using the following dimensionless equation on the Nusselt number (Incropera et al., 2007):