PSI - Issue 42

A. Sulamanidze et al. / Procedia Structural Integrity 42 (2022) 412–419 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Induction coil systems (ICS) function by passing an alternating current through a copper induction coil to create an electromagnetic field, which producing eddy currents and thus resulting in the heating of the specimen. ICSs offering a relatively inexpensive and reliable heating solution, however, has downside with respect to the homogeneity of the applied temperature, which is often far less uniform than in a conventional resistance furnace. This thesis is confirmed by the results of calculations of the temperature distributions for characteristic points of 5 th IP loading cycle, e.g. start, end, max and min temperature where distributions have gradients in all three directions (thickness, width and height of the sample). Clearly this illustrates the importance of developing an understanding of the 3D temperature variation with time ahead of TMF crack growth testing.

Fig. 6. Elastic-plastic hoop stress distributions for IP and OOP 5 th TMF cycle.

The studies mentioned previously have focused on experimental analysing temperature distributions and it has become apparent through a lack of literature that elastic-plastic stress behaviour for IP and OOP TMF, despite being an important aspect to understand, is one that has not been investigated to the same extent. As already expressed, TMF is a complicated phenomenon and in order to successfully conduct TMF tests in aid of component lifing, stress control and temperature measurement is of paramount importance. In some of the tests with relatively high nominal stress, significant nonlinear deformation is observed. This suggests that small scale yielding conditions are not fulfilled and that the applicability of elastic stress intensity factor is questionable. In contrast, the present study fully reproduces the sequence of electromagnetic induction, fluid dynamic and elastic-plastic deformation (in accordance with the constitutive Eq. 3) as a function of the duration of the cyclic process. Figure 6 shows the numerically determined elastic-plastic hoop stress fields for 5 th TMF cycle under IP and OOP conditions with the applied nominal stress ranged of 80/8 MPa. Characteristic points of this cycles for IP and OOP are 0 sec, 30 sec and 60 sec that correspond to start or end of heating/cooling with loading/unloading processes as well as intermediate state. As expected, the maximum values of elastic-plastic stresses arise in the front of the initial