PSI - Issue 42

Jürgen Bär et al. / Procedia Structural Integrity 42 (2022) 1061–1068

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Author name / Structural Integrity Procedia 00 (2019) 000 – 000

0.2

0.2

Near the crack tip

0.1

0.1

0.0

0.0

-0.1

-0.1

-0.2

-0.2

Distance to crack tip 0.79 mm 0.28 mm 0.21 mm 0 mm

-0.3

-0.3

Temperature change [K]

Temperature change [K]

-0.4

-0.4

-0.5

-0.5

0.00

0.25

0.50

0.75

1.00

-3

-2

-1

0

1

2

3

245

285

325

365

405

445

485

525

Cycle time [1/T]

Force [kN]

Position on the Ligament [px]

(a)

(b)

(c)

Fig. 5. E-Mode image (a) showing the positions of the time-temperature curves (b) and the temperature-force loops (c) near the crack tip maximale Temperatur im Druck Maximu gewichtete cos-E-Amplitude min Temp bei Zugmax +max D-Amp Maximum gewichtete cos-Amplitude + maximum E-Phase

Behind the crack tip, along the crack flanks the temperature time diagram shows only in the compression half cycle a sinusoidal run can be observed. Under tension loading amount of the temperature drop decreases with increasing distance to the crack tip. At 1.49 mm behind the crack tip nearly no temperature change under tension loading is visible. The force temperature loops show a normal hysteresis loop in the compression half cycle, but a plateau with nearly no temperature change under tension loading. With increasing distance to the crack tip the plateau-level tends to zero.

0.2

0.2

0.1

0.1

Crack flanks

0.0

0.0

Distance to crack tip -0.36 mm -0.61 mm -0.99 mm -1.45 mm

-0.1

-0.1

Temperature change [K]

Temperature change [K]

-0.2

-0.2

0.00

0.25

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0.75

1.00

-3

-2

-1

0

1

2

3

245

285

325

365

405

445

485

525

Cycle time [1/T]

Force [kN]

Position on the Ligament [px]

(a)

(b)

(c)

Fig. 6. E-Mode image (a) showing the positions of the time-temperature curves (b) and the temperature-force loops (c) along the crack flanks.

3.3. Comparison of the results To compare the two evaluation methods, Fig. 7 compares the stress-temperature curves from the PT diagram and a Lock-In-evaluation according to equation 2 (2 modes) and with an extended Lock-In evaluation with 5 modes according to equation 3 for 4 different positions on the ligament. The PT diagram provides the true temperature changes, which, however, is only almost correctly reproduced by the two different Lock-In-evaluations in the case of almost pure elastic loading. In all other cases, more dissipative effects occur. In these cases, a description of the temperature changes is neither complete with the use of 2 nor with 5 Lock-In-modes. In both evaluations, parts of the hysteresis are described correctly, but it is not possible to say which of the two Lock-In-evaluations is better. This clearly shows that the LI evaluation does not provide a completely correct quantitative evaluation when dissipative temperature changes occur. Whether the quality of the description is influenced by the amount of dissipative temperature changes could not be investigated within the scope of this work.