Fatigue crack behaviour under thermal stresses

• Published in: The International journal of pressure vessels and piping 1982-01, Vol.10 (5), p.335-359
• Main Authors: Grüter, L., Huget, W.
• Format: Article
• Language: English
• ISSN: 0308-0161; 1879-3541
• DOI: 10.1016/0308-0161(82)90017-5

In some parts of nuclear reactors fluids at different temperatures are mixed. Temperature fluctuations occur in the flowing fluids which are transferred to the surface of downstream components. The stochastically impinging temperature waves penetrate into the component in a decreasing manner. Only the surface area is heavily deformed. Cycles of thermal stresses of up to 10 9 may be expected. Crack propagation in two plates has been calculated with the following boundary conditions. The temperature changes proceed across the wall with a damped vibration. Those stresses which, to a first approximation, exhibit affinity with various temperatures are described by an enveloping curve. The stress intensity factor is calculated by means of the Dawson integral. The temperature range, frequency, plate thickness and initial and final crack lengths, respectively are all varied. The following results have been found. 1. (1) Three or more additional magnitudes of cycles are needed for crack propagation to ‘failure’ (final crack length) than quoted by the design curves of the ASME-Code Case N-47 (1592-10). This effect is favoured by high frequencies and a thick-walled structure. 2. (2) The uniform stress distribution corresponding to f = 0 Hz ( f = frequency ) is the most severe situation. The corresponding cycle numbers calculated for crack propagation to ‘failure’ are relatively high. 3. (3) A thick plate is more favourable than a thin plate. 4. (4) A longer initial crack will grow faster to the final crack length. This effect decreases with increasing frequency and wall thickness. Under low stress, high frequency, conditions and with a thick plate variation in the initial crack length becomes almost negligible. The results show that the assumption of different stress distributions is most important for crack growth calculations.