No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Cleavage and Ductile Thermal Shock Fractures of Corner-Cracked Nozzles
Abstract
In order to study the structural integrity of the reactor pressure vessel under pressurized thermal shock, both the cleavage and the ductile thermal shock fracture experiments using initially corner-cracked nozzle specimens made of Type A508 class 3 pressure vessel steel were performed. In both experiments, unstable fractures were realized, although the test conditions were very conservative compared to those of real plants. Finally, the three-dimensional and time-dependent fracture parameter obtained with the finite element method was successfully employed to discuss the fracture phenomenon.
This paper describes some simplified stable crack growth analyses of two kinds of inhomogeneous CT specimens. The one is machined from a submerged are welded plate of a nuclear pressure vessel A533B Class 1 steel, while the other is machined from an electron-beam welded plate of the A533B Class 1 steel and a high strength HT80 steel. In both specimens, initial cracks are placed to be normal to the fusion line. The ratio of yield stresses of the weld metal and the base metal of the A533B Class 1 steel is about 1·15, while that of the HT80 and the A533B Class 1 steels is about 1·4.The generation phase crack growth analyses using the and the reference stress methods are performed, calculating an applied load (P) and the J-value, while the application phase analyses of analyses using the R6 method are performed to calculate the maximum value of the applied load (Pmax). Finally, some modification procedures of the three simplified estimation schemes are discussed in order to apply them to inhomogeneous material regimes.
Repeated thermal shock cracking is common in the operation of pressure equipment where water and steam are present. Surprisingly it is not directly covered in the ASME Boiler and Pressure Vessel code nor in fitness-for-purpose recommended practice such as API 579. An example of thermal shock stresses occurs when hot surfaces exposed to splashing of cold water. This eventually may lead to crack nucleation and crack growth. However not all thermal shock cracks lead to failures (such as rupture, leak or in more brittle material fragmentation), indeed the most frequent situation is that the cracking arrests at a depth of a few millimeters. This paper presents a unique experimental study and analysis the information being gained from this study in terms of design guidelines and crack growth mechanisms. In the experiments, cracks are initiated and then grown in low carbon steel specimens exposed to repeated thermal shock. The test-rigs achieve large thermal shocks through the repeated water quenching of heated flat plate specimens. The effect of steady state loads on the growth and environmental effects due to the aqueous nature of the testing environment are found to be major contributors to the crack growth kinetics. The most important findings are that are that the conditions leading to both the initiation and the arrest of cracks can be identified and that the depth of a starter notch contributes little to the crack propagation.
Repeated thermal shock cracking is common in the operation of pressure equipment where water and steam are present. Surprisingly, it is not fully covered in the ASME Boiler and Pressure Vessel code nor in fitness-for purpose recommended practice such as API 579. An example of thermal shock stresses occurs when hot surfaces are exposed to splashing of cold water This eventually may lead to crack nucleation and crack growth. However not all thermal shock cracks lead to failures (such as rupture, leak, or, in more brittle material, fragmentation), indeed the most frequent situation is that the cracking arrests at a depth of a few millimeters. This paper presents a unique experimental study and analysis of the information being gained from this study in terms of design guidelines and crack growth mechanisms. In the experiments, cracks are initiated and then grown in low carbon steel specimens exposed to repeated thermal shock. The test-rigs achieve large thermal shocks through the repeated water quenching of heated flat plate specimens. The effect of steady state loads on the growth and environmental effects due to the aqueous nature of the testing environment are found to be major contributors to the crack growth kinetics. The most important findings are that the conditions leading to both the initiation and the arrest of cracks can be identified and that the depth of a starter notch contributes little to the crack propagation.
This paper examines the use of the ASME and British Standard codes to estimate the growth of cracks driven mainly by thermal shocks. Thermal shock loading of operating pressure equipment is a common occurrence, particularly in thermal power stations. The tensile stresses that are produced at the surface of a heated component exposed to a rapid thermal down shock can be high, particularly in the presence of stress concentrations. Repeated application of the thermal shocks may lead to crack initiation and crack growth. The ability to use current codes and standards to describe this type of crack growth is desirable. Unfortunately, thermal shock is a complex transient situation with highly non-linear stress distributions and environmental effects that are not well described by some codes. This paper describes attempts to use the techniques described in the ASME Boiler and Pressure Vessel code Section XI and British Standard BS7910 to predict crack growth rates derived from Monash University experiments. Areas of large conservatism in the methods currently used in industry are identified and possible alternative, less conservative approaches are suggested. If the methods are fully applied, the possibility of crack growth slowing can be captured and the replacement or repair of equipment with thermal shock cracking might be avoided. (C) 2002 Published by Elsevier Science Ltd.
In this paper, recent neural network applications, epecially to the fields related with the computational mechanics, were
surveyed. The most outstanding characteristics of the neural network aided computation is that neither complicated programmings
nor rigid algorithms are needed. Another important point is that the neural network's inherent parallelism, that is, concurrent
signal transmissions over numerous, information processing elements suits the massively parallel computer architectures. First,
we briefly review the neural network applications to the computational mechanics fields from recent publications, and describe
the mathematical basis of the neural network. Next, the following topics are detailed: quantitative nondestructive evaluation,
structural identification, modeling of viscoplastic material behaviors, crack growth analysis of welded specimens, structural
design, parameter estimation for nonlinear finite element analyses, and equation solver.
Repeated thermal shock loading is common in the operation of pressure equipment particularly in thermal power stations. Thermal shock can produce a very high stress level near the exposed surface that eventually may lead to crack nucleation and crack growth. This paper presents a unique experimental study and outlines the information being gained from this work. In the experiments, cracks are initiated and then grown in low carbon steel specimens exposed to repeated thermal shock. The test-rigs achieve large thermal shocks through the repeated water quenching of heated flat plate specimens. The effect of steady state loads on the growth and environmental effects due to the aqueous nature of the testing environment are found to be major contributors to the crack growth kinetics. The most important findings are that the conditions leading to the arrest of cracks can be identified and that the depth of a starter notch contributes little to the crack propagation.
ResearchGate has not been able to resolve any references for this publication.