Hiroaki Doi

Development of an Automatic 3D Finite Element Crack Propagation System

When cracks are detected in piping in nuclear power plants during in-service inspections, the crack propagation is usually calculated using approximation formulas of stress intensity factor (SIF) provided in the ASME Code, the JSME Rules or the literature. However, when the crack is detected in complicated-shaped locations in components, finite element analysis (FEA) needs to be used to calculate the SIFs. Accordingly, a method of automatically conducting FEA for crack propagations in nuclear power plants is needed. Therefore, we, the Nuclear Regulation Authority (NRA, Japan) have developed an automatic 3D finite element crack propagation system (CRACK-FEM) for nuclear components. The developed CRACK-FEM uses three methods of SIF calculation: the Virtual Crack Extension Method (VCEM), the Virtual Crack Closure-Integral Method (VCCM) and the Domain Integral Method (DIM). Each method uses different meshes, so users can select a method which uses a suitable mesh for the problem. The software includes a geometry generator to create complicated weld models, and a mesh generator which can deal with interior boundaries formed between different materials. The functions and accuracy of the new software are demonstrated by solving several sample problems involving crack propagation.The contents of this paper were conducted as a research project of the Japan Nuclear Energy Safety Organization (JNES) when one of the authors (Doi) belongs to JNES. After this project, JNES was abolished and its staff and task were absorbed into NRA on March 1, 2014.Copyright

Verification Analyses for Newly Developed Automatic 3D Finite Element Crack Propagation System

In order to calculate the crack propagation in complicated-shaped locations in components such as weld in penetration structures of reactor pressure vessel of nuclear power plants, an automatic 3D finite element crack propagation system (CRACK-FEM) has been developed by the Nuclear Regulation Authority (NRA, Japan). To confirm the accuracy and effectiveness of this analysis system, a verification analysis was performed. The program used for comparison is PipeFracCAE developed by Engineering Mechanics Corporation of Columbus, which has been used for many crack propagation analyses in various applications. In this paper, the axial crack propagation analysis for primary water stress corrosion cracking (PWSCC) in a steam generator inlet nozzle of a pressurized water reactor (PWR) plant is presented. The results demonstrate that the two codes are in good agreement.The contents of this paper were conducted as a research project of the Japan Nuclear Energy Safety Organization (JNES) when one of the authors (Doi) belongs to JNES. After this project, JNES was abolished and its staff and task were absorbed into NRA on March 1, 2014.Copyright

Stress Intensity Factors for Cracks With Large Aspect Ratio in Cylinder

A number of surface cracks with large aspect ratio have been detected in components of nuclear power plants in recent years. The depths of these cracks are even larger than the half-lengths. The solution of the stress intensity factor is very important for the structural integrity assessment of such cracked components. However, in the current codes, such as ASME Boiler and Pressure Vessel Code Section XI and the JSME Rules on Fitness-for-Service for Nuclear Power Plants, solutions of the stress intensity factors are provided for semi-elliptical surface cracks with a limitation of a/l ≤ 0.5, where a is the crack depth and l is the crack length. In order to assess structural integrity in a more rational way, the authors previously developed solutions of the stress intensity factor for semi-elliptical surface cracks in flat plates with a/l = 0.5 to 4 and a/t = 0.0 to 0.8, where t is the wall thickness. In this study, the solutions of the stress intensity factors were calculated for circumferential and axial surface semi-elliptical cracks with large aspect ratios in cylinders. The geometrical dimensions focused on were in the ranges of a/l = 0.5 to 4, a/t = 0.0 to 0.8 and t/Ri = 0 to 1/2, where t is the wall thickness and Ri is the inner radius of the cylinder. Some solutions were compared with the available existing solutions in order to confirm their applicability.Copyright

Micro-Vickers Indentation for Measuring Residual Sintering Stress in a Glass-Ceramic Substrate

A method for measuring residual sintering stress in glass-ceramic substrates with multilayer copper circuits has been investigated. This method uses the length of a crack produced from a Micro-Vickers impression on the substrate. First, the relation between the stress and the crack length is obtained by applying the method to mechanically stressed glass-ceramic plates without copper. Next, we determine the conditions under which we can apply this method to substrates with multilayer copper circuits. If the measurement is conducted very near to a copper layer, the crack produced bends toward the copper. From finite-element stress analyses, we found that this bending is caused by the indentation-produced bending deformation of the substrate. This deformation only occurs where the substrate has been softened by the presence of copper. Therefore, to prevent such crack bending, the regions to which our method is applicable are restricted to those at distances of more than 50 μm from the copper.

Development of mechanical fatigue test method for flip-chip solder joints

A controlled displacement mechanical fatigue test machine for specimens of flip-chip solder joints has been developed using PZT actuators. The extension response of the PZT exhibits good linearity using a charge control circuit. As a result of this control, errors in the strain of the specimen caused by the deflection of the test machine frame can be corrected by measuring the load. This test machine produces a cycle constant strain range in the solder joints. A fatigue test is conducted for specimens of flip-chip solder joints, and the fatigue strength of the joints is obtained. The strength of the joints seems to be higher than that of bulk solder.<<ETX>>