Evaluation Criteria for Alternating Loads Based on Partial Inelastic Analyses

2002 ◽  
Author(s):  
Asao Okamoto ◽  
Yasuhiro Ohtake ◽  
Norimichi Yamashita
Keyword(s):  
Finite Element ◽  
Evaluation Method ◽  
Three Dimensional ◽  
Evaluation Criteria ◽  
Inelastic Behavior ◽  
Element Analysis ◽  
Plastic Strain Increment ◽  
Elastic Plastic ◽  
Stress Classification ◽  
Plastic Analysis

This paper discusses the evaluation criteria for alternating loads utilizing partial inelastic analyses and free from the stress classification. As finite element analysis becomes popular, it has been noticed by designers that in some cases the conventional stress classification does not work well. The stress classification itself had been engineered as a practical tool to evaluate the integrity of a structure by elastic analyses, which actually could have inelastic behavior. For example, primary stress limits were determined reflecting the stress level at collapse. Therefore, the problem concerning the stress classification can be solved recalling how it had been engineered. In other words, the key to solve the problem is the inelastic evaluation method corresponding to each stress category. From this point of the view, the application of the inelastic analyses becomes widely studied. Consequently, as for primary loads, it has been proven that the collapse load evaluation by Limit or Plastic Analysis is effective and practical for design analyses. On the other hand, as for the alternating loads, it is not sufficiently discussed how the alternative criteria should be without stress classification. In this paper, the following are discussed based on the calculation results in the Committee on Three Dimensional Finite Element Stress Evaluation in JPVRC. 1. Prerequisite of the elastic-plastic analysis for shakedown evaluation, and the evaluation criteria based on plastic strain increment and its distribution. 2. The advantage to use simplified elastic-plastic analysis method than to perform fully elastic-plastic analyses, and the calculation procedure for Ke factors to be used with. The associated code rules are proposed.

Verification of Alternative Criteria for Shakedown Evaluation Using 2-Dimensional and 3-Dimensional Nozzle Models

2002 ◽  
Author(s):  
Seiji Asada ◽  
Asao Okamoto ◽  
Isoharu Nishiguchi
Keyword(s):  
Finite Element ◽  
3D Model ◽  
Three Dimensional ◽  
Evaluation Criteria ◽  
Symmetric Model ◽  
Element Analysis ◽  
Stress Evaluation ◽  
Elastic Plastic ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Alternative stress evaluation criteria suitable for Finite Element Analysis (FEA) proposed by Okamoto et al. [1] have been studied by the Committee on Three Dimensional Finite Element Stress Evaluation (C-TDF) in Japan. Thermal stress ratchet criteria in plastic FEA are now under consideration. Two criteria are proposed: evaluating variations in plastic strain increments and evaluating variations in the elastic core region. To verify the validity of these criteria, calculations were performed for several typical models in C-TDF [2]. This paper shows calculations and evaluation results of 2-dimensional and 3-dimentinal nozzles for shakedown and Ke-factors, as defined by equation 2. Two models are used. One is a 2-dimensional (2D) axi-symmetric model of a typical nozzle. The other is a 3-dimantional (3D) model of the nozzle of which shell radius is half of 2-dimensional model. The primary and secondary stress, shakedown analyses using elastic-plastic FEA and Ke-factors which are directly calculated from elastic-plastic FE analyses are surveyed. The results show that the alternative criteria are applicable for those models. The analysis results of the 2D model show good relation to those of the 3D model.

Overview of Code Case on Alternative Design Methodology by Using Elastic-Plastic Finite Element Analysis for Class 1 Vessels in the JSME Rules on Design and Construction

2010 ◽  
Author(s):  
Seiji Asada ◽  
Takashi Hirano ◽  
Tetsuya Nagata ◽  
Naoto Kasahara
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Design Methodology ◽  
Evaluation Method ◽  
Plastic Collapse ◽  
Element Analysis ◽  
Alternative Design ◽  
Elastic Plastic ◽  
Plastic Analysis ◽  
Design And Construction

An alternative design methodology by using elastic-plastic finite element analysis has been developed and published as a code case of the JSME Rules on Design and Construction for Nuclear Power Plants (The First Part: Light Water Reactor Structural Design Standard). This code case applies elastic-plastic analysis to evaluation of such failure modes as plastic collapse, shakedown, thermal ratchet and fatigue. Advantages of this evaluation method are no use of stress linearization/classification, consistent use of Mises equivalent stress and applicability to complex 3-dimentional structures which are hard to be treated by the conventional stress classification method. The evaluation method for plastic collapse consists of the Lower Bound Approach Method, Twice-Elastic-Slope Method and Elastic Compensation Method. Cyclic Yield Area (CYA) criterion based on elastic analysis is applied to screening evaluation of shakedown limit instead of secondary stress evaluation, and elastic-plastic analysis is performed when the CYA screening criterion is not satisfied. Strain concentration factors can be directly calculated based on elastic-plastic analysis.

Verification of Alternative Criteria for Shakedown Evaluation Using Flat Head Vessel

2002 ◽  
Author(s):  
Seiji Asada ◽  
Norimichi Yamashita ◽  
Asao Okamoto ◽  
Isoharu Nishiguchi
Keyword(s):  
Finite Element ◽  
Plastic Strain ◽  
Evaluation Method ◽  
Three Dimensional ◽  
Evaluation Criteria ◽  
Strain Range ◽  
Element Analysis ◽  
Plastic Strain Range ◽  
Stress Evaluation ◽  
Elastic Shakedown

Alternative stress evaluation criteria suitable for Finite Element Analysis (FEA) proposed by Okamoto et al. [1] have been studied by the Committee on Three Dimensional Finite Element Stress Evaluation (C-TDF) in Japan. Thermal stress ratchet criteria in plastic FEA are now under consideration. Two criteria are proposed: evaluating variations in plastic strain increments and evaluating variations in the elastic core region. To verify the validity of these criteria, calculations were performed for several typical models in C-TDF [2]. This paper shows calculations and evaluation results of a Flat Head Vessel for shakedown. To study shakedown criteria for gross structural discontinuity, a flat head vessel is surveyed. The flat head vessel consists of a stiff flat head and a shell and is subjected internal pressure and thermal cycle. The elastic shakedown area and the plastic area are compared and plastic strain increments are surveyed. A shakedown evaluation method based on distribution of elastic-plastic strain range is proposed.

Ductile Fracture Behaviour of Class 2 and 3 LWR Piping and Its Implications for Flaw Evaluation Criteria

2007 ◽  
Vol 120 ◽  
pp. 85-94 ◽  
Author(s):  
Naoki Miura ◽  
Katsumasa Miyazaki ◽  
Masakazu Hisatsune ◽  
Kunio Hasegawa ◽  
Koichi Kashima
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Evaluation Method ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Evaluation Criteria ◽  
Element Analysis ◽  
Reference Stress ◽  
Class 1 ◽  
Fracture Tests

To achieve a rational maintenance program for aged Light Water Reactor components, it is important to establish and to improve the flaw evaluation criteria. The current flaw evaluation criteria such as ASME Boiler and Pressure Vessel Code Section XI are focused on Class 1 piping which usually shows relatively higher toughness. On the other hand, flaw evaluation criteria suitable for Class 2, 3 piping with moderate-toughness are also required because some Class 2, 3 piping systems are as important to plant safety analysis as Class 1 piping. In this study, both analytical and experimental studies were conducted to provide the evaluation method of fracture loads for acceptance criteria for Class 2, 3 piping. Pipe fracture tests by four-point bending were conducted on circumferentially cracked carbon steel pipes with moderate-toughness. The Net-Section Collapse criterion overpredicted experimental maximum loads for through-wall-cracked pipes, which suggested the necessity of Z-factor. Three-dimensional finite element analysis and simplified analysis based on the reference stress method were conducted to complement the limited pipe fracture tests. It was ascertained that the reference stress method always gave moderately conservative fracture loads compared with the finite element analysis and pipe fracture tests as well. Z-factor for Class 2, 3 piping was then derived and formulated using the reference stress method. Z for Class 2, 3 piping was affected by radius-to-thickness ratio, and was higher than Z for Class 1 piping in the present codes.

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