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CRACK TIP OPENING DISPLACEMENT AND ANGLE FOR A GROWING CRACK IN CARBON STEEL

Description: The crack tip opening displacements and angles (CTOD/CTOA) are calculated with finite element method based on the test data of a set of constraint-dependent J-R curves for A285 carbon steel. The values of the CTOD/CTOA are initially high at initiation, but rapidly decrease to a nearly constant value. When the common practice is adopted by using only the constant part of CTOD/CTOA as the fracture criterion, the crack growth behavior is shown to be severely underestimated. However, with a bilinear form of CTOD/CTOA fracture criterion which approximates the initial non-constant portion, the experimental load vs. crack extension curves can be closely predicted. Furthermore, it is demonstrated that the CTOD/CTOA is crack tip constraint dependent. The values of CTOD/CTOA for specimens with various ratios of crack length to specimen width (a/W) are reflected by the J-R curves and their slopes.
Date: January 18, 2005
Creator: LAM, POH-SANG
Partner: UNT Libraries Government Documents Department

Comparison of Fracture Methodologies for Flaw Stability Analysis of Storage Tanks

Description: Fracture mechanics methodologies for flaw stability analysis of a storage tank were compared in terms of the maximum stable through-wall flaw sizes or ''instability lengths.'' The comparison was made at a full range of stress loading at a specific set of mechanical properties of A285 carbon steel and with the actual tank configuration. The two general methodologies, the J-integral-tearing modulus (J-T) and the failure assessment diagram (FAD), and their specific estimation schemes were evaluated. A finite element analysis of a flawed tank was also performed for validating the J estimation scheme with curvature correction and for constructing the finite element-based FAD. The calculated instability crack lengths show that the J-T methodology that uses an estimated scheme, and the material-specific FAD, most closely approximate the result calculated with finite element analysis for the stress range that bounds those expected at the highest fill levels in the storage tanks. The results from the other FAD methods show instability lengths less than the J-T results over this range.
Date: April 5, 2004
Creator: LAM, POH-SANG
Partner: UNT Libraries Government Documents Department

THE NON-CONSTANT CTOD/CTOA IN CRACK PROPAGATION

Description: Unlike the common belief that crack propagation behavior can be predicted successfully by employing fracture criteria based on a constant crack tip opening displacement or angle (CTOD/CTOA), this paper shows that the initially non-constant portion of the CTOD/CTOA plays an essential role in predicting the fracture load for a growing crack. Three- and two-dimensional finite element analyses indicate that a severe underestimate of the experimental load vs. crack extension curve would occur if a constant CTOD/CTOA criterion is used. However, the use of a simplified, bilinear CTOD/CTOA criterion including its non-constant portion will closely duplicate the test data. Furthermore, as a result of using the experimental data from J-integral test with various crack length to specimen width ratios (a/W), it is demonstrated that the CTOD/CTOA is crack tip constraint dependent. The initially higher values of the CTOD/CTOA are in fact a natural consequence of crack growth process which is refl ected by the J-resistance curve and its slope (tearing modulus).
Date: July 19, 2004
Creator: LAM, POH-SANG
Partner: UNT Libraries Government Documents Department

Analytical modeling of the effect of crack depth, specimen size, and biaxial stress on the fracture toughness of reactor vessel steels

Description: Fracture, toughness values for A533-B reactor pressure vessel (RPV) steel obtained from test programs at Oak Ridge National Laboratory (ORNL) and University of Kansas (KU) are interpreted using the J-A{sub 2} analytical model. The analytical model is based on the critical stress concept and takes into consideration the constraint effect using the second parameter A{sub 2} in addition to the generally accepted first parameter J which represents the loading level. It is demonstrated that with the constraint level included in the model effects of crack depth (shallow vs deep), specimen size (small vs. large), and loading type (uniaxial vs biaxial) on the fracture toughness from the test programs can be interpreted and predicted.
Date: February 1, 1995
Creator: Chao, Yuh-Jin & Lam, Poh-Sang
Partner: UNT Libraries Government Documents Department

SRTC Contribution to EMSP 81898 Annual Report 2003

Description: The following describes the SRTC contributions to EMSP 81898 with emphasis on the specific applications to the SRS high level radioactive waste tanks. In particular, the crack growth criteria, constraint effects, and the weld residual stress effects are covered. The write-up consists of two parts: (1) Crack Growth Simulation, and (2) Stress Corrosion Cracking in Weld Residual Stress.
Date: June 1, 2004
Creator: Lam, Poh-Sang
Partner: UNT Libraries Government Documents Department

Effect of Saltstone Vault Roof Configuration on the Rate of Contaminant Transport

Description: At the Savannah River Site, low-level radioactive decontaminated salt solution is mixed with slag, flyash, and cement to form a grout-like material called ``Saltstone``. The Saltstone is poured into concrete vaults constructed at the Saltstone Disposal Facility (SDF). The impact of SDF on groundwater has been studied in a radiological performance assessment (PA). Sophisticated groundwater models were used to predict the groundwater flow and contaminant transport problems. The modeling effort was divided into two parts: the unsaturated-zone model and the saturated zone model. One of the major performance objectives is to show that the impacted groundwater will be in compliance with the Safe Drinking Water Act.
Date: December 28, 1994
Creator: Hsu, R. H.; Yu, A. D. & Lam, Poh-Sang
Partner: UNT Libraries Government Documents Department

Effect of roof slope and thickness on the performance of a saltstone vault

Description: At the Savannah River Site, low-level radioactive decontaminated salt solution is mixed with slag, flyash, and cement to form a grout-like material called ``Saltstone.`` The Saltstone is poured into concrete vaults constructed at the Saltstone Disposal Facility (SDF). The SDF is designed for the release of contaminants in a slow, controlled manner over thousands of years. The impact of SDF on groundwater has been studied in a radiological performance assessment (PA). Groundwater models were used to predict the fluid flow and contaminant transport at SDF. The models predicted a spatial contaminant concentration distribution in groundwater as a function of time. This study focuses on the roof configuration of Saltstone vault, with special interests in cost-effectiveness. We conducted a study to evaluate the effect of roof slope and thickness on the performance of a Saltstone vault. Four roof configurations were simulated. The tool used for the simulation was ECLIPSE, a finite-difference petroleum reservoir engineering code with an environmental tracer option. Nitrate was used as the ``tracer`` contaminant. In this study, ECLIPSE solves the two-phase two-dimensional flow and transport problem up to 10,000 years. This paper describes a modeling study used to evaluate roof design options for the Saltstone vault.
Date: September 1995
Creator: Yu, A. D.; Lam, Poh-Sang & Hsu, R. H.
Partner: UNT Libraries Government Documents Department

Increasing Safety and Reducing Environmental Damage Risk from Aging High-Level Radioactive Waste Tanks

Description: There exists a paramount need for improved understanding the behavior of high-level nuclear waste containers and the impact on structural integrity in terms of leak tightness and mechanical stability. The current program, which at the time of this writing is in its early stages, aims to develop and verify models of crack growth in high level waste tanks under accidental overloads such as ground settlement, earthquakes and airplane crashes based on extending current fracture mechanics methods. While studies in fracture have advanced, the mechanics have not included extensive crack growth. For problems at the INEEL, Savannah River Site and Hanford there are serious limitations to current theories regarding growth of surface cracks through the thickness and the extension of through-thickness cracks. We propose to further develop and extend slip line fracture mechanics (SLFM, a ductile fracture modeling methodology) and, if need be, other ductile fracture characterizing approaches with the goal of predicting growth of surface cracks to the point of penetration of the opposing surface. We also aim to quantify the stress and displacement fields surrounding a growing crack front (slanted and tunneled) using generalized plane stress and fully plastic, three-dimensional finite element analyses. Finally, we will quantify the fracture processes associated with the previously observed transition of stable ductile crack growth to unstable cleavage fracture to include estimates of event probability. These objectives will build the groundwork for a reliable predictive model of fracture in the HLW storage tanks that will also be applicable to standardized spent nuclear fuel storage canisters. This predictive capability will not only reduce the potential for severe environmental damage, but will also serve to justify life extension through retrieval of waste. This program was initiated in November of 2001.
Date: June 1, 2002
Creator: Steffler, Eric D.; McClintock, Frank A.; Lam, Poh-Sang & Lloyd, W. R.
Partner: UNT Libraries Government Documents Department

Increasing Safety and Reducing Environmental Damage Risk from Aging High-Level Radioactive Waste Tanks

Description: There exists a paramount need for improved understanding the behavior of high-level nuclear waste containers and the impact on structural integrity in terms of leak tightness and mechanical stability. The current program aims to develop and verify models of crack growth in high level waste tanks under accidental overloads such as ground settlement, earthquakes and airplane crashes based on extending current fracture mechanics methods. While studies in fracture have advanced, the mechanics have not included extensive crack growth. For problems at the INEEL, Savannah River Site and Hanford there are serious limitations to current theories regarding growth of surface cracks through the thickness and the extension of through-thickness cracks. We propose to further develop and extend slip line fracture mechanics (SLFM, a ductile fracture modeling methodology) and, if need be, other ductile fracture characterizing approaches with the goal of predicting growth of surface cracks to the point o f penetration of the opposing surface. Ultimately we aim to also quantify the stress and displacement fields surrounding a growing crack front (slanted and tunneled) using generalized plane stress and fully plastic, three-dimensional finite element analyses. Finally, we will investigate the fracture processes associated with the previously observed transition of stable ductile crack growth to unstable cleavage fracture to include estimates of event probability. These objectives will build the groundwork for a reliable predictive model of fracture in the HLW storage tanks that will also be applicable to standardized spent nuclear fuel storage canisters. This predictive capability will not only reduce the potential for severe environmental damage, but will also serve to guide safe retrieval of waste. This program was initiated in November of 2001.
Date: June 1, 2003
Creator: Steffler, Eric D.; McClintock, Frank A.; Lam, Poh-Sang; Williamson, Richard L.; Lloyd, W. R. & Rashid, Mark M.
Partner: UNT Libraries Government Documents Department

Increasing Safety and Reducing Environmental Damage Risk from Aging High-Level Radioactive Waste Tanks

Description: The research activities of this EMSP project at the U. S. Department of Energy Savannah River Site (SRS) are developed for the site-specific needs in the area of high level nuclear waste tanks. Traditional and advanced fracture methodologies are assessed, the crack growth resistance properties for the material of construction (A285 carbon steel) are measured in terms of crack tip constraint, crack growth criteria based on crack opening displacement (CTOD) or angle (CTOA) are developed, and the relationship between stress corrosion cracking (SCC) and the weld residual stress is investigated. All these activities lead to the development of predictive tools for the structural integrity of the SRS waste tanks. The methodologies can be extended to commercial applications.
Date: June 1, 2004
Creator: Steffler, Eric D.; McClintock, Frank A.; Lam, Poh-Sang; Lloyd, W. R. & Rashid, Mark M.
Partner: UNT Libraries Government Documents Department