The Idaho National Laboratory is conducting moderate strain rate (5 to 200 per second) research on stainless steel materials in support of the Department of Energy's National Spent Nuclear Fuel Program. For this research, strain rate effects are characterized by comparison to quasi-static tensile test results. Considerable tensile testing has been conducted resulting in the generation of a large amount of basic material data expressed as engineering and true stress-strain curves. The purpose of this paper is to present the results of quasi-static tensile testing of 304L and 316L stainless steels in order to add to the existing data pool for these materials and make the data more readily available to other researchers, engineers, and interested parties.Standard tensile testing of round specimens in accordance with ASTM procedure A 370-03a was conducted on 304L and 316L stainless steel plate materials at temperatures ranging from -20°F to 600°F. Two plate thicknesses, eight material heats, and both base and weld metal were tested. Material yield strength, ultimate strength, ultimate strain, fracture strength, fracture strain and reduction in area were determined. Engineering and true stress-strain curves to failure were developed and comparisons to ASME Code minimums were made. The procedures used during testing and the typical results obtained are presented in this paper. INTRODUCTIONThe Department of Energy's (DOE) National Spent Nuclear Fuel Program (NSNFP), working with the Office of Civilian Radioactive Waste Management (OCRWM), the Idaho National Laboratory (INL) and other DOE sites, has supported development of canisters for loading and interim storage, transportation, and disposal of DOE spent nuclear fuel (SNF). To assess the integrity of these SNF canisters under dynamic, impact loading, the INL is conducting moderate strain rate (5 to 200 per second) research on 304L and 316L stainless steels which are the preferred materials for construction. The goal of this research is to define and justify elevated strain rate effects for these materials over a range of applicable temperatures and develop corresponding true stress-strain relationships that can be used to perform accurate analytical assessments of canister impact events. Both base metal and weld metal are of significance and are being investigated.
The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code is primarily a stress-based acceptance criteria code. These criteria are applicable to force, displacement, and energy-controlled loadings and ensure a factor of safety against failure. However, stress-based acceptance criteria are often excessively conservative for one time energy-limited events such as accidental drops and impacts. For several years, the ASME Working Group on Design of Division 3 Containments has been developing the Design Articles for Section III, Division 3, “Containments for Transportation and Storage of Spent Nuclear Fuel and High-Level Radioactive Material and Waste,” and has wanted to expand the design articles to include strain-based acceptance criteria for accidental drops of containments. The Division 3 Working Group asked the Working Group on Design Methodology (WGDM) to assist in developing strain-based acceptance criteria. This paper discusses the current proposed strain-based acceptance criteria, associated limitations of use, its background development, and the current status.
The Task Group on Computational Modelling for Explicit Analyses in the ASME Boiler and Pressure Vessel Code committee was set up in August 2008 to develop a quantitative finite element modelling guidance document for the explicit dynamic analysis of energy-limited events. This guidance document will be referenced in the ASME Boiler and Pressure Vessel Code Section III Division 3 and NRC Regulatory Guide 7.6 as a means by which the quality of a finite element model may be judged.In energy limited events, which the guidance document will address, ductile metallic materials will suffer significant plastic strains to take full advantage of their energy absorption capacity. Accuracy of the analyses in predicting large strains is therefore essential.One of the issues that this guidance document will address is the issue of the quality of a finite element mesh, and in particular, mesh refinement to obtain a convergent solution. That is, for a given structure under a given loading using a given type of element, what is the required mesh density to achieve sufficiently accurate results.One portion of the guidance document will be devoted to a series of element convergence studies that can aid designers in establishing the mesh refinement requirements necessary to achieve accurate results for a variety of different elements types in regions of high plastic strain. These convergence studies will also aid reviewers in evaluating the quality of a finite element model and the apparent accuracy of its results.The first convergence study consists of an elegantly simple problem of a cantilevering beam, simply supported at one end and built in at the other, loaded by a uniformly-distributed load that is ramped up over a finite time to a constant value. Three different loads were defined, with the smallest load to cause stresses that are entirely elastic and the largest load to cause large plastic deformations. Material properties, loading rates and boundary conditions were also defined.A number of the members of the Task Group analysed the problem. The results were collated and compared, and this paper presents some preliminary results of this study.
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