Evaluation of weldment creep and fatigue strength-reduction factors for elevated-temperature design

New explicit weldment strength criteria in the form of creep and fatigue strength-reduction factors were recently introduced into the American Society of Mechanical Engineers Code Case N-47, which governs the design of elevated-temperature nuclear plants components in the United States. This paper provides some of the background and logic for these factors and their use, and it describes the results of a series of long-term, confirmatory, creep-rupture and fatigue tests of simple welded structures. The structures (welded plates and tubes) were made of 316 stainless steel base metal and 16-8-2 weld filler metal. Overall, the results provide further substantiation of the validity of the strength-reduction factor approach for ensuring adequate life in elevated-temperature nuclear component weldments. 16 refs., 7 figs

AN EXPERIMENTAL INVESTIGATION OF INSTANTANEOUS-COLLAPSE AND CREEP-BUCKLING CHARACTERISTICS OF CYLINDRICAL SHELLS

Instantaneous-collapse and creep, or time-dependent, buckling tests were conducted on nominally 8.0-in.-OD by 0.25-in.-wall and 4.0-in.-OD by 0.12-in.- wall specimens made from commercial pipe and tubing. The material for the larger specimens was type 304 stainless steel, while the smaller ones were made of both type 304 and type 347 stainless steel. The length chosen in each case was infinite from the buckling standpoint. The instantaneous-collapse test temperatures ranged from room temperature to 1200 deg F, and all the time- dependent collapse tests were made at 1200 deg F. The results show that tube out- of-roundness is a major factor in determining the collapse pressure. They also show that, under creepcollapse conditions, the critical pressure decreases rapidly with time, initially. This decrease is then followed by a leveling off, with very little change after the first few hundred hours. Although the load- carrying abilities of the 8.0-in.-OD specimens exceeded those for 4.0in.-OD specimens of the same material for instantaneous and short-time collapse conditions, the critical pressures were about the same in the two cases for collapse after several hundred hours. The ratio of experimental values to the allowable working pressure given by the ASME Boiler and Pressure Vessel Code, Section VIII, Rules for Construction of Unfired Pressure Vessels, ranges from about 6.0 for instantaneous buckling to about 3.4 at 3400 hr in the case of the 8.0-in.-OD tubes. For the 4.0-in.-OD type 304 stainless steel tubes, the ratio is about 4.5 for instantaneous buckling and about 3.4 for buckling after a few thousand hours. (auth

Elastic-plastic-creep analysis of thermal ratchetting in straight pipe and comparisons with test results

From winter meeting of American Society of Mechanical Engineers; Detroit, Michigan, USA (11 Nov 1973). An experimental and analytical study of ratchetting in a simple structural component is described. A straight pipe from a wellcharacterized heat of Type 304 stainless steel was subjected to a series of thermal downshocks followed by sustained periods of high-temperature operation under internal pressure. The test was performed in a special sodium test facility built for the purpose. The inelastic analysis predictions were obtained using a one-dimensional finite-element procedure, and they were based on interim constitutive equations that have been recommended for use in design analyses of liquid-metal fast-breeder reactor components. The agreement between the measured and predicted ratchetting behavior is good. (8 references) (auth

Durability-Based Design Criteria for a Quasi-Isotropic Carbon-Fiber Automotive Composite

This report provides recommended durability-based design properties and criteria for a quasi-isotropic carbon-fiber composite for possible automotive structural applications. The composite, which was made by a rapid molding process suitable for high-volume automotive applications, consisted of continuous Thornel T300 fibers (6K tow) in a Baydur 420 IMR urethane matrix. The reinforcement was in the form of four {+-}45{sup o} stitch-bonded mats in the following layup: [0/90{sup o}/{+-}45{sup o}]{sub S}. This material is the second in a progression of three candidate thermoset composites to be characterized and modeled as part of an Oak Ridge National Laboratory project entitled Durability of Carbon-Fiber Composites. The overall goal of the project, which is sponsored by the U.S. Department of Energy's Office of Advanced Automotive Technologies and is closely coordinated with the industry Automotive Composites Consortium, is to develop durability-driven design data and criteria to assure the long-term integrity of carbon-fiber-based composite systems for large automotive structural components. This document is in two parts. Part I provides the design criteria, and Part 2 provides the underlying experimental data and models. The durability issues addressed include the effects on deformation, strength, and stiffness of cyclic and sustained loads, operating temperature, automotive fluid environments, and low-energy impacts (e.g., tool drops and kickups of roadway debris). Guidance is provided for design analysis, time-dependent allowable stresses, rules for cyclic loadings, and damage tolerance design guidance, including the effects of holes. Chapter 6 provides a brief summary of the design criteria

BASIC PROPERTIES OF REFERENCE CROSSPLY CARBON-FIBER COMPOSITE

This report provides basic in-air property data and correlations-tensile, compressive, shear, tensile fatigue, and tensile creep-for a reference carbon-fiber composite being characterized as a part of the Durability of Carbon-Fiber Composites Project at Oak Ridge National Laboratory. The overall goal of the project, which is sponsored by the Department of Energy's Office of Advanced Automotive Materials and is closely coordinated with the Advanced Composites Consortium, is to develop durability-based design guidance for polymeric composites for automotive structural applications. The composite addressed here is a {+-}45{degree} crossply consisting of continuous Thornel T300 fibers in a Baydur 420 IMR urethane matrix. Basic tensile, compressive, and shear properties are tabulated for the temperature range from {minus}40 to 120 C. Fatigue response at room-temperature and 120 C are presented, and creep and creep rupture at room temperature only are reported. In all cases, two fiber orientations--0/90{degree} and {+-}45{degree}--relative to the specimen axes are addressed. The properties and correlations presented are interim in nature. They are intended as a baseline for planning a full durability test program on this reference composite

Key technological issues in LMFBR high-temperature structural design - the US perspective

The purpose of this paper is: (1) to review the key technological issues in LMFBR high-temperature structural design, particularly as they relate to cost reduction; and (2) to provide an overview of activities sponsored by the US Department of Energy to resolve the issues and to establish stable, standardized, and defensible structural design methods and criteria. Specific areas of discussion include: weldments, structural validation tests, simplified design analysis procedures, design procedures for piping, validation of the methodology for notch-like geometries, improved life assessment procedures, thermal striping, extension of the methodology to new materials, and ASME high-temperature Code reform needs. The perceived problems and needs in each area are discussed, and the current status of related US activities is given

Overview of US efforts to validate analysis methods and design criteria

As a part of its basic breeder reactor technology activities, the United States has a High-Temperature Structural Design Program aimed at establishing, and transferring to designers a rationally sound and experimentally validated structural design technology that will assure freedom from structural failures. Both development and validation efforts are centered on three main ingredients of the technology: (1) mathematical descriptions (constitutive equations) of the deformation behavior of the alloys of interest, (2) time-dependent rupture, or cracking, models, again for the alloys of interest, and (3) detailed design analysis methods and failure criteria based on these inputs. The objective of this presentation is to provide a brief overview of the status of efforts to experimentally assess and validate each of these three technology ingredients. In the case of deformation and rupture models, the current procedures and rules are outlined, and their significant features are assessed through comparisons with results from uniaxial and multiaxial material behavior tests. Design analysis methods and failure criteria are, on the other hand, discussed relative to the results of experimental benchmark structural tests. Although several significant needs and problem areas remain, data generated to date tend to provide limited validation of key aspects of the existing technology. Current constitutive equations represent many of the observed behavioral features; limited available data support current time-dependent rupture criteria reasonably well; and it is observed that structural analysis predictions capture most of the experimentally observed features of inelastic structural behavior