Verification of a Finite Element Analysis Procedure for Modeling the Nonlinear, Monotonic In-Plane Behavior of 4 Inch, Schedule 10, Stainless Steel, 90° Elbows

A project has been conducted to verify a finite element analysis procedure for studying the nonlinear behavior of 90°, stainless steel, 4 inch schedule 10, butt welding elbows. Two displacement controlled monotonic in-plane tests were conducted, one closing and one opening, and the loads, displacements, and strains at several locations were recorded. Stacked 90° tee rosette gages were used in both tests because of their ability to measure strain over a small area. ANSYS shell element 181 was used in the FEA reconciliations. The FEA models incorporated detailed geometric measurements of the specimens, including the welds, and material stress-strain data obtained from the attached straight piping. Initially, a mesh consisting of sixteen elements arrayed in 8 rings was used to analyze the elbow. The load-displacement correlation was quite good using this mesh, but the strain reconciliation was not. Analysis of the FEA results indicated that the axial and hoop strain gradients across the mid-section of the elbow were very high. In order to generate better strain correlations, the elbow mesh was refined in the mid-section of the elbow to include 48 elements per ring and an additional six rings, effectively increasing the element density by nine times. Using the refined mesh produced much better correlations with the strain data.

Analytical Solutions of Crack Tip Plasticity Zone Shape for a Semi-Infinite Crack

In this work, closed-form analytical solutions for the plasticity zone shape at the lip of a semi-infinite crack are developed. The material is assumed isotropic with a linear elastic-perfectly plastic constitution. The solutions have been developed for the cases of plane stress and plane strain. The three crack modes, mode I, II and III have been considered. Finally, prediction of the plasticity zone extent has been performed for both the Von Mises and Tresca yield criterion. Significant differences have been found between the plane stress and plane strain conditions, as well as between the three crack modes’ solutions. Also, significant differences have been found when compared to classical plasticity zone calculations using the Irwin approach.

Effect of Plasticity on Fatigue Life of Welded Nuclear Component With Local Brittle Zone

The local brittle zone (LBZ), which has lower tensile properties as well as lower fracture toughness than base metal and weldment, can occur on the heat affected zone (HAZ) of some nuclear components made of low alloy steels due to the carbide coarsening by multi-pass welding and post-weld heat treatment. These variations of material strengths across the welds due to the LBZ can produce strain concentrations when the stress amplitude is large enough to cause cyclic plastic flow. But, it is difficult to find the previous researches about a relation between the fatigue life of LBZ on real nuclear components and plasticity. So, in this study, the microstructures and tensile properties of HAZ on nuclear components are predicted by using the semi-analytical method, and the fatigue lifetimes of welds on nuclear components with the LBZ are evaluated by the finite element method considering the local plasticity and the variations of tensile properties, and the fatigue analysis procedure of ASME B&PV Code Sec.III. Finally, the effect of LBZ on nuclear components on fatigue lifetime is reviewed.

Implementation of an Outer Can Welding System for Savannah River Site Plutonium Processing Facility

This paper details three phases of testing to confirm use of a Gas Tungsten Arc (GTA) system for closure welding the 3013 outer container used for stabilization/storage of plutonium metals and oxides. The outer container/lid closure joint was originally designed for laser welding, but for this application, the gas tungsten arc (GTA) welding process has been adapted. The testing progressed in three phases: (1) system checkout to evaluate system components for operational readiness, (2) troubleshooting to evaluate high weld failure rates and develop corrective techniques, and (3) pre-installation acceptance testing. A total of 190 can/lid welds were made and evaluated. During Phase I, weld failures were common due to pressure buildup and venting through the weld pool. During Phase II, characterization of the electrode contact to the weld pool and weld pool blowouts helped in the development of a corrective technique. During Phase III, a reduction in internal pressure, by controlling the final helium backfill of the can before welding, provided satisfactory weld results. The work described was performed during 2002 pre-installation testing at the Savannah River Technology Center in Aiken, S.C. before installation of an Outer Can Welder (OCW) system at the Savannah River Site (SRS) plutonium processing facility. The first OCW system was originally developed at the SRS to support similar plutonium stabilization/storage efforts at the Hanford Site (operated by Fluor Hanford Corporation).

Crack Growth Behavior in a Residual Stress Field for Vessel Type Structures

Detailed residual stress analysis was performed for a multi-pass butt weld, representing the middle butt-girth weld of a storage tank. The analysis procedures addressed welding parameters, joint detail, weld pass deposition sequence, and temperature-dependent properties. The predicted residual stresses were then considered in stress intensity factor calculations using a three-dimensional finite element alternating model (FEAM) for investigating crack growth behavior for both small elliptical surface and through-wall cracks. Two crack orientations were considered: one is parallel to the vessel girth weld and the other is perpendicular to the girth weld. Since the longitudinal (parallel to weld) and transverse (perpendicular to weld) residual stresses exhibit drastically different distributions, a different crack growth behavior is predicted. For a small surface crack parallel to the weld, the crack tends to grow more quickly at the surface along the weld rather than into the thickness. The self-equilibrating nature of the transverse residual stress distribution suggests that a through-wall crack parallel to crack cannot be fully developed solely due to residual stress actions. For a crack that is perpendicular to the weld, a small surface crack exhibit a rapid increase in K at the deepest position, suggesting that a small surface crack has the propensity to become a through-wall crack. Once the through crack is fully developed, a significant re-distribution in longitudinal residual stress can be seen. As a result, in the absence of external loads there exists a limiting crack length beyond which further crack growth is deemed unlikely.

Two Numerical Models for Prediction of an Industrial Concasting Process

This paper introduces the application of two three-dimensional (3D) numerical models of the temperature field of a caster. The first model simulates the temperature field of a caster—either as a whole, or any of its parts. Experimental research and data acquisition take place simultaneously with the numerical computation in order to enhance the numerical model and to perfect it in the course of the process. In order to apply the second original numerical model—a model of dendritic segregation of elements—it is necessary to analyze the heterogeneity of samples of the constituent elements and impurities in characteristic places of the solidifying slab. The samples are taken from places, which provide information on the distribution of elements under both standard and extreme conditions for solidification, where the mean solidification (crystallization) rate is known for points between the solidus and liquidus curves. Using this method, it is possible to forecast the occurrence of the critical points of a slab from the viewpoint of its susceptibility to crack and fissure. Verification of the technological impact of optimization, resulting from both models, is conducted on a real industrial caster.

Dynamic Analysis of a Radioactive Material Package Primary Containment Vessel in a High Pressure Event

This paper discusses the evaluation of the structural integrity of the Primary Containment Vessel (PCV) of a 9975 Shipping Package for radioactive materials subjected to an instantaneously applied pressure load. The instantaneous pressure increase is based on the postulated structural failure of a plutonium oxide container caused by either over pressurization due to detonation or gradual gas buildup. A nonlinear dynamic analysis was performed for a partial 9975 shipping package to evaluate the structural response of the PCV excited by the instantaneous pressurization. The structural integrity of the PCV is justified based on the analytical results in comparison with the stress criteria specified in the ASME Code, Section III, Appendix F for Level D service loads.

Prediction of the Cutting Forces on Stainless Steels When Using a Turning Process

Stainless steels have a great application in the manufacturing process especially due to their characteristic high corrosion resistance. The machining of these materials, the study of the cutting forces, and the power required for the cutting are important parameters to be evaluated. Their relationship with other cutting variables process is crucial for the optimization of the machining process. The results of this research are empirical expressions relating cutting parameters (cutting speed, feed rate and depth of cut) to cutting forces for each stainless steel studied, AISI 304, AISI 420 and AISI 420HT (HT: Heat treated). A general expression was also developed which includes the mechanical properties of these stainless steels. These results enable the user to predict cutting forces when using a turning process.

Die Design and Blanking Analysis

The modified fine blanking technique is the subject of this research, along with a comparison of conventional blanking and shaving. The modified process does not require the use of a triple-action press and the press can be run at the same rate as conventional blanking. A counter-pressure punch and assembly are used to prevent the fracturing of the cut, which is similar to standard fine blanking. The difference between the two fine blanking techniques is that the modified method does not hold the material from lateral movement during the perforating operation. Furthermore, to achieve an optimum comparison of all three methods (conventional blanking, shaving, and modified fine blanking), a die set was designed that could produce parts for each of these processes. The evaluation of each method was done by cutting similar samples of each method and placing them in plastic, which allowed microscopic comparisons to be made of the three methods. A trade-off analysis of the various methods demonstrated that the modified fine blanking technique is superior to the other techniques.

Study of Burst Conditions of Thin-Walled Pressure Vessels Subjected to Hypervelocity Impact

The present paper is devoted to analysis of burst conditions of thin-walled cylindrical pressure vessels subjected to hypervelocity impact of space debris particles. Two types of gas-filled pressure vessels onboard the International Space Station were considered: inhabited or laboratory pressurized modules and onboard system vessels with a gas under high pressure. The central concern of this study is to determine the border between simple perforation and catastrophic fracture of gas-filled pressure vessels of both types under hypervelocity impact. Non-linear fracture mechanics techniques were used to analyze and predict whether a vessel perforation will lead to mere leakage of gas, or whether unstable crack propagation will occur that could lead to catastrophic fracture of the vessel. Damage patterns and mechanisms leading to unstable crack growth are discussed. A model of fracture of an impact damaged pressure vessel is presented. A developed model was successfully applied to the simulation of experimental results obtained at Ernst-Mach-Institute (Germany).