Adsorption and Desporption of Radionucleides on Cecil Clay and Its Trace Minerals
W. R. Roy,* J. F. Stubbins,* P. Huggins
Illinois State Geological Survey

This work is to determine the adsorption and desorption behavior of specific radionucleides onto Cecil clay and several of its trace minerals. The specific radionucleides under investigation are Cs-137 and Eu-152 to represent typical radioisotopes in nuclear waste forms. The adsorption and desorption characteristics are critical parameters in determining issues related to potential transport of such isotopes in waste repository soils. The study will include competitional effects between mixtures of the two isotopes in the systems under study.

Copper and Copper Alloys for Fusion Applications
J. F. Stubbins,* M. M. Li, F. A. Garner, D. J. Edwards (Battelle), B. N. Singh (Riso)
Associated Western Universities; OMG America; Brush Wellman; Battelle Pacific Northwest National Laboratory; Riso National Laboratory, Denmark; University of Illinois

This research project is aimed at developing an understanding of the performance of copper and copper alloys for fabrication of high heat flux components in nuclear fusion applications. Service performance will be based on irradiation damage behavior and elevated temperature mechanical properties. These features are being examined by testing alloys that have been subjected to high fluences of neutrons in FFTF, and performing room and elevated temperature mechanical properties testing.

Crack Growth for APT Relevant Materials Conditions
J. F. Stubbins,* M. M. Li, J. Heuer, V. Voyevodin
Los Alamos National Laboratory, H65540019-84

The goal of this study is to develop a technique to determine fatigue crack growth rates (i.e., da/dN, change in crack length per cycle) as a function of the loading parameters. Typical design approaches use the applied stress intensity factor, delta K (or delta J). The program will then develop APT design-relevant crack growth data on APT design-base materials. This goal is complicated in the current context by the small specimen sizes available from irradiation exposure to make of crack growth rate measurements.

Cyclic Softening in Ferritic/Martensitic Steels for Fusion Reactor Application
J. F. Stubbins,* D. Gelles,* V. Voyevodin
Associated Western Universities: NORCUS

Ferritic/martensitic steel alloys have been under investigation for structural applications in fusion reactors. They are very appealing because of adequate mechanical properties and extremely good irradiation performance when compared to austenitic stainless steels. The strength of the alloy comes from the complicated dislocation lath structure that forms on heat treating. This imparts good initial strength, but the strength can degrade under cyclic or fatigue loading conditions. This program is studying the loss of strength of an advanced ferritic/martensitic steel as a function of cyclic loading.

Durability of Advanced Materials
H. Sehitoglu* (Mech. & Indus. Engr.), F. V. Lawrence, Jr.* (Civil & Environ. Engr.), D. F. Socie* (Mech. & Indus. Engr.), J. F. Stubbins,* K. J. Hsia* (Theoret. & Appl. Mech.), N. Chen, H. Hsieh, S. Andrews, T. McGreevy
Fracture Control Program

Recent developments in processing technology have resulted in advanced materials with lower fabrication costs and improvements in microstructural uniformity. To utilize the full potential of these materials, new design tools have to be developed in collaboration with industry. Examples of such materials include metal matrix composites and short reinforcement fibers in epoxy matrices. The metal matrix composites with higher elastic modulus, higher temperature capabilities, and lower weight compared to their counterparts represent excellent opportunities for engine, brake, and rotating components in the ground vehicle industry.

Fatigue Crack Growth and Crack Closure
H. Sehitoglu* (Mech. & Indus. Engr.), F. V. Lawrence, Jr.* (Civil & Environ. Engr.), D. F. Socie* (Mech. & Indus. Engr.), J. F. Stubbins,* K. J. Hsia* (Theoret. & Appl. Mech.), N. Chen, H. Hsieh, S. Andrews, T. McGreevy
Fracture Control Program

The aim of this study is to develop a life prediction methodology for fatigue crack growth based on the changes in crack opening levels with maximum stress level, crack length, geometry, mean stress, and microstructure. The primary tool for the determination of opening stress is an elastic-plastic finite-element simulation of fatigue crack growth. Stress-strain behavior in the model accounts for slip at the microlevel as well as elastic anisotrophy. Fatigue crack growth data obtained under conditions of intermediate- and large-scale yielding, including low-cycle fatigue and biaxial loading, are successfully correlated only when closure-modified parameters are employed.

Fatigue of Welds and Adhesive Joints
H. Sehitoglu* (Mech. & Indus. Engr.), F. V. Lawrence, Jr.* (Civil & Environ. Engr.), D. F. Socie* (Mech. & Indus. Engr.), J. F. Stubbins,* K. J. Hsia* (Theoret. & Appl. Mech.), N. Chen, H. Hsieh, S. Andrews, T. McGreevy
Fracture Control Program

Factors that control the fatigue behavior of welded components are currently being studied. Analytical methods for estimating the total fatigue life of butt and fillet welds subjected to variable-amplitude loading histories are evaluated. Surface treatments, such as shot peening and laser dressing of the weld toe, are investigated as possible methods for improving the fatigue strength. A new model for estimating the fatigue life of weldments has been proposed for butt, T-joint, and cruciform weldments using the concepts of 'crack closure' for cracks emanating from a notch. Results compare favorably with experimental data in the UIUC fatigue data bank and with experimental work in the literature.

First Wall, Blanket, and Shield Development for the International Tokamak Experimental Reactor
J. F. Stubbins,* B. G. Thomas,* B. G. Jones,* M. M. Li, J. W. Collins
Boeing Corp.

The major structural components of the International Tokamak Experimental Reactor (ITER) are presently under development in the program. The design and performance of a fusion plasma chamber are being assessed and improved in the joint industrial program. The thermal performance of the structure; materials selection, performance and fabricability routes of the first wall-blanket-shield structure; and nondestructive examination and in situ serviceability of the structure are all being examined in this program.

Investigation of Pd Hydride Formation Using Small-Angle Neutron Scattering
B. Heuser,* W. Chen
American Chemical Society

Small-angle neutron scattering (SANS) is being used to investigate hydride (deuteride) precipitation in single- crystal palladium (Pd). There are many aspects of Pd-H phase transformation behavior that are not clearly understood. SANS is extremely sensitive to the presence of hydrogen and deuterium in metals. An initial set of experiments is planned to investigate deuteride precipitation in single-crystal Pd, primarily to deduce the particle morphology and give general characteristics of the SANS response. These results indicate that a shift from classical coherent nucleation to spinodal decomposition occurs as the over-pressure driving force is increased during deuterium loading at room temperature.

Life Prediction Methods for Notched Members under Nonproportional Multiaxial Fatigue
H. Sehitoglu* (Mech. & Indus. Engr.), F. V. Lawrence, Jr.* (Civil & Environ. Engr.), D. F. Socie* (Mech. & Indus. Engr.), J. F. Stubbins,* K. J. Hsia* (Theoret. & Appl. Mech.), N. Chen, H. Hsieh, S. Andrews, T. McGreevy
Fracture Control Program

To develop fatigue life prediction methods for notched components subjected to nonproportional multiaxial fatigue, the local stresses and strains must be related to the global stresses and strains by some approximation procedure, such as Neuber's rule. Experimental tests on notched shafts subjected to proportional and nonproportional loading in tension and torsion are being performed. The results are being used to develop and verify the approximation procedure. Fatigue life estimates will then be made using an appropriate damage model that is based upon observations made during the tests. A life prediction scheme will be developed from the approximation procedure and the appropriate damage model and will be verified from the results of the tests.

Materials Radiation Effects for Spallation Neutron Systems Applications
V. Voyevodin,* J. F. Stubbins,* F. Garner* (Pacific Northwest National Lab)
National Research Council, COBASE Program

This project examines neutron energy spectral effects on materials irradiation damage evolution for spallation, fast fission, and fusion environments. Effort will be concentrated on a wide range of materials at a variety of irradiation conditions (fluence, dose rate, temperature) of relevance to spallation facility design. The aim is to compare and contrast damage evolution and effects for spallation sources compared to the others.

Mathematical Behavior and Fracture Characteristics of Strongly Bonded Bilayer Materials
J. F. Stubbins,* J. Collins
U.S. Department of Energy, LM 19X-SY481V

The use of bilayer materials is being studied to understand the fracture behavior. This behavior depends strongly on the character of the bond and the characteristics of the structural loads. In this study, we are concentrating on Cu alloy to 316L SS bilayers where joining has been accomplished by hot isostatic pressing. This develops a strong bond layer where fracture seems to be controlled by the differing materials properties near, but not precisely on, the interface. The interdiffusion zone leaves a region in the copper alloy side where the microstructure is altered from the starting microstructure. The fracture process and a useful means to quantify the bond strength are being studied using experimental techniques and by finite-element modeling.

Metallurgical and Chemical Studies on Lead, Lead-Bismuth, and Structural Materials for Accelerator Transmutation of Waste (ATW) Systems
J. F. Stubbins,* J. Heuer, N. Li (LANL), F. Venneri (LANL), J. Collins, X. Chen
U.S. Department of Energy, LANL E337800173C

The development of accelerator-driven systems for the transmutation of nuclear waste materials will consist of liquid metal-based targets and processing systems, likely based on liquid lead or lead-bismuth eutectic. The processing structure must be resilient at elevated operating temperatures, consistent with the use of liquid metals, and in an extremely aggressive irradiation environment. This work is focused on the selection and use of structural materials compatible with these aggressive environments where radiation damage and liquid metal corrosion are important.

Probabilistic Methods
H. Sehitoglu* (Mech. & Indus. Engr.), F. V. Lawrence, Jr.* (Civil & Environ. Engr.), D. F. Socie* (Mech. & Indus. Engr.), J. F. Stubbins,* K. J. Hsia* (Theoret. & Appl. Mech.), N. Chen, H. Hsieh, S. Andrews, T. McGreevy
Fracture Control Program

A comprehensive fatigue damage model is being developed to address the following issues: What governs the nucleation of a microcrack within a single grain or other suitable microstructural unit cell? What governs the growth of this microcrack into adjacent microstructural unit cells? When does the microcrack develop enough plasticity to sustain its growth? These elements will be combined into a model for the entire fatigue damage process.

Surface Modification by Ion Bombardment
J. F. Stubbins,* M. Giacobbe, N. Lam (ANL)
Argonne National Laboratory; University of Illinois

Surface and near-surface compositional modifications are being modeled to take into account various computing processes due to energetic ion bombardment of materials surfaces. This work is developing methods to model complex alloys, three constituents, using techniques to take full advantage of the present generation of supercomputers. Experiments are being carried out on model alloy systems to further elucidate the behavior of materials under surface ion bombardment.