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.

Near-Surface Deuterium in Titanium
B. Heuser,* C. Costescu
National Science Foundation, DMR-94-96297

The effect of a surface nitride film (Ti2N) on the near-surface concentration profiles of deuterium is being investigated with SIMS, AES, and the volumetric loading technique. The nitride reduces the deuterium absorption kinetics, consistent with diffusion in the ternary system at the surface. The concentration profile in this region also indicates that the solubility of deuterium is suppressed in the presence of nitrogen or the Ti2N phase. Analysis will center on the reduced solubility and diffusivity in the modified surface layer.

Hydride Formation in Nb
B. Heuser,* W. Chen
National Science Foundation, DMR-94-96297

Small-angle neutron scattering (SANS), TEM, and metallographical analysis are employed to characterize deuterium precipitation in Nb. The effect of lattice defects such as dislocations and grain boundaries on the phase transformation characteristics are of interest. We have investigated the effect of lattice defects on the temperature hysteresis in the Nb-D system. Dislocations, either formed by deformation or by previous deuteride precipitation, reduced significantly the observed hysteresis. On the other hand, grain boundaries had little effect. The data will be analyized with a thermodynamic model yielding the energy associated with the temperature hysteresis.

Deuterium Phase Behavior in Metal Thin Films
B. Heuser,* A. Munter, N. Barber
National Science Foundation, DMR 94-96297

Neutron reflectometry is used to characterize deuterium phase behavior in thin-film Pd. In situ measurements simultaneously provide the phase diagram, out-of-plane film expansion, and depth profile. We have found that the phase diagram of the thin-film Pd-D system altered significantly from that of the bulk, and that this is due to a substrate clamping effect. This conclusion is based on the observed exclusion of deuterium at the film-substrate interface (due to clamping stresses) and from the out-of-plane expansion following a clamped, isotropic behavior. More work on epitaxial layers is planned.

Temperature-controlled, In-Core, Neutron Irradiation Materials Facility
B. G. Jones,* J. F. Stubbins,* R. Holm,* G. Malone
University of Illinois

A temperature-controlled, high flux level, neutron irradiation facility is being developed for installation and use in the central core region of the TRIGA reactor. The facility will provide both steady and cyclical temperature control of material specimens during neutron irradiation. This will enable study of effects of specimen temperature on the radiation damage and property changes resulting from neutron bombardment. Specimen temperature control from near liquid-nitrogen (~77 K) to relatively high levels (900 K) will be provided in the facility. Out of core, electrically treated prototype tests confirm thermal performance of the design.

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* (Nucl. Engr.), 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.

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* (Nucl. Engr.), 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.

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* (Nucl. Engr.), 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.

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

Fiber-reinforced sheet molding compound is an attractive material used in ground-vehicle structural applications. It experiences cyclic loading in service, therefore, understanding the fatigue behavior as a function of processing conditions, chemistry of constituents, and loading conditions is important. The purpose of this work is to analyze some of the available fatigue data on these materials and to conduct experiments to identify the nature of damage mechanisms and to study cumulative fatigue damage. Tension-compression testing will be considered to gain insight into mean stress effects. In all these cases the fiber orientation of the molded part affects the progression of damage.

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* (Nucl. Engr.), 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.

Probabilistic Methods
H. Sehitoglu* (Mech. & Indus. Engr.), F. V. Lawrence, Jr.* (Civil & Environ. Engr.), D. F. Socie* (Mech. & Indus. Engr.), J. F. Stubbins* (Nucl. Engr.), 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.

Processing Existing Materials to Enhance Performance and Reduce Cost
H. Sehitoglu* (Mech. & Indus. Engr.), F. V. Lawrence, Jr.* (Civil & Environ. Engr.), D. F. Socie* (Mech. & Indus. Engr.), J. F. Stubbins* (Nucl. Engr.), K. J. Hsia* (Theoret. & Appl. Mech.), N. Chen, H. Hsieh, S. Andrews, T. McGreevy
Fracture Control Program

It is no longer possible to specify a material without first considering its processing. In some applications, the so-called old materials processed in new ways are often more cost effective than some of the new advanced materials. Surface treatments such as carburizing and nitriding have been used for many years. Flexible manufacturing processes, such as those using lasers, now offer the potential to modify surfaces selectively to produce superior mechanical properties of traditional lower cost materials.

First Wall, Blanket, and Shield Development for the International Tokamak Experimental Reactor
J. F. Stubbins,* B. G. Thomas,* B. G. Jones,* K. Leedy, G. Li, M. James
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.

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

Surface Modification by Ion Bombardment
J. F. Stubbins,* M. James, 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.

Cyclic Softening in Ferritic/Martensitic Steels for Fusion Reactor Application
J. F. Stubbins,* D. Gelles*
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.

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.

Mathematical Behavior and Fracture Characteristics of Strongly Bonded Bilayer Materials
J. F. Stubbins,* J. Collins, J. Min
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.