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A novel method to synthesize high purity, nanostructured copper

Description: Nanostructured high purity (99.999%) copper foils, 10 cm in diameter and 22-25 microns thick were produced using nanoscale multilayer technology. The foils were produced using five different layer thicknesses ranging from 1.25 to 43.6 nm (18,000 to 520 layers). This process delivers the ability to produce multiple large-scale samples during a single deposition run with very small residual stresses. Tensile and indentation tests demonstrate that the material produced is a high strength copper ({sigma}{sub y} {approx} 540-690 MPa).
Date: August 30, 2005
Creator: Hodge, A M; Wang, Y M & Barbee, T W
Partner: UNT Libraries Government Documents Department

Experimental measurement and numerical simulation of residual stresses in a carburized layer of a 5120 steel

Description: A combined experimental and numerical study of residual stress and microstructure has been performed for a carburized steel 5120 specimen. Specimens were cut from 5120 steel bar stock, in the shape of hockey pucks and were subsequently carburized and quenched. X-ray diffraction was used to record stress profiles through the case for the martensite and retained austenite on the two flat surfaces oriented up and down during the quench. Layer removal was performed by electropolishing. Rietveld analysis was used to determine the lattice parameters of the phases at each depth varying with both carbon content and stress. The experimental measurements are compared with a numerical simulation of the phase transformation and the metallurgical changes following the carburization and quench. Results am discussed in the context of the microstructure and the role played by the retained austenite in interpretation. In addition the carbon profile obtained from the lattice parameters is compared with profiles measured using burnout.
Date: September 1, 1995
Creator: Rangaswamy, P.; Bourke, M.A.M.; Shipley, J.C. & Goldstone, J.A.
Partner: UNT Libraries Government Documents Department

Accuracy evaluation of residual stress measurements

Description: The accuracy of residual stress measurement techniques is difficult to assess due to the lack of available reference standards. To satisfy the need for reference standards, two specimens were designed and developed to provide known stress magnitudes and distributions: one with a uniform stress distribution and one with a nonuniform linear stress distribution. A reusable, portable load fixture was developed for use with each of the two specimens. Extensive bench testing was performed to determine if the specimens provide desired known stress magnitudes and distributions and stability of the known stress with time. The testing indicated that the nonuniform linear specimen and load fixture provided the desired known stress magnitude and distribution but that modifications were required for the uniform stress specimen. A trial use of the specimens and load fixtures using hole drilling was successful.
Date: May 1, 1996
Creator: Yerman, J.A.; Kroenke, W.C. & Long, W.H.
Partner: UNT Libraries Government Documents Department

X-ray diffraction characterization of suspended structures for MEMS applications

Description: Mechanical stress control is becoming one of the major challenges for the future of micro and nanotechnologies. Micro scanning X-ray diffraction is one of the promising techniques that allows stress characterization in such complex structures at sub micron scales. Two types of MEMS structure have been studied: a bilayer cantilever composed of a gold film deposited on poly-silicon and a boron doped silicon bridge. X-ray diffraction results are discussed in view of numerical simulation experiments.
Date: September 15, 2005
Creator: Goudeau, P.; Tamura, N.; Lavelle, B.; Rigo, S.; Masri, T.; Bosseboeuf, A. et al.
Partner: UNT Libraries Government Documents Department

A technique for determining the Poisson`s ratio of thin films

Description: The theory and experimental approach for a new technique used to determine the Poisson`s ratio of thin films are presented. The method involves taking the ratio of curvatures of cantilever beams and plates micromachined out of the film of interest. Curvature is induced by a through-thickness variation in residual stress, or by depositing a thin film under residual stress onto the beams and plates. This approach is made practical by the fact that the two curvatures air, the only required experimental parameters, and small calibration errors cancel when the ratio is taken. To confirm the accuracy of the technique, it was tested on a 2.5 {mu}m thick film of single crystal silicon. Micromachined beams 1 mm long by 100 {mu} wide and plates 700 {mu}m by 700 {mu}m were coated with 35 nm of gold and the curvatures were measured with a scanning optical profilometer. For the orientation tested ([100] film normal, [011] beam axis, [0{bar 1}1] contraction direction) silicon`s Poisson`s ratio is 0.064, and the measured result was 0.066 {+-} 0.043. The uncertainty in this technique is due primarily to variation in the measured curvatures, and should range from {+-} 0.02 to 0.04 with proper measurement technique.
Date: April 18, 1996
Creator: Krulevitch, P.
Partner: UNT Libraries Government Documents Department

Residual stress and microstructural characterization using Rietveld refinement of a carburized layer in a 5120 steel

Description: Rietveld refinement of X-ray diffraction patterns has been used to provide microstructural information complementary to conventional X-ray residual stress measurements through a carburized layer containing a maximum vol. 25 % of retained austenite. Layers in a simple specimen were removed incrementally by electropolishing and, at each depth in addition to conventional residual stress measurements in both the martensite and retained austenite, data were collected at {Psi} = 0 for Rietveld refinement. The refinements provide accurate values for the lattice parameters in the respective phases that can be related to carbon content and microstructure. Besides to providing qualitative information concerning the microstructure and possible surface decarburization, the c/a ratio of the martensite potentially offers an independent technique for determining carbon content profiles.
Date: September 1, 1995
Creator: Rangaswamy, P.; Bourke, M.A.M.; Lawson, A.C.; O`Rourke, J. & Goldstone, J.A.
Partner: UNT Libraries Government Documents Department

Finite element prediction of elastic strains in beryllium compact tension specimens

Description: Three-dimensional finite element (FE) calculations using ABAQUS version 5.5.9 were compared to neutron diffraction measurements of a loaded, pre-cracked beryllium compact tension (CT) specimens. The objective was to validate the FE results with the experimental {open_quotes}elastic strain{close_quotes} measurements. Then the FE calculations could be used to study residual stress and other aspects of these problems in the unloaded state and the crack tip stress in the loaded state which is hard to measure experimentally. A graded FE mesh was focused on the regions containing high strain gradients, the smallest elements were approximately 0.5 mm x 0.5 mm x 0.4 mm. A standard 20-node brick element model was complemented by a model with 1/4-point elements at the crack tip. Since the neutron diffraction measurements provided a volume average of approximately a cube of edge 3.0 mm, various averaging (or integrating) techniques were used on the FE results. Several integration schemes showed good agreement with the experimental results.
Date: May 1, 1997
Creator: Guerra, F.; Varma, R. & Bourke, M.
Partner: UNT Libraries Government Documents Department

Stress transfer problems for a fully embedded fiber with a bonded interface and bonded ends

Description: Stress transfer between fibers and matrix in fiber-reinforced composite was analyzed extensively using a shear lag model. Ends of the embedded fiber are generally assumed to debond from the matrix and stress transfer occurs only at the interface along the fiber length. The debonded ends are stress-free and the boundary condition at debonded ends in solving the stress transfer problem is trivial. When the fiber ends are bonded to the matrix, stress transfer also occurs at bonded ends, and the sress at bonded endsis finite. However, this finite stress is not a predetermined value, and the boundary condition at bonded ends becomes ambiguous. To resolve this ambiguity, a technique of adding imaginary fibers in the shear lag model is developed. Stress trnafer problems are analyzed when the composite is subjected to residual stresses or load. Comparison with experimental result is also made.
Date: June 1, 1996
Creator: Hsueh, Chun-Hway
Partner: UNT Libraries Government Documents Department

Characterization of welding residual stresses with neutron diffraction

Description: Welding residual stresses are a key concern in the fabrication and use of structural components containing welds. Residual stresses in welds are caused by non-uniform expansion and shrinkage of differently heated zones during the thermal transient of a weld pass. In some alloys, solid state phase transformations occurring during the welding transient contribute additional residual stresses. Manufacturing problems arising from welding residual stresses include cracking and dimensional distortion. During use, tensile stresses in the welded zone limit the fatigue resistance of the component under cyclic loading. In an aggressive environment, tensile welding residual stresses also create a necessary condition for stress-corrosion cracking to take place.
Date: March 1, 1998
Creator: Wang, X.L.; Spooner, S.; Hubbard, C.R.; Taljat, B. & Feng, Z.
Partner: UNT Libraries Government Documents Department

Residual stress distribution in an Al{sub 2}O{sub 3}-Ni joint bonded with a composite layer

Description: Neutron diffraction was used to study the residual stress distribution in an axisymmetric Al{sub 2}O{sub 3}-Ni joint bonded with a 40 vol% Al{sub 2}O{sub 3}-60 vol% Ni composite layer. A series of measurements was taken along the axis of symmetry through the Al{sub 2}O{sub 3} and composite layers. It is shown that after taking into account the finite neutron diffraction sampling volume, both the trends and peak values of the experimental strain distribution were in excellent agreement with calculations of a simple finite element model, where the rule-of-mixtures approach was used to describe the constitutive behavior of the composite interlayer. In particular, the predicted steep strain gradient near the interface was confirmed by the experimental data.
Date: July 1, 1996
Creator: Wang, X.L.; Watkins, T.R.; Rabin, B.H.; Williamson, R.L. & Bruck, H.A.
Partner: UNT Libraries Government Documents Department

Residual stress depth profiles of ausrolled 9310 gear steel

Description: Residual Stress analysis utilizing x-ray diffraction in conjunction with material removal by chemical polishing provides a very effective method of analyzing the near surface residual stress profile of steels. In this experiment, residual stress profiling has been used to analyze the effects of surface ausrolling during the marquenching of a 9310 gear steel which has been carburized to 1% carbon. The ausrolling process is an advanced thermomechanical processing technique used to ausform only the critical surface layer of gears and produce a hard, tough, fine-grained martensitic product. This study compares the residual stress profile of a marquenched specimen with a moderately deformed ausrolled specimen and with a heavily deformed ausrolled specimen, in order to correlate the effects of residual stress with the improved fatigue properties of the gear steel. While no significant variation was observed between the residual stress profile of the marquenched specimens (no deformation) and the line contact ausrolled specimens (moderate deformation), significant increases in the amount of compressive residual stress was noted in the residual stress profile of the point contact ausrolled (heavily deformed) samples. The maximum increase in compressive residual stress due to point contact ausrolling was approximately 500 MPa, when compared to the marquenched sample. This increased residual compressive stress will lower the effective shear stresses during rolling contact fatigue and would therefore explain some of the increase the rolling contact fatigue endurance of the point contact ausrolled specimens.
Date: December 31, 1995
Creator: Paliani, C.M.; Queeney, R.A. & Kozaczek, K.J.
Partner: UNT Libraries Government Documents Department

Evaluation of interfacial properties of fiber-reinforced ceramic composites

Description: The mechanical behavior of fiber-reinforced ceramic composites is closely related to their interfacial properties. The application of a single-fiber push-out test to evaluate these interfacial properties is addressed, and the stress-displacement relation during the push-out process is analyzed. The interfacial bonding, Coulomb friction at the debonded interface, Poisson`s effect of the loaded fiber, residual stresses, and the interfacial roughness effect are included in the analysis. Closed-form analytical solutions are obtained. Based on these analytical solutions, a methodology is established to extract the interfacial properties from the experimental fiber push-out curve.
Date: October 1, 1996
Creator: Hsueh, Chun-Hway
Partner: UNT Libraries Government Documents Department

Determination of residual stresses by local annealing to laser speckle pattern interferometry

Description: One of the most common methods of experimentally determining residual stresses is Blind Hole Drilling (BHD). A new method which is a thermo-optical analog to BHD is being developed. This method uses local heating to anneal a tiny spot and uses laser speckle interferometry to measure the strain that results. This strain is used to determine the state of stress prior to heating. The peak temperatures are on the order of 200 Celsius so that for most metals, there will be no changes in phase or other material properties except for a slight reduction in yield stress. Preliminary experiments with type 304 stainless steel were performed using resistance heating. The experimental results were in excellent agreement with finite element model predictions of the process. Subsequently, the resistance heating was replaced with laser heating. The heat input (22.5 Watt peak) from a small sealed radio frequency excited Carbon Dioxide laser was used. In order to both control the heating temperature and efficiently couple the infrared photons from the laser into the test specimen, a substance known as Liquid Temperature Indicating Paint was used. Without this substance the laser power would be so large as to make this approach impractical. Furthermore the measurement and control for the heat input would be very complicated. Using this laser heating approach was successful in obtaining similar results to those obtained in other work. Since this laser based technique is a thermo-optical analog to blind hole drilling a simple stress model is required to interpret the measured results. This simple stress model is presented. As in BHD, the simple model must be modified by empirical coefficients to be useful. These empirical coefficients are determined by experimentation and/or numerical analysis
Date: May 1, 1997
Creator: Pechersky, M. & Vikram, C.S.
Partner: UNT Libraries Government Documents Department


Description: The new ''contour method'' was used to measure a cross-sectional map of residual stresses in a welded plate. Comparisons with neutron diffraction measurements confirm the capability of the contour method to measure complex, 2-D stress maps. Compared to other methods, the contour method is relatively simple and inexpensive to perform, and the equipment required is widely available.
Date: March 1, 2001
Creator: PRIME, M. & AL, ET
Partner: UNT Libraries Government Documents Department

Measurement and modeling of residual stress in net-shape plasma sprayed tubes

Description: Residual stresses in net-shaped plasma sprayed MoSi{sub 2} tubes were measured by x-ray microdiffraction as a function of radial position in the sample. A tensile to compressive hoop stress profile was measured, ranging 200 MPa in tension at the outer diameter, to -125 MPa at the inner. A force balance model was used to explain the evolution of stresses when incrementally adding layers to the pre-existent material.
Date: September 1, 1996
Creator: Bartlett, A. & Castro, R.G.
Partner: UNT Libraries Government Documents Department

Residual stress measurement in YBCO thin films.

Description: Residual stress in YBCO films on Ag and Hastelloy C substrates was determined by using 3-D optical interferometry and laser scanning to measure the change in curvature radius before and after film deposition. The residual stress was obtained by appropriate analysis of curvature measurements. Consistent with residual thermal stress calculations based on the thermal expansion coefficient mismatch between the substrates and YBCO film, the measured residual stress in the YBCO film on Hastelloy C substrate was tensile, while it was compressive on the Ag substrate. The stress values measured by the two techniques were generally in good agreement, suggesting that optical interferometry and laser scanning have promise for measuring residual stresses in thin films.
Date: May 13, 2002
Creator: Cheon, J. H. & Singh, J. P.
Partner: UNT Libraries Government Documents Department