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Macrostrain measurement using radial collimators at LANSCE

Description: A series of `short` radial collimators have been implemented in the 90{degrees} scattering geometries on the neutron powder diffractometer at Los Alamos. The capability to perform macrostrain measurements has been improved by the commensurate ability to rapidly select a sampling volume appropriate to the specimen. The compact design of the collimators was dictated by the need to fit them in a cylindrical vacuum chamber as well as providing space in which to manipulate a specimen in three dimensions. Collimators of different vane lengths were fabricated to give 4 different resolutions for which 2/3 of the diffracted intensity comes form distances of 0.75, 1. 25, 2.5, and 4.0 mm along the incident beam. Qualifying scans and a demonstration of a cracked ring, containing a steep stress gradient, are included.
Date: June 1, 1996
Creator: Bourke, M.A.M.; Roberts, J.A. & Davis, D.
Partner: UNT Libraries Government Documents Department

Relaxation of thermal mismatch in discontinuously reinforced composites

Description: We have measured the dislocation density vol % and thermal residual elastic strain in NiAl matrices of 20 vol % Al{sub 2}O{sub 3} discontinuously-reinforced composites. As the size of the reinforcement increases the average dislocation density increases, and the corresponding thermal residual elastic strains decrease. The changes with respect to particle size in the dislocation density and residual strain can neither be explained by continuum theory nor by dislocation mechanics for homogeneous medium. A previously developed model (that satisfactorily describes the SiC/Al system) suggests that the misfit dislocation density decreases with increase in reinforcement size but this disagrees wit the current Al{sub 2}O{sub 3}/NiAl results. A new model is proposed to describe low-symmetry intermetallics, which are constrained in their ability to relax thermal mismatch because of a paucity of independent slip systems. The results are discussed in the context of continuum mechanics using finite element analyses and crystal plasticity.
Date: August 1, 1995
Creator: Shi, N.; Bourke, M.A.M.; Goldstone, J.A. & Arsenault, R.J.
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

Influence of thermal residual stresses on the elastic phase-strain

Description: The development of elastic lattice phase strains in a 15 vol. pct TiC particulate reinforced 2219-T6 Al composite was modeled as a function of tensile uniaxial loading by finite element method (FEM). In the relationship of applied stress vs. elastic lattice phase strain, the slopes vary with the applied load even before the macroscopic yielding. The slopes for the phase-strain perpendicular to loading follow nonmonotonic changes with loading, while, in the direction parallel to loading, the slopes change monotonically with the applied load. In this investigation, we have demonstrated via FEM that thermal residual stresses from thermal expansion mismatch between phases affect initiation of matrix plasticity. And the differences in the matrix plasticity initiation influence the internal stress distribution. The changes in the slope are dictated by the internal stress transfer between phases. FEM models with and without thermal history show significant differences in the response of elastic strain component, a mechanics equivalent of the lattice elastic strain. Agreement with experiment can only be obtained by including the thermal history. From a simple elasto-plastic spring model we are able to demonstrate that, with matrix plasticity propagating as predicted by FEM, the elastic strain component responds similarly to the more rigorous numerical predictions, suggesting that the morphology of elastic strain evolution is dictated by the development of matrix plasticity.
Date: April 1, 1996
Creator: Shi, N.; Bourke, M.A.M. & Goldstone, J.A.
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

Phase transformations in engineering materials

Description: Phase transformations in engineering materials are inevitably related to mechanical behavior and are often precursors to residual stress and distortion. Neutron scattering in general is a valuable tool for studying their effects, and pulsed neutrons are of special value, because of the inherently comprehensive crystallographic coverage they provide in each measurement. At the Manuel Lujan neutron scattering center several different research programs have addressed the relationships between phase transformation/mechanical behavior and residual strains. Three disparate examples are presented; (1) stress induced transformation in a NiTi shape memory alloy, (2) cryogenically induced transformation in a quenched 5180 steel, and (3) time resolved evolution of strain induced martensite in 304 stainless steel. In each case a brief description of the principle result will be discussed in the context of using neutrons for the measurement.
Date: June 1, 1996
Creator: Bourke, M.A.M.; Lawson, A.C.; Dunand, D.C. & Priesmeyer, H.G.
Partner: UNT Libraries Government Documents Department

Stress-induced martensitic transformations in NiTi and NiTi-TiC composites investigated by neutron diffraction

Description: Superelastic NiTi (51.0 at% Ni) with 0, 10 and 20 vol% TiC particles were deformed under uniaxial compression as neutron diffraction spectra were simultaneously obtained. The experiments yielded in-situ measurements of the thermoelastic stress-induced transformation. A detailed Rietveld determination is made of the phase fractions and the evolving strains in the reinforcing TiC particles and the austenite as it transforms to martensite on loading (and its subsequent back transformation on unloading). These strains are used to shed light on the phenomenon of load transfer in composites where the matrix undergoes a stress-induced phase transformation.
Date: December 31, 1998
Creator: Vaidyanathan, R.; Bourke, M.A.M. & Dunand, D.C.
Partner: UNT Libraries Government Documents Department

Effect of texture on hkl dependent intergranular strains measured in-situ at a pulsed neutron source

Description: In this paper we examine the elastic moduli, during tensile loading, of textured and untextured Nitronic 40 stainless steel. In-situ neutron diffraction experiments were performed at the LANSCE pulsed neutron source. The stress-strain response of various hkl planes are reported, and compared with predictions from a self-consistent elasto-plastic model. Residual strain predictions from the model after plastic loading to 1% strain, are compared with experimental results for the untextured specimen. The implications for diffraction residual stress measurements are considered.
Date: September 1, 1997
Creator: Daymond, M.R.; Bourke, M.A.M.; Clausen, B. & Tome, C.
Partner: UNT Libraries Government Documents Department

Investigation of the reduction of NiAl{sub 2}O{sub 4}. 1: Neutron diffraction studies

Description: In-situ metal-ceramic composites consisting of Ni particles embedded in alumina matrices were obtained by the partial reduction of NiAl{sub 2}O{sub 4}. The volume shrinkage that accompanies the reduction reaction generates residual stresses. Neutron diffraction studies were performed for the first time at various temperatures to study the evolution of phases in situ during reduction and to determine their stress state. It was determined that compressive stresses of several hundred MPa in magnitude can be generated inside the unreduced part of spinel. It was also found that the stress generation is strongly influenced by material and processing variables such as reduction temperature and the initial density of spinel. The diffraction results were then compared to finite element calculations and a reasonable agreement was obtained.
Date: September 1, 1998
Creator: Uestuendag, E.; Hanan, J.C.; Clausen, B.; Bourke, M.A.M.; Sass, S.L. & Barbieri, T.J.
Partner: UNT Libraries Government Documents Department

Texture and residual strain in SiC/Ti-6-2-4-2 titanium matrix composites

Description: Residual strain and texture variations were measured in two Titanium matrix composites reinforced with Silicon Carbide fibers (Ti/SiC) having the same composition but fabricated by dramatically different processing routes. In both specimens the Titanium matrix comprised an {alpha}/{beta} alloy (Ti-6242) containing approximately 35% by volume of continuous SiC fibers. In one case the matrix was produced by a plasma spray (PS) route and the other by a wire drawing (WD) process. The resulting textures in the matrix differ significantly, from approximately random for the PS matrix to 6.25X random in the WD matrix. No significant differences in matrix residual strains between the composites prepared by the two procedures were noted. Plane-specific elastic moduli, measured in load tests on the unreinforced matrices also showed little difference.
Date: November 1, 1997
Creator: Rangaswamy, P.; Bennett, K.; Bourke, M.A.M.; Dreele, R. von; Roberts, J.A. & Jayaraman, N.
Partner: UNT Libraries Government Documents Department

Integrated approach to advanced machining

Description: The residual stress state induced by machining in a Ti alloy as function of cutting tool sharpness and depth of cut was predicted and measured. Residual stresses were greater for the dull tool than for the sharp tool. XRD was used to measure the residual stress state of the material; these measurements revealed that the hoop stress increased with depth of cut; however the radial stress decreased with depth of cut. An elastic-plastic model provided a possible explanation for this behavior in that, for small depths of cut, the tool makes multiple passes through the damage subsurface layer. This causes both residual stress components to increase, but the radial stress increases by a much greater amount than the hoop stress.
Date: August 1, 1997
Creator: LeSar, R.A.; Bourke, M.A.M.; Rangaswamy, P.; Day, R.D. & Hatch, D.J.
Partner: UNT Libraries Government Documents Department

Investigations of the reduction of NiAl{sub 2}O{sub 4}. 2: X-ray diffraction studies

Description: The volume shrinkage that accompanies the reduction of NiAl{sub 2}O{sub 4} to a metal-ceramic composite of nickel and alumina leads to residual stress buildup. The authors have attempted to utilize these stresses to temper a ceramic component by placing it under compression. To prove the concept, they produced model specimens which they investigated using X-ray diffraction. Employing the conventional d vs. sin{sup 2} {Psi} method to map surface stresses, the results obtained from these measurements are presented together with finite element calculation predictions used to interpret experimental stress data.
Date: September 1, 1998
Creator: Clausen, B.; Rangaswamy, P.; Bourke, M.A.M.; Uestuendag, E.; Sass, S.L. & Barbieri, T.J.
Partner: UNT Libraries Government Documents Department

Texture and residual strain in SiC/Ti-6-2-4-2 titanium matrix composites

Description: Residual strain and texture variations were measured in two Titanium matrix composites reinforced with Silicon Carbide fibers (Ti/SiC) of similar composition but fabricated by different processing routes. Each composite comprised a Ti-6242 {alpha}/{beta} matrix alloy containing 35% by volume continuous SiC fibers. In one composite, the matrix was produced by a plasma spray (PS) route, and in the other by a wire drawing (WD) process. The PS and WD composites were reinforced with SCS-6 (SiC) and Trimarc (SiC) fibers, respectively. The texture in the titanium matrices differed significantly, from approximately {approx} 1.1x random for the monolithic and composite produced by PS route to {approx} 17x random in the monolithic and {approx}6x random in the composite produced by the WD route. No significant differences in matrix residual strains between the composites prepared by the two procedures were noted. The Trimarc (WD) fibers recorded higher ({approx}1.3x) compressive strains than the SCS-6 (PS) fibers in all the measured directions. The plane-specific elastic moduli, measured in load tests on the un-reinforced matrices, showed little difference.
Date: December 31, 1998
Creator: Rangaswamy, P.; Bourke, M.A.M.; Von Dreele, R.; Bennett, K.; Roberts, J.A.; Daymond, M. et al.
Partner: UNT Libraries Government Documents Department

Design and implementation of an x-ray strain measurement capability using a rotating anode machine

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Residual stresses close to the surface can improve the reliability and lifetime of parts for technological applications. X-ray diffraction plays a significant role in gaining an exact knowledge of the stresses at the surface and their depth distribution. An x-ray capability at Los Alamos is key to developing and maintaining industrial collaborations in strain effects. To achieve this goal, the authors implemented a residual strain measuring station on the rotating anode x-ray instrument at the Lujan Center. This capability has been used to investigate residual strains in heat treated automotive components, machining effects on titanium alloys, resistance welded steel joints, titanium matrix fiber reinforced composites, ceramic matrix composites, thin films, and ceramic coatings. The overall objective is to combine both x-ray and neutron diffraction measurements with numerical models (e.g., finite element calculations).
Date: December 31, 1998
Creator: Roberts, J.A.; Rangaswamy, P.; Lujan, M. Jr. & Bourke, M.A.M.
Partner: UNT Libraries Government Documents Department

Neutron diffraction study of NiTi during compressive deformation and after shape-memory recovery

Description: Neutron diffraction measurements of internal elastic strains and texture were performed during compressive deformation of martensitic NiTi deforming by twinning. Rietveld refinement of the diffraction spectrum was performed in order to obtain lattice parameter variations and preferred orientation of martensitic variants. The elastic internal strains, are proportional to the externally applied stress but strongly dependent on crystallographic orientation. Plastic deformation by matrix twinning is consistent with type I (1-1-1) twinning, whereby (100) and (011) planes tend to align perpendicular and parallel to the stress axis, respectively. The preferred orientation ratio r according to the model by March and Dollase is proportional to the macroscopic plastic strain for (100) and (011) planes for loading, unloading and shape-memory recovery. To the best of our knowledge, this is the first in situ bulk measurement of reversible twinning in NiTi. Finally, shape-memory recovery results in a marked change of NiTi cell parameters.
Date: September 1995
Creator: Dunand, D. C.; Mari, D.; Bourke, M. A. M. & Goldstone, J. A.
Partner: UNT Libraries Government Documents Department