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Femtosecond laser materials processing

Description: Femtosecond lasers enable materials processing of most any material with extremely high precision and negligible shock or thermal loading to the surrounding area Applications ranging from drilling teeth to cutting explosives to making high-aspect ratio cuts in metals with no heat-affected zone are made possible by this technology For material removal at reasonable rates, we developed a fully computer-controlled 15-Watt average power, 100-fs laser machining system.
Date: June 2, 1998
Creator: Stuart, B. C., LLNL
Partner: UNT Libraries Government Documents Department

Numerical implementation of a state variable model for friction

Description: A general state variable model for friction has been incorporated into a finite element code for viscoplasticity. A contact area evolution model is used in a finite element model of a sheet forming friction test. The results show that a state variable model can be used to capture complex friction behavior in metal forming simulations. It is proposed that simulations can play an important role in the analysis of friction experiments and the development of friction models.
Date: March 1995
Creator: Korzekwa, D. A. & Boyce, D. E.
Partner: UNT Libraries Government Documents Department

Relative sensitivity of formability to anisotropy

Description: This work compares the relative importance of material anisotropy in sheet forming as compared to other material and process variables. The comparison is made quantitative by the use of normalized dependencies of depth to failure (forming limit is reached) on various measures of anisotropy, as well as strain and rate sensitivity, friction, and tooling. Comparisons are made for a variety of forming processes examined previously in the literature as well as two examples of complex stampings in this work. 7 The examples rover a range from nearly pure draw to nearly pure stretch situations, and show that for materials following a quadratic yield criterion, anisotropy is among the most sensitive parameters influencing formability. For materials following higher-exponent yield criteria, the dependency is milder but is still of the order of most other process parameters. However, depending on the particular forming operation, it is shown that in some cases anisotropy may be ignored, whereas in others its consideration is crucial to a good quality analysis.
Date: January 1, 1997
Creator: Logan, R.W. & Maker, B.N.
Partner: UNT Libraries Government Documents Department

Application of damage models in metal forming

Description: The development of damage models in the analysis of metal forming processes, to characterize the formability limits, is an important area of ongoing research. In this paper, two energy-based damage models for the simulation of crack initiation in metal forming processes are presented. The first one is an isotropic damage model with two damage variables. The second one is an anisotropic model with a damage characteristic tensor. The damage models are developed within the general framework of continuum thermodynamics for irreversible processes by identifying a proper set of internal variables together with their associated generalized forces. An approach is proposed to account for microcrack opening and closing. A viscoplastic regularization algorithm is used to take into account the strain rate effect and to improve numerical stability. Both models have been incorporated into the finite element code, LAGAMINE. The models were applied to simulations of upsetting of collar cylinders and nonisothermal hemispherical punch stretching. The results of the analyses were validated by comparing the finite element simulations with experimentally obtained data.
Date: June 1, 1995
Creator: Zhu, Y. Y. & Zacharia, T.
Partner: UNT Libraries Government Documents Department

Directed light fabrication of iron-based materials

Description: Directed light fabrication (DLF) is a process that fuses gas delivered metal powders within a focal zone of a laser beam to produce fully dense, 3-dimensional metal components. From a computer generated solid model, deposition ``tool paths`` are constructed that command the laser movement to fabricate near net shape parts a layer at a time. Among potential candidate systems to study, iron-based alloys are particularly attractive for rapid prototyping. To evaluate the processing parameters in the DLF process, studies have been performed on the microstructural development in 1-dimensional and 2-dimensional Fe-based components. For example, continuous microstructural features are evident, implying a continuous liquid/solid interface during processing. In addition, solidification cooling rates have been determined based upon secondary dendrite arm spacings in Fe-25wt. % Ni and 316 stainless steel. Cooling rates vary from 10{sup 1}{minus}10{sup 5} K s{sup {minus}1}, and the solidification behavior has been simulated using macroscopic heat transfer analyses.
Date: January 1, 1995
Creator: Thoma, D.J.; Charbon, C.; Lewis, G.K. & Nemec, R.B.
Partner: UNT Libraries Government Documents Department

Numerical simulation and experimental observations of initial friction transients

Description: Experiments were performed to better understand the sliding frictional behavior between metals under relatively high shear and normal forces. Microstructural analyses were done to estimate local near-surface stress and strain gradients. The numerical simulation of the observed frictional behavior was based on a constitutive model that uses a state variable approach.
Date: July 1, 1995
Creator: Hughes, D.A.; Weingarten, L.I. & Dawson, D.B.
Partner: UNT Libraries Government Documents Department

The influence of surface topography on the forming friction of automotive aluminum sheet

Description: Interest in utilizing aluminum alloys in automobiles has increased in recent years as a result of the desire to lower automobile weight and, consequently, increase fuel economy. While aluminum alloy use in cast parts has increased, outer body panel applications are still being investigated. The industry is interested in improving the formability of these sheet alloys by a combination of alloy design and processing. A different avenue of improving the formability of these alloys may be through patterning of the sheet surface. Surface patterns hold the lubricant during the forming process, with a resulting decrease in the sheet-die surface contact. While it has been speculated that an optimum surface pattern would consist of discrete cavities, detailed investigation into the reduction of forming friction by utilizing discrete patterns is lacking. A series of discrete patterns were investigated to determine the dependence of the forming friction of automotive aluminum alloys on pattern lubricant carrying capacity and on material strength. Automotive aluminum alloys used in outer body panel applications were rolled on experimental rolls that had been prepared with a variety of discrete patterns. All patterns for each alloy were characterized before and after testing both optically and, to determine pattern lubricant capacity, using three dimensional laser profilometry. A draw bead simulation (DBS) friction tester was designed and fabricated to determine the forming friction of the patterned sheets. Tensile testing and frictionless DBS testing were performed to ascertain the material properties of each sheet. The most striking result of this work was the inversely linear dependence of forming friction on the lubricant carrying capacity of the discrete patterns.
Date: May 1, 1998
Creator: Kramer, P.A.
Partner: UNT Libraries Government Documents Department

Superplastic forming using NIKE3D

Description: The superplastic forming process requires careful control of strain rates in order to avoid strain localizations. A load scheduler was developed and implemented into the nonlinear finite element code NIKE3D to provide strain rate control during forming simulation and process schedule output. Often the sheets being formed in SPF are very thin such that less expensive membrane elements can be used as opposed to shell elements. A large strain membrane element was implemented into NIKE3D to assist in SPF process modeling.
Date: December 4, 1996
Creator: Puso, M.
Partner: UNT Libraries Government Documents Department

Accuracy issues in modeling superplastic metal forming

Description: The utility of finite element modeling in optimizing superplastic metal forming is dependent on accurate representation of the material constitutive behavior and the frictional response of the sheet against the die surface. This paper presents work conducted to estimate the level of precision that is necessary in constitutive relations for finite element analysis to accurately predict the deformation history of actual SPF components. Previous work identified errors in SPF testing methods that use short tensile specimens with gauge length-to-width ratios of 2:1 or less. The analysis of the present paper was performed to estimate the error in predicted stress that results from using the short specimens. Stress correction factors were developed and an improved constitutive relation was implemented in the MARC finite element code to simulate the forming of a long, rectangular tray. The coefficient of friction in a Coulomb friction model was adjusted to reproduce the amount of material draw-in observed in the forming experiments. Comparisons between the finite element predictions and the forming experiments are presented.
Date: February 1, 1995
Creator: Johnson, K.I.; Khaleel, M.A.; Lavender, C.A. & Smith, M.T.
Partner: UNT Libraries Government Documents Department

Femtosecond laser materials processing

Description: The use femtosecond pulses for materials processing results in very precise cutting and drilling with high efficiency. Energy deposited in the electrons is not coupled into the bulk during the pulse, resulting in negligible shock or thermal loading to adjacent areas.
Date: February 1, 1997
Creator: Stuart, B.C.
Partner: UNT Libraries Government Documents Department

Superplasticity in aluminum alloys

Description: We have characterized in the Al-Mg system the microstructure and mechanical properties of a cold-rolled Al-6Mg-0.3Sc alloy. The alloy exhibited superplasticity at relatively high strain rates (about 10-2 s-1). At a strain rate of 10-2 s-1 there exists a wide temperature range (475-520`C) within which the tensile elongation is over 1000%. There also exists a wide strain rate range (10-3 - 10-1 s-1) within which the tensile elongation is over 500%. The presence of Sc in the alloy results in a uniform distribution of fine coherent Al3SC precipitates which effectively pin grain and subgrain boundaries during static and continuous recrystallization. As a result, the alloy retains its fine grain size (about 7 micron), even after extensive superplastic deformation (>1000%). During deformation, dislocations Mg with a high Schmidt factor slip across subgrains but are trapped by subgrain boundaries, as a result of the strong pining of Al3Sc. This process leads to the conversion of low-angled subgrain boundaries to high-angled grain boundaries and the subsequent grain boundary sliding, which produces superelasticity. A model is proposed to describe grain boundary sliding accommodated by dislocation glide across grains with a uniform distribution of coherent precipitates. The model predictions is consistent with experimental observations.
Date: December 1, 1997
Creator: Nieh, T. G.
Partner: UNT Libraries Government Documents Department

Quasi-optical gyrotron materials processing at Los Alamos

Description: Los Alamos has recently obtained and installed quasi-optical gyrotrons of 37 and 84 GHz with power outputs up to 35 kW. A quasi-optical gyrotron is unique in that the output is a Gaussian beam which can be focused and manipulated using mirrors. The Gaussian beam output is ideally suited for one and two dimensional materials processing applications such as joining and surface treatment. Working with the National Center for Manufacturing Sciences (NCMS) we have formed a consortium of companies to investigate several materials processing applications.
Date: May 1, 1995
Creator: Katz, J.D. & Rees, D.E.
Partner: UNT Libraries Government Documents Department

Numerical simulation of industrial superplastic forming

Description: Superplastic forming is a metal forming process that allows a variety of components with very complex geometries to be produced at one tenth the cost of conventional machining. The industrial superplastic forming process can be optimized with the application of the finite element method to predict the optimal applied pressure history and the final part thickness distribution. This paper discusses the application the nonlinear implicit, three dimensional finite element code, NIKE3D to the problem of numerically simulating and optimizing the superplastic forming of Ti-6AI-4V components.
Date: March 1, 1995
Creator: Haberman, K.S.; Bennett, J.G.; Miller, E.L.; Piltch, M.S.; Leyer, L.K. & Leodolter, W.
Partner: UNT Libraries Government Documents Department

Refinement of the Kansas City Plant site conceptual model with respect to dense non-aqueous phase liquids (DNAPL)

Description: This document presents a refinement of the site conceptual model with respect to dense non-aqueous phase liquid (DNAPL) at the US Department of Energy Kansas City Plant (KCP). This refinement was prompted by a review of the literature and the results of a limited study that was conducted to evaluate whether pools of DNAPL were present in contaminated locations at the KCP. The field study relied on the micropurge method of sample collection. This method has been demonstrated as a successful approach for obtaining discrete samples within a limited aquifer zone. Samples were collected at five locations across 5-ft well screens located at the base of the alluvial aquifer at the KCP. The hypothesis was that if pools of DNAPL were present, the dissolved concentration would increase with depth. Four wells with highly contaminated groundwater were selected for the test. Three of the wells were located in areas where DNAPL was suspected, and one where no DNAPL was believed to be present. The results demonstrated no discernible pattern with depth for the four wells tested. A review of the data in light of the available technical literature suggests that the fine-grained nature of the aquifer materials precludes the formation of pools. Instead, DNAPL is trapped as discontinuous ganglia that are probably widespread throughout the aquifer. The discontinuous nature of the DNAPL distribution prevents the collection of groundwater samples with concentrations approaching saturation. Furthermore, the results indicate that attempts to remediate the aquifer with conventional approaches will not result in restoration to pristine conditions because the tortuous groundwater flow paths will inhibit the efficiency of fluid-flow-based treatments.
Date: October 1, 1995
Creator: Korte, N.E.; Hall, S.C. & Baker, J.L.
Partner: UNT Libraries Government Documents Department

Preparation of bismuth powder

Description: The Purpose of this manual is to describe preparation of bismuth powder for use in process operations. Bismuth powder is to be prepared in Room 232 of ``T`` Building where all necessary apparatus is installed.
Date: February 15, 1949
Creator: Cox, G.C.
Partner: UNT Libraries Government Documents Department

Characterization of SF6/Argon Plasmas for Microelectronics Applications

Description: This report documents measurements in inductively driven plasmas containing SF{sub 6}/Argon gas mixtures. The data in this report is presented in a series of appendices with a minimum of interpretation. During the course of this work we investigated: the electron and negative ion density using microwave interferometry and laser photodetachment; the optical emission; plasma species using mass spectrometry, and the ion energy distributions at the surface of the rf biased electrode in several configurations. The goal of this work was to assemble a consistent set of data to understand the important chemical mechanisms in SF{sub 6} based processing of materials and to validate models of the gas and surface processes.
Date: March 1, 2002
Partner: UNT Libraries Government Documents Department

Crush Grinding

Description: Crush Grinding is a special process used at the Kansas City Plant to finish stem sections of reservoir products. In this process, a precise profile of the desired product is formed on a tungsten carbide roll. This roll slowly transfers a mirror image of the profile onto the grinding surface of a wheel. The transfer rate of the profile is between 0.001 and 0.010 inches per minute. Crush grinding is desirable since it provides consistent surface finishes and thin walls at a high production rate. In addition, it generates very sharp fillet radii. However, crush grinding is a complex process since many variables affect the final product. Therefore, the process requires more attention and knowledge beyond basic metal removal practices. While the Kansas City Plant began using these machines in 1995, a formal study regarding crush grinding has not been conducted there. In addition, very little literature is available in the grinding industry regarding this process. As a result, new engineers at the Kansas City Plant must learn the process through trial and error. The purpose of this document is to address this literature deficit while specifically promoting a better understanding of the stem crush grinding process at the Kansas City Plant.
Date: April 1, 2005
Creator: Nguyen, T. Q.
Partner: UNT Libraries Government Documents Department

Multi-stage slurry system used for grinding and polishing materials

Description: A slurry system draws slurry from a slurry tank via one of several intake pipes, where each pipe has an intake opening at a different depth in the slurry. The slurry is returned to the slurry tank via a bypass pipe in order to continue the agitation of the slurry. The slurry is then diverted to a delivery pipe, which supplies slurry to a polisher. The flow of shiny in the bypass pipe is stopped in order for the slurry in the slurry tank to begin to settle. As the polishing continues, slurry is removed from shallower depths in order to pull finer grit from the slurry. When the polishing is complete, the flow in the delivery pipe is ceased. The flow of slurry in the bypass pipe is resumed to start agitating the slurry. In another embodiment, the multiple intake pipes are replaced by a single adjustable pipe. As the slurry is settling, the pipe is moved upward to remove the finer grit near the top of the slurry tank as the polishing process continues.
Date: March 1, 2000
Creator: Hed, P. Paul & Fuchs, Baruch A.
Partner: UNT Libraries Government Documents Department