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Analysis of interaction phenomena between liquid jets and materials

Description: The interaction phenomena of high-velocity liquid jets impinging on a material surface have been investigated theoretically and experimentally to gain an understanding of the physical mechanisms involved in material removal by fluidjet machining processes. Experiments were performed to determine conditions under which the liquid jet impacting a solid material will cause material removal and also to delineate possible physical mechanisms of mass removal at optimum jet-cutting conditions. We have also carried out numerical simulations of jet-induced surface pressure rises and of the material deformation and spallation behavior due to multiple droplet impacts. Results obtained from the experiments and theoretical calculations and their physical implications are also discussed.
Date: February 1, 1995
Creator: Kang, Sang-Wook; Reitter, T. & Carlson, G.
Partner: UNT Libraries Government Documents Department

Analysis of interaction phenomena between liquid jets and materials. Revision 1

Description: The interaction phenomena of high-velocity liquid jets impinging on a material surface have been investigated theoretically and experimentally to understand the physics of material removal by jet-machining processes. Experiments were performed to delineate conditions under which liquid jet impacts will cause mass removal, and to determine optimum jet-cutting conditions. Theoretical analyses have also been carried out to study the effects of multiple jet-droplet impacts on a target surface as a material deformation mechanism. The calculated target response and spallation behavior following droplet impacts and their physical implications are also discussed.
Date: April 1, 1995
Creator: Kang, S.W.; Reitter, T. & Carlson, G.
Partner: UNT Libraries Government Documents Department

Deformation mechanisms in crystalline solids and Newtonian viscous behavior

Description: The three principal mechanisms of plastic flow in crystalline solids at elevated temperature are crystal slip, grain boundary sliding, and diffusional flow. All three mechanisms involve the diffusion of atoms as the rate-controlling process, either in the lattice or in the grain boundary. Under the correct conditions of microstructure, temperature, and stress, each mechanism can lead to Newtonian-viscous behavior. That is, the strain rate increases linearly with the applied stress. In the case of crystal slip, Newtonian-viscous behavior is observed at very � low stresses and, in pure metals, is known as Harper-Dom (H-D) creep. This Newtonian behavior can also be observed in anisotropic crystalline solids that are deformed under thermal cycling conditions. The dislocation density and the stacking fault energy are important structural factors that contribute to crystal slip-controlled Newtonian flow. In the case of grain boundary sliding, Newtonian-viscous behavior is observed in fine-grained, solid solution alloys under conditions where grain-boundary sliding is accommodated by dislocation glide controlled by the diffusion of solute atoms. In the case of diffusional creep, which is rigorously described by the Nabarro-Herring (N-H) theory, the creep rate is controlled by grain size and by the rate of atom diffusion in the lattice and in the grain boundary. Deformation mechanism maps describe the conditions of dislocation density, grain size, stress, and temperature under which each deformation process can be expected to be rate-controlling.
Date: November 4, 1999
Creator: Ruano, O A; Sherby, O D & Wadsworth, J
Partner: UNT Libraries Government Documents Department

Structure-dependent hydrostatic deformation potentials of individual single-walled carbon nanotubes

Description: Summary: The hydrostatic pressure coefficients of interband transition energies of a number of single-walled carbon nanotubes with different chiralities were measured. Both optical absorption and photoluminescence experiments were performed on de-bundled, single-walled carbon nanotube suspensions with hydrostatic pressure applied by diamond anvil cells. The pressure coefficients of the first van Hove transition (bandgap) energies are negative and dependent on the nanotube structure, while the second van Hove transitions are much less sensitive to hydrostatic pressure. The hydrostatic deformation potentials of individual nanotubes are deduced within an elastic model. An empirical equation that relates the pressure coefficients to nanotube structure is presented and discussed.
Date: November 7, 2003
Creator: Wu, J.; Walukiewicz, W.; Shan, W.; Bourret-Courchesne, E. D.; Ager, J. W., III; Yu, K. M. et al.
Partner: UNT Libraries Government Documents Department

Development of local shear bands and orientation gradients in fcc polycrystals

Description: A finite element formulation which derives constitutive response from crystal plasticity theory is used to examine localized deformation in fcc polycrystals. The polycrystals are simple, idealized arrangements of grains. Localized deformations within individual grains lead to the development of domains that are separated by boundaries of high misorientation. Shear banding is seen to occur on a microscopic scale of grain dimensions. The important consequences of these simulations are that the predicted local inhomogeneities are meeting various requirements which make them possible nucleation sites for recrystallization.
Date: May 1, 1995
Creator: Beaudoin, A. J., Jr.; Mecking, H. & Kocks, U. F.
Partner: UNT Libraries Government Documents Department

Extensions of the Stoney Formula for Substrate Curvature to Configurations with Thin Substrates or Large Deformations

Description: Two main assumptions which underlie the Stoney formula relating substrate curvature to mis-match strain in a bonded thin film are that the film is very thin compared to the substrate, and the deformations are infinitesimally small. Expressions for the curvature-strain relastionship are derived for cases in which thses assumptions are relaxed, thereby providing a biasis for interpretation of experimental observations for a broader class of film-substrate configurations.
Date: April 26, 1999
Creator: Chason, E.; Floro, J.A. & Freund, L.B.
Partner: UNT Libraries Government Documents Department

Source Analysis of the Crandall Canyon, Utah, Mine Collapse

Description: Analysis of seismograms from a magnitude 3.9 seismic event on August 6, 2007 in central Utah reveals an anomalous radiation pattern that is contrary to that expected for a tectonic earthquake, and which is dominated by an implosive component. The results show the seismic event is best modeled as a shallow underground collapse. Interestingly, large transverse surface waves require a smaller additional non-collapse source component that represents either faulting in the rocks above the mine workings or deformation of the medium surrounding the mine.
Date: February 28, 2008
Creator: Dreger, D S; Ford, S R & Walter, W R
Partner: UNT Libraries Government Documents Department

Computer simulations of mechanical behavior of polymer liquid crystals

Description: In this dissertation molecular dynamics simulations of behavior of polymer liquid crystals (PLC's) under tensile deformation have been performed. PLC's composed of random or block copolymers of rigid and flexible segments have been studies. Systems of fully flexible chains have been simulated for comparison. Stress-strain relations and fracture mechanics have been investigated.
Date: December 1991
Creator: Blonski, Slawomir
Partner: UNT Libraries

Instrument to Measure the Initial Deformation of Rock Around Underground Openings

Description: Report issued by the Bureau of Mines over development of the tunnel stress relaxation gage. As stated in the introduction, "this report summarizes development and modification of a tunnel stress relaxation gage (TSR) designed to measure initial and long-term deformation around underground excavations" (p. 1). This report includes tables, illustrations, and photographs.
Date: 1978
Creator: Beus, Michael J.; Phillips, Earl L. & Waddell, Galen G.
Partner: UNT Libraries Government Documents Department

Influence of shockwave obliquity on deformation twin formation in Ta

Description: Energetic loading subjects a material to a 'Taylor wave' (triangular wave) loading profile that experiences an evolving balance of hydrostatic (spherical) and deviatoric stresses. While much has been learned over the past five decades concerning the propensity of deformation twinning in samples shockloaded using 'square-topped' profiles as a function of peak stress, achieved most commonly via flyer plate loading, less is known concerning twinning propensity during non-I-dimensional sweeping detonation wave loading. Systematic small-scale energetically-driven shock loading experiments were conducted on Ta samples shock loaded with PEFN that was edge detonated. Deformation twinning was quantified in post-mortem samples as a function of detonation geometry and radial position. In the edge detonated loading geometry examined in this paper, the average volume fraction of deformation twins was observed to drastically increase with increasing shock obliquity. The results of this study are discussed in light of the formation mechanisms of deformation twins, previous literature studies of twinning in shocked materials, and modeling of the effects of shock obliquity on the evolution of the stress tensor during shock loading.
Date: January 1, 2009
Creator: Gray Iii, George T; Livescu, V; Cerreta, E K; Mason, T A; Maudlin, P J & Bingert, J F
Partner: UNT Libraries Government Documents Department

Dislocation Dynamics Simulations of Plasticity in Cu Thin Films

Description: Strong size effects in plastic deformation of thin films have been experimentally observed, indicating non-traditional deformation mechanisms. These observations require improved understanding of the behavior of dislocation in small size materials, as they are the primary plastic deformation carrier. Dislocation dynamics (DD) is a computational method that is capable of directly simulating the motion and interaction of dislocations in crystalline materials. This provides a convenient approach to study micro plasticity in thin films. While two-dimensional dislocation dynamics simulation in thin film proved that the size effect fits Hall-Petch equation very well, there are issues related to three-dimensional size effects. In this work, three-dimensional dislocation dynamics simulations are used to study model cooper thin film deformation. Grain boundary is modeled as impenetrable obstacle to dislocation motion in this work. Both tension and cyclic loadings are applied and a wide range of size and geometry of thin films are studied. The results not only compare well with experimentally observed size effects on thin film strength, but also provide many details on dislocation processes in thin films, which could greatly help formulate new mechanisms of dislocation-based plasticity.
Date: August 2013
Creator: Wu, Han
Partner: UNT Libraries

Statistical physics ""Beyond equilibrium

Description: The scientific challenges of the 21st century will increasingly involve competing interactions, geometric frustration, spatial and temporal intrinsic inhomogeneity, nanoscale structures, and interactions spanning many scales. We will focus on a broad class of emerging problems that will require new tools in non-equilibrium statistical physics and that will find application in new material functionality, in predicting complex spatial dynamics, and in understanding novel states of matter. Our work will encompass materials under extreme conditions involving elastic/plastic deformation, competing interactions, intrinsic inhomogeneity, frustration in condensed matter systems, scaling phenomena in disordered materials from glasses to granular matter, quantum chemistry applied to nano-scale materials, soft-matter materials, and spatio-temporal properties of both ordinary and complex fluids.
Date: January 1, 2009
Creator: Ecke, Robert E
Partner: UNT Libraries Government Documents Department

Linearized theory of peridynamic states.

Description: A state-based peridynamic material model describes internal forces acting on a point in terms of the collective deformation of all the material within a neighborhood of the point. In this paper, the response of a state-based peridynamic material is investigated for a small deformation superposed on a large deformation. The appropriate notion of a small deformation restricts the relative displacement between points, but it does not involve the deformation gradient (which would be undefined on a crack). The material properties that govern the linearized material response are expressed in terms of a new quantity called the modulus state. This determines the force in each bond resulting from an incremental deformation of itself or of other bonds. Conditions are derived for a linearized material model to be elastic, objective, and to satisfy balance of angular momentum. If the material is elastic, then the modulus state is obtainable from the second Frechet derivative of the strain energy density function. The equation of equilibrium with a linearized material model is a linear Fredholm integral equation of the second kind. An analogue of Poincare's theorem is proved that applies to the infinite dimensional space of all peridynamic vector states, providing a condition similar to irrotationality in vector calculus.
Date: April 1, 2009
Creator: Silling, Stewart Andrew
Partner: UNT Libraries Government Documents Department

In-situ white beam microdiffraction study of the deformation behavior in polycrystalline magnesium alloy during uniaxial loading

Description: Scanning white beam X-ray microdiffraction has been used to study the heterogeneous grain deformation in a polycrystalline Mg alloy (MgAZ31). The high spatial resolution achieved on beamline 7.3.3 at the Advanced Light Source provides a unique method to measure the elastic strain and orientation of single grains as a function of applied load. To carry out in-situmeasurements a light weight (~;;0.5kg) tensile stage, capable of providing uniaxial loads of up to 600kg, was designed to collect diffraction data on the loading and unloading cycle. In-situ observation of the deformation process provides insight about the crystallographic deformation mode via twinning and dislocation slip.
Date: January 19, 2007
Creator: Source, Advanced Light; Tamura, Nobumichi; Lynch, P.A.; Stevenson, A.W.; Liang, D.; Parry, D. et al.
Partner: UNT Libraries Government Documents Department