Academic literature on the topic 'Deformation Field'

Defects, i.e. hot tears, macrosegragation, and pores, formed in metal castings are a result of stresses and strains in the solid-liquid mushy zone. Numerical simulation of solidification of deforming dendrite crystal promises to improve insight into the mechanical behavior of mushy zones under an applied load. The primary goal of this thesis is to develop numerical methodologies for performing solidification simulation of deforming dendrites. Such simulation encounters difficulties associated with the interface dynamics due to phase change or interaction among the dendrites, and large visco-plastic deformation applied to them. Phase-field simulation of dendritic solidification is promising for the treatment of the complex interface dynamics. Free energy based formulation allows the model to incorporate bridging and wetting phenomena occurring at grain boundaries through an extra energy term which arises from a mismatch of the crystallographic orientation. The particle method would be attractive to handle large inelastic deformation without suffering mesh entanglement. In order to investigate the effect of solid deformations on the evolving microstructure, the material point method with elasto-visco-plasticity constitutive model is developed to couple to a phase-field model of solidification. The changes in the crystallographic orientation of a growing dendrite crystal due to solid deformation are carefully accounted for through the coupling methodology. The developed numerical framework is applicable to the simulation for single and multiple crystals, and is capable of handling complex morphological change. The wide variety of validations and practical problems solved in this thesis demonstrates the capability of investigating deformation behavior of growing crystals.

<p>A digital image processing system was used to non-destructively measure the full-field deformation on aluminum and wood specimens loaded in compression and bending. The measurement technique consisted of creating a random speckle pattern on the specimen surface, recording images before deformation and after deformation, and computing the relative displacements of small image subsets. Two methods for producing speckle patterns on the specimens were studied: spray paint and adhesive-backed photographic film.</p> <p>Baseline tests were conducted to evaluate the influence of signal noise on the measurement system. Uniform translation tests were conducted to evaluate the capability of the system for measuring finite motion. the technique was used to monitor the full-field deformation response of aluminum and wood specimens tested in bending and static compression. Moderate duration compression creep tests were conducted, on the wood specimens to investigate the suitability of the system for monitoring the creep response of materials. The results obtained from the two speckle techniques were also. compared. The results showed that for the magnification and speckle patterns tested displacement measurements smaller than 3.29x10-4 inch may be unreliable due to signal noise.</p><br>Master of Science

Naturally deformed clastic rocks such as breccias and conglomerates provide a useful way to study strain and, indh:ectly, the rheology of rocks. However plastic deformation processes may potentially compromise many of the commonly used methods of determining strain in such rocks at high temperatures, since many of these strain analysis techniques rely upon changes in object e.g. grain shape, orientation and distribution. The work reported in this. thesis explores this matter quantitatively by performing a number of deformation experiments on synthetic calcite 'conglomerates' at temperatures where the rate-dependence of grain size-sensitive deformation processes in the clast and matrix can beú varied. In order to control the microstructures of the experimental samples, specimens were fabricated by mixing granulated Solnhofen limestone with powders of Chelometric grade calcite. The mixtures were tumbled for 3 hours duration to ensure uniform intermixing of the powders, and were then hot-isostatically pressed at a temperature of 700úC under a confining pressure of 190 MPa for 72 hours. The resulting samples were fully dense and consisted of sub-angular Solnhofen limestone clasts 60-90J.Ull in diameter, in a foam-textured matrix of Chelometric grade calcite with a grain size of22.2J.Ull ñ7.5J.Ull. All experiments were conducted at temperatures ranging between 400ú -700úC, and at a constant confining pressure (158 MPa) and strain rate (3.0xlO-4 S-I). An initial set of deformation experiments were performed upon pure Solnhofen limestone and Chelometric grade calcite to establish the flow behaviour of the clasts and matrix, respectively. Subsequent experiments were performed upon samples in which the volume fraction of clasts and matrix varied in the range 9:91 to 37:63. In order to assess the accuracy of strain measurements made on deformed conglomerates and, in particular, the potential complicating influence of grain size-sensitive flow on those measurements, the Rf/J and Fry techniques have been used to determine the clast and matrix strains, respectively, in the experimental samples. Detailed microstructural analyses were performed using an automated Electron Backscatter Diffraction (EBSD) technique. The experimental results obtained emphasize the significant role that viscosity contrasts, volume fraction and microstructure have in controlling the bulk strengths of polyphase materials. The results also show that at 550úC there is no strain partitioning between the clast and matrix despite the large viscosity contrast between them whereas at 700úC there is a small but consistent strain partitioning. A rigorous interrogation of the results using the law of mixtures has shown that the component of strain which is accommodated by grain boundary sliding can be quantified in these experiments. Microstructural analysis has shown clearly a temperature dependent change in the development of fabric intensity with strain which may provide a new insight into inferring true bulk strains in rocks deformed at high temperatures.

The paper discusses issues concerning the deformation of a system of conductive bodies under the action of the electromagnetic field. Problem of nonlinear deformation of technological system for electromagnetic forming is considered as a practical application. The problem is solved by the finite element method. Spatial-temporal distributions of the main components of the electromagnetic field are obtained. The ability to review the problem of deformation in the quasi-stationary formulation is justified. The distribution of the main component of the stress-strain state is presented. The influence of the current magnitude at the maximum stresses is evaluated.

Thermocapillary motion is considered in an electrically conducting fluid with a free and open surface, and in the presence of a strong vertical magnetic field. The motion is considered initially without specifying the geometry of the fluid. Any walls are electrically insulating. Applications are discussed, for situations such as crystal growth, where thermocapillary motion affects the distribution of dopants, or the use of liquid metal in fusion reactors, where heat and magnetic field are both very large causing potentially significant thermocapillary motions. An inertialess approximation is made, and the characteristic velocity of the fluid is selected so that the surface tension forces governing the thermocapillary motion are as significant as the Lorentz force. Asymptotic solutions are obtained for high values of the Hartmann Number Ha in both the two dimensional and three dimensional cases. The equation of the free surface is found for two dimensional flow in a cavity for various arbitrary temperature distributions. This and the pressure within the fluid is found to be dependent on the dynamic boundary conditions at the surface. The equations governing the free surface of a rivulet flowing in a strong vertical magnetic . field are similar to those obtained using the lubrication approximation for the rivulet where there is no magnetic field. . In the three dimensional case the fluid velocity in the core may be an order higher in Ha than in the two dimensional case. This higher velocity is induced by a ,(relatively) large electric potential, and is two dimensional horizontal flow following .the Contours of the free surface, superimposed on a slower three dimensional flow. 'fhelatter flow returns the fluid back to the free surface to supply the thermocapillary motion The condition for the higher order flow is that vertical cnrrent flow in the core is non-zero, and that this current flow enters and leaves the Hartmann layer that is adjacent to the fluid surface. Jf the heating is synuuetric in the two horizontal coordinate directions, the Hartmann layer is passive, and the vertical current is zero. Flow in the core is slow, and there is a radial flow to supply the thermocapillory motion at the free surface. Electric current lines are in concentric horizontal circles.

Understanding the growth and differentiation of silicic magma chambers is a central issue in volcanology. Specifically, the injection, deformation and breakup of new pulses of magma can influence how the chamber evolves thermally and chemically, as well as the potential for eruption. Magmatic structures (e.g. enclaves, ladder dikes, and schlieren) preserved in plutonic and volcanic rocks record information about the physical processes that occur within the chamber prior to solidification. A key outstanding issue is how to use magmatic structures to extract information about magma rheology and host chamber dynamics within the chamber and during magma ascent--processes that are inherently inaccessible to direct observation. This thesis is an attempt to elucidate the fundamental physics that governs the breakup of an injected magma into a preexisting chamber. One major obstacle for the popular model that mafic inputs trigger big eruptions (Pallister et al., 1992, Murphy et al., 1998) and govern the long-term growth of silicic chambers is the way the new magma is injected. In particular, the scale length at which thermal and compositional heterogeneity is introduced controls how efficiently heat is transferred and the extent to which chamber convection causes mixing. This thesis provides a new understanding of how injections breakup to such small sizes, which can lead to a greater efficiency for mixing and remobilization of an otherwise immobile magma. I use field and experimental studies to investigate specific magmatic features preserved in plutonic and volcanic rocks that can be used to constrain the magma rheology within the chamber at the time of deformation. First, I use experiments and scaling theory to investigate the mechanical and rheological conditions leading to the deformation and breakup of analog crystal-rich dikes. Second, I use field observations of ``ladder dikes'' from the Tuolumne Intrusive Suite, together with experiments and scaling theory to demonstrate that prior to solidification, these features are deformed and broken by shearing motions in the magma chamber. And third, using experimental results along with thermodynamic and modeling constraints on key physical properties of the injected and host magmas, I use size distributions of enclaves preserved in lava flows to characterize the flow regime governing enclave formation.