Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 35 for “"Strain gradient"”.
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Numerical investigation of theories of strain-gradient plasticity
In this work, a higher-order irrotational strain gradient plasticity theory is studied in the small strain regime. This theory is based on that originally developed by Gurtin and Anand, and includes both dissipative and energetic contributions. A detailed numerical study is based on the problem of …
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Variational constitutive updates for strain gradient isotropic plasticity
In the past decades, various strain gradient isotropic plasticity theories have been developed to describe the size-dependence plastic deformation mechanisms observed experimentally in micron-indentation, torsion, bending and thin-film bulge tests in metallic materials. Strain gradient plasticity …
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Strain gradient plasticity-based modeling of damage and fracture
… At the continuum level, phenomenological strain gradient plasticity (SGP) formulations have been developed to extend plasticity theory to small scales. Grounded on the physical notion of geometrically necessary dislocations (GNDs, associated with non-uniform plastic deformation), SGP …
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A Conventional Theory of Mechanism-Based Strain Gradient Plasticity
CMSG is also used to study the indentation size effect (ISE) observed in micro and nanoindentation experiments. Different hardness trends with different indenter shapes obtained from CMSG agree very well with the experimental measurement.
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Continuum and crystal strain gradient plasticity with energetic and dissipative length scales
… transfer. A thermodynamic-based higher order gradient framework is developed in order to characterize the mechanical and thermal behavior of metals in small volume and on the fast transient time. The concept of the thermal activation energy, the dislocations interaction mechanisms, nonlocal …
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On a class of strain gradient plasticity theories : formulation and numerical implementation
This study develops strain-gradient theories for isotropic and crystal plasticity. The following four theories were developed and numerically implemented: * A one-dimensional theory to understand the basic nature of strain gradient theories; * A small deformation crystal plasticity theory; * A …
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The Strain Gradient Effect on Material Behavior at the Micron and Submicron Scales
… micromirror device (DMD) and find that the strain gradient effect significantly increases the mechanical strain energy in the DMD and reduces the rotation time of the micromirror.
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Analysis of Plane Strain Deformations of Linearly Elastic Strain-Gradient Materials by the Finite Element Method
… to explain this size dependence, whereas a strain gradient continuum theory has intrinsic length scales and may well describe mechanical deformations of small size bodies. In the current contribution, we develop a numerical software based on the finite element method (FEM) to analyze …
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Length-Scale Effects on Nano-Scale Materials Behavior
… the first time, we observe absence of permanent strain hardening in aluminum for grain sizes below 50 nm. We propose that this is due to the absence of dislocations at interior of grains at this length-scale. (5) For the first time, we observe grain size dependence of the strain gradient …
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Towards using seismic anisotropy to interpret ductile deformation in mafic lower crust
… relationship between seismic properties, finite strain and fabric orientation thus provides a useful tool in the remote sensing and interpretation of deformation in the lower crust. This thesis outlines a work-flow model by which the seismic properties of a single and representative lower crustal …
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Structural analysis of the Paint Lake Deformation Zone, Northern Ontario /
… supported by thin section analysis, defines five strain domains increasing in intensity of deformation from shear zone boundary to centre. A change in the dominant microstructural deformation mechanism from dislocation creep to diffusion creep is observed with increasing strain during …
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Passive and active Bragg gratings for optical networks
… central wavelength is invariant as the linear strain gradient along the FBG is altered. Two new devices are developed by embedding a pair of FBGs in a single uniform beam for S-bending. One is the tunable dispersion compensator with a wide tuning range, and the other is a tunable pure …
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Complex Crustal Stratification Within the Chugach Mountains, Southern Alaska
<p>Strain within the crust is accommodated along vertical gradients, but a general characterization is difficult given the heterogeneity of the earth's outermost layer. The western termination of the Chugach metamorphic complex in southern Alaska includes a uniquely well exposed crustal section …
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Development of discontinuous Galerkin method for nonlocal linear elasticity
… formulation for boundary value problems in small strain, non-local linear elasticity is proposed. The underlying theory corresponds to the phenomenological strain-gradient theory developed by Fleck and Hutchinson within the Toupin-Mindlin framework. The single-field displacement method obtained …
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Control of Excitons and Quantum Emitters in Two-Dimensional Materials
… thesis tackles the problem by applying external strain to control the emission energy of quantum emitters in hBN. Photophysical studies at cryogenic temperature show the coupling efficiency of different phonon modes to the quantum emitters in hBN, and a correlation between the local strain and …
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The Impact of Prolonged Strenuous Exercise on Right Ventricular Structure and Function: Insights from Novel Echocardiography and Electrocardiography
… Chapter 3 was a 10% reduction (P = 0.007) in RV strain and early diastolic strain rate immediately post-race that remained depressed following 6 hours of recovery. The application of area-deformation loops in Chapter 4 highlighted a leftward shift of the LV loop and rightwards shift of the RV …
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Practical Pathways to Efficient MRAM: Spin-Orbit Torques, Low-Damping, and Anomalous Hall Conductivity in Polycrystalline Materials
… axis by creating an intentional compositional gradient that is purely ferromagnetic and maintains low damping. Crucially, we find that a compositional gradient is not necessary to achieve large damping-like SOTs, instead finding direct evidence from grazing-incidence x-ray diffraction for a …
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Atomistic characterization of stress-driven configurational instability and its activation mechanisms
… considering that the relatively small strain gradient beneath the indenter will lead to a mode of long wavelength phonon instability suitable for a study
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Optical Characterisation of Strain and Defects in 2D Photonic Materials
Strain and defect engineering have shown to be powerful tools in modifying optoelectronic properties of semiconductors. This thesis aims to advance the fundamental understanding of electronic and optical properties in material systems with broken inversion symmetries and to use this understanding …
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III-V compositionally graded buffers for heterostructure integration
… greater than InP. We report the effects of strain gradient, growth temperature, and strain initiation sequence (gradual or abrupt strain introduction) on threading dislocation density, surface roughness, epi-layer relaxation, and tilt. We find that gradual introduction of strain causes …
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