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Articles 1 - 10 of 10
Full-Text Articles in Engineering
Dislocation Structures And The Deformation Of Materials, Marisol Koslowski, Richard Alan Lesar, Robb Thomson
Dislocation Structures And The Deformation Of Materials, Marisol Koslowski, Richard Alan Lesar, Robb Thomson
Richard Alan Lesar
We present results from phase-field simulations of a two-dimensional model of dislocation microstructure development under increasing strain that incorporates the effects of the full, three-dimensional, microstructure in an approximate way. Despite its simplicity, the model yields quantitative predictions of both the deformation properties of face-centered cubic metals as well as key descriptors of the evolving microstructure over a wide range of stress and strain. The present results have important implications for how we interpret and describe the deformation properties of fcc materials.
Ordered Network Phases In Linear Poly(Isoprene-B-Styrene-B-Ethylene Oxide) Triblock Copolymers, Thomas H. Epps Iii, Eric W. Cochran, Travis S. Bailey, Ryan S. Waletzko, Cordell M. Hardy, Frank S. Bates
Ordered Network Phases In Linear Poly(Isoprene-B-Styrene-B-Ethylene Oxide) Triblock Copolymers, Thomas H. Epps Iii, Eric W. Cochran, Travis S. Bailey, Ryan S. Waletzko, Cordell M. Hardy, Frank S. Bates
Eric W. Cochran
The equilibrium phase behavior of 43 linear poly(isoprene-b-styrene-b- ethylene oxide) (ISO) triblock copolymer melts, with molecular weights that place these materials near the order-disorder transition, is reported. Ordered phase morphologies were characterized using small-angle X-ray scattering, transmission electron microscopy, dynamic mechanical spectroscopy, and static birefringence measurements. Interpretation of these results was aided by a modeling technique that facilitates resolution of reciprocal and real-space experimental data, leading to definitive three-dimensional morphological structures. Three distinct multiply continuous network morphologies are identified across a range of compositions between 0.1 ≤ f o ≤ 0.3, situated between two-domain and three-domain lamellae, where f o …
Avalanches And Scaling In Plastic Deformation, Marisol Koslowski, Richard Alan Lesar, Robb Thomson
Avalanches And Scaling In Plastic Deformation, Marisol Koslowski, Richard Alan Lesar, Robb Thomson
Richard Alan Lesar
Plastic deformation of crystalline materials is a complex nonhomogeneous process characterized by avalanches in the motion of dislocations. We study the evolution of dislocation loops using an analytically solvable phase-field model of dislocations for ductile single crystals during monotonic loading. The distribution of dislocation loop sizes is given by P(A)∼A−σ, with σ=1.8±0.1. The exponent is in agreement with those found in acoustic emission experiments. This model also predicts a range of macroscopic behaviors in agreement with observation, including hardening with monotonic loading, and a maximum in the acoustic emission signal at the onset of yielding.
Network Phases In Abc Triblock Copolymers, Thomas H. Epps Iii, Eric W. Cochran, Cordell M. Hardy, Travis S. Bailey, Ryan S. Waletzko, Frank S. Bates
Network Phases In Abc Triblock Copolymers, Thomas H. Epps Iii, Eric W. Cochran, Cordell M. Hardy, Travis S. Bailey, Ryan S. Waletzko, Frank S. Bates
Eric W. Cochran
Many naturally occurring and engineered products are influenced by network structures. Collagen networks provide a scaffold for living tissue, while swollen arrays of physically cross-linked polypeptides constitute gelatin, the familiar dessert and electrophoresis medium. Although the associated mesh sizes differ by several orders of magnitude, these examples share a common feature: three-dimensional connectivity that imparts mechanical rigidity. Intercalating additional interconnected components can yield broader functions, e.g., ionic or electrical conductivity, optical band gaps, and tailored heat and mass transfer.
Shear-Induced Network-To-Network Transition In A Block Copolymer Melt, Eric W. Cochran, Frank S. Bates
Shear-Induced Network-To-Network Transition In A Block Copolymer Melt, Eric W. Cochran, Frank S. Bates
Eric W. Cochran
The tricontinuous (10, 3)c shear-induced network-to-network transition in a block copolymer melt was analyzed using small-angle x-ray scattering. Investigations show that field-induced network-to-network phase transition was unprecedented in soft condensed matter. It was found that shear transforms were used for self-assembling the soft material into a single crystal (10, 3)d network. The results show the delicate nature of block copolymers phase behavior, where candidate morphologies were spaced closely together on the free energy surface.
Reliable First-Principles Alloy Thermodynamics Via Truncated Cluster Expansions, Nikolai A. Zarkevich, Duane D. Johnson
Reliable First-Principles Alloy Thermodynamics Via Truncated Cluster Expansions, Nikolai A. Zarkevich, Duane D. Johnson
Nikolai A. Zarkevich
In alloys cluster expansions (CE) are increasingly used to combine first-principles electronicstructure calculations and Monte Carlo methods to predict thermodynamic properties. As a basis-set expansion in terms of lattice geometrical clusters and effective cluster interactions, the CE is exact if infinite, but is tractable only if truncated. Yet until now a truncation procedure was not well defined and did not guarantee a reliable truncated CE. We present an optimal truncation procedure for CE basis sets that provides reliable thermodynamics. We then exemplify its importance in Ni3V, where the CE has failed unpredictably, and now show agreement to a range of …
Modeling Crosshatch Surface Morphology In Growing Mismatched Layers. Part Ii: Periodic Boundary Conditions And Dislocation Groups, A. M. Andrews, Richard Alan Lesar, M. A. Kerner, J. S. Speck, A. E. Romanov, A. L. Kolesnikova, M. Bobeth, W. Pompe
Modeling Crosshatch Surface Morphology In Growing Mismatched Layers. Part Ii: Periodic Boundary Conditions And Dislocation Groups, A. M. Andrews, Richard Alan Lesar, M. A. Kerner, J. S. Speck, A. E. Romanov, A. L. Kolesnikova, M. Bobeth, W. Pompe
Richard Alan Lesar
We present further developments and understanding of the commonly observed crosshatch surface morphology in strain-relaxed heteroepitaxialfilms. We have previously proposed that the crosshatch morphology is directly related with strain relaxation via threading dislocation glide which results in both surface step and misfit dislocation (MD) formation [see Andrews et al., J. Appl. Phys. 91, 1933 (2002)—now referred to as Part I]. In this article, we have used solutions for the stress fields and displacement fields for periodic MD arrays which include the effects of the free surface. These solutions avoid truncation errors associated with finite dislocation arrays that were used in …
Incorporation Of Local Structure In Continuous Dislocation Theory, Richard Alan Lesar, J. M. Rickman
Incorporation Of Local Structure In Continuous Dislocation Theory, Richard Alan Lesar, J. M. Rickman
Richard Alan Lesar
Continuous dislocation theory has not had great practical applicability, owing largely to the dislocation density tensor being an average quantity that includes very limited information about dislocation structures and energetics at length scales smaller than the averaging volume. Here we present a straightforward way to include the effects of underlying structure based on moments of the dislocation distribution and show that the addition of a small number of order parameters enables one to accurately characterize the energetics.
Multipole Representation Of The Elastic Field Of Dislocation Ensembles, Zhiqiang Wang, Nsar Ghoniem, Richard Alan Lesar
Multipole Representation Of The Elastic Field Of Dislocation Ensembles, Zhiqiang Wang, Nsar Ghoniem, Richard Alan Lesar
Richard Alan Lesar
A multipole expansion method is developed to determine the elastic field of dislocation loop ensembles of arbitrary geometric complexity. The method results in reduction of the severe computational requirements in large-scale dislocation dynamics (DD) computer simulations without an artificial cutoff on the interaction range. Order of N, O(N), algorithms for DD simulations is immediately accessible on the basis of the developed procedure. Examples of dislocation interaction with large dislocation arrays representing a tilt boundary and a dislocation wall show that the method results in speeding up the calculation of Peach-Kohler interaction forces by a factor of 100, with an error …
Consequences Of Block Number On The Order-Disorder Transition And Viscoelastic Properties Of Linear (Ab)N Multiblock Copolymers, Lifeng Wu, Eric W. Cochran, Timothy P. Lodge, Frank S. Bates
Consequences Of Block Number On The Order-Disorder Transition And Viscoelastic Properties Of Linear (Ab)N Multiblock Copolymers, Lifeng Wu, Eric W. Cochran, Timothy P. Lodge, Frank S. Bates
Eric W. Cochran
The effect of block number on the order-disorder transition (ODT) and viscoelastic properties were studied for linear (AB) n multiblock copolymers. A series of symmetric poly(styrene-b-isoprene) n multiblocks ((SI) n, n = 1-10) were synthesized by anionic polymerization, and their order-disorder transition temperatures (T ODT) were located using dynamic mechanical spectroscopy. As n increases, T ODT approaches an asymptotic value, consistent with random phase approximation calculations. A systematic difference between the experimental and theoretical results is attributable to the effects of fluctuations, independent of the number of blocks. Addition of up to 20 vol % of a nonselective solvent depresses …