Interfacial diffusion in high-temperature deformation of composites: A discrete dislocation plasticity investigation

© 2016 Elsevier Ltd We present a discrete dislocation plasticity (DDP) framework to analyse the high temperature deformation of multi-phase materials (composites) comprising a matrix and inclusions. Deformation of the phases is by climb-assisted glide of the dislocations while the particles can also deform due to stress-driven interfacial diffusion. The general framework is used to analyse the uniaxial tensile deformation of a composite comprising elastic particles with dislocation plasticity only present in the matrix phase. When dislocation motion is restricted to only glide within the matrix a strong size effect of the composite strength is predicted with the strength increasing with decreasing unit cell size due to dislocations forming pile-ups against the matrix/particle interface. Interfacial diffusion decreases the composite strength as it enhances the elongation of the elastic particles along the loading direction. When dislocation motion occurs by climb-assisted glide within the matrix the size effect of the strength is reduced as dislocations no longer arrange high energy pile-up structures but rather form lower energy dislocation cell networks. While interfacial diffusion again reduces the composite strength, in contrast to continuum plasticity predictions, the elongation of the particles is almost independent of the interfacial diffusion constant. Rather, in DDP the reduction in composite strength due to interfacial diffusion is a result of changes in the dislocation structures within the matrix and the associated enhanced dislocation climb rates in the matrix.Support from ONR under grant number N62909-14-1N242 on Multi-scale methods for creep resistant alloys (program manager Dr. David Shifler) is gratefully acknowledged

Role of pumping and wrinkle propagation mechanisms in exciting different acoustic-modes in turbulent syngas combustion

International audienc

Investigation of Oscillatory States Involving Acoustic Mode Shifts in a Turbulent Syngas Combustion using Non-stationary Time-series Analysis

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Dynamic mode decomposition of syngas (H2/CO) flame during transition to high-frequency instability in turbulent combustor

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Experimental Analysis of Transition to Higher Acoustic Mode in Syngas Combustion Dynamics

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Experimental Investigation Into the Role of Mean Flame Stabilization on the Combustion Dynamics of High-Hydrogen Fuels in a Turbulent Combustor

International audienceAbstract A bluff-body turbulent combustor is mapped for its thermo-acoustic stability across variation in airflow rate, nondimensionalized as the Reynolds number (Re) and fuel composition. The combustor stability is evaluated for three fuels, namely, pure hydrogen (PH), synthesis natural gas (SNG), and syngas (SG). The combustion dynamics display markedly different behavior across the fuels, in the extent of the unstable region, as well as the observed dominant Eigenvalues. At low Re, SNG displays stable combustion, while SG exhibits high amplitude oscillations at the fundamental duct acoustic mode. As the Re is increased, SNG displays very high amplitude oscillations at the duct acoustic mode, while SG exhibit relatively low amplitude oscillations at the third harmonic. In the case of PH, high amplitude oscillations observed at higher Re at the first harmonic. These peculiarities are investigated in light of the role of mean flame stabilization. The combustion dynamics of the fuels is influenced by the global equivalence ratio, as well as the jet momentum ratio. These effects significantly demarcate the dynamics of SNG and SG combustion. This is seen manifested in the mean flame structure of flame at high amplitude oscillations, whereby result in SNG flame to be present in the wake, while the SG flame resides in the shear layer. The driving by the flame because of their mean stabilization is quantified by a spatial Rayleigh index. It confirms the presence of large driving regions for SNG compared to that of SG, results in the observed differences in amplitude of the oscillations

Surgical Outcomes in Patients with Congenital Cervical Spinal Stenosis.

OBJECTIVE: To evaluate the differences in surgical outcomes of patients with cervical spondylotic myelopathy with and without congenital cervical spinal stenosis (CCSS). METHODS: Institutional review board approval was obtained to conduct a retrospective chart review of patients with cervical spondylotic myelopathy who underwent decompression and fusion surgeries from 2010-2016 at a single institution. CCSS was identified using the Torg-Pavlov ratio on lateral cervical radiographs. Pre- and postoperative outcome measures were assessed using the modified Japanese Orthopedic Association (mJOA) and the EuroQol 5-dimension questionnaire (EQ-5D). RESULTS: Of 208 patients, Torg-Pavlov ratio identified 85 patients with CCSS. There were no significant differences between the CCSS patient and control patient groups in EuroQol 5-dimension questionnaire and mJOA scores at all 4 designated time points in the study (preoperative, earliest postoperative, 6 month postoperative, and 1 year postoperative). Although not statistically significantly, there was a notable trend for patients with CCSS to be less likely to have mJOA-defined severe myelopathy at the postoperative (odds ratio [OR], 0.75; P = 0.38), 6 month postoperative (OR, 0.66; P = 0.20), and 1 year postoperative (OR, 0.64; P = 0.14) time points. CONCLUSIONS: Postoperatively, compared with non-CCSS patients, patients with congenital cervical stenosis reported equal quality of life for all markers. Our findings suggest that in patients with CCSS and relatively mild symptoms of myelopathy, equal consideration should be given for surgical intervention. The findings of this study warrant further large-scale, multi-institutional investigation to further understand the generalizability of these surgical outcome results