Stress-displacement relation during fiber pullout

During fiber pullout tests of fiber-reinforced composites, initial debonding, partial debonding, complete debonding at the interface, and fiber pullout occur sequentially. Adopting the shear lag model for stress analyses and the strength criterion for interfacial debonding, a bond length dependence of the initial debond stress is derived. During partial debonding, the stress initially increases with the increasing fiber displacement. The partial debond stress reaches a maximum value and begins to decrease with an accompanying decreasing fiber displacement until the interface is completely debonded. Theoretically, the stress-displacement curve shows a nose'' at the maximum debond stress. However, the pullout test is generally conducted under the condition of an increasing fiber displacement. Hence, at the maximum debond stress, the observed stress drops abruptly as the increasing fiber displacement type test obscures the nose-type characteristic

Criteria for progressive interfacial debonding with friction in fiber-reinforced ceramic composites

Criteria for progressive debonding at the fiber/matrix interface with friction along the debonded interface are considered for fiber-reinforced ceramic composites. The energy-based criterion is adopted to analyze the debond length, the crack-opening displacement, and the displacement of the composite due to interfacial debonding. The analytical solutions are identical to those obtained from the mismatch-strain criterion, in which interfacial debonding is assumed to occur when the mismatch in the axial strain between the fiber and the matrix reaches a critical value. Furthermore, the mismatch-strain criterion is found to bear the same physical meaning as the strength-based criterion

Analyses of residual thermal stresses in ceramic matrix composites

Residual thermal stresses in ceramic matrix composites containing either ellipsoidal inclusions or short fibers (i.e., fibers of finite length) are considered. First, the residual stresses in ellipsoidal inclusions are uniform, and they are analyzed using a modified Eshelby model. Although closed-form analytical solutions are obtained, their formulations are formidable. When the aspect ratio of the ellipsoid is 0, 1, or infinity, simple analytical solutions can be obtained using different models, and they are in excellent agreement with those obtained from the modified Eshelby model. Second, residual stresses in short fibers are nonuniform, and they are analyzed using a modified shear lag model, in which imaginary fibers are introduced to satisfy the continuity condition at the fiber ends. The analytical solutions are compared to the experimental results

Interfacial debonding versus fiber fracture in fiber-reinforced ceramic composites

Toughening of fiber-reinforced ceramic composites by fiber pullout relies on debonding at the fiber/matrix interface prior to fiber fracture when composites are subjected to tensile loading. The criterion of interfacial debonding versus crack penetration has been analyzed for two semi-infinite elastic plates bonded at their interface. When a crack reaches the interface, the crack either deflects along the interface or penetrates into the next layer depending upon the ratio of the energy release rate for debonding versus that for crack penetration. This criterion has been used extensively to predict interfacial debonding versus fiber fracture for a crack propagating in a fiber-reinforced ceramic composite. Two modifications were considered in the present study to address the debonding/fracture problem. First, the authors derived the analysis for a strip of fiber, which had a finite width and was sandwiched between two semi-infinite plates of matrix. It was found that the criterion of interfacial debonding versus fiber fracture depended on the fiber width. Second, a bridging fiber behind the crack tip was considered where the crack tip initially circumvented the fiber. Subsequent to this, either the interface debonded or the fiber fractured. In this case, the authors have considered a bridging-fiber geometry to establish a new criterion

Design and modeling of electrolyte pumping power reduction in redox flow cells

Because of flexible design, long life, and low-cost maintenance, redox flow cell has been recognized as one of the reliable energy storage techniques in remote power systems. In redox flow cells, electrolyte circulation through carbon felt is necessary in order to produce effective ion exchange during the charge and discharge operations. Pumping power required for electrolyte circulation could be significant, especially for multi-stack cell, due to low permeability of the porous carbon felt. Moreover, effective method for transporting bubbles formed inside the electrode is necessary for increasing the effective area of reaction of the electrodes. To further improve the overall performance of the redox flow cells, we proposed several novel designs of electrolyte inlet/outlet port and flow passage in carbon felt intending to reduce the electrolyte pumping power and to increase the effective area. Based on our numerical modeling, it is found that pumping power can be reduced by appropriate inlet/outlet port design and carbon felt with flow channel. The non-uniform flow pattern may cause the bubbles to be carried away from the electrodes effectively. The proposed designs can be applied not only for the single-stack cell but also applicable for the multiple-stacked cells

The trans-ancestral genomic architecture of glycemic traits

Glycemic traits are used to diagnose and monitor type 2 diabetes and cardiometabolic health. To date, most genetic studies of glycemic traits have focused on individuals of European ancestry. Here we aggregated genome-wide association studies comprising up to 281,416 individuals without diabetes (30% non-European ancestry) for whom fasting glucose, 2-h glucose after an oral glucose challenge, glycated hemoglobin and fasting insulin data were available. Trans-ancestry and single-ancestry meta-analyses identified 242 loci (99 novel; P < 5 x 10(-8)), 80% of which had no significant evidence of between-ancestry heterogeneity. Analyses restricted to individuals of European ancestry with equivalent sample size would have led to 24 fewer new loci. Compared with single-ancestry analyses, equivalent-sized trans-ancestry fine-mapping reduced the number of estimated variants in 99% credible sets by a median of 37.5%. Genomic-feature, gene-expression and gene-set analyses revealed distinct biological signatures for each trait, highlighting different underlying biological pathways. Our results increase our understanding of diabetes pathophysiology by using trans-ancestry studies for improved power and resolution.A trans-ancestry meta-analysis of GWAS of glycemic traits in up to 281,416 individuals identifies 99 novel loci, of which one quarter was found due to the multi-ancestry approach, which also improves fine-mapping of credible variant sets.Diabetes mellitus: pathophysiological changes and therap