Sensitivity Analysis of Stress State and Bond Strength of Fiber-reinforced Polymer/Concrete Interface to Boundary Conditions in Single Shear Pull-out Test

The bond between fiber-reinforced polymer and concrete substrate plays a key role in the performance of concrete structures after strengthened by externally bonded fiber-reinforced polymer composite materials. The single shear pull-out test is generally used to determine the interface characteristics, and various bond–slip models have been proposed based on the results of this test. However, the sensitivity of the bond strength to the boundary conditions has not yet been considered in the available models in the literatures. This article presents an experimental and numerical study targeted at understanding the influence of the boundary conditions on the bond strength of the fiber-reinforced polymer/concrete interface in the single shear pull-out test. The validated finite element analysis by experimental results is used for the sensitivity study of the bond strength and stress state of the interface to the boundary conditions of the concrete block. It is found that the constraint height of the concrete block at the loaded side is an influential parameter on the stress state of the interface and the bond strength

Bond–slip Behavior of Fiber-reinforced Polymer/concrete Interface in Single Shear Pull-out and Beam Tests

It has been assumed that the fiber-reinforced polymer/concrete interface is subjected to in-plane shear condition when intermediate crack debonding failure occurs. Therefore, the single shear pull-out test results are often used to predict the intermediate crack debonding failure in beams. In this study, the behavior of fiber-reinforced polymer-strengthened concrete beams and single shear pull-out specimens were studied experimentally and numerically. The bond–slip behavior of the fiber-reinforced polymer/concrete interface was obtained by single shear pull-out and beam tests. In all beam specimens, a concrete wedge located at the edge of the notch detached with the fiber-reinforced polymer debonding failure. This phenomenon shows that the initiation of debonding is due to a diagonal crack formation close to the major flexural/shear crack inside the concrete. The diagonal crack formation is due to a local moment at the tip of the notch. This causes the different stress state and slip of the fiber-reinforced polymer/concrete interface of beam specimens from that of the pull-out specimens. It is found that the bond–slip relation obtained from the pull-out test does not represent the bond–slip relation of the fiber-reinforced polymer/concrete interface in the fiber-reinforced polymer-strengthened concrete beams, and it cannot be directly used for predicting the load capacity of the fiber-reinforced polymer-strengthened concrete beams

On a three-dimensional lattice approach for modelling corrosion induced cracking and its influence on bond between reinforcement and concrete

The present work involves the discrete modelling of corrosion induced cracking and its influence on the bond between reinforcement and concrete. A lattice approach is used to describe the mechanical interaction of a corroding reinforcement bar, the surrounding concrete and the interface between steel reinforcement and concrete. The cross-section of the ribbed reinforcement bar is taken to be circular, assuming that the interaction of the ribs of the deformed reinforcement bar and the surrounding concrete is included in a cap-plasticity interface model. The expansion of the corrosion product is represented by an eigenstrain in the lattice elements forming the interface. The lattice modelling approach is applied to the analysis of corrosion induced cracking and its influence of the bond strength. The model capabilities are assessed by comparing results of analyses with those from unconfined pull-out tests reported in the literature. Future work will investigate the influence of the stiffness of interface elements and the effect of lateral confinement on corrosion induced cracking.Comment: Preprint of conference paper for Fracture Mechanics of Concrete and Concrete Structures, South Korea, 201

Three-body Hydrogen Bond Defects Contribute Significantly to the Dielectric Properties of the Liquid Water-Vapor Interface

In this Letter, we present a simple model of aqueous interfacial molecular structure and we use this model to isolate the effects of hydrogen bonding on the dielectric properties of the liquid water-vapor interface. By comparing this model to the results of atomistic simulation we show that the anisotropic distribution of molecular orientations at the interface can be understood by considering the behavior of a single water molecule interacting with the average interfacial density field via an empirical hydrogen bonding potential. We illustrate that the depth dependence of this orientational anisotropy is determined by the geometric constraints of hydrogen bonding and we show that the primary features of simulated orientational distributions can be reproduced by assuming an idealized, perfectly tetrahedral hydrogen bonding geometry. We also demonstrate that non-ideal hydrogen bond geometries are required to produce interfacial variations in the average orientational polarization and polarizability. We find that these interfacial properties contain significant contributions from a specific type of geometrically distorted three-body hydrogen bond defect that is preferentially stabilized at the interface. Our findings thus reveal that the dielectric properties of the liquid water-vapor interface are determined by collective molecular interactions that are unique to the interfacial environment.Comment: 5 pages, 4 figure, S

Structure and oxidation kinetics of the Si(100)-SiO2 interface

We present first-principles calculations of the structural and electronic properties of Si(001)-SiO2 interfaces. We first arrive at reasonable structures for the c-Si/a-SiO2 interface via a Monte-Carlo simulated annealing applied to an empirical interatomic potential, and then relax these structures using first-principles calculations within the framework of density-functional theory. We find a transition region at the interface, having a thickness on the order of 20\AA, in which there is some oxygen deficiency and a corresponding presence of sub-oxide Si species (mostly Si^+2 and Si^+3). Distributions of bond lengths and bond angles, and the nature of the electronic states at the interface, are investigated and discussed. The behavior of atomic oxygen in a-SiO2 is also investigated. The peroxyl linkage configuration is found to be lower in energy than interstitial or threefold configurations. Based on these results, we suggest a possible mechanism for oxygen diffusion in a-SiO2 that may be relevant to the oxidation process.Comment: 7 pages, two-column style with 6 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/index.html#ng_sio

The effects of interface morphology on Schottky barrier heights: a case study on Al/GaAs(001)

The problem of Fermi-level pinning at semiconductor-metal contacts is readdressed starting from first-principles calculations for Al/GaAs. We give quantitative evidence that the Schottky barrier height is very little affected by any structural distortions on the metal side---including elongations of the metal-semiconductor bond (i.e. interface strain)---whereas it strongly depends on the interface structure on the semiconductor side. A rationale for these findings is given in terms of the interface dipole generated by the ionic effective charges.Comment: 5 pages, latex file, 2 postscript figures automatically include

Oxidation of Monolayers of Partly Converted Dimethoxy-Substituted Poly(p-phenylenevinylene) Precursor Polymers at the Air-Water Interface

We observed that the poly(p-phenylenevinylene) units in Langmuir monolayers of partly converted dimethoxy-substituted poly(p-phenylenevinylene) precursor polymers oxidize at the air-water interface. This reaction even happened in the dark and therefore can not be attributed to a photooxygenation reaction with singlet oxygen. We assume that ground-state triplet oxygen is polarized at the air-water interface and forms a weakly bound complex with the double bond to give a reactive intermediate state, which lowers the activation energy of the oxidation reaction. The air-water interface thus works as a catalyst in this reaction.

Low-temperature bonding of temperature-resistant electronic connections

Bonding of flat metal surfaces utilizes low temperature melting intermediate material, pulse heating, and pressure application to produce strong, electrically conductive bond resistant to melting at temperatures well above melting point of intermediate material. Little or no intermediate material remains at the interface

Experimental study of ceramic coated tip seals for turbojet engines

Ceramic gas-path seals were fabricated and successfully operated over 1000 cycles from flight idle to maximum power in a small turboshaft engine. The seals were fabricated by plasma spraying zirconia over a NiCoCrAlX bond boat on the Haynes 25 substrate. Coolant-side substrate temperatures and related engine parameters were recorded. Post-test inspection revealed mudflat surface cracking with penetration to the ceramic bond-coat interface