Fiber Element for Cyclic Bending and Shear of RC Structures.?II: Verification

The fiber beam element with shear modeling developed in the companion paper is calibrated and verified by comparison with test data. The verification is carried out for the material constitutive behavior and for single beam and column elements using available test results from literature. A structural analysis of a shear sensitive viaduct pier subjected to ground input motion is presented. Details of the algebraic expressions used for the concrete and steel constitutive behaviors are provided.     

Flutter and Buffeting Analysis.?I: Finite-Element and RPE Solution

A finite-element formulation is developed for analyzing flutter instability and buffeting response of long-span bridges and their interaction. The flutter derivatives, instead of the indicial functions used by previous researchers, are applied in the random parametric excitation (RPE) analysis. This application makes finite-element formulation possible and results in much less computational effort in RPE analysis than those of previous analyses. With the finite-element program developed in the present study, as many modes as desired can be easily included in the flutter and buffeting analyses. Users have the choice of RPE or eigenvalue method for flutter analysis and RPE or spectral method for buffeting analysis.     

Finite Strain, Anisotropic Modified Cam Clay Model with Plastic Spin.?I: Theory

There are several approaches that can take into account the micromechanical and anisotropic behavior of soils. One is Dafalias's plastic spin approach. It is a convenient approach that utilizes an internal variable called “the plastic spin tensor.” The plastic spin is a function of the embedded stress (back stress) that causes the induced anisotropy and, consequently, the isotropic soil models cannot account for it. This paper presents a formulation of the plastic spin and related constitutive equations based on Dafalias's “anisotropic modified Cam clay model” with an updated Lagrangian reference frame. The required parameters are the typical consolidation and stress-strain parameters. The only additional parameters used in this work are the back-stress parameters c and x. These features are relatively simple and easy to use compared to other models.     

Analysis of Surface Longitudinal Crack of Slab and Crack of Cold Bending for Cu-P-RE Weathering Steels

The surface morphology of longitudinal crack at corner of slab and the crack morphology of cold bending for Cu-P-RE weathering sleels were analyzed by metalographic examination and SEM.The feature of erack and the composition of inclusions on the surface of erack were detected by EMPA,     

Seismic Repair and Strengthening of Lap Splices in RC Columns: Carbon Fiber–Reinforced Polymer versus Steel Confinement

A design approach, developed specifically for seismic bond strengthening of the critical splice region of reinforced concrete columns or bridge piers, is presented and discussed. The approach is based on providing adequate concrete confinement within the splice zone for allowing the spliced bars to theoretically develop enough postelastic tension strains demanded by large earthquakes before experiencing splitting bond failure. The accuracy of the approach was validated experimentally by evaluating the seismic behavior of full-scale gravity load-designed (as-built) rectangular columns that were strengthened or repaired in accordance with the proposed approach. Three types of confinement were used and compared, namely, internal steel ties, external fiber polymer reinforced jackets, and a combination of both. The repaired/strengthened columns developed sizable postyield strains of the spliced bars, considerable increases in the lateral load and drift capacities, and much less concrete damage within the splice zone when compared with the as-built columns. As a further support of the adequacy of the design strengthening approach, the backbone lateral load-drift response of the strengthened columns showed a good agreement with the envelope response generated using nonlinear flexural analysis assuming perfect bond between the column reinforcement and concrete.     

Developing Dislocation Subgrain Structures and Cyclic Softening During High-Temperature Creep–Fatigue of a Nickel Alloy

The complex cyclic deformation response of Alloy 617 under creep–fatigue conditions is of practical interest both in terms of the observed detriment in failure life and the considerable cyclic softening that occurs. At the low strain ranges investigated, the inelastic strain is the sole predictor of the failure life without taking into consideration a potentially significant environmental influence. The tensile-hold creep–fatigue peak stress response can be directly correlated to the evolving dislocation substructure, which consists of a relatively homogenous distribution of subgrains. Progressive high-temperature cycling with a static hold allows for the rearrangement of loose tangles of dislocations into well-ordered hexagonal dislocation networks. The cyclic softening during tensile-hold creep–fatigue deformation is attributable to two factors: the rearrangement of dislocation substructures into lower-energy configurations, which includes a decreasing dislocation density in subgrain interiors through integration into the subgrain boundaries, and the formation of surface grain boundary cracks and cavity formation or separation at interior grain boundaries, which occurs perpendicular to the stress axis. Effects attributable to the tensile character of the hold cycle are further analyzed through variations in the creep–fatigue waveform and illuminate the effects of the hold-time character on the overall creep–fatigue behavior and evolution of the dislocation substructure.     

Cyclic deformation of ferritic steel—I. Stress-strain response and structure evolution

The complete CSS-curve has been established for a low alloyed structural steel tested under plastic strain control. The curve which can be divided into three separate regimes has a plateau region between cyclic strain levels of 10⁻⁴ and 8·10⁻⁴. PSBs are formed on the specimen surface when the plastic strain range corresponds to the plateau regime. The PSBs are sites for crack nucleation. The substructure evolution as seen going along the CSS-curve and with accumulating numbers of cycles is documented in detail and includes: dislocation loops, veins, walls including the ladder-like walls usually associated with PSBs, labyrinths, cells, subgrains, banded cells and subgrains. At low and intermediate plastic strain ranges the surface grains contain a more fine-scaled substructure and develop features which appear in the interior at higher plastic strain ranges. At larger cyclic strain levels microbands and noncrystallographic deformation bands become dominating features. Heavily displaced and serrated grain boundaries are observed at intermediate and high plastic strains both in interior- and surface grains containing microbands, banded cells or banded subgrains.     

Are Available Models Reliable for Predicting the FRP Contribution to the Shear Resistance of RC Beams?

In this paper the trustworthiness of the existing theory for predicting the fiber-reinforced plastic contribution to the shear resistance of reinforced concrete beams is discussed. The most well-known shear models for external bonded reinforcement are presented, commented on, and compared with an extensive experimental database. The database contains the results from more than 200 tests performed in different research institutions across the world. The results of the comparison are not very promising and the use of the additional principle in the actual shear design equations should be questioned. The large scatter between the predicted values of different models and experimental results is of real concern bearing in mind that some of the models are used in present design codes.     

Experiments on Downstream Fining of Gravel.?II: Wide and Sandy Runs

This is the second of two papers about experiments on downstream fining of gravel. Here we briefly summarize the complete series of runs described in the first paper, where the influence of sediment feed rate was evaluated in a narrow channel. We then present results for variation in two more conditions: sand content and channel width. The experiments were carried out in a long flume with an effective 40-m-long test section, with two different widths of 0.3 and 2.7 m. In addition, two sediment mixtures were used with different sand contents (i.e., 33 and 55%) with the remainder being gravel. The following results were obtained. The increase in channel width allowed the formation of transverse topography, enhanced the development of sediment patches, and increased the fining rate of gravel for D50 and finer percentiles. Increasing sand content rendered the long profile of the bed much more concave, caused marked patch development, and most notably increased the fining rate for all percentiles of gravel-sized bed material.     

Spatial Postbuckling Analysis of Nonsymmetric Thin-Walled Frames.?I: Theoretical Considerations Based on Semitangential Property

To present the spatial postbuckling analysis procedures of shear deformable thin-walled space frames with nonsymmetric cross sections, theoretical considerations based on the semitangential rotation and the semitangential moment are presented. First, similarity and difference between Rodriguez' rotations and semitangential rotations are addressed. Next, the improved displacement field is introduced using the second-order terms of semitangential rotations and rotational properties of off-axis loads and conservative moments are discussed based on the proposed displacement field. Finally, it is deduced that the resulting potential energy due to stress resultants corresponds to semitangential bending and torsional moments. In a companion paper, the elastic strain energy including bending-torsion coupled terms and shear deformation effects is newly derived and a clearly consistent finite-element procedure is presented based on the updated Lagrangian corotational formulation. Tangent stiffness matrices of the thin-walled space frame element are derived using Hermitian polynomials considering shear deformation effects, and a new scheme to evaluate incremental member forces and load correction stiffness matrices due to off-axis loads is presented and its physical meaning is addressed. Furthermore, finite-element solutions displaying spatial postbuckling behaviors are evaluated and compared with available solutions.     

Time–Temperature–Precipitation Relations for Nitrides and Evaluation of Internal Oxidation Theory for Nitridation of Austenitic Stainless Steel

Metallurgical and Materials Transactions A - Internal nitridation kinetics were determined for a UNS N08810/800H alloy using a general model of the form $$x^{n}=kt$$ . Nitridation behavior was...     

Electromagnetically Modified Filtration of Aluminum Melts—Part I: Electromagnetic Theory and 30 PPI Ceramic Foam Filter Experimental Results

In the present work, laboratory-scale continuous filtration tests of liquid A356 aluminum alloy have been performed. The tests were conducted using standard 30 PPI (pores per inch) ceramic foam filters combined with magnetic flux densities (~0.1 and 0.2 T), produced using two different induction coils operated at 50 Hz AC. A reference filtration test was also carried out under gravity conditions, i.e., without an applied magnetic field. The obtained results clearly prove that the magnetic field has a significant affect on the distribution of SiC particles. The influence of the electromagnetic Lorentz forces and induced bulk metal flow on the obtained filtration efficiencies and on the wetting behavior of the filter media by liquid aluminum is discussed. The magnitudes of the Lorentz forces produced by the induction coils are quantified based on analytical and COMSOL 4.2^® finite element modeling.     

A potentiostatic double-step method for measuring hydrogen atom diffusion and trapping in metal electrodes—I. Theory

Hydrogen atom ingress into a planar metal electrode can be measured using a potentiostatic method. Hydrogen atoms are generated during a defined period at a constant cathodic potential. The potential is then stepped to a more positive value at which the hydrogen atoms are re-oxidised, giving a transient anodic current corresponding to removal of the hydrogen atoms from the electrode. This paper gives the theory of the method. Fick's law for diffusion of hydrogen atoms in the metal is modified by allowing for trapping of some of the hydrogen. The trapping process is assumed to be of first order and irreversible, with no significant saturation of the traps. The ingress problem has been formulated and solved for two distinct cases:

• 1.(a) equilibrium ingress, giving a constant hydrogen atom concentration at the surface with the flux being controlled solely by diffusion and trapping in the metal; and
• 2.(b) constant ingress flux through the metal surface.

These cases have been solved to give explicit expressions, as functions of charging time, for the concentration profiles during the ingress and egress steps, the anodic current transients, and the charge densities corresponding to ingress and egress and trapped hydrogen.     

Theory and Practice of γ + α2 Ti Aluminide: A Review

Among the high temperature materials γ + α₂ Ti aluminide is the most promising material, which has unique characteristics of low density coupled with high temperature properties. However, the low room temperature ductility of the alloy has limited its commercial application. Many studies have been carried out on this alloy to understand the phase transformation and role of alloying elements. Several processing methodologies have been attempted and advantages of various routes have been explored. However, poor ductility at room temperature is still a concern. In the present paper a thorough review of relevant studies has been carried out and viable route for industrial processing has been suggested. This paper includes theoretical concepts behind limited ductility of alloy at room temperature and its processing difficulty through the conventional methods. Modification in binary Ti aluminide alloy through alloying addition, selection of suitable processing route and heat treatment are noted as important areas which can provide a practical solution for this alloy to bring it to industrial processing and application.     

Revisiting “Steady-State” Monotonic and Cyclic Deformation: Emphasizing the Quasi-Stationary State of Deformation

Metallurgical and Materials Transactions A - High-temperature creep, cyclic deformation in saturation, and a number of technologically important processes are typical examples of the so-called...     

Grain boundary motion—I. Theory of vacancy production and vacancy drag during grain boundary motion

Under the assumption that a grain boundary contains sinks and sources for vacancies, the concentration distribution of vacancies about a moving grain boundary has been calculated. Additionally, the vacancies have been considered which are formed to compensate for the volume surplus if by the moving grain boundary dislocations are annihilated. It has been found that by grain boundary motion the vacancy concentration can considerably be increased independently of whether or not the grain boundary motion occurs by means of vacancies. It has further been found that, analogously to the impurity drag, the grain boundary experiences a retarding force in case of attractive interaction between boundary and vacancies (“vacancy drag”). In further papers additional aspects of the problem will be treated.