Correction: Snoek-Dominated Internal Friction Response in bcc Steel: Relating Experiments With a Multi-scale Atomistic Computational Framework

Metallurgical and Materials Transactions A -     

Restraining Steel Brace Buckling Using a Carbon Fiber-Reinforced Polymer Composite System: Experiments and Computational Simulation

This paper presents an experimental and computational study of the buckling behavior of steel members strengthened with carbon fiber-reinforced polymer (CFRP) wraps. In the proposed strengthening system, steel members are first sandwiched within a core comprised of mortar or PVC blocks and then the entire system is wrapped with CFRP sheets. A matrix of specimens is tested under monotonic compression to investigate the parameters that influence system response. Test results show that the proposed strengthening method can provide enough lateral support to a steel bar member to allow it to reach yield in compression and to continue deforming inelastically beyond. Key failure modes are identified in the test program. Important parameters that influence behavior are also pinpointed and studied in more detail through a computational simulation model that is validated using the test data. Parameters identified as influential in the experimental and computational studies include: number of CFRP layers, core thickness, bond between CFRP layers and the core, bond between the core and the inner steel member, and strength of transverse sheets at the member ends.     

Tetragonality of bcc Phases in a Transformation-Induced Plasticity Steel

In a low-alloyed multi-phase transformation-induced plasticity steel, solute carbon content in polygonal ferrite, bainitic ferrite, and martensite was characterized using site-specific atom probe tomography. Selected area diffraction patterns were obtained using transmission electron microscopy, and the geometric distortion thereof was determined. The results showed that the lattice distortion increased in a sequence of polygonal ferrite, lath-like bainitic ferrite, and martensite. This increasing distortion corresponded to an increase in carbon content of the phase.     

Impulse Excitation Internal Friction Study of Dislocation and Point Defect Interactions in Ultra-Low Carbon Bake-Hardenable Steel

The simultaneous presence of interstitial solutes and dislocations in an ultra-low carbon bake-hardenable steel gives rise to two characteristic peaks in the internal friction (IF) spectrum: the dislocation-enhanced Snoek peak and the Snoek–Kê–Köster peak. These IF peaks were used to study the dislocation structure developed by the pre-straining and the static strain aging effect of C during the bake-hardening process. A Ti-stabilized interstitial-free steel was used to ascertain the absence of a γ-peak in the IF spectrum of the deformed ultra-low carbon steel. The analysis of the IF data shows clearly that the bake-hardening effect in ultra-low carbon steel is entirely due to atmosphere formation, with the dislocation segment length being the main parameter affecting the IF peak amplitude. Recovery annealing experiments showed that the rearrangement of the dislocation structure lead to the elimination of the C atmosphere.     

Coherent Structures in Flat-Bed Abutment Flow: Computational Fluid Dynamics Simulations and Experiments

Numerical computations and laboratory experiments are carried out to investigate the three-dimensional structure of large-scale (coherent) vortices induced by bridge abutments on a flat bed. A finite-volume numerical method is developed for solving the unsteady, three-dimensional Reynolds-averaged Navier–Stokes equations, closed with the k–ω turbulence model, in generalized curvilinear coordinates and applied to study the flow in the vicinity of a typical abutment geometry with a fixed, flat bed. The computed flowfields reveal the presence of multiple, large-scale, unsteady vortices both in the upstream, “quiescent,” region of recirculating fluid and the shear-layer emanating from the edge of the foundation. These computational findings motivated the development of a novel experimental technique for visualizing the footprints of large-scale coherent structures at the free surface. The technique relies on digital photography and employs averaging of instantaneous images over finite-size windows to extract coherent eddies from the chaotic turbulent flow. Application of this technique to several abutment configurations yielded results that support the numerical findings.     

Computational Fluid Dynamic (CFD) Simulations of Liquid Steel Infiltration in Ceramic Foam Structures. Part II: Application to Laboratory‐Scale Experiments

The infiltration of liquid TRIP steel into a porous zirconium dioxide foam ceramics is a possible production line for a new composite material. This composite is currently under investigation and development in the Collaborative Research Center 799. Coupled numerical simulations of the hot infiltration process at the pore scale are presented in the paper. The results of the simulations are analysed in order to study similarities and differences between heat and fluid flow phenomena during the infiltration of the foam ceramics. Among others, temperature distributions in the liquid steel and the ceramics are evaluated for typical casting conditions in a laboratory‐scale experiment.     

Friction Stir Brazing: a Novel Process for Fabricating Al/Steel Layered Composite and for Dissimilar Joining of Al to Steel

A novel process of friction stir brazing (FSB) for fabricating Al/steel layered composite (by multipass) and for joining Al to steel (by single pass) was proposed to avoid the wear of pin by steel, in which a tool without pin was used. FSB of 1.8-mm-thick Al sheet to steel sheet was conducted using a cylindrical tool with 20-mm diameter but without pin and using 0.1-mm-thick zinc foil as filler metal. For the rotational speed of 1500 rpm, sound joints were reliably obtained at the medium range of traverse speed of 75 to 235 mm/min, which fractured within Al parent sheet during tensile shear test. Furthermore, for peel test on the sound joints, Al and steel parent sheets tended to crack and deform, respectively. Metallographic examination showed that most Zn was extruded and the resultant interfacial structure consisted of several Al-Fe intermetallic compounds (IMCs) with a little Zn, less than 3 at. pct. The thickness of IMCs can be controlled to be less than 10 μm by properly increasing traverse speed (e.g., 150 mm/min). The metallurgical process of FSB was investigated by observing the microstructure of the longitudinal section of a friction stir brazed joint obtained by the suddenly stopping technique.     

Galvanic Corrosion of Steel in Contact with Carbon-Polymer Composites. II: Experiments in Concrete

Studies were conducted to understand the galvanic interactions between CFRP and steel in chloride-contaminated concrete. CFRP-pultruded rod samples (6 mm in diameter), #3 deformed plain rebar (PR, uncoated), and #4 epoxy-coated reinforcing (ECR) steel bars were tested. After 350 days, potential measurements of CFRP and steel samples in chloride-contaminated concrete were ?200 and ?600 mV (versus CSE), respectively. These results confirm that chloride contamination in concrete could allow galvanic corrosion between CFRP and steel. The measured galvanic current densities were up to 0.7 and 100 μA/m2 for the CFRP-PR and CFRP-ECR couples, respectively, raising concerns about the degradation of both CFRP and steel. The results showed that PR steel was unaffected, as the corrosion rates estimated before and after the coupling with CFRP were similar. In contrast, coupling CFRP and ECR steel showed an increase of 10 times of the estimated corrosion rate, suggesting that galvanic interaction might affect the ECR steel.     

Galvanic Corrosion of Steel in Contact with Carbon-Polymer Composites. I: Experiments in Mortar

Galvanic corrosion is a possible form of deterioration when carbon fiber-reinforced polymer (CFRP) composites and steel are in direct contact in concrete, as in stirrups tied to prestressing CFRP tendons. Laboratory experiments were performed to determine the magnitude of galvanic currents that may take place as a consequence. Preliminary results show little galvanic corrosion of steel (between 10?6 to 0.08 μA/cm2 of steel current density) when coupled with CFRP composites in mortar free of chlorides with a 0.5 water-to-cement ratio (w/c=0.5). However, significant galvanic action (steel current densities as high as 1.5 μA/cm2) was observed in chloride contaminated mortar. The study suggests that steel corrosion caused by deicing salts or marine exposure may be aggravated by the direct contact between steel and CFRP.     

Investigation of Decarburization in Spring Steel Production Process – Part I: Experiments

Decarburization and oxidation have considerable influence on the product properties of spring steels. The investigations in part I of this paper concentrate on the experimental determination of the influence of different thermal cycles on the decarburization process. With the thermo‐mechanical simulator Gleeble 1500, the influence of different process parameters, such as the time between furnace reheating and hot rolling, the hot rolling temperature, finish rolling temperature, laying temperature, and the α→γ phase transformation temperature range, is systematically investigated. In part II of this paper [15], numerical simulation techniques are applied to simulate the decarburization behavior under the experimental conditions, which are described in the present part I.     

Dislocation structure behind a shock front in fcc perfect crystals: Atomistic simulation results

Large-scale molecular dynamics simulations are used to investigate the dislocation structure behind a shock front in perfect fcc crystals. Shock compression in both the 〈100〉 and 〈111〉 directions induces dislocation loop formation via a sequential emission of partial dislocations, but in the 〈100〉 case, this process is arrested after the first partial, resulting in stacking-fault loops. The large mobility of the bounding partial dislocations results in a plastic wave that is always overdriven in the 〈100〉 direction; the leading edges of the partials are traveling with the plastic front, as in the models of Smith and Hornbogen. In contrast, both partials are emitted in 〈111〉 shock compression, resulting in perfect dislocation loops bounded only by thin stacking fault ribbons due to the split partial dislocations. These loops grow more slowly than the plastic shock velocity, so new loops are periodically nucleated at the plastic front, as suggested by Meyers. This article is based on a presentation given in the symposium “Dynamic Deformation: Constitutive Modeling, Grain Size, and Other Effects: In Honor of Prof. Ronald W. Armstrong,” March 2–6, 2003, at the 2003 TMS/ASM Annual Meeting, San Diego, California, under the auspices of the TMS/ASM Joint Mechanical Behavior of Materials Committee.     

Maintenance of Response Readiness in Patients With Parkinson's Disease: Evidence From a Simple Reaction Time Task.

The authors explored the effect of Parkinson's disease (PD) on the generation and maintenance of response readiness in a simple reaction time task. They compared performance of idiopathic PD patients without dementia, age-matched controls, and younger controls over short (1-, 3-, and 6-s) and long (12- and 18-s) foreperiod intervals. After each trial, the authors probed memory for visual information that also had to be maintained during the trial interval. Patients and controls did not differ overall in their ability to maintain readiness over long delays. However, within the PD group only, errors in maintaining visual information were correlated with difficulty in maintaining readiness, suggesting that systems impaired in PD may facilitate the maintenance of processing in both motor and cognitive domains. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Assessing Personality With a Structured Employment Interview: Construct-Related Validity and Susceptibility to Response Inflation.

The authors evaluated the extent to which a personality-based structured interview was susceptible to response inflation. Interview questions were developed to measure facets of agreeableness, conscientiousness, and emotional stability. Interviewers administered mock interviews to participants instructed to respond honestly or like a job applicant. Interviewees completed scales of the same 3 facets from the NEO Personality Inventory, under the same honest and applicant-like instructions. Interviewers also evaluated interviewee personality with the NEO. Multitrait-multimethod analysis and confirmatory factor analysis provided some evidence for the construct-related validity of the personality interviews. As for response inflation, analyses revealed that the scores from the applicant-like condition were significantly more elevated (relative to honest condition scores) for self-report personality ratings than for interviewer personality ratings. In addition, instructions to respond like an applicant appeared to have a detrimental effect on the structure of the self-report and interview ratings, but not interviewer NEO ratings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Influence of Friction on the Texture Formation of a IF Steel during Hot Rolling in the Ferrite Region

The effect of friction on evolution of the microstructure and texture during hot rolling in the ferrite region was studied with secondary electromicroscopy (SEM), X‐ray diffractometer, and FEM simulation. The friction between a roll and a steel sheet surface leads to the formation of notable through‐thickness texture gradients. The finite element method (FEM) simulation shows that the large friction coefficient between a roll and sample results in a pronounced variation of ${\dot {\varepsilon }}_{13} $ (shear strain rate) and large ε₁₃/ε₁₁ value which accounts for strong {110}<001> texture components and weak γ‐fiber components at rolled sheet surface; whereas the friction condition do not exert notable effect on texture formation at the sheet center.     

Friction Stir Welding in HSLA-65 Steel: Part I. Influence of Weld Speed and Tool Material on Microstructural Development

A systematic set of single-pass full penetration friction stir bead-on-plate and butt-welds in HSLA-65 steel were produced using a range of different traverse speeds (50 to 500?mm/min) and two tool materials (W-Re and PCBN). Microstructural analysis of the welds was carried out using optical microscopy, and hardness variations were also mapped across the weld-plate cross sections. The maximum and minimum hardnesses were found to be dependent upon both welding traverse speed and tool material. A maximum hardness of 323?Hv(10) was observed in the mixed martensite/bainite/ferrite microstructure of the weld nugget for a welding traverse speed of 200?mm/min using a PCBN tool. A minimum hardness of 179?Hv(10) was found in the outer heat-affected zone (OHAZ) for welding traverse speed of 50?mm/min using a PCBN tool. The distance from the weld centerline to the OHAZ increased with decreasing weld speed due to the greater heat input into the weld. Likewise for similar energy inputs, the size of the transformed zone and the OHAZ increased on moving from a W-Re tool to a PCBN tool probably due to the poorer thermal conductivity of the PCBN tool. The associated residual stresses are reported in Part II of this series of articles.