Kinetics of Post-dynamic Coarsening and Reverse Transformation in Ti-6Al-4V

Experiments were carried out on the post-dynamic coarsening of alpha and reverse transformation of Ti-6Al-4V. The post-dynamic coarsening followed rⁿ vs time kinetics and the n = 3 best fit indicated that it was controlled by bulk diffusion, i.e., by vanadium diffusion through the beta matrix. Its rate was one order of magnitude faster than that applicable to static coarsening. The reverse transformation was characterized using a compression dilatometer and occurred in two stages; the first was transformation on dislocations; the second involved the growth of the alpha structure.     

Turbulence modeling of atmospheric boundary layer flow over complex terrain: a comparison of models at wind tunnel and full scale

The aim of this work is to evaluate the performance of two popular k ? ? turbulence closure schemes for atmospheric boundary layer (ABL) flow over hills and valleys and to investigate the effect of using ABL‐modified model constants. The standard k ? ? and the RNG k ? ? models are used to simulate flow over the two‐dimensional analytical shapes from the RUSHIL and RUSHVAL wind tunnel experiments. Furthermore, the mean turbulent flow over the real complex terrain of Blashaval hill is simulated and the results verified with a data set of full‐scale measurements. In general, all models yield similar results. However, use of ABL‐modified constants in both models tends to decrease the predicted velocity and increase the predicted turbulent kinetic energy. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigation on surface finish and metallic particle emission during machining of aluminum alloys using response surface methodology and desirability functions

The surface finish of a mechanical part plays an important role as it determines the part’s field performance. The machining parameters and conditions governing the part surface finish also impact on the other machining process performance indicators such as tool wear, tool life, cycle time, machining cost, and undesirable emissions of aerosols and metallic particles. In today’s metal cutting industry, a major concern is the occupational safety and health hazard associated with cutting fluids usage and metallic particle emission. It is therefore necessary to determine machining conditions that could improve the part surface finish while maintaining low the aerosol emission. In this research study, statistical methods are used to study the surface finish parameters and the metallic particle emissions during milling of aluminum alloys (6061-T6, 7075-T6, and 2024-T351) with two coated carbide tools (TiCN and a multilayer TiCN?+?Al₂O₃?+?TiN). Following an implementation of multilevel design of experiment, machining trials and determination of mains most influential factors, surface responses and desirability functions are used to determine the best process operational conditions and windows. The results of this research demonstrate that TiCN-coated tool generates fewer respirable airborne particles during machining than multilayers TiCN?+?Al₂O₃?+?TiN-coated tool. Overall, it is shown that the use of TiCN coating tool provides a better opportunity for an environmentally benign dry machining along with improvement on surface quality.     

Interface control document modeling with Citrus (avionics systems interfaces)

International Journal on Software Tools for Technology Transfer - Avionics systems integration based on interfaces control documents (ICDs) may be well handled when leveraging the strength of the...     

Design of T-shaped tube hydroforming using finite element and artificial neural network modeling

Journal of Mechanical Science and Technology - Tube hydroforming (THF) is a frequently used manufacturing method in the industry, especially on automotive and aircraft industries. Compared with...     

CSBF: A static ensemble fusion method based on the centrality score of complex networks

Ensemble of classifiers can improve classification accuracy by combining several models. The fusion method plays an important role in the ensemble performance. Usually, a criterion for weighting the decision of each ensemble member is adopted. Frequently, this can be done using some heuristic based on accuracy or confidence. Then, the used fusion rule must consider the established criterion for providing a most reliable ensemble output through a kind of competition among the ensemble members. This article presents a new ensemble fusion method, named centrality score-based fusion, which uses the centrality concept in the context of social network analysis (SNA) as a criterion for the ensemble decision. Centrality measures have been applied in the SNA to measure the importance of each person inside of a social network, taking into account the relationship of each person with all others. Thus, the idea is to derive the classifier weight considering the overall classifier prominence inside the ensemble network, which reflects the relationships among pairs of classifiers. We hypothesized that the prominent position of a classifier based on its pairwise relationship with the other ensemble members could be its weight in the fusion process. A robust experimental protocol has confirmed that centrality measures represent a promising strategy to weight the classifiers of an ensemble, showing that the proposed fusion method performed well against the literature.     

Microstructure-Based FEM Modeling of Phase Transformation During Quenching of Large-Size Steel Forgings

The current investigation encompasses the development of a microstructure-based 3D finite element model (FEM) of water quenching process of large-size, high-strength steel forgings with accurate predictions of the volume fraction of phases. The approach is based on modified TTT/CCT curves that consider a lower martensite start temperature value. An experimental procedure consisting in the validation of the FEM simulations was conducted using high-resolution dilatometry, optical and scanning electron microscopy, and instrumentation of a large-size steel block with several thermocouples at different locations. Results showed a very good agreement between the temperature predictions of the 3D FEM model and those obtained from direct measurement of instrumented forged block with an average error of about 1 pct in the quarter region. The volume fraction of phases and hardness distribution across the block were also predicted by the proposed 3D FEM model. The numerical results revealed bainitic volume fractions of about 74 pct at the center of the block and about 91 pct in the quarter region. These predictions were also confirmed by dilatometry test and metallographic examination of the microstructure. Micro hardness measurements were conducted on dilatometry samples that simulate the heat treatment cycle of different thicknesses of the forged block were compared with those predicted by the FEM, and very good agreements were obtained, further confirming the validity of the simulations. The proposed procedure in this research improves the quality of predictions by increasing the reliability of material parameters such as TTT optimization and accurate determination of thermo-physical parameters.

     

Performance of Axially Loaded Short Rectangular Columns Strengthened with Carbon Fiber-Reinforced Polymer Wrapping

This paper presents results of a comprehensive experimental investigation on the behavior of axially loaded short rectangular columns that have been strengthened with carbon fiber-reinforced polymer (CFRP) wrap. Six series, a total of 90 specimens, of uniaxial compression tests were conducted on rectangular and square short columns. The behavior of the specimens in the axial and transverse directions is investigated. The parameters considered in this study are (1) the concrete strength; (2) the aspect ratio of the cross section; and (3) the number of CFRP layers. The findings of this research can be summarized as follows: The CFRP wrapping enhances the compressive strength and the ductility of both square and rectangular columns, but to a lesser degree than that of circular columns. The ultimate strength and the ductility of the CFRP confined concrete increase with increasing number of confining layers. The increase in strength and ductility is more significant for lower strength concrete, representing poor or degraded concrete, than for normal-to-high strength concrete; that is, the maximum gain in strength that can be achieved for 3 ksi concrete wrapped columns is approximately 90%, as compared to only 30% for 6 ksi concrete wrapped columns. The CFRP confining jacket must be sufficiently stiff to develop appropriate confining forces at relatively low axial strain levels. The gain in compressive strength obtained by the CFRP confined concrete depends mainly on the relative stiffness of the CFRP jacket to the axial stiffness of the column.