Structure-Properties-Processing Relationships in Metallic Materials

In the current Special Issue of Metals, we present six contributions from academia and industry. Based on their latest research developments, and achievements in their applied research field, the contributors elucidate the effect of temperature during forming operations that were closely analyzed via texture evaluation, present the opportunities that derive from microstructure and process simulation, and show how trace elements may affect critical properties in the performance of metallic materials. Bridging the gap between academia and industry, they provide all the necessary theoretical background through basic and applied research to meet the requirements for industrial application of the new and steadily optimized materials and concepts

Differential Evolution: A Survey and Analysis

Differential evolution (DE) has been extensively used in optimization studies since its development in 1995 because of its reputation as an effective global optimizer. DE is a population-based metaheuristic technique that develops numerical vectors to solve optimization problems. DE strategies have a significant impact on DE performance and play a vital role in achieving stochastic global optimization. However, DE is highly dependent on the control parameters involved. In practice, the fine-tuning of these parameters is not always easy. Here, we discuss the improvements and developments that have been made to DE algorithms. In particular, we present a state-of-the-art survey of the literature on DE and its recent advances, such as the development of adaptive, self-adaptive and hybrid techniques.http://dx.doi.org/10.3390/app810194

Large-Scale Evolutionary Optimization Using Multi-Layer Strategy Differential Evolution

Differential evolution (DE) has been extensively used in optimization studies since its development in 1995 because of its reputation as an effective global optimizer. DE is a population-based meta-heuristic technique that develops numerical vectors to solve optimization problems. DE strategies have a significant impact on DE performance and play a vital role in achieving stochastic global optimization. However, DE is highly dependent on the control parameters involved. In practice, the fine-tuning of these parameters is not always easy. Here, we discuss the improvements and developments that have been made to DE algorithms. The Multi-Layer Strategies Differential Evolution (MLSDE) algorithm, which finds optimal solutions for large scale problems. To solve large scale problems were grouped different strategies together and applied them to date set. Furthermore, these strategies were applied to selected vectors to strengthen the exploration ability of the algorithm. Extensive computational analysis was also carried out to evaluate the performance of the proposed algorithm on a set of well-known CEC 2015 benchmark functions. This benchmark was utilized for the assessment and performance evaluation of the proposed algorithm

NASA Tech Briefs, June 1994

Topics covered include: Microelectronics; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences; Life Sciences; Books and Report

MEASUREMENT AND APPLICATION OF GEOMETRIC IMPERFECTIONS IN COLD-FORMED STEEL MEMBERS

Cold-formed steel members provide a unique solution to framing walls and floors of buildings and are popular in low and mid-rise construction in North America. Members are formed from coils of thin sheet steel and cold bent into useful shapes. Advantages of cold-formed steel construction include ease of transportation and erection, thanks to its light-weight properties. This same light-weight property; however, creates a thin-walled member and such members are vulnerable to geometric imperfections. Strength and stiffness of thin-walled structural members can be impaired due to imperfections, which has inspired studies on imperfection sensitivity of cold-formed steel, including: measurement techniques, imperfection characterization, and numerical simulations. In this study, an innovative imperfection measurement rig employing a laser triangulation technique is used to scan along targeted cold-formed steel members. The scan results in abundant measurement point clouds and these allow further exploration into the impact of geometric imperfections, especially for cross-section imperfections, which are constrained by conventional measurement techniques. In addition, the point clouds enable additional applications such as dimensional characterization and an ability to study the impact of different imperfection characterization approaches as compared to actual measured imperfections. In this dissertation, a newly developed imperfection measurement rig is carefully detailed and the results illustrated with examples. Collected data from the laser-based imperfection measurement rig requires specific post-processing to achieve useful and reliable geometric information. The post-processing procedures generally comprise data trimming, surface registration, and feature recognition algorithms. Modifications to the surface registration algorithm, i.e. iterative closest point), are described along with development of the feature recognition algorithm. These processing effects are demonstrated with three different section shapes of cold-formed steel members, i.e. C, Z, and Built-up C studs. Dimensional variations, which are considered as primary geometric imperfections, are statistically summarized for future research studies. For the fist-time, correlation matrices for the dimensions are estimated from measured data. These correlation matrices can be used to improve simulations of realized member geometry that underpin reliability analysis of cold-formed steel members. Based on measured point clouds, geometric imperfections are characterized into five classes when following conventional imperfection classification, i.e. bow (major axis bending), camber (minor axis bending), twist, flare/overbend, and crown. This method is carried out in this dissertation and compared with another characterization method known as modal imperfection characterization. Instead of using flare/overbend and crown as the cross-section imperfections, the cross-section buckling mode shapes in distortional and local buckling are utilized as the reference to the cross-section imperfections. Imperfections based on MID measures exist along the longitudinal length of a specimen and can be interpreted as power spectrums in the frequency domain, which provide an insightful understanding on classified imperfections involved with multiple frequency (reciprocals of half-wave lengths) content. These results enable another imperfection modeling approach, the 1D spectral approach, and potentially improve prediction accuracy for member strength. Numerical modeling of imperfections comprising both traditional and 1D spectral approach has been carried out and is validated through material and geometric nonlinear shell finite element analysis on the true geometry. Taken together this thesis provides a new platform for measuring imperfections and dimensions of structural members, and demonstrates the use of this platform in enabling advanced analysis methods on imperfect models of cold-formed steel members and improving the strength reliability predictions for cold-formed steel members

NASA Tech Briefs, April 1997

Topics covered include: Video and Imaging; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences; Life Sciences; Books and Reports

Energy: A continuing bibliography with indexes

This bibliography lists 1096 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System from April 1, 1979 through June 30, 1979