Determination of optimal EDM machining parameters for machined pure titanium-porcelain adhesion

The objective of this experimental study is to determine electrical discharge machining (EDM) parameters that offer the best adhesion at the interface of a machined titanium–porcelain composite. First of all, with Taguchi method, machining parameters that will be effective in the bonding strength as well as their interactions on each other were determined in the test. Then, multiple level experiments were conducted to determine how the effective parameters varied over a wide area. Slopes of the curves obtained in these tests were studied, and then, final tests were conducted to obtain the best bonding strength possible. In this way, machining parameters that would offer the highest bonding strength of the titanium–porcelain matrix in a stepwise adjustable EDM machine were obtained. By taking into consideration the steps on the EDM machine where the tests were conducted, it is seen that, when a full factorial experiment is undertaken, 5 power?×?2 polarity?×?2 type of dielectric?×?2 sandblasting or non-sandblasting?×?2 kind of electrode?×?10 pulse-on time, it necessitates 800 different tests to be executed, but, with the applied method, 16?+?18?+?3 yields 37 different tests where the results that include all possible alternatives were obtained. As a result, EDM machining parameters that offer the highest adhesion and are relatively higher, 31.5 N/mm², than the acceptable minimum value of 25 N/mm² were specified.     

Controlled synthesis of transition metal/conducting polymer nanocomposites

A novel displacement reaction has been observed to occur between conducting polymers (CP) and metal salts which can be used to fabricate nanostructured CP-metal composites in a one-pot manner. Vanadium pentoxide (V (2)O(5)) nanofiber is used during the synthesis as the reactive seeds to induce the nanofibril CP-metal network formation. The CP-metal nanocomposites exhibit excellent sensory properties for hydrogen peroxide (H(2)O(2)) detection, where both high sensitivity and a low detection limit can be obtained. The sensory performance of the CP-metal composite can be further enhanced by a facile microwave treatment. It is believed that the CP-metal nanofibril network can be converted to a carbon-metal network by a microwave-induced carbonization process and result in the sensory enhancement.     

Subjective wear trials to evaluate thermal comfort of the foot clothing system including a sweat pad

Subjective wear trials were conducted to evaluate effects of disposable antibacterial sweat pads on foot thermal comfort. Sweat pads were produced with polypropylene and polylactic acid nonwoven topsheet layers which were treated with different herbal antibacterial materials. Trials were carried out with 10 male subjects under 10 °C and 50% relative humidity simulating sweating during a moderate activity in cold environments. Besides microclimate temperature and relative humidity measurements, subjective thermal (coolness, dampness, and comfort) and other sensations (stickiness, slippiness, etc.) were obtained by five point rating scales. Bending rigidity, friction coefficients, and moisture management properties of the topsheet fabrics and pads were tested. Results show that foot sweat pads enabled drier microclimate, warmer sensations, and higher comfort evaluations. Antibacterial treatments did not affect bending rigidity values of the nonwoven topsheet fabrics, but some applications decreased spreading speed, increased roughness of the pad surfaces, and wetting time values which are not preferable.     

CIRCUMFERENTIAL CRACK PROBLEM FOR AN FGM CYLINDER UNDER THERMAL STRESSES

The main objective of this study is to determine the stress intensity factors associated with a circumferential crack in a thin-walled cylinder subjected to quasi-static thermal loading. The cylinder is assumed to be a functionally graded material. In order to make the problem analytically tractable, the thin-walled cylinder is modeled as a layer on an elastic foundation whose thermal and mechanical properties are exponential functions of the thickness coordinate. Hence a plane strain crack problem is obtained. First temperature and thermal stress distributions for a crack-free layer are determined. Then using these solutions, the crack problem is reduced to a local perturbation problem where the only nonzero loads are the crack surface tractions. Both internal and edge cracks are considered. Stress intensity factors are computed as functions of crack geometry, material properties, and time.     

A mathematical model and a heuristic approach for periodic material delivery in lean production environment

One of the important design elements for a good production system is material handling. In cases where it is not well-designed, it can be the bottleneck in the system. Moreover, it can cause a lot of wastes such as waiting time, idle time, and excessive transportation and cost. In this study, material handling in lean-based production environments is taken into account. Depending on the lean structure of the production systems such as being pull-based, smooth, and repetitive, delivering the materials to the stations periodically becomes important. At this point, milk-run trains are highly used in real applications since they enable the handling of required amount of materials on a planned basis. With this study, it is aimed to develop a specific model for milk-run trains which travel periodically in the production environment on a predefined route in equal cycle times with the aim of minimizing work-in-process and transportation costs. Since the milk-run trains having equal cycle times start their tours at the same time intervals, it becomes simple to manage them. For this reason, they are used in lean production systems where level scheduling is performed. The developed model is based on mixed-integer linear programming, and since it is difficult to find the optimum solution due to the combinatorial structure of the problem, a novel heuristic approach is developed. A numerical example is provided so as to show the applicability of the mathematical model and the heuristic approach.     

A Thienothiophene-Based Cation Treatment Allows Semitransparent Perovskite Solar Cells with Improved Efficiency and Stability

Perovskite surface treatment with additives has been reported to improve charge extraction, stability, and/or surface passivation. In this study, treatment of a 3D perovskite ((FAPbI₃)_1−x(MAPbBr₃)_x) layer with a thienothiophene-based organic cation (TTMAI), synthesized in this work, is investigated. Detailed analyses reveal that a 2D (n = 1) or quasi-2D layer does not form on the PbI₂-rich surface 3D perovskite. TTMAI-treated 3D perovskite solar cells (PSCs) fabricated in this study show improved fill factors, providing an increase in their power conversion efficiencies (PCEs) from 17% to over 20%. It is demonstrated that the enhancement is due to better hole extraction by drift-diffusion simulations. Furthermore, thanks to the hydrophobic nature of the TTMAI, PSC maintains 82% of its initial PCE under 15% humidity for over 380 h (the reference retains 38%). Additionally, semitransparent cells are demonstrated reaching 17.9% PCE with treated 3D perovskite, which is one of the highest reported efficiencies for double cationic 3D perovskites. Moreover, the semitransparent 3D PSC (TTMAI-treated) maintains 87% of its initial efficiency for six weeks (>1000 h) when kept in the dark at room temperature. These results clearly show that this study fills a critical void in perovskite research where highly efficient and stable semitransparent perovskite solar cells are scarce.     

Flow-line scheduling problem with controllable processing times

In this paper we address the simultaneous scheduling and optimal-processing-times selection problem in a multi-product deterministic flow line operated under a cyclic scheduling approach. The selection of processing times plays an important role in achieving the desired production rate with the least possible operating cost. We first formulate the important subproblem of optimal-processing-times selection for different objectives, when the sequence of jobs is fixed, and then develop an efficient solution procedure for it. The fast solution of the fixed sequence problem is necessary for the development of efficient approximate solution procedures for the simultaneous scheduling and optimal-processing-times problem. A computational study on the effectiveness of the proposed solution procedure is presented. For the solution of the simultaneous scheduling and optimal-processing-times problem we suggest an iterative solution procedure, and report our computational experience with this procedure. For the solution of large problems we present a genetic algorithm. The effectiveness of the algorithm is demonstrated through computational results and by evaluating the performance of the obtained solutions against lower bounds that we developed for the problem.     

Development of metal supported solid oxide fuel cells for operation at 500–600 °C

A novel metal-supported solid oxide fuel cell has been developed that is capable of operating at temperatures of 500–600 °C. The rationale behind the materials used to construct this fuel cell type is given, and results are presented from cell testing on hydrogen and reformed natural gas, including durability trials of some 2500 h duration. This new fuel cell variant is shown to be tolerant of carbon monoxide, durable, robust to thermal and redox cycling, and capable of delivering technologically relevant power densities. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.