Determination of Strain Rate Sensitivity of Micro-struts Manufactured Using the Selective Laser Melting Method

Micro-lattice structures manufactured using the selective laser melting (SLM) process provides the opportunity to realize optimal cellular materials for impact energy absorption. In this paper, strain rate-dependent material properties are measured for stainless steel 316L SLM micro-lattice struts in the strain rate range of 10^?3 to 6000 s^?1. At high strain rates, a novel version of the split Hopkinson Bar has been developed. Strain rate-dependent materials data have been used in Cowper–Symonds material model, and the scope and limit of this model in the context of SLM struts have been discussed. Strain rate material data and the Cowper–Symonds model have been applied to the finite element analysis of a micro-lattice block subjected to drop weight impact loading. The model output has been compared to experimental results, and it has been shown that the increase in crush stress due to impact loading is mainly the result of strain rate material behavior. Hence, a systematic methodology has been developed to investigate the impact energy absorption of a micro-lattice structure manufactured using additive layer manufacture (SLM). This methodology can be extended to other micro-lattice materials and configurations, and to other impact conditions.     

All‐carbon hybrids for high performance supercapacitors

A hybrid nanostructure with partially reduced graphene oxide (rGO) and carbon nanofibers (CNFs) was fabricated and used as supercapacitor electrodes. A straightforward, environmentally friendly, and low‐cost microwave‐assisted reduction process was developed for the synthesis of rGO/CNF hybrid structures. The fabricated supercapacitor devices showed a specific capacitance of 95.3 F g^?1 and a superior long‐term cycling stability. A capacitance retention of more than 97% after 11 000 galvanostatic charge discharge cycles was obtained. These and other results reported in this paper indicate that high‐rate, all‐carbon, rGO/CNF hybrid nanostructures are highly promising supercapacitor electrode materials.     

Vertically aligned carbon nanotube – Polyaniline nanocomposite supercapacitor electrodes

We develop a fast and cost effective method for the fabrication of a nanocomposite supercapacitor electrode. In this study aluminum foils were decorated with vertically aligned carbon nanotubes (VACNT) via chemical vapor deposition (CVD) method, which was followed by the electrodeposition of polyaniline (PANI) layer on top of the VACNTs. Electrochemical behavior of the fabricated nanocomposite electrodes were evaluated through cyclic voltammetry, galvanostatic charge discharge cycles and electrochemical impedance spectroscopy method. Fabricated VACNT/PANI nanocomposite electrodes through 15 electrodeposition cycles showed significant electrochemical performance. The specific capacity of these electrodes was calculated as 16.17 mF/cm² at a current density of 0.25 mA/cm².     

Cellular Biocatalysts Using Synthetic Genetic Circuits for Prolonged and Durable Enzymatic Activity

Cellular biocatalysts hold great promise for the synthesis of difficult to achieve compounds, such as complex active molecules. Whole-cell biocatalysts can be programmed through genetic circuits to be more efficient, but they suffer from low stability. The catalytic activity of whole cells decays under stressful conditions, such as prolonged incubation times or high temperatures. In nature, microbial communities cope with these conditions by forming biofilm structures. In this study, it is shown that the use of biofilm structures can enhance the stability of whole-cell biocatalysts. We employed two different strategies to increase the stability of whole-cell catalysts and decrease their susceptibility to high temperature. In the first approach, the formation of a biofilm structure is induced by controlling the expression of one of the curli component, CsgA. The alkaline phosphatase (ALP) enzyme was used to monitor the catalytic activity of cells in the biofilm structure. In the second approach, the ALP enzyme was fused to the CsgA curli fiber subunit to utilize the protective properties of the biofilm on enzyme biofilms. Furthermore, an AND logic gate is introduced between the expression of CsgA and ALP by toehold RNA switches and recombinases to enable logical programming of the whole-cell catalyst for biofilm formation and catalytic action with different tools. The study presents viable approaches to engineer a platform for biocatalysis processes.     

The influences of the residual forming data on the quasi-static axial crash response of a top-hat section

In this paper the influences of residual effects of a deep drawing forming process on the axial quasi-static crash behaviour of straight thin-walled top-hat section were numerically investigated. The residual forming data on the plastic strains, residual stresses and thickness variations were transferred to crash models, which include both deformed and nominal meshes. The influence of spring-back or spring-in on crash performance of the member was also considered. Numerical simulations were carried out by using the nonlinear finite element code LS-DYNA. As a result of these analyses it appears that the residual forming data and the effects of spring-back significantly influence the crash response and they should be considered in computational impact simulations.     

Bofy-fuzzy logic control for the basic oxygen furnace (BOF)

In this paper, fuzzy modeling for the control of basic oxygen furnace (BOF) processes is proposed. BOF is a widely preferred and effective steel making method due to its higher productivity and considerably low production cost. Therefore, today almost 65% of the total crude steel production in the world is met by using the BOF method. Higher steel output at lower cost is one of the main objectives of modern steel making methods. In order to accomplish this objective, fuzzy modeling was employed in this study in order to control some variables related to the BOF process. Fuzzy modeling and control in BOF promise a solution to the strongly non-linear problems associated with the process, which have so far proven extremely difficult to be solved by conventional control methods. Data set was selected as inputs from the real empirical BOF data in an integrated steel plant based in Turkey. Although there were negligible deviations from the target values, most of the fuzzy results obtained using MATLAB-Fuzzy Logic Toolbox version 5.0 were found to be acceptable. As a result of the application of the proposed modeling, acceptable levels of compatibility were achieved compared to the empirical BOF data and targeted steel composition. The paper indicates how fuzzy logic would be effectively used for improved process control of BOF furnace in steel making industry.     

Variable Upper Bounding Approach for Adaptive-Robust Control in Robot Control

This paper presents a new adaptive-robust control law for robot manipulators with parametric uncertainty. Stability of the uncertain system has been guaranteed using the Lyapunov theory and the control law is derived by means of analytical approach. In this scheme, the manipulator parameters are determined with an estimation law, and both adaptive gain and additional control input are also updated as a function of the estimated value. The proposed adaptive control input includes a parameter estimation law as an adaptive controller and an additional control input vector as a robust controller. The developed approach has the advantages of both adaptive and robust control laws, and besides it eliminates the disadvantages of them.     

Adsorptive features of polyacrylamide-apatite composite for Pb2+, UO(2)2+ and Th4+

Micro-composite of polyacrylamide (PAA) and apatite (Apt) was prepared by direct polymerization of acrylamide in a suspension of Apt and characterized by means of FT-IR, XRD, SEM and BET analysis. The adsorptive features of PAA-Apt and Apt were then investigated for Pb(2+), UO(2)(2+) and Th(4+) in view of dependency on ion concentration, temperature, kinetics, ion selectivity and reusability. Experimentally obtained isotherms were evaluated with reference to Langmuir, Freundlich and Dubinin-Radushkevich (DR) models. Apt in PAA-Apt had higher adsorption capacity (0.81, 1.27 and 0.69 mol kg(-1)) than bare Apt (0.28, 0.41 and 1.33 mol kg(-1)) for Pb(2+) and Th(4+), but not for UO(2)(2+). The affinity to PAA-Apt increased for Pb(2+) and UO(2)(2+) but not changed for Th(4+). The values of enthalpy and entropy changed were positive for all ions for both Apt and PAA-Apt. Free enthalpy change was DeltaG<0. Well compatibility of adsorption kinetics to the pseudo-second-order model predicated that the rate-controlling step was a chemical sorption. This was consistent with the free energy values derived from DR model. The reusability tests for Pb(2+) for five uses proved that the composite was reusable to provide a mean adsorption of 53.2+/-0.7% from 4x10(-3)M Pb(2+) solution and complete recovery of the adsorbed ion was possible (98+/-1%). The results of this investigation suggested that the use of Apt in the micro-composite form with PAA significantly enhanced the adsorptive features of Apt.     

Experimental determination of thermal conductivity of solid and liquid phases in Bi−Sn and Zn−Mg binary eutectic alloys

The thermal conductivities of solid phases, K_s, for Bi-43 wt.% Sn and Zn-0.15 wt.%Mg binary alloys at their eutectic temperature are found to be 28.0 τ 1.4 and 137.4–6.9 W/Km, respectively, with a radial heat flow apparatus. The thermal conductivity ratios, R, of liquid phase to solid phase for the same alloys at their eutectic temperature are found to be 0.93 and 0.78, respectively, with a Bridgman type directional solidification apparatus. Thus, the thermal conductivities of the liquid phases, K_L, for Bi-43 wt.%Sn and Zn-0.15 wt.%Mg binary alloys at their eutectic temperature are evaluated to be 26.0−1.3 and 107.2−5.4 W/Km, respectively, from the measured values of K_s and R.