On the characteristics of tubular materials for hydroforming—experimentation and analysis

Increasing acceptance and use of hydroforming technology within the automotive industry demands a comprehensive understanding of related issues such as material characteristics, tribology, part and tooling design. Among these issues, characterization and specification of tubular material properties under hydroforming conditions is the main concern of this paper. Analytical improvements and their comparison with experimental findings on measurement of material properties of tubes under hydraulic bulging conditions are explained. With these improvements, ‘on-line’ and continuous measurement of flow stress for tubular materials become possible, and are proven to be in good agreement with previous ‘off-line’ measurements presented by the authors.     

Design and analysis of an integrated concentrated solar and wind energy system with storage

This study analyzes a renewable energy‐driven innovative multigeneration system, in which wind and solar energy sources are utilized in an efficient way to generate several useful commodities such as hydrogen, oxygen, desalted water, space cooling, and space heating along with electricity. A 1‐km² heliostat field is considered to concentrate the solar light onto a spectrum splitter, where the light spectrum is separated into two portions as reflected and transmitted to be used as the energy source in the concentrated solar power (CSP) and concentrated photovoltaics (CPV) receivers, respectively. As such, CSP and CPV systems are integrated. Wind energy is proposed for generating electricity (146 MW) or thermal energy (138 MW) to compensate the energy need of the multigeneration system when there is insufficient solar energy. In addition, multiple commodities, 46 MW of electricity, 12 m³/h of desalted water, and 69 MW of cooling, are generated using the Rankine cycle and the rejected heat from its condenser. Further, the heat generated on CPV cells is recovered for efficient photovoltaic conversion and utilized in the space heating (34 MW) and proton exchange membrane (PEM) electrolyzer (239 kg/h) for hydrogen production. The energy and exergy efficiencies of the overall system are calculated as 61.3% and 47.8%, respectively. The exergy destruction rates of the main components are presented to identify the potential improvements of the system. Finally, parametric studies are performed to analyze the effect of changing parameters on the exergy destruction rates, production rates, and efficiencies.     

Design and feasibility tests of a flexible gripper based on inflatable rubber pockets

In this paper, we present feasibility test results of a flexible gripper design following a literature survey on various types, design and control strategies of the existing grippers. A flexible gripper based on the use of compliant materials (i.e., rubber) with pneumatic inflation was designed, analyzed, built and tested. Parametric FE analyses were conducted to investigate the effects of process and design parameters, such as rubber material, pressure, initial jaw displacement and friction. Based on the FEA results, a simple, single rubber-pocketed flexible gripper was designed and built. Feasibility experiments were performed to demonstrate and obtain an overall understanding about the capability and limitations of the gripper. It was found that objects with different shapes (cylindrical, prismatic and complex), weight (50 g–20 kg.), and types (egg, steel hemi-spheres, wax cylinders, etc.) could be picked and placed without any loss of control of the object. The range of positioning error for two different part shapes (i.e., prismatic or cylindrical) was found to be 20–90 μm (translational) and 0.03–0.9° (rotational).     

An empirical research for CNC technology implementation in manufacturing SMEs

The aim of this research is to investigate whether CNC technology affects the firm performance and to determine the manufacturing parameters and competitive priorities that are affected by the adoption of CNC technology. In order to understand the effect of CNC adoption on firm performance, CNC user and non-user firms were investigated statistically to determine any significant difference between them. Then, the investigation was carried out on the effect of CNC technology on manufacturing parameters and competitive priorities. For this purpose a sampling pool including 100 SMEs (small and medium sized enterprises) was investigated. Thirty-eight of these SMEs had previously implemented CNC technology. Our findings show that CNC implementation makes a significant difference on firm performance. Similar results were also found in the analysis on manufacturing parameters and competitive priorities indicating that firms gain significant benefits. However, surprisingly no significant difference was found with respect to delivery performance and volume flexibility between the two groups of firms.     

A 5-b 10-GSample/s a/D converter for 10-gb/s optical receivers

A 5-b flash A/D converter (ADC) is developed in an 0.18-/spl mu/m SiGe BiCMOS that supports sampling rates of 10 Gsample/s. The ADC is optimized to operate in digital equalizers for 10-Gb/s optical receivers, where the ADC has to deliver over three effective number of bits (ENOBs) at Nyquist. A fully differential flash ADC incorporating a wide-band track-and-hold amplifier (THA), a differential resistive ladder, an interpolation technique, and a high-speed comparator design is derived to resolve the aperture jitter and metastability error. The ADC achieves better than 4.1 effective bits for lower input frequencies and three effective bits for Nyquist input at 10 GS/s. The ADC dissipates about 3.6 W at the maximum clock rate of 10 GS/s while operating from dual -3.7/-3V supplies and occupies 3/spl times/3mm/sup 2/ of chip area.     

Simulation of springback variation in forming of advanced high strength steels

Variations in the mechanical and dimensional properties of the incoming material, lubrication and other forming process parameters are the main causes of springback variation. Variation of springback prevents the applicability of the springback prediction and compensation techniques. Hence, it leads to amplified variations and problems during assembly of the stamped components, in turn, resulting in quality issues. To predict the variation of springback and to improve the robustness of the forming process, variation simulation analysis could be adopted in the early design stage. Design of experiment (DOE) and finite element analysis (FEA) approach was used for the variation simulation and analysis of the springback for advanced high strength steel (AHSS) parts. To avoid the issues caused by the deterministic FEA simulation, random number generation was used to introduce uncertainties in DOE. This approach was, then, applied to investigate the effects of variations in material, blank holder force and friction on the springback variation for an open-channel shaped part made of dual phase (DP) steel. This approach provides a rapid and accurate understanding of the influence of the random process variations on the springback variation of the formed part using FEA techniques eliminating the need for lengthy and costly physical experiments.     

Spherical wave expansion of the time-domain free-space dyadic Green's function

The importance of expanding Green's functions, particularly free-space Green's functions in terms of orthogonal wave functions is practically self-evident when frequency domain scattering problems are of interest. With the relatively recent and widespread interest in time-domain scattering problems, similar expansions of Green's functions are expected to be useful in the time-domain. In this paper, an expression, expanded in terms of orthogonal spherical vector wave functions, for the time-domain free-space dyadic Green's function is presented and scattering by a perfectly conducting sphere is studied as an application to check numerically the validity and to demonstrate the utility of this expression.     

Physical and surface properties of polyurethane hydrogels in relation with their chemical structure

Polyethylene glycol (PEG)/castor oil (CO)‐based polyurethanes were prepared by one‐shot bulk polymerization method with the potential for biomedical applications. Hexamethylene diisocyanate and 1,4‐buthane diol were used as diisocyanate component and chain extender, respectively. Polyurethanes were prepared (1) with crosslinker and catalyst, (2) with crosslinker and without catalyst, and (3) without crosslinker and catalyst. The effects of the ratio of CO to PEG, and presence/absence of the crosslinker and catalyst on some physical and surface properties of the polyurethanes were investigated. The glass transition temperatures of prepared polyurethanes are below room temperature. The swelling ratio increased and the water contact angle decreased with increasing amount of PEG in polymer structure. The samples prepared with crosslinker and without catalyst showed the highest swelling ratio. Gas permeability of the samples was measured in a gas permeability system and surface roughness was determined by scanning electron microscope and atomic force microscope. Protein adsorption studies were performed for the samples synthesized without crosslinker and catalyst by using bovine serum albumin and bovine serum fibrinogen. Unexpected results were obtained for the samples which have low contact angles. They exhibited relatively high protein adsorption. POLYM. ENG. SCI., 54:1182–1191, 2014. © 2013 Society of Plastics Engineers