On the tube hydroforming process using rectangular,trapezoidal, and trapezoid-sectional dies: modeling and experiments

It is generally known that the contact between tube and die, in the case of tube hydroforming process, leads to the appearance of friction effects. In this context, there are many different models for representing friction and many different tests to evaluate it. In the present paper, the pin-on-disk test has been used and the theoretical model of Orban-2007 has been chosen and developed to evaluate friction coefficient. The main goal is to prove the capacity of theoretical model to present the friction conditions in comparison with the pin-on-disk test. From the Orban model, values of 0.05 and 0.25 of friction coefficient have been found under lubricated and dry tests, respectively. On the other hand, by the classical pin-on-disk test, other values were experimentally obtained as friction coefficient at the copper/steel interface. In the case of pure expansion hydroforming, based on an internal pressure loading only, a “corner filling” test has been run for tube hydroforming. Both dry and lubricated contacts have been considered. Various configurations and shapes have been studied such as the rectangular, trapezoidal, and trapezoid-sectional dies. Finite element simulations with 3D shell and 3D solid models have been performed with different values of friction coefficients. From the main results, it was found that the critical thinning occurs in the transition zone for the square and rectangular section die and in the sharp angle for the trapezoidal and trapezoid-sectional die. The comparison between numerical data and experimental results shows a good agreement. Moreover, the thickness distribution along the cross section is relatively consistent with those measured for the 3D shell model; however, the 3D solid models do not provide a realistic representation of the thickness distribution in the shaped tube. Finally, the results obtained from the theoretical model were more efficient than the results obtained from the pin-on-disk test.     

Enhanced Heat Transfer Properties of Magnetite Nanofluids due to Neel and Brownian Relaxation Mechanisms

Fe₃O₄ nanoparticles were prepared through solvo-thermal method for further heat transfer applications. TEM, XRD, TGA, and VSM were applied to characterize the obtained nanoparticles. XRD pattern confirmed that nanoparticles were composed of 6-nm crystallites; however, TEM images showed the formation of ca. 75-nm highly dispersed magnetite clusters, made up of about 6-nm nanoparticles. Since, VSM analysis confirmed the superparamagnetic characteristics of Fe₃O₄ nanoclusters, heat transfer properties of the resulting nanofluids were studied to investigate the influence of the magnetic field on the behavior of the magnetite-based nanofluids. The findings indicated that the convective heat transfer coefficient increased up to 48% and 15%, respectively, for nanofluids containing 0.005 wt% magnetite particles dispersed in water and EG, when the frequency of the alternating magnetic field was changed from 50 Hz to 1 MHz. According to the results, compared to the water-based nanofluids, at higher field amplitudes, the h enhancements of EG-based ones were more pronounced, for instance, at H₀ = 36,000 A/m, the h measurements are augmented by about 74% and 109%, respectively, compared to the water and EG as the base fluids. These findings could be explained by the use of specific lost powers of the nanofluids in the exposure of an external alternating magnetic field.     

Nested and interleaved direct sequence spread spectrum to enhance CDMA security and bit error rate performance

Two new methods, the nested direct sequence spread spectrum and interleaved direct sequence spread spectrum, are introduced in view of the previously investigated spread spectrum methods. In the nested direct sequence method, the security is maintained, and the cross‐correlation between different codes resulting in multi‐user interference that corresponds to BER performance is improved, while in the interleaved direct sequence spread spectrum, the security is improved and BER performance is maintained. Both methods are analysed by mathematical relations as well as computer simulations and are compared with the existing methods. Copyright © 2016 John Wiley & Sons, Ltd.     

Inhibition of the mesoamygdala dopaminergic pathway impairs the retrieval of conditioned fear associations.

Previous findings have demonstrated that systemic dopaminergic manipulations impair the retrieval of Pavlovian conditioned fear. A second-order fear-conditioning paradigm was used to test whether the dopaminergic projection from the ventral tegmental area (VTA) to the lateral and basal amygdala (LBA) can affect conditioned fear. Phase 1 entailed conditioned stimulus-unconditioned stimulus (CS1-US) pairings. In Phase 2, drugs were infused in either the LBA or VTA prior to pairings of CS2 (a second cue) with CS1. In Phase 3, freezing behavior elicited by CS2 was tested without drugs. Infusions of the D2 agonist quinpirole into the VTA or of the D1 antagonist SCH 23390 into the LBA caused a decrease in freezing to CS2. Both manipulations decrease D1 receptor activation in the LBA. Infusions of the D1 agonist SKF 38393 into the LBA had no effect. This pattern of results is consistent with the hypothesis that the VTA-LBA dopaminergic projection modulates the retrieval of an association between a CS and footshock US. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nondestructive Evaluation of Fiberglass Reinforced Plastic Subjected to Combined Localized Heat Damage and Fatigue Damage Using Acoustic Emission

The effect of fatigue damage to unidirectional fiberglass composite specimens with prior contact heat damage was investigated. After damaging the specimens by contacting them to a hot tip at 360°C, the specimens were subjected to fatigue loading at cyclic stress amplitude corresponding to 65% of the specimens' ultimate tensile strength. The fatigue experiments was halted after 3,000 cycles. The specimens were then subjected to tensile tests while monitoring their acoustic emission (AE) activity. In addition, acoustic emission activities of undamaged and contact heat-damaged specimens were monitored during tensile tests for comparison with specimens with combined fatigue and heat damage. AE activities of all specimens can be categorized into three regions: an early rise in activity, a relatively dormant period in activity, and a high exponential activity before failure. The early rise in activity did not appear on the specimens with combined contact heat and fatigue damage. For undamaged and contact heat-damaged specimens, the period of the dormant activity was independent of the contact heat duration of less than 15 minutes. However, the period was a function of the contact heat duration for combined contact heat and fatigue damaged specimens. Analyzing event duration distribution identified micro-mechanisms of the damage growth upon tensile loading. AE-stress delay concept was used to predict the state of the damage in the composite. A correlation between stress delay parameter and damage parameter was obtained for all of the specimens. Fatigue life of contact heat damaged specimen was also studied. It was found that localized heat damage reduced the fatigue life significantly. Loss of matrix to transfer the load to the fibers uniformly was believed to be responsible for the reduction in the fatigue life.     

Estimation of permeation rate of chemicals through elastometric materials

Elastometric materials are used as barriers to protect workers against exposure to chemicals. The effectiveness of a polymer as a chemical protective material therefore depends on the rate of the permeation of chemicals through it. The permeation rate depends on the solubility and the diffusion coefficient of chemicals in the materials. The diffusion coefficient itself is a strong function of concentration of the chemicals in the polymeric material. Permeation rates can be measured directly using a permeation cell or they can be calculated from the solubility and the diffusion coefficient data. Sorption/desorption experiments can be used to determine solubility and an expression for the diffusion coefficient in terms of concentration. Experiments were conducted for the sorption and desorption of ethyl acetate in three glove (one butyl and two neoprene materials) and two garment (neoprene and chlorinated polyethylene) materials. The data collected were used to estimate the steady‐state permeation rates of ethyl acetate through the materials. The results of the experiments show that the solubility of ethyl acetate in butyl rubber is 0.795 g/cm³, and the steady‐state permeation rate is 0.32 μg cm⁻² s⁻¹. The solubility of the chemical through the three neoprene materials is in the range of 2.25–5.31 g/cm³, and the steady‐state permeation rates vary from 27 to 43 μg cm⁻² s⁻¹. The solubility of ethyl acetate in the chlorinated polyethylene is 7.14 g/cm³, and the steady‐state permeation rate is 62.43 μg cm⁻² s⁻¹. The experimental method is very simple to use and it requires a small sample of the material (less than 1 cm²) and only a few milliliters of the chemical. Sorption/desorption experiments can also provide information on the amount of additives extracted from an elastomeric material during contact with a chemical. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1265–1272, 2001     

Effect of Bonding Temperature on Microstructure and Mechanical Properties of WC–Co/Steel Diffusion Brazed Joint

In this work, the diffusion brazing of AISI 4145 steel to WC–Co cemented carbide using RBCuZn-D interlayer with bonding temperature values of 930, 960, 990 and 1020 °C was studied. The microstructure of the joint zone was evaluated by scanning electron microscope (SEM) and X-ray diffraction (XRD). Vickers microhardness and shear strength tests were performed to investigate mechanical behaviors of the brazed joints. The XRD and SEM results indicated that with increase of bonding temperature, the elements readily diffused along the interface and formed various compounds such as γ, α and β and Co₃W₃C. The results also showed that with the increase of bonding temperature from 930 to 960 °C, a sound metallurgical bond was produced, however in higher bonding temperatures (990 and 1020 °C) a decrease in mechanical properties of the joints was observed which could be due to the excessive zinc evaporation, interface heterogeneity and voids formation. The maximum shear strength of 425 MPa was obtained for the bond made at 960 °C.     

Petrographic and petrophysical characterization of some Paleozoic rocks,Um Bogma area,Southwest Sinai,Egypt

Sixty-two samples were collected from the five formations at Um Bogma area, (Southwest Sinai, Egypt). Nine samples were collected from Sarabit El Khedim Formation, ten samples were collected from Abu Hamata Formation, eighteen samples were collected from Adedia Formation, eight samples were collected from Um Bogma Formation and eighteen samples were collected from Abu Thora Formation.The Paleozoic rocks at Um Bogma area, consist mainly of sandstones, siltstones, shales, limestone and dolostones, which are unconformably overlie igneous and metamorphic rocks (granite, diorite and gneiss) of Precambrian age.The petrographic studies were applied to identify different rock units, different facies and its diagenetic history and to reveal its effect on the storage capacity properties. Different types of porosity (oversized, intergranular, fracture and vuggy porosities) have been identified based on the petrographic investigation of the studied thin sections.The Paleozoic sandstone rock samples are characterized by porosity average about 19% for Facies 1 (quartz wack) and about 18%for Facies 2 (quartz arenite) and permeability average 420?mD for Facies 1 (quartz wack) and 690?mD for Facies 2 (quartz arenite), so these rocks can be considered as good reservoir rocks. The Paleozoic carbonate rock samples (Facies 3) are characterized by poor porosity (less than 7%) and very low permeability (less than 0.5?mD), which caused by matrix and diagenetic processes and refer to bad reservoir rocks.Porosity can be linked to the two derived electrical properties (formation resistivity factor and electrical tortuosity) of the studied Paleozoic rocks at Um Bogma area. The electrical tortuosity has significant effects on both permeability and formation resistivity factor. The permeability decreases with increasing electrical tortuosity and the relation between both of them is inverse relationship with good coefficient of correlation. The permeability decreases with increasing electrical tortuosity and the relations between both of them are inverse relationships with high coefficient of correlation. The formation resistivity factor increases with increasing electrical tortuosity and the relations between both of them are positive relationships with a fair to very high coefficient of correlation.     

Current rectification with poly-l-lysine-coated quartz nanopipettes

Ion current rectification with quartz nanopipette electrodes was investigated through the control of the surface charge. The presence and absence of a positively charged poly-l-lysine (PLL) coating resulted in the rectified current with opposite polarity. The results agreed with the theories developed for current-rectifying conical nanopores, suggesting the similar underlying mechanism among asymmetric nanostructure in general. This surface condition dependence can be used as the fundamental principle of multi-purpose real-time in vivo biosensors.     

Volume computed tomography air kerma index and image quality evaluation in Brazil

The aim of this study was to evaluate the image quality of 29 computed tomography (CT) scanners in Brazil and to perform estimations of patient dose and image quality of common CT examinations at these equipment. The volume CT air kerma indexes (C(VOL)) were estimated, using normalised weighted air kerma indexes, supplied by the ImPACT group. The image quality tests were performed using the phantom and accreditation protocol from the American College of Radiology (ACR). The C(VOL) values for head scans varied between 8.7 and 108 mGy. The Hi-res chest examinations presented C(VOL) values varying from 0.4 to 32 mGy. For abdominal scans, the estimated C(VOL) values varied between 4.1 and 94 mGy. This wide variation of air kerma between different centres is related to the scanner type and also to the scanning parameters. The results also showed that the image quality did not attend all ACR CT accreditation requirements.