Abstract: This paper focuses on the electromechanical modelling and analysis of piezolaminated functionally graded polymer composites reinforced with graphene nanoplatelets considering strong electric field nonlinearities. Non-uniform distribution of reinforcement of graphene nanoplatelets is assumed along the thickness direction in multilayer polymer nanocomposites, whereas uniform dispersion GPLs in each layer is assumed. Modified Halpin-Tsai micromechanics is used to determine the effective Young’s modulus of GPLs considering the effects of geometry and dimension changes. Electro-elastic nonlinear constitutive relations are used to model the piezoelectric layers under strong applied electric fields. Through variational formulation, a finite element is derived to model and analyse the layered GPL/polymer composite structures. Various simulations are performed to study the effects of several parameters like distribution pattern and size of GPLs by applying actuation voltages to piezoelectric layers.
Abstract: Hybrid adhesives epoxy-silica-zirconia were prepared and applied to bond aluminum sheet specimens. Silica nanoparticles were synthesized with the sol-gel “in situ” technique utilizing two different precursors, namely tetraethyl orthosilicate (TEOS) and 3 glycidyloxypropyltrimethoxysilane (GPTMS). Zirconia nanoparticles were prepared also with sol-gel technique and added to the hybrid adhesives before curing. The adhesive properties of the prepared materials were improved after performing several physical and chemical treatments to the aluminium specimens. The best apparent shear strength tests were for the adhesive hybrid materials prepared at 100°C with TEOS.
Abstract: Anode surface plays important role for extracellular electron transfer (EET) of exoelectrogenic microbes in microbial fuel cell (MFC). In this report, the electrochemical performance of a TiO2 nanorod array modified carbon paper electrode (TiO2 NRs/CP) is greatly improved by controlled chemical etching process. The etching process keeps the array morphology but yields obvious hollows on tops of TiO2 nanorods. The etched electrode (TiO2 NRs-HOT/CP) exhibits better hydrophilicity than carbon paper (CP) and TiO2 NRs/CP electrode as seen from smaller contact angle (CA) and more attached microbes S.loihica PV-4. Meanwhile, the hollows allow higher local concentration of microbial self-secreted flavins that can act as electron mediators for interfacial electron transfer of PV-4 through in-direct pathway. Accordingly, PV-4 produces larger current density at TiO2 NRs-HOT/CP electrode with maximum current density of 0.038 mA cm –2, which was much higher than that at CP electrode, and almost five times higher than that at un-etched TiO2 NRs/CP electrode.
Abstract: The scanning electrochemical microscope (SECM) offers a highly sensitive route to evaluate degradation reactions and protection methods with chemical selectivity by using ion-selective microelectrodes as tips, thus operating SECM potentiometrically. Spatially resolved imaging of electrochemical reactivity related to each component of the investigated material can thus be effectively monitored selectively both in situ and in real time. The applicability of this method has been illustrated using a practical example of a metal-coating system, consisting in the exposure of cut edges of coil-coated galvanized steel to aqueous saline environment. In this contribution, localized pH and zinc(II) ion distributions originated around cut edges of coil coated steel immersed in 1 mM NaCl solution are shown.
Abstract: Finite Element Method (FEM) is one of the most useful techniques to analyze problems in metal forming process because of this technique can reduce cost and time in die design and trial step . This research is aimed to predict the optimal parameters in order to eliminate cracks and wrinkles on automotive deep drawing product “Shell Bar RR Impact RH/LH”. The material was made from high strength steel JSC440W sheet with thickness 1.8 mm. The parameters that had been investigated were blank holder force (BHF) and drawbead restraining force (DBRF). In order to simplify the process, punch and die in the simulation were assumed to be a rigid body, which neglected the small effect of elastic deformation. The material properties assumed to be anisotropic, behaved according to the constitutive equation of power law and deformed elastic-viscoplastic, which followed Barlat 3 components yield function. Most of the defects such as cracks and wrinkles were found during the processes on the parts. In the past, the practical productions were performed by trial and error, which involved high production cost, long lead time and wasted materials. From the results, when decreased blank holder force to 30 tons, cracks on the part were removed but wrinkles had a tendency to increase in part area because of this part is the asymmetrical shape. Finally, applying about drawbead restraining force at 154.49 and 99.75 N/mm could improve product quality. In conclusion, by using the simulation technique, the production quality and performance had been improved.
Abstract: In this study, the forging operations of gear has been modeled. This gear is a part which is manufactured with the help of hot forging industry for reduce the cost. The authors propose to reduce the initial billet volume of AISI 4340 steel for the forged through process optimization using the Finite Element (FE)method. The object of this research was to predict the effect of several parameters, such as effective stress, effective plastic strain, temperature and die contact, on the forming of the gear, utilizing computer simulation and experimental results. For this purpose, Solidworks CAD and Simufact Forming FE software were used for the modeling and analysis of the forging process. The billet volume and the preform design were predefined in order to reduce scrap by using preform type C. The experimental results showed that the initial billet volume was reduced at 32 %, which compared favorably with the simulation result of a 40 % reduction. The maximum preforming force of simulation result was diferent with the experiment result at 18 along with the maximum finishing force of simulation result was different with the experiment result at 11 %. It was also found that the effective stress decreased with increasing the temperature, and the press force decreased when the initial billet volume was decreased, which resulted in a decrease of effective plastic strain as well.
Abstract: This paper aims to report the influence of water vapor on thermal oxide scale grown on incoloy800HT at 850°C. Alloy was prepared in coupons with a surface finishing up to 1200 SiC abrasive paper. Oxidization was performed in tubular furnace at 850°C during 50 hours. The oxidizing gases were varied as a dry oxygen gas and a wet oxygen gas. Thermal oxide morphology was characterized by scanning electron microscopy (SEM). Oxide phases were identified by X-ray diffraction (XRD) and Raman spectroscopy techniques. The oxide multilayers were revealed in all the oxidized samples. Oxide spallation was obviously detected on the samples oxidized under a dry oxygen gas, whereas, the spallation was not detected on the samples oxidized under a wet oxygen gas. Moreover, by water vapor mixing gas, the alloy surface presented a finer oxide. XRD and Raman spectroscopy provided the coincident oxide identification results. The corundum oxide of (Fe,Cr)2O3 and the spinel oxide of (Fe,Cr)3O4 were identified as a typical thermal oxide, however, the oxides were different in stoichiometry. The existence of water vapor promoted a Cr2O3 corundum oxide, whereas, a Fe3O4 spinel oxide was hindered from the outer oxide layer. Hence, water vapor not only clearly influenced on oxide scale morphology but also affected on stoichiometry of (Fe,Cr)2O3 and (Fe,Cr)3O4 solid solution.
Abstract: TiB2 particulate reinforced titanium matrix composites were prepared by mechanical alloying and spark plasma sintering. Volume fraction of TiB2 powders in the composites are 5%, 10%, 15%. The effect of milling time and the volume fraction of reinforcement on microstructure and properties of the composites were studied. The results show that with increasing milling time, the size of powder particles decreases, quantity of them increases, and microstructure of the sintered samples becomes finer and more uniform. When milling time reaches 30h, the trend of powder agglomeration increases, the downward trend of the particle size becomes slowly. With the milling time, the density of titanium matrix composites is on the rise. The density of 10vol%TiB2 particulate reinforced titanium matrix composites can reach 4.799 g/cm3, with 30h milling time and sintering at 900°C. The density and hardness of the composites increase with increasing the volume fraction of TiB2. When the volume fraction of TiB2 is 15%, after milling 10h and sintered at 800°C, the density and hardness of the composites can reach 4.713g/cm3 and HV851.58.
Abstract: The aim of this work was to investigate whether the low alloy steel and the explosively welded metals used for salt caverns equipment's are susceptible to hydrogen degradation. The materials described in this article are cheap and widely used 09G2S low alloy steel and titanium grade1 as a clad material for its superior resistance to corrosive environment joined explosively with low alloy steel S355J2+N. It was observed that at the explosive bonded interface between the base steel and the stainless steel some local melting zones are formed. It was found that the cathodic hydrogen charging causes changes in the microstructure of low alloy steel and decreases the shear strength of bonds and tensile stress as well as the corrosion resistance of clads.