Abstract: Unidirectional solidification is preferred to multidirectional solidification for growing crystals in a particular direction. An experimental set-up consisting of Bridgman type of upward directional solidification was employed for the present investigation. The main aim of the present investigation was to assess the effect of unidirectional upward solidification on the segregation of off-eutectic Pb-Sn alloys at different translational speeds of the experimental set-up. Solidification experiments were conducted on hypoeutectic and hypereutectic Lead-Tin alloys. Different combinations of growth rate V and composition Co. were used to investigate their effect on longitudinal macro segregation. Macro segregation along the length of the samples was observed in hypoeutectic Pb-Sn alloys whereas no such macro segregation was observed in hypereutectic alloys. The intensity of longitudinal macro segregation was found to increase with the increase in initial tin content of the alloy, increase in distance from the chill end and decrease in the solidification rate.
Abstract: Shape Memory Alloys (SMA) are used in diverse engineering and medical applications capitalizing on their sensing and actuation capabilities. This is attributed to the high magnitude of recovery strain and recovery stress that they are capable of generating. But shape memory alloys exhibit complex behaviour in the presence of electrical and magnetic fields as well as mechanical stress. Their behaviour in these domains is to be rightly and comprehensively understood if these are to be used in these applications. Over the years finite element analysis has proved to be a powerful tool for studying the behaviour of SMAs under different conditions and has therefore been applied in many important applications. In this paper an attempt has therefore been made to understand the behaviour of an equiatomic NiTi alloy wire under mechanical stress by finite element analysis using commercially available software MSC Marc.Simulation of an SMA wire with 0.5 mm diameter and 351 mm length was carried out in uniaxial tension by finite element analysis. The simulation involves three stages: geometric modelling using the software MSC.Patran. Finite element modelling also uses the same software, and finally arriving at the solution using the software MSC.Marc.The finte element model is created by meshing the geometric model using Element type Tetmesh4. Boundary conditions are then applied using MSC Mentat software followed by arriving at the solution using Auricchio model. The stress-strain behaviour of the equiatomic NiTinol wire under simple uniaxial tensile loading at different temperatures was simulated.
Abstract: Two kinds of representative volume elements (RVEs) are introduced to represent the experimental γ/γ′ morphology to study the influences of microstructures on the creep behavior of [0 0 1]-oriented single crystal nickel-based superalloys under tensile loading. One RVE (RVE1) is consisted with one cuboidal γ′ phase surrounded by γ phase. The other (RVE2) is constructed by two cuboidal γ′ phases and one rectangle γ′ phase. A raft criterion is implemented into a user subroutine to predict the rafting type. The misfit stress is considered by different thermal expansion coefficients of the two phases. The rafting type is correctly predicted. The evolutions of the stresses distributions are discussed.
Abstract: In this work we deposited a Ge thin layer under or upon Cu-Zn-Sn-S precursor by sputtering, followed by selenization process to obtain Ge doped CZTSSe thin films. A comparison of structural, morphology and optoelectrical property on Ge doped CZTSSe thin films with different Ge layer position was studied. It was found that even a little amount of Ge doping could affect the crystallization of CZTSSe grains. The solar cells based on two kinds of precursors both had VOC improvement compared with undoped CZTSSe solar cell. However, due to the inner stress in CZTSSe thin film, cracks appeared between the interface of buffer layer and window layer in CZTSSe solar cell with Ge bottom layer, leading to the decrease of conversion efficiency. With the help of Ge in reducing bulk recombination, CZTSSe solar cell based on Cu-Zn-Sn-S precursor with Ge top layer had a conversion efficiency of 5.38%, in contrast to 3.01% and 4.30% of CZTSSe solar cell with Ge bottom layer and undoped CZTSSe solar cell, respectively.
Abstract: Micro-Si films were deposited using Ar diluted SiH4 gaseous mixture by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD). The effects of the substrate temperature on microstructure and electrical conductivity of micro-Si film were investigated. The results show that, with the increasing of substrate temperature, crystallinity and grain size increased monotonously, of which a competing balance would determine the electrical conductivity of micro-Si films. Based on these results, relatively small grain size and appropriate crystallinity would be beneficial to improve the electrical properties of micro-Si films.
Abstract: Our work consists to the deposition of copper oxide (CuO) thin films onto glass substrates by the spray pyrolysis method. The precursor solution was copper chloride of 0.1 M and the deposition rate was 5 ml/h. The time of spray varied between 5 and 20 min and the substrate temperature was kept at 350°C. The structural, optical and electrical properties of CuO films were investigated, as a function of the spray time, by X-ray diffraction (XRD), Raman scattering, UV-visible spectroscopy in addition to the measurements of the thickness and the electrical resistivity. The obtained results indicated that our films were polycrystalline with a preferential orientation along the (111) planes. The peaks intensity as well as the grain size increased as a function of the spray time indicating the improvement of the films crystalline structure. The Raman spectroscopy confirmed the formation of the CuO phase. The UV-visible transmission varied between 36% and 53% and the band gap energy decreased from 2 to 1.72 eV as a function of the spray time. The electrical resistivity of the films decreased from 514 to 72 kΩcm and correlated with the decrease of the band gap energy and the increase of the grain size.
Abstract: The nonlinear refraction and absorption properties of a PEI (phthalocyanine indium) tetrasulphonated chlorinated phthalocyanine electrostatic self-assembled film were studied using a simple and high sensitivity technique. We adopted picosecond laser pulses as source light and modified top-hat Zscan technique with a disk and a small aperture to explore the nonlinear refraction of the film. Experimental results show that the measuring sensitivity is increased by two orders of magnitude. Through theoretical fitting, we obtain the nonlinear refraction index and nonlinear absorption coefficients of the film are 2.1×10-14 m2/W and 2.4×10-7 m/W, respectively.
Abstract: Commercial production of synthetic resin has begun at the beginning of the XX century. In 1950s in the USA, small-span dome roofs, scanner assemblies and spherical hangars for radars made of plastic began to appear. Later, invention of reinforced plastics gave a possibility to use them in thin-walled shells for civil and industrial buildings. The subject of the paper associates with today’s renewed interest in thin shells. The modern theoretical base of strength analyses of composite structures give a possibility to design different structures and buildings. The possibility of the application of composites as the basic elements of thin-walled shell structures of industrial and civil purpose are illustrated by the concrete examples. The paper presents information on the well-known composite shells of positive Gaussian curvature in the form of spherical and umbrella domes or with more complex middle surfaces and presents materials that are absent in other publications. The paper contains 9 figures and 15 references.
Abstract: In this article greencomposites based on gypsum reinforced with date palm fibers (DPF) were fabricated and investigated experimentally in terms of thermal and mechanical properties. This paper deals with two aspects, the first one is a study on the influence of fibers sizes and content on thermal diffusivity and Young’s modulus of date palm fibers (DPF) reinforced gypsum composite. The second one is an experimental correlation investigation between Young’s modulus and thermal properties (thermal conductivity, thermal diffusivity). According to the results of this study, the Young’s modulus and the thermal diffusivity of the greencomposites is mainly influenced by the interfacial adhesion between the matrix and fibers. The experimental correlation between Young’s modulus and thermal properties shows variant results.