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A Simple Locking-Alleviated 4-Node Mixed-Collocation Finite Element with Over-Integration, for Homogeneous or Functionally-Graded or Thick-Section Laminated Composite Beams
Get PDFIn this study, a simple 4-node locking-alleviated mixed finite element (denoted as CEQ4) is developed, for the modeling of homogeneous or functionally graded or laminated thick-section composite beam structures, without using higher-order (in the thickness direction) or layer-wise zig-zag theories of composite laminates which are widely popularized in current literature. Following the work of [Dong and Atluri (2011)], the present element independently assumes a 5-parameter linearly-varying Cartesian strain field. The independently assumed Cartesian strains are related to the Cartesian strains derived from mesh-based Cartesian displacement interpolations, by exactly enforcing 5 pre-defined constraints at 5 pre-selected collocation points. The constraints are rationally defined to capture the basic kinematics of the 4-node element, and to accurately model each deformation mode of tension, bending, and shear. A 2 by 2 Gauss quadrature is used when each element is used to model a piece of a homogeneous material or structure, but over-integration (using a higher-order Gauss Quadrature, a layer-wise Gauss Quadrature, or a simple Trapezoidal Rule in the thickness direction) is necessary if functionally-graded materials or thick-section laminated composite structures are considered. Through several numerical examples, it is clearly shown that the present CEQ4 is much more accurate than the well-known Pian-Sumihara (1984) element as well as the primal four-node element, for the modeling of homogeneous beams. For functionally-graded materials, the presently-developed element can accurately capture the stress distribution even when very few elements are used; but the Pian-Sumihara element fails, because the assumption of linearly-varying stressfield is generally invalid unless a very fine mesh is used in the thickness direction. For thick-section laminated composite beams, reasonably accurate solutions (for axial as well as transverse stresses) are obtained even when only one CEQ4 element is used in the thickness direction. Without using higher-order theories or layer-wise zig-zag assumptions for displacement or stress fields in the thickness direction, for thick-section laminates, the present method can accurately compute the jumps in axial stresses at the interfaces of layers. Extension of the present CEQ4 concept to C0 elements of higher-order, for plates and shells as well as for multi-physics will be pursued in future studies
Fabrication of Functionally Gradient Cemented Carbide with Ultrafine Grains
Get PDFAt present, the functionally gradient cemented carbide (FGCC) substrate with enrich cobalt on surface is mainly formed from medium grained WC grains. In order to further improve the properties of gradient cemented carbides, the ultrafine powder was chosen in this study and the functionally gradient cemented carbide with ultrafine grains was prepared by a two-step process, where the cemented carbide is first lower pressure pre-sintered and then subjected to a gradient sintering. The results show that it is possible to form gradient layer with enriched cobalt on surface by this method and also the grain growth can be inhibited by low pressure pre-sintering. Ultrafine grain gradient cemented carbide was fabricated after the gradient sintering, the thickness of gradient layer was about 43μm and the average grain size of WC is about 0.42μm. The formational mechanism of the functionally gradient cemented carbide with ultrafine grains are discussed through analyzing the influence of ultrafine microstructure, which was obtain by lower pressure pre-sintering, on atomic diffusion and grain growth during gradient sintering process
High Velocity Impact Behaviour of Layered Steel Fibre Reinforced Cementitious Composite (SFRCC) Panels
Get PDFBehaviour of layered steel fibre reinforced cementitious composite (SFRCC) panels is studied under high velocity impact of short projectiles. The panels consist of slurry infiltrated fibre concrete (SIFCON) layers in external faces and an intermediate (core) layer of latex modified concrete (LMC) and steel wire mesh embedded in cement sand slurry. In order to minimize acoustic impedance mismatch at the interfaces, judiciously selected materials are provided in the layers with appropriate lay-up sequences. For relative evaluation of high velocity impact performances of these panels', impact experiments are conducted in controlled environment. Two most commonly used types of short projectiles having calibre diameter of 5.56 mm and 7.62 mm are used in this study. Various important response parameters like depth of penetration (DOP), crater size, spalling, and cracking in the panels are considered for the performance evaluation. This paper presents the results of experimental study conducted on SFRCC panels. Considering the results obtained from experimental study, relative assessment of impact performances of SFRCC panels is carried out with respect to the materials of core layer. Influence of steel fibre volume on impact performance of the panels is also investigated and expressions are proposed based on regression analysis. In order to determine the residual impact resistance of the SFRCC panel after first hit, the same panel was impacted consecutively two to three times, generally within the damage zone of the first hit. Promising potential to resist high velocity impact is exhibited by the SFRCC panels. The structural integrity of the SFRCC panels is found intact even under multiple hits
Design, Fabrication, Characterization and Simulation of PIP-SiC/SiC Composites
Get PDFContinuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have been studied and developed for high temperature and fusion applications. Polymer impregnation and pyrolysis (PIP) is a conventional technique for fabricating SiC/SiC composites. In this research, KD-1 SiC fibers were employed as reinforcements, a series of coatings such as pyrocarbon (PyC), SiC and carbon nanotubes (CNTs) were synthesized as interphases, PCS and LPVCS were used as precursors and SiC/SiC composites were prepared via the PIP method. The mechanical properties of the SiC/SiC composites were characterized. Relationship between the interphase shear strength and the fracture toughness of the composites was established. X-ray tomographic scans of the SiC/SiC composites were performed and the closed porosities of the composites were calculated. The compatibility of the SiC/SiC composites with liquid LiPb at 800 °C and 1000 °C was investigated. High-resolution synchrotron X-ray tomography was applied to the SiC/SiC composite and digital volume correlation was employed for Hertzian indentation testing of the SiC/SiC composite. A Cellular Automata integrated with Finite Elements (CAFE) method was developed to account for the effect of microstructure on the fracture behavior of the SiC/SiC composite
Magneto-Mechanical Finite Element Analysis of Single Crystalline Ni2MnGa Ferromagnetic Shape Memory Alloy
Get PDFBased on an existing micromechanical constitutive model for Ni2MnGa ferromagnetic shape memory alloy single crystals, a three-dimensional quasi-static isothermal incremental constitutive model that is suitable for finite element analysis is derived by using Hamilton's variational principle. This equation sets up the coupling relation between the magnetic vector potential and the mechanical displacement. By using the incremental equation and ANSYS software, the mechanical behaviors of martensitic variant reorientation for Ni2MnGa single crystals are analyzed under magneto-mechanical coupling action. And the finite element results agree well with the experimental data. The methods used in the paper can well describe the mechanical behaviors of the material in complex fields
Prediction of Fracture Parameters of High Strength and Ultra-High Strength Concrete Beams using Minimax Probability Machine Regression and Extreme Learning Machine
Get PDFThis paper deals with the development of models for prediction of facture parameters, namely, fracture energy and ultimate load of high strength and ultra high strength concrete based on Minimax Probability Machine Regression (MPMR) and Extreme Learning Machine (ELM). MPMR is developed based on Minimax Probability Machine Classification (MPMC). ELM is the modified version of Single Hidden Layer Feed Foreword Network (SLFN). MPMR and ELM has been used as regression techniques. Mathematical models have been developed in the form of relation between several input variables such as beam dimensions, water cement ratio, compressive strength, split tensile strength, notch depth, and modulus of elasticity and output is fracture energy and ultimate load A total of 87 data sets (input-output pairs) are used, 61 of which are used to train the model and 26 are used to test the models. The data-sets used in this study are derived from experimental results. A comparative study has been presented between the developed MPMR and ELM models. The results showed that the developed models give reasonable performance for prediction of fracture energy and ultimate load
Measurement Techniques of Torsional Vibration in Rotating Shafts
Get PDFThe measurement of torsional vibration is a common practice in certain fields, such as the automotive industry, power generation, or large alternative engines. Similarly, functional analysis and diagnostic of other equipment, which are not traditionally measured, can benefit greatly from this type of measurement. This review discusses some techniques used in industry to measure torsional vibration, briefly describing the types of sensors used and the transduction procedures. Choosing the most appropriate technique in each case not only responds to economic reasons, but also to other conditions of the given equipment, such as its design, coupled machines or devices, functional status and operating environment, and the possibilities to install the instrumentation
Emerging Trends in Terahertz Metamaterial Applications
Get PDFThe terahertz spectrum of electromagnetic waves is finding its position in various applications of day to day life because of its unique properties, including the penetration through opaque materials. Naturally occurring materials in this range are rare due to the display of a natural breakpoint of both electric, and magnetic resonances in these materials. However recent advances in artificially engineered materials, which show resonance in this region are able to harness desirable properties in the terahertz region. In this paper, terahertz design and fabrication issues have been explored along with their applications. A brief review of metamaterial terahertz applications has been carried out including metamaterial absorbers, filters, modulators, switches, lenses, and cloaking structures. The various patterns of metamaterial unit cells are discussed elaborately along with the possibility of flexible active terahertz structures
Some Applications of Metamaterial Resonators Based on Symmetry Properties
Get PDFMetamaterial resonators are electrically small resonant particles useful for the implementation of effective media metamaterials. In this paper, some applications of metamaterial resonators (such as the split ring resonator -SRR-, the complementary split ring resonator -CSRR-, the folded stepped impedance resonator -SIR-, and the electric LC resonator), that exploit the symmetry properties of transmission lines loaded with such symmetric particles, are reviewed. This covers differential (balanced) lines with common mode suppression, linear and angular displacement sensors (including alignment sensors), angular velocity sensors, and radiofrequency barcodes. Advantages and drawbacks as compared to existing implementations are also discussed
Liquid Spray Impact onto Flat and Rigid Walls: Formation and Spreading of Accumulated Wall Film
Get PDFThis study presents a combined experimental and theoretical investigation on the formation and spreading of a liquid film on a flat and rigid wall due to spray impact. A dual-mode phase Doppler instrument is used to characterise the spray while the average film thickness is measured using a high-speed CCD camera. The experimental results are complemented with theoretical expressions derived under the assumption that the spray is stationary. A new model for the prediction of the average wall film thickness is formulated taking into account the mean Reynolds number of the impacting drops, the flux density of the impacting droplets, and the average drop diameter. The theoretically determined average film thickness exhibits a good agreement with the measured data when the film can be considered thin