Abstract: In high entropy alloys (HEA) a disordered solid solution is entropically stabilized, in competition with possible intermediate compounds or phase segregation. It has been reported that disordered solid solutions are stabilized by the presence of five or more elements in the alloys; typically in an equimolar ratio. In the current investigation, the effect of Cu addition on the microstructure of CrFeNi alloy is rationalized by Gibbs free energy calculations. Two phase (both are FCC) solid solution are seen to form in CuCrFeNi alloy. The alloys are prepared by induction melting and are characterized by x-ray diffraction and scanning electron microscopy (in as-cast and annealed state). Enthalpies of mixing were calculated using Miedema's model and the regular solution model. Entropy of mixing is determined by using the Boltzmann's hypothesis.
Abstract: Reports on the alloys formed from immiscible atoms when they are contained in a nano-sized system have initiated several research activities in the recent years. Bridging of the miscibility gap at nanoscale is significant as it has the potential to produce novel alloy materials with useful technological applications. Although the literature contains noticeable number of reports on the formation of solid solution between bulk immiscible atoms, several issues related to phase stability and microstructure remain unaddressed. This article discusses some of these issues using examples from the work done by the author’s research group on isolated nanoparticles of bulk immiscible binary systems such as Ag-Ni, Ag-Fe and Ag-Co.
Abstract: A numerical simulation of the heat-transfer process within polypropylene matrix composite filled with micro-sized aluminium particles using Finite Element Method is proposed in this paper. Three-dimensional spheres-in-cube lattice array models are constructed to simulate the microstructure of composite materials with aluminium content ranging from about 1.5 to 42 vol% and the effective thermal conductivities of the composites are estimated. A commercially available finite-element package ANSYS is used for this numerical analysis. The result shows that the effective thermal conductivity (Keff) increases with increase in the volume fraction of the aluminium in the composites. The simulated values are compared with calculated Keff values obtained from other established correlations such as Rule-of-Mixture (ROM), Maxwell’s model and with published experimental results. This study reveals that the incorporation of aluminium particles results in enhancement of thermal conductivity of polypropylene thereby increasing its heat transportation capability. It is found that with incorporation of about 42 vol% of 100 micron sized aluminium particles thermal conductivity of the composite increases from 0.239 W/m-K to 0.875 W/m-K. This study also shows that the effect of particle size with same volume percentage on thermal conductivity is marginal.
Abstract: The present work predicts the thermal behavior of a hot steel strip analytically where the strip is cooled with water spray. The cooling process is represented by a steady 2-D energy conservation equation. An effective heat transfer coefficient is considered to represent the water spray and the strip surface heat interaction. The solution considers the separation of variables method with appropriate boundary conditions. Finally, the work involves quick evolution of temperature variation in the strip. It is found that the present analytical prediction agrees well with numerical prediction.
Abstract: A technique is proposed to predict crack growth for the estimation of Strain Energy Release Rate (SERR) of Double Cantilever Beam (DCB) bi-metallic specimen, employing ultrasonic Lamb waves. Techniques based on the Time-of-Flight (ToF) of the Turning Lamb Mode (TLM) and Direct Lamb Mode (DLM) explored to determine the crack growth. Sensitivity analysis revealed that the Lamb mode with low velocity is more sensitive to crack growth than that of the high velocity Lamb mode.
Abstract: In the present study, both critical buckling load maximization and face-sheet laminate thickness minimization problems for the composite sandwich panel, subjected to bi-axial compressive loading under various imposed constraints have been investigated using genetic algorithms. In the previously published work, the optimization of simple composite laminate panels with only even number of laminae has been considered [1, 3]. The present work allows the optimization of a composite sandwich panel with both even and odd number of laminae in the face-sheet laminates. Also, the effects of the bending-twisting coupling terms (D16 and D26) in bending stiffness matrix which were neglected in the previous studies [1, 2, 3], are considered in the present work for exact solutions. In addition effect of both balanced and unbalanced face-sheet laminates on the optimum solutions have also been investigated, whereas only balanced laminates were considered in the previous studies [1, 2, 3].
Abstract: Modeling and numerical simulation of aluminum foam filled square tubes under axial impact loading is presented. The foam-filled thin-walled square tubes are modeled as shell wherein, foam core is modeled by incorporating visco-elastic plastic foam model in Altair® RADIOSS. Deformation and energy absorption studies with single, bi-tubular, and multi-tube structure with and without aluminum foam core are carried out for assessing its effectiveness in crashworthiness under the identical conditions. It is observed that the multi-tube structure with foam core modify the deformation modes considerably and results in substantial increase in energy absorption capacity in comparison with the single and multi-tube without foam core. Moreover, the multi-tube foam filled structure shows complicated deformation modes due to the significant effect of stress wave propagation. This study will help automotive industry to design superior crashworthy components with multi-tube foam filled structures and will reduce the experimental trials by conducting the numerical simulations.
Abstract: During the growth of an epitaxial overlayer on a thick substrate (GeSi on Si), an interfacial misfit dislocation becomes energetically favourable on exceeding the critical thickness. In substrates of finite thickness, the value of critical thickness is altered with respect to thick substrates. Thin substrates can bend and partially relax the coherency stresses, thus contributing to the altered value of the critical thickness. The current work aims at simulating the stress state of a growing finite epitaxial overlayer on a substrate of finite thickness, using finite element method. The numerical model is used to calculate the critical thickness for substrates with finite thickness. Eigenstrains will be imposed in selected regions in the domain towards this end. Size of the substrate for which it is not energetically favourable to accommodate a misfit dislocation is determined from the simulations (i.e. the system remains coherent for substrates below this thickness). Important effects arising in the transition regime of substrate thicknesses are also investigated.
Abstract: In the present investigation, free vibration behaviour is studied for the laminated composite skew hypar shells having twist radius of curvature. A higher-order shear deformation theory is employed in the C0 finite element formulation. Higher-order terms in the Taylor’s series expansion are used to represent the higher-order transverse cross sectional deformation modes. The formulation includes Sanders’ approximation for doubly curved shells considering the effect of transverse shear. The structural system is considered to be undamped. The correctness of the formulation is established by comparing the present results of problems with those available in the published literature. The effects of different parameters are studied on the free vibration aspects of laminated composite skew hypar shells. Effect of cross curvature is included in the formulation. The C0 finite element formulation has been done quite efficiently to overcome the problem of C1 continuity associated with the HSDT. The isoparametric FE used in the present model consists of nine nodes with seven nodal unknowns per node. Since there is no result available in the literature based on HSDT on the problem of free vibration of laminated composite skew hypar shells, new results are presented by varying geometry, boundary conditions, ply orientations and skew angles which will serve as benchmark for future researchers.