Finite element modeling of transient heat transfer and microstructural evolution in welds: Part II. Modeling of grain growth in austenitic stainless steels

During welding, structures are subjected to localized heating and cooling cycles, as described in Part I.[1] A mathematical model is proposed to determine the metallurgical changes that occur in austenitic stainless steel due to the welding thermal cycle. The proposed kinetic model computes the austenite grain growth as a function of time and temperature. It is based on a Zener pinning grain growth model. The results obtained indicate that the model is in good agreement with the experimental data reported in the literature. Furthermore, it was observed that rewriting the kinetic constant in the grain growth equation as a function of the peak temperature led to improved results for the majority of the cases examined.     

Calendering analysis without the lubrication approximation

A general-purpose finite-element program has been used to simulate the flow of Newtonian, power-law, and viscoelastic fluids in calendering. The analysis is fully two-dimensional and does not make use of the lubrication approximation. Isothermal and nonisothermal calendering is studied and the results are compared with predictions from the lubrication approximation. The free surface is determined and circulatory flow patterns are predicted in the melt bank. Detailed calculations have been performed for a rigid poly(vinyl chloride) (PVC) resin that exhibits slip at the wall using rheological data for the melt and machine parameters. The results include determination of the shape and location of the free surface, vortex patterns, temperature and pressure distributions, and predictions of roll-separating force, torque, and power consumption. Comparisons are made with experimental data available in the literature.     

Fuzzy reliability analysis of nanocomposite ZnO beams using hybrid analytical-intelligent method

A hybrid analytical-intelligent approach is proposed for fuzzy reliability analysis of the composite beams reinforced by zinc oxide (ZnO) nanoparticle. The fuzzy reliability index corresponding to buckling failure mode of nanocomposite beam under thickness-direction external voltage is computed based on three-levels: (1) fuzzy analysis, (2) reliability analysis and (3) analytical buckling analysis. In fuzzy analysis level, an improved gravitational search algorithm has been applied to determine uncertainty interval for membership levels of reliability index. The adaptive formulation with a dynamical self-adjusting process is used for reliability analysis level based on conjugate first-order reliability method (FORM). The self-adjusting term in conjugate sensitivity vector is used to satisfy the sufficient descent condition for controlling instability of FORM formula while the proposed conjugate scalar factor is computed less than the original conjugate FORM, thus it may be provided with the efficient results for the convex problem. The new and previous sensitivity vectors obtained by conjugate and steepest descent vectors dynamically adjusted the proposed conjugate factor. In the buckling analysis level, an exponential theory in conjunction with the method of energy is utilized. Fuzzy random variables including applied voltage, the volume fraction of ZnO, thickness of beam, spring constant and shear constant of the foundation are considered in studied nanocomposite beam. Survey results indicated that the proposed method can provide stable and acceptable fuzzy membership functions for parametric study. Moreover, the ratio of length to thickness and spring constant of foundation are the more sensitive parameters which affect fuzzy reliability index significantly.

     

An isogeometrical approach to structural topology optimization by optimality criteria

The Isogeometric Analysis (IA) method is applied for structural topology optimization instead of finite elements. For this purpose, a control point based Solid Isotropic Material with Penalization (SIMP) method is employed and the material density is considered as a continuous function throughout the design domain and approximated by the Non-Uniform Rational B-Spline (NURBS) basis functions. To prevent the formation of layouts with porous media, a penalization technique similar to the SIMP method is used. For optimization an optimality criteria is derived and implemented. A few examples are presented to demonstrate the performance of the method. It is shown that, dissimilar to the element based SIMP topology optimization, the resulted layouts by this method are independent of the number of the discretizing control points and checkerboard free.     

A numerical study of the effect of normal stresses and elongational viscosity on entry vortex growth and extrudate swell

A general-purpose finite element program has been used to simulate the flow of a typical polystyrene melt in the entry and exit regions of a slit die. Instead of using a general viscoelastic constitutive equation, simplified models were used that include correlations based on experimental data available in the literature for the shear and elongational viscosities and the normal stresses. With such simple models convergence of the iterative scheme is extended to relatively high Deborah numbers (De ≈ 5). The models predict vortex growth in the entry region and an increase of extrudate swell at the exit in qualitative agreement with experimental observations. It was found that the normal stresses are primarily responsible for these phenomena, while the elongational viscosity tends to increase the end (Bagley) correction and decrease the swelling.     

Your comments matter: incorporating viewers’ comments for ranking online video content using bibliometrics

ABSTRACT

The quality of user-generated content over World Wide Web media is a matter of serious concern for both creators and users. To measure the quality of content, webometric techniques are commonly used. In recent times, bibliometric techniques have been introduced to good effect for evaluation of the quality of user-generated content, which were originally used for scholarly data. However, the application of bibliometric techniques to evaluate the quality of YouTube content is limited to h-index and g-index considering only views. This paper advocates for and demonstrates the adaptation of existing Bibliometric indices including h-index, g-index and M-index exploiting both views and comments and proposes three indices h_vc, g_vc and m_vc for YouTube video channel ranking. The empirical results prove that the proposed indices using views along with the comments outperform the existing approaches on a real-world dataset of YouTube.     

Investigation of deep drawing concept of multi-point forming process in terms of prevalent defects

Multi-point forming is a novel flexible process that is economically suitable for both rapid prototyping and batch production of sheet metal parts. This technique is established based on altering rigid dies by matrices of adjustable punch elements. In this paper, the basic principle of this technique is implemented on deep drawing process. A reconfigurable die was constructed to investigate the multi-point deep drawing process. AA 2024-O Aluminum alloy was designated as test material. The formed specimens were evaluated in terms of dimpling defect, rupture, thickness distribution and dimensional accuracy. The onset of rupture was predicted by integrating the forming limit diagram of employed material with finite element Code. The predicted results were in a reasonable agreement with the experimental tests. It was found that for complete elimination of dimpling defect and acquiring maximum drawing depth, the proper allocation of elastic layer parameters such as thickness and hardness was crucial. The conducted investigations indicated that, in general, dimensional accuracy of formed parts was acceptable. However, for areas with sharp changes in geometry such as corners and side walls, deviation from desired geometry was evident. This phenomenon was remarkably dominant for manufactured parts utilizing softer elastic layer.