Novel solution for acceleration motion of a vertically falling spherical particle by HPM–Padé approximant

In this paper the acceleration motion of a vertically falling spherical particle in incompressible Newtonian media is investigated. The velocity is evaluated by using homotopy perturbation method (HPM) and Padé approximant which is an analytical solution technique. The current results are then compared with those derived from HPM and the established fourth order Runge–Kutta method in order to verify the accuracy of the proposed method. It is found that this method can achieve more suitable results in comparison to HPM.     

Potency of Different Carbon Sources in Reduction of Microsilica to Synthesize SiC from Mechanically Activated Powder Mixtures

In the present study, the influences of three different types of carbon (carbon black, graphite, and petroleum coke) on SiC synthesis via mechanical activation and sintering were evaluated. In this regard, the phase components, morphology, and the formation mechanism were investigated. SiC nanoparticles were detected to be formed after 4 h of milling and sintering at 1450°C, regardless of the sources of carbon. The carbon types exert their effects on the morphology of the as‐synthesized particles, where carbon black leads to form rod‐like SiC particles and the other two carbon types result in semi‐spherical SiC particles. This is due to the dominant mechanism in the mentioned process. The rod‐like particles obtained from the carbon black‐containing powder were synthesized via the VSL mechanism, whereas the solid‐state reactions occurred to form the SiC particles in the graphite‐ or petroleum coke‐containing samples. In the VSL mechanism, any increase in the milling time leads to facilitate the SiC formation due to entrance of Fe debris, whereas in the other samples (graphite or petroleum coke) the procedure is reversed.     

The application of differential transformation method to nonlinear equations arising in heat transfer

In this paper two nonlinear heat transfer problems were solved by considering variable specific heat coefficient. The calculations are carried out by using differential transformation method (DTM) which is a semi-numerical-analytical solution technique. By using DTM, the nonlinear constrained governing equations are reduced to recurrence relations and related initial conditions are transformed into a set of algebraic equations. The principle of differential transformation is briefly introduced, and then applied for the aforementioned problems. The solutions are subsequently solved by a process of inverse transformation. The current results are then compared with those derived from the variational iteration method (VIM), homotopy perturbation method (HPM), perturbation method (PM) and the exact solutions in order to verify the accuracy of the proposed method. The findings reveal that the DTM can achieve more suitable results in predicting the solution of such problems.     

Exact Solution for Thermal Buckling of Functionally Graded Plates Resting on Elastic Foundations with Various Boundary Conditions

In this article, we investigate the buckling analysis of plates that are made of functionally graded materials (FGMs) resting on two-parameter Pasternak's foundations under thermal loads. Three different thermal loads were considered, i.e., uniform temperature rise (UTR), linear and non-linear temperature distributions (LTD and NTD) through the thickness. The mechanical and thermal properties of functionally graded material (FGM) vary continuously along the plate thickness according to a simple power law distribution. Employing an analytical approach, the five coupled governing stability equations, which are derived based on first-order shear deformation plate theory, are converted into two uncoupled partial differential equations (PDEs). Considering the Levy-type solution, these two PDEs are reduced to two ordinary differential equations (ODEs) with variable coefficients. Then, the ODEs are solved using an exact analytical solution, which is called the power series Frobenius method. The appropriate convergence study and comparison with previously published related articles was employed to verify the accuracy of the proposed method. After such verifications, the effects of parameters such as the plate aspect ratio, side-to-thickness ratio, gradient index, and elastic foundation stiffnesses on the critical buckling temperature difference are illustrated and explained. The critical buckling temperatures of functionally graded rectangular plates with six various boundary conditions are reported for the first time and can serve as benchmark results for researchers to validate their numerical and analytical methods in the future.     

Mechanism of the reversibility of asphaltene precipitation in crude oil

Asphaltene precipitation and deposition occur in petroleum reservoirs as a change in pressure, temperature and liquid phase composition and reduce the oil recovery considerably. In addition to these, asphaltene precipitates may deposit in the pore spaces of reservoir rock and form plugging, which is referred to as a type of formation damage, i.e. permeability reduction. In all cases above, it is of great importance to know under which conditions the asphaltenes precipitate and to what extent precipitated asphaltenes can be re-dissolved. In other words, to what extent the process of asphaltene precipitation is reversible with respect to change in thermodynamic conditions. In present work, a series of experiments was designed and carried out to quantitatively distinguish the reversibility of asphaltene precipitation upon the change in pressure, temperature and liquid composition. Experiments were conducted in non-porous media. Generally it was observed that the asphaltene precipitation is a partial reversible process for oil under study upon temperature change with hysteresis. However, the precipitation of asphaltene as a function of mixture composition and pressure is nearly reversible with a little hysteresis.     

Frequency response of thin film heads with longitudinal andtransverse anisotropy

A transmission surface model (TSM) that analyzes the conduction of flux by rotation and wall motion is reported. It has been used to quantitatively compare the predicted performance of thin-film heads with longitudinal and transverse magnetic anisotropy. The TSM analysis predicts that a transversely oriented type of thin-film head can be operated at much higher frequencies than a longitudinally oriented head. In addition, its group delay dispersion is much less. Finally, its susceptibility to wall pinning is an order of magnitude less. Therefore, it is concluded that the traditional aversion of head designers to the longitudinal orientation is justified for frequencies above several megahertz     

Activity-based costing in flexible manufacturing systems with a case study in a forging industry

The objective of this paper is to apply the activity-based costing (ABC) approach together with traditional costing (TC) for parts costing in flexible manufacturing systems (FMS) with the A(2) level of automation. We propose a new model for the implementation of ABC using the product cost tree concept. First, the required resources and activities for each part are recorded, and then their costs are calculated using the appropriate cost formulae. This model was applied in a forging industry. A comparison and analysis between ABC and TC was then carried out based on the computational results obtained from the case study. The results indicate that the ABC outputs are more reliable than the TC outputs, and thus the ABC approach is a more acceptable tool for parts costing in FMS.     

Brittle fracture in rounded-tip V-shaped notches

Two failure criteria are proposed in this paper for brittle fracture in rounded-tip V-shaped notches under pure mode I loading. One of these criteria is developed based on the mean stress criterion and the other based on the point stress criterion which both are well known failure criteria for investigating brittle fracture in elements containing a sharp crack or a sharp V-notch. To verify the validity of the proposed criteria, first the experimental data reported by other authors from three-point bend (TPB) and four-point bend (FPB) tests on PMMA at −60 °C and Alumina–7% Zirconia ceramic are used. Additionally, some new fracture tests are also carried out on the rounded-tip V-notched semi-circular bend (RV-SCB) specimens made of PMMA for various notch opening angles and different notch tip radii. A very good agreement is shown to exist between the results of the mean stress criterion and the experimental data.     

Brittle fracture assessment of engineering components in the presence of notches: a review

Brittle fracture of notched components has been widely investigated in recent decades both experimentally and theoretically. This is because of designers' concern about catastrophic failure in notched engineering components made of brittle or quasi‐brittle materials. Up to now, extensive studies have been performed on brittle fracture analysis of engineering components weakened by notches of various features under mode I, mode II, mode III and mixed mode loading conditions. In the present paper, the attempt is made to review the research articles published in the open literature on brittle fracture assessment of notched components by means of notch fracture mechanics concepts. The main focus of this paper is on the stress‐based fracture criteria, which are the basis of authors' experience in recent years.     

Fracture assessment of graphite V‐notched and U‐notched specimens by using the cohesive crack model

This article explores the capability of the Cohesive Zone Model in predicting the critical load of blunt notched specimens made of coarse‐grained polycrystalline graphite, a brittle material that has gained the attention of researchers because of its favourable properties for protection against thermal loads. To that aim, 39 different tests on U‐notched and V‐notched specimens made of this material, with loading modes raging from mode I to mixed mode I/II, have been modelled by using the Cohesive Zone Model. The model has been implemented through the embedded crack approach, avoiding thus the necessity of defining the crack trajectory prior to the simulation because it is automatically generated once the maximum principal stress overcomes the tensile strength of the material. The numerical predictions obtained show good agreement with the experimental results.