Sharif Digital Repository

Abstract Sintering response and phase formation during sintering of WC-Co/316L stainless steel composites produced by assembling of powder injection molding (PIM) parts were studied. It is shown that during cosintering a significant mismatch strain (> 4 pct) is developed in the temperature range of 1080° C to 1350° C. This mismatch strain induces biaxial stresses at the interface, leading to interface delamination. Experimental results revealed that sintering at a heating rate of 20 K/min could be used to decrease the  

In this study, the effects of mold constraints and cooling rate on residual stress were analyzed during the shaped casting process. For this purpose, an H-shaped sample was designed in which the contraction of its middle portion is highly restricted by the mold during the cooling process. The effects of an increasing cooling rate combined with mold constraints were analyzed by reducing the thickness of the middle portion in the second sample. A three-dimensional coupled temperature-displacement analysis was performed in finite-element code ABAQUS to simulate residual stress distribution, and then numerical results were verified by the hole-drilling strain-gauge method. It was concluded that... 

In the present paper, an improvement in high temperature fatigue properties of the AZ91 magnesium alloy with rare earth elements has been obtained by a typical heat treatment, denoted by T6. For this objective, out-of-phase thermo-mechanical fatigue, room temperature and high temperature low cycle fatigue tests are performed to compare lifetimes. Several rare earth elements are initially added to the AZ91 alloy during a gravity casting process in permanent molds. Also, the type of the heat treatment is examined. Results of specimens with only the solution (the T4 heat treatment) and the solution with the ageing process (the T6 heat treatment) are compared under isothermal fatigue loadings.... 

The effects of melt quality and the placement of a filter in the filling system on Weibull distributions of tensile strength and elongation of Al-7%Si-Mg alloy castings were investigated. Three different combinations of melt quality and filtering were used: (a) unstirred, with filter in the filling system, (b) stirred to produce and entrain surface oxide films with no filter in the filling system to emulate poor initial melt preparation and melt handling, and (c) stirred and with a filter placed in the filling system. The results showed that the highest elongation and tensile strength values were obtained from the unstirred, filtered condition and lowest values were from stirred and... 

Gas porosities and Fe-rich phases and entrapped double oxide films (hereafter: oxides) are known to be the most detrimental defects in cast Al-Si-Mg alloys. The effects of H (gas porosities) and Fe (Β-Al5FeSi phase) on reproducibility of tensile properties in Al-7Si-0.35Mg alloy have been investigated in this study. Four different casting conditions (Low H-Low Fe, Low H-High Fe, High H-Low Fe and High H-High Fe) were studied. In each case, 30 tensile test samples were prepared by casting in a metallic mold and machining (total of 120 tensile test samples). Results of tensile test were analyzed by Weibull three-parameter analyses. The microstructures of samples were studied by optical... 

Double oxide films (hereafter: oxides), inclusions and Fe-rich phases are known to be the most detrimental defects in cast Al-Si-Mg alloys. The effects of these defects on reproducibility of tensile properties in Al-7Si-0.35Mg alloy have been investigated in this study. Four different casting conditions (low oxide-low Fe, high oxide-low Fe, low oxide-high Fe and high oxide-high Fe) were studied. In each case, 30 tensile test samples were prepared by casting in a metallic mold and machining (total of 120 tensile test samples). Results of tensile test were analyzed by Weibull three-parameter and mixture analyses. The microstructure and fracture surface of samples were studied by optical and... 

A numerical analysis for determination of the stagnant and dispersion thermal conductivities in the Resin Transfer Molding (RTM) process is presented. A solution was obtained for the momentum and energy equations, which are used in this study and which represent the Brinkman- Forchheimer-extended Darcy model, and one-temperature energy equation. Subject to the appropriate boundary conditions, the governing equations are solved by the finite volume method on a collocated grid. In order to satisfy the pressure-velocity coupling in the solution, the SIMPLE algorithm was used and for determining the mass flux flowing past the cell faces, the Rhie-Chow interpolation was applied. Both constant and... 

Gas porosities and entrapped double oxide film (hereafter: oxides) are known to be the most detrimental defects in cast Al-Si-Mg alloys. This study investigated the effects of dissolved hydrogen (hereafter: H) and oxides on reproducibility of tensile properties in Al-7Si-0.35 Mg alloys. Also the effects of H and oxides content on the morphology of defects were studied. Four different casting conditions (low oxide-low H, low oxide-high H, high oxide-low H, high oxide-high H) were tested using tensile test bars that were cast in a metallic mold. Results of tensile test that were obtained for each casting condition were analyzed using Weibull two-parameter analysis. Microstructure and fracture... 

Injection molding is one of the most important manufacturing processes for mass production of complex plastic parts. In this study, mold filling is simulated by using the OpenFOAM software for Non- isothermal Newtonian fluid. The OpenFOAM is an open source software that is used in Computational Fluid Dynamics (CFD) tools. The studied mold shape has a rectangular structure with a gate for Newtonian fluid injection. The simulation carried out at non-isothermal conditions and two-dimensional flow is considered. The velocity, shear stress and temperature changes in different parts of the mold are critically studied. We show that vortex formation plays an important role on changes of shear stress... 

UHMWPE composite materials are increasingly used in armors design due to their high strength-to-weight ratios and energy absorption capacities. In this study the effect of production parameters upon the terminal ballistic properties of UHMWPE composite were examined under different conditionings. The composite armor plate laminates were produced by hot pressing with three different pressing times from 10-30 minutes and the laminates conditioned at +115, +125, and +135°C. The molding temperature of SK66 fiber composite has the main direct effect on the ballistic absorption energy, so the relation of molding temperature with the adhesive bonding force between layers, the thickness of the... 

The aim of this paper is to correlate interfacial heat transfer coefficient (IHTC) to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of casting under different pressures were obtained using the inverse heat conduction problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula was presented for correlation between external pressure and heat transfer coefficient. Acceptable... 

During solidification and casting in metallic molds, the heat flow is controlled by the thermal resistance at the casting-mold interface. Thus heat transfer coefficient at the metal-mold interface has a predominant effect on the rate of heat transfer. In some processes such as low pressure and die-casting, the effect of pressure on molten metal will affect the rate of heat transfer at least at initial steps of solidification. In this study interfacial heat transfer coefficient at the interface between A356 alloy casting and metallic mold during the solidification of casting under pressure were obtained using the IHCP (Inverse Heat Conduction Problem) method. Temperature measurements are then... 

The effect of mould preheating temperature, casting modulus and graphite addition method on surface decarburisation during lost wax casting of CK 45 steel has been investigated. For this purpose, a novel image analysis program was developed to determine the carbon concentration profile. It was observed that on increasing the preheating temperature and casting modulus, the depth of decarburisation increases significantly. This behaviour was related to the decreased cooling rate of the samples which enhances the loss of carbon by reaction with the surrounding atmosphere. It was also found that the distribution of graphite in different layers of the mould and the distance of these layers from... 

The effects of the mold preheating and the silicon content of ductile iron on the percentage of carbides, graphite nodule counts and shrinkage volume were investigated. The results showed that the percentage of carbides and the shrinkage volume decreased when the mold preheating increased. The ductile iron with the carbon equivalent of 4.45% and the silicon content of 2.5% without any porosity defects was achieved when the mold preheating was 450 °C. Increasing the silicon content in the range of 2.1%-3.3% led to the increase in graphite nodule count and graphite size and the decrease in percentage of carbides. It is due to the increase in induced expansion pressure during the graphite... 

The uniaxial viscosity and sintering stress of WC-10Co-0·9VC (wt-%) were obtained by a loading dilatometer as functions of fractional density (0·64<ρ<0·93) and temperature (1084