Sharif Digital Repository

The heat-affected zone (HAZ)softening is considered one of the most significant challenges during welding of ferrite–martensite dual-phase (DP) steels. In fact, the strain localization in the softened area results in a premature fracture that degrades the mechanical properties of the joint. Herein, the objective is to investigate the effectiveness of improved cooling using a high thermal diffusivity backing plate (BP) to reduce HAZ softening and enhance the mechanical properties of friction stir-welded DP700 steel. Accordingly, friction stir butt welding of DP700 steel was conducted using copper and mild steel BPs. The findings show that the replacement of steel BP with copper significantly... 

The heat-affected zone (HAZ) softening is considered one of the most significant challenges during welding of ferrite–martensite dual-phase (DP) steels. In fact, the strain localization in the softened area results in a premature fracture that degrades the mechanical properties of the joint. Herein, the objective is to investigate the effectiveness of improved cooling using a high thermal diffusivity backing plate (BP) to reduce HAZ softening and enhance the mechanical properties of friction stir-welded DP700 steel. Accordingly, friction stir butt welding of DP700 steel was conducted using copper and mild steel BPs. The findings show that the replacement of steel BP with copper significantly... 

Ultrahigh-molecular-weight polyethylene (UHMWPE)/fumed silica nanocomposites were prepared via in situ polymerization using a bi-supported Ziegler-Natta catalytic system. Nanocomposites with different nanoparticle weight fractions were produced in order to investigate the effect of fumed silica on thermal and mechanical properties of UHMWPE/fumed silica nanocomposites. The viscosity average molecular weight (M) of all samples including pure UHMWPE as the reference sample and nanocomposites were measured. Scanning electron microscope (SEM) images showed the homogenous dispersion of nanoparticles throughout the UHMWPE matrix while no nanoparticle cluster has been formed. Crystallization... 

The oxygen-barrier properties of poly(lactic acid) (PLA)/poly(vinyl acetate-co-vinyl alcohol) [P(VAc-co-VA)] were investigated. P(VAc-co-VA)s with vinyl alcohol (VA) contents of 5, 10, and 15 mol % were prepared with the acid-catalyzed hydrolysis of poly(vinyl acetate). The obtained copolymers with various contents of VA were blended with PLA at 5/95, 10/90, and 15/85 compositions. Films of the blends were prepared by a solution-casting method with chloroform as the cosolvent. Although the blend with 5% VA in the copolymer appeared to be miscible, the blends with 10 and 15% VA content in the copolymer were immiscible, as verified by dynamic mechanical analysis. The oxygen-barrier properties... 

4340 steel bars were austenitized at 850°C for 1 hour followed by heating at 700°C (ferrite and austenite region) for 90 min and quenching into a salt bath with different temperatures of 300, 350, 400 and 450°C. The steel bars were held for 1 hour at these temperatures before air cooling to room temperature. Various ferrite-bainite microstructures with 34% volume fraction of ferrite and different bainite morphologies were obtained. The results of SEM studies showed that by increasing the austempering temperature, the morphology of bainite varies from lower to upper bainite. According to the T-T-T diagram of the studied steel, the bainite transformation will not complete for the holding time... 

Ethylene vinyl acetate/graphene oxide (EVA/GO) nanocomposite films were prepared via solution casting method. The morphological studies investigated using SEM and XRD methods and the results confirmed the formation of likely exfoliation structures and good interaction between matrix and fillers. The results of permeability measurements showed that films have good resistance against oxygen. Mechanical measurements revealed that Young’s modulus and tensile strength of EVA have improved with introducing GO because of proper dispersion of GO into matrix and good interaction between them; however, elongation at break decreased due to formation of strong and rigid polymer/filler network preventing... 

In the present study, SiC samples with 3, 5, 7.5 and 10 wt% Al2O3–Y2O3 as additives were made by powder metallurgy method, then sintering was performed by microwave-assisted process. β–SiC samples sintering was performed for 100 min. The highest sintered relative density 91.06% was achieved at 10 wt% additives content. The maximum values of hardness and toughness were up to 23.3 GPa and 6.14 MPa.m− 1/2. α–SiC and α–SiC/β–SiC samples sintering was performed for 120 min. The maximum value of density and hardness were up to 96.38% T.D and 24.88 GPa in α–SiC with 7.5 wt% additives, whereas the highest toughness was achieved at 10 wt% additives content in β–SiC samples. The α–SiC samples... 

Flow stress and ductility behaviors of the annealed and severely deformed Al were investigated at warm deformation temperatures. Constrained groove pressing (CGP) method as a severe plastic deformation process was used. The tensile test was carried out at the temperature range of the 298-573 K and strain rate range of 0.001-0.1 s−1 to present the elevated temperature deformation behavior utilizing hyperbolic sine constitutive equation. The flow stress of the CGPed sample is increased with the number of CGP passes and decreased with temperature. Dynamic recovery and strain softening are found as main restoration mechanisms. Flow stress amounts are not remarkably affected by the strain rate.... 

It is well known that strain localization and indeed displacement discontinuity can arise in materials exhibiting plastic behaviour. Indeed such localization is almost certain to occur if strain softening or non-associated behaviour exists, though it can be triggered even when ideal plasticity is assumed. This study is concerned mainly with the manner in which the numerical discretization process has to be devised so as to capture the localization phenomenon. In this paper, a method is presented for applying the mixed formulation to study the prediction of localization phenomenon in powder-forming processes. This study is focused on the performance of mixed u - π triangular elements to study... 

Stress-relieved Al-Mn-Si specimens were constrained groove pressed (CGPed) and in the following, cold-rolled under different strains of 0.47, 0.8 and 1.27. Dual strained sheets were isothermally heat treated at 150, 250, and 350 °C. Microstructure survey revealed that generated shear-bands by CGP acted as talent sites for further strain-induced grain boundary migration (SIGBM) during annealing. SEM micrographs pointed out that coarse particles (1 μm <) had not preferential positions within the aluminum matrix and often comminuted into fine dispersoids (0.5 μm >) under heavy strains. Assessment of the softening fraction (Rrec) depicted that greater accumulated strains along with higher... 

The in vitro endothelial response of human umbilical vein endothelial cells was investigated on a poly (caprolactone)-based polyurethane surface vs an in situ TiO2-polyurethane nanocomposite surface, which has been produced as scaffolds for artificial vascular graft. The in situ synthesis of TiO2 nanoparticles in polyurethane provided surface properties that facilitated cellular adhesion, cell sensing, cell probing and especially cell migration. Cells on the nanocomposite surface have elongated morphology and were able to produce more extracellular matrix. All of these advantages led to an increase in the rate of endothelialization of the nanocomposite scaffold surface vs pure polyurethane.... 

An artificial neural network model, using a back-propagation learning algorithm is utilized, to predict the yield stress, elongation, ultimate tension stress, over(R, -) and {divides}ΔR{divides} during hot rolling, cold rolling and annealing of AA3004 aluminum alloy. Input nodes were chosen as the ratio of initial to final thicknesses, reduction, preheating time and temperature, finish rolling temperature and the final annealing temperature. The maximum error for predicted values was 6.35%, the average of absolute relative error was 0.57% and the RMS was 0.00998. It was found that the mechanical properties and anisotropy of AA3004 alloy sheets can be predicted by this approach. © 2006... 

S500MC high strength low alloy automotive steel is exposed to bulk severe plastic deformation (SPD) via constrained groove pressing (CGP) and surface severe plastic deformation (S2PD) via severe shot peening (SSP) and ultrasonic nanocrystal surface modification (UNSM). SSP and UNSM could create a nanocrystallization layer till 50–100 µm away from outmost surface. EBSD investigations showed average nano-grain size obtained via SSP and UNSM was found to be below 100 nm regime. The strength was improved via 1st to 4th pass of CGP, but elongation percentage decreased abruptly. UNSM achieves both strength-ductility improvement with gradient structure. SSP improves the total elongation however a... 

In this study, the properties of poly (vinyl alcohol)(PVA) films incorporated with Zataria multiflora essential oil (ZMO) as a potential antioxidant/antibacterial material was investigated. PVA films were prepared from PVA solutions (2% w/v) containing different concentrations of ZMO. Water solubility, moisture absorption, water swelling, and water vapor permeability for pure PVA films were 57 ± 1.1, 99 ± 3.2%, 337 ± 8%, and 0.453 ± 0.015 g mm/m2 h, respectively. Incorporation of ZMO into PVA films caused a significant decrease in water swelling and moisture absorption and increase in solubility and water vapor permeability. Tensile strength, elastic modulus, and elongation at break for pure... 

Nano-biocomposites are a new class of hybrid materials composed of nano-sized filler (nanofiller) incorporated into a bio-based matrix. Such an association between eco-friendly biopolymers and nano-objects, with the aim to obtain synergic effects, is one of the most innovating routes to enhance the properties of these bio-matrices. In recent years, there has been an increasing interest in Starch as an inexpensive and renewable source has been used as a filler for environmentally friendly plastics for about two decades. However, the poor mechanical properties of starch based biopolymers, leads to use of nanoparticles as reinforcing materials. In the present study, the influence of a... 

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... 

This work was carried out to investigate the effect of different Ti concentrations as a modifying agent on the microstructure and tensile properties of an in-situ Al-15 pctMg2Si composite. Cast, modified, homogenized small ingots were extruded at 753 K (480°C) at the extrusion ratio of 18:1 and ram speed of 1 mm/s. Various techniques including metallography, tensile testing, scanning electron microscopy were used to characterize the mechanical behavior, microstructural observations, fracture mechanisms of this composite. The results showed that 0.5 pctTi addition and homogenizing treatment were highly effective in modifying Mg2Si particles. The results also exhibited that the addition of Ti... 

In this study, a near equiatomic NiTi shape memory alloy was hot rolled at 800°C using thethickness reductions of 30 and 50%. Optical and transmission electron microscopy, together withX-ray diffraction were used to demonstrate the microstructural changes associated with the hotrolling at different thickness reductions. Repeated transformation cycling was employed toinvestigate the evolution of R phase during cycling. Microstructural observations revealed thepresence of deformation twins embedded in an elongated grain matrix in the hot rolled material.Moreover, it was found that with increasing degree of thickness reduction, the size and number ofdeformation twins increased throughout the...