Sharif Digital Repository

A new test specimen for a tensile test of industrial graphite is introduced using experiment and finite element results. The most influencing factors on the tensile strength of the test specimens are considered and the number of tests, which are necessary to optimize the tensile strengths are reduced based on the design of experiment using the Taguchi method and the effects of all factors on strength of test samples are studied. Comparison of the predicted strengths based on the Taguchi approach with the measured experimental results and finite element analysis shows a good correlation between them. In addition, results show that the new introduced specimen makes a 33% increase in the... 

A new refill friction spot welding process called Threaded Hole Friction Spot Welding (THFSW) was introduced to join AA5052 aluminum to short-carbon-fiber-reinforced polypropylene (PP-SCF) composite sheets. The process was based on filling of the pre-threaded hole by melted and re-solidified polymer. The results showed that THFSW was successful to join aluminum to polymer sheets and the hole was completely filled with melted polymer. Formation of a reaction layer composed mostly of Al, C and O as well as interlocking between the threaded hole and the re-solidified polymer were recognized as main bonding mechanisms. Maximum shear-tensile strength of the joints reached to ∼80 percent of the... 

During the past decades, development of reinforcing materials caused a revolution in the structure of high strength and high performance cement-based concrete. Among the most important and exciting reinforcing materials, Steel Fiber (SF) becomes a widely used in the recent years. The main reason for addition of SF is to enhance the toughness and tensile strength and limit development and propagation of cracks and deformation characteristics of the SF blended concrete. Basically this technique of strengthening the concrete structures considerably modifies the physical and mechanical properties of plain cement-based concrete which is brittle in nature with low flexural and tensile strength... 

Reinforcement of polydimethylsiloxane (PDMS) was investigated using untreated nanodiamond (uND) and silane functionalized ND (sND) at various degrees of silanization. Scanning electron microscopy revealed an improved dispersion of ND in PDMS by silanization. The incorporation of uND and sNDs enhanced tensile strength up to 45% and 70%, respectively; however, greater improvement was observed for sNDs at very low concentrations, e.g. 0.2 wt%. The much improvement in crosslinking density, analyzed by Flory-Rehner model and Mooney-Rivlin plot, and interfacial interaction, characterized by Kraus and Cunneen-Russell plots, was also observed for sNDs. Interestingly, it was found that the extent of... 

Joining feasibility of aluminium alloy to polypropylene sheets via friction stir lap joining was examined. Effects of heat-input on microstructure and mechanical behaviour of the joints were investigated. A covering plate was used to confine flow of molten polymer. The results showed a distinctive interaction layer at polymer/aluminium interface, consisted mainly of C, O and Al. Shear strength of the joints decreased by enhancement of the heat-input due to increase in the thickness of the interaction layer as well as the gap width between this layer and both aluminium and polymer matrices. Maximum shear-tensile strength of 5.1MPa (∼20% of polymer shear strength) was obtained, which was... 

The quasi-static and strain-controlled fatigue characteristics of ZK60 extrusion have been investigated along three different directions: the extrusion direction (ED), the radial direction (RD), and 45° to the extrusion direction (45°). The quasi-static response showed symmetric behavior for the samples tested along RD and 45° whereas the ED samples manifested completely asymmetric behavior. Although the ED samples exhibited longer fatigue lives than the RD and 45° in the high cycle fatigue, the fatigue lives in the low cycle fatigue regime were similar. The texture measurement indicated a sharp basal texture along ED, explaining its asymmetric behavior. Higher tensile mean stress and less... 

This paper investigates the influence of intumescent paint on the performance of FRP bars subjected to low (25–450 °C) and severe (450–800 °C) elevated temperatures. In this research, glass and carbon FRP bars with epoxy resin and coated with nitrogen-based intumescent paint were used. In addition to the temperature effects, a variety of FRP bar diameters were employed to determine its effect on the tensile behavior of FRP bars in the presence of intumescent paint. Further, Bayesian regression methods and ANOVA (ANalysis Of VAriance) were applied on the results to develop a predictive model form and quantify the contribution of the variables in the tensile performance of FRP bars,... 

In the present work, the feasibility of friction stir welding (FSW) of poly(methyl methacrylate) sheets was studied experimentally and theoretically by employing thermomechanical simulations. The effect of processing parameters including tool plunge depth, tilt angle, tool rotational speed (w), and transverse velocity (v) was investigated to determine suitable conditions to attain sound and defect-free joints. It is shown that a low tool plunge depth of 0.2 mm and a tilt angle of 2° provide suitable material flow to gain sound joints. By controlling the heat input into stir zone by increasing the tool rotational speed and decreasing linear velocity, the formation of defects can be minimised.... 

In this work, the effect of hot deformation temperature on microstructure and mechanical properties of micro alloyed steel was studied. The results indicated that by decreasing the deformation temperature final microstructure is refined and the volume fraction of grain boundary ferrite is increased and some pearlite is produced. Therefore both the yield strength and ultimate tensile strength is increased, while the toughness is preserved in comparison to a ferritic-pearlitic microstructure. Also a model was developed to relate the deformation condition to the volume fraction of acicular ferrite at mixed microstructure. © 2008 Elsevier Ltd. All rights reserved  

The anisotropic fatigue behavior of ZK60 is investigated through stress-control tests along two different material directions: extrusion (ED) and radial (RD) directions. The in-plane random texture along RD promotes activation of twinning/detwinning deformations in both tension and compression reversals, which brings about a sigmoidal but near-symmetric shape for hysteresis loops. The stress-strain response along ED is asymmetric, which is attributed to different deformation mechanisms in tension and compression reversals. The higher fatigue strength along ED is related to lower plastic strain energy in this direction. An energy damage parameter showed a good correlation with tests performed... 

The aim of this study was to investigate the influences of combination of the two different SiO2 nanoparticles (15 nm and 80 nm) on compressive, flexural and tensile strength of ternary blended concrete. SiO2 nanoparticles with two different sizes of 15 and 80 nm have been used as a partial cement replacement by 0.5, 1.0, 1.5 and 2.0 wt.% in 16 different proportions of mixture followed by curing in lime solution for 7, 28 and 90 days. The results indicate that in all curing ages in lime solution specimens with 2.0% of 15 nm plus 1.5% of 80 nm cement replacement achieved higher mechanical properties. The continuous cement paste with the lowest delicate zones might be due to the fact of quick... 

The present study aimed to join AA4014 to AA7075 by using magnetic pulse welding (MPW). In addition, acceptable joints were achieved by selecting welding parameters such as collision angle and discharge energy appropriately. Changing collision angle and discharge energy can influence the velocity, leading to the formation of three different types of welding interfaces with wavy, molten wavy and porous morphologies. The formation of these various morphologies is mainly associated with different collision angle parameters. The hardness of the welding interface with molten layer was significantly higher than that of the base metals due to the grain refinement phenomenon occurring through the... 

In this study, polyaniline nanoparticles (PANI NPs) in emeraldine base (EB) form were prepared by a modified method and characterized by FTIR and UV–vis spectroscopies. The average size of the nanoparticles was 140 nm measured by DLS method. The nanoparticles were embedded into polylactic acid (PLA) nanofibers prepared by electrospinning method. It was found that inclusion of PANI NPs in PLA resulted in reduced diameter of the fibers during the electrospinning process. Also, the surface of nanofibers appeared smooth in FE-SEM images without formation of beads. Improvement in mechanical and electrical properties of PLA/PANI nanofibers over the neat PLA nanofibers implied a good dispersion of... 

Peripheral nerve injuries remain among the most challenging medical issues despite numerous efforts to devise methods in fabrication of nerve conduits to functionally regenerate axonal defects. In this regard, the current study offers a holistic perspective in design by considering the mechanical, topographical and structural aspects which are crucial for a successful nerve guide conduit. Poly(e-caprolactone) and gelatin were employed to serve this purpose in the form of dual-electrospun films which were rolled and later shaped the assembly of a multichannel conduit. Polyaniline/graphene (PAG) nanocomposite was incorporated to endow the conduit with conductive properties. FTIR analysis,... 

In this study, effects of glycerol (10, 20, and 30 wt%) and Sodium Montmorillonite (Na-MMT) (0%, 2.5%, and 5%) contents on the degradation of corn starch polymers were investigated. Films were prepared by casting corn starch solution using a modified method to enhance the nanoclay distribution. Biodegradability studies were performed by enzymatic and burial tests using pristine and enriched soils. The biodegradability of samples in pristine soil was faster, and all samples were fully degraded in 6 months. The effect of nanoparticles on the mass reduction in degradation was more pronounced than that of glycerol. In all glycerol concentrations, Na-MMT addition increased tensile strength. FTIR... 

In this study, active poly lactic acid (PLA) films containing 0, 10, 20 and 40% w/w propolis extract (PE), as active agent, were developed. A high amount of phenolic content (PC) was measured in PE. The antioxidant effect of active PLA films was determined by measuring the PC of sausage slices after 0, 2 and 4 days storage at refrigerator. Results showed that phenolic compounds of PE were released from PLA films in quantities proportional to PE concentration. Disc diffusion test indicated that PE showed an inhibitory effect against Staphylococcus aureus and Pseudomonas aeruginosa bacterial species but was more effective against gram-positive species. PE containing PLA films had antimicrobial... 

Aluminum alloy series 5xxx lose their strength, especially in the heat affected zone (HAZ) of welds, due to thermal cycle during welding process. Because of this thermal cycle, re-crystallization and grain coarsening in HAZ occur, which result in decreasing of mechanical properties. In this paper the influence of "overloading" and "shot peening" as methods of post weld treatment on mechanical properties of AA5083 aluminum alloy welded joints is investigated. The results show that both overloading and shot peening treatments increase the hardness and tensile strength of welded joints. It is observed that the influence of overloading is stronger than shot peening on increasing hardness of the... 

A hybrid scaffold of gelatin-glycosaminoglycan matrix and fibrin (FGG) has been synthesized to improve the mechanical properties, degradation time and cell response of fibrin-like scaffolds. The FGG scaffold was fabricated by optimizing some properties of fibrin-only gel and gelatin-glycosaminoglycan (GG) scaffolds. Mechanical analysis of optimized fibrin-only gel showed the Young module and tensile strength of up to 72 and 121 KPa, respectively. Significantly, the nine-fold increase in the Young modulus and a seven-fold increase in tensile strength was observed when fibrin reinforced with GG scaffold. Additionally, the results demonstrated that the degradation time of fibrin was enhanced... 

In this research, the effect of adding graphene-based aerogel ((G)A) nanoparticles on the tensile and fatigue behavior of the epoxy polymer was investigated. Specimens of nanocomposites were prepared by adding 0.05, 0.1, 0.2, 0.5, 1, and 2 wt.-% (G)A nanoparticles to the epoxy polymer. Tensile tests revealed that the 0.1 wt.-% graphene-based aerogel/ epoxy ((G)A/E) nanocomposites had the highest increase in tensile strength with 19 % growth compared to neat epoxy. Also, the tensile modulus increased by 15 % in the 0.5 wt.-% (G)A/E nanocomposites. A substantial improvement in fatigue life of the epoxy polymer was observed on adding 0.1 wt.-% (G)A nanoparticles. For instance, the fatigue life... 

The effect of an impact polypropylene copolymer (IPC) having excellent stiffness–toughness balance on the microstructure and properties of a blend comprising 80 wt% recycled high density polyethylene (rHDPE) and 20 wt% recycled isotactic polypropylene (rPP) was studied. Morphological observations revealed improved interfacial interactions, a finer dispersion state and a more homogeneous phase morphology upon IPC incorporation into the blend up to 20 wt%. Flexural modulus, flexural strength, tensile strength and tensile ductility were steadily increased with IPC loading, and exhibited 13%, 14%, 35% and 520% improvement at 20 wt% IPC. A monotonic rise in Izod impact energy, accompanied by a...