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Using in low temperatures causes embrittlement of many structures, consequently, selection of welding parameters for maintaining the toughness of welded structures, is so important. In this paper, effects of arc heat input and welding speed on the cryogenic impact strength of type 304L austenitic stainless steel weld metal, are investigated. For this purpose, 304L austenitic stainless steel sheet with 5 mm thickness, was welded with gas tungsten arc welding process and by changing the parameters of arc heat input and welding speed, the effect of these parameters on the microstructure, the weld metal ferrite content and low temperature charpy impact energy of samples, was determined. The arc heat input range applied was between 1.04 and 3.23 kW, and the welding speed varied between 30 and 240 mm/min. It was found that, increasing of arc heat input can reduce weld metal ferrite content, which improves low temperature impact strength, but on the other hand, slow cooling due to increasing heat input results in coarser dendritic structures in the weld metal, and can adversely affect on impact strength. Changes of Welding speed can also affect on the amount of ferrite and microstructure and thus have influence on the impact strength. Finally having carried out the numerous tests, optimum impact properties at low temperature, were obtained at 1.67 kW arc heat input and 120 mm/min welding speed.

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In this study, using design of experiments, the effect of hybrid graphenenanosheets and nano clay and compatibilizer maleic anhydride -grafted -polypropylene (PP-g-MA) on the impact strength polypropylene-based nanocomposites were investigated. Design of experiments and analysis of experimental data with Minitab 16 software and response surface methodology were carried out. Making nanocomposites, based on the melt mixing was performed. Statistical models provided by response surface methodology good agreement with experimental results and with respect to the values of R-sq and R-sq (adj) have a good reputation. Statistical analysis showed that increasing the percentage of nanoparticles, impact strength decreases. Compounds morphology by Scanning Electron Microscopy (SEM) was performed. Micrographes showed better dispersion of the particles in lower percentages. Thermal analysis using differential scanning calorimetry (DSC) showed that the presence of graphene have little effect on the melting temperature of the sample being tested, but Tc of nanocomposites compared with pure PP, has increased about 4 percent. Also Thecrystallinity was reduced by adding graphene. In the non-graphenenanocomposites, the clay did not affect the melting temperature,but the crystallinityand crystallization temperature increased 10.73 % and 2.23 % respectively compared with pure PP that showed nucleation effect of nano clay.

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Various fibers have been used by researchers to reinforce concrete and extend the service life of structures, also researchers are using different fibers to improve behavior of different concretes, especially high-strength concrete, against impact and dynamic loads. This study investigate the effect of different contents and lengths of steel fiber on the mechanical properties of high-strength concrete. In this study, wavy hooked-ended fibers of two length (30, 50 mm) with three volume fraction 0.5%, 1% and 1.5% were added to concrete mixes and 150×300 mm cylindrical specimens were made, then different tests were performed for determination of compressive strength, splitting tensile strength and impact resistance at 7 and 28 days, in accordance with standards and procedure proposed. The results indicated that the addition of different contents and lengths of steel fiber caused significant change in the mechanical properties of high-strength concrete. In the best case, using 1.5% of 50 mm long steel fibers, increased compressive strength and splitting tensile strength by 25% and 40%, respectively, compared to non-fibrous high-strength concrete. A remarkable improvement was observed in impact resistance of the fibrous concretes, as compared with the reference materials. By incorporating steel fibers into the mixtures, specially longer fibers, a conclusive increase in the number of blows required for first and final cracking (as compared to reference values) was observed, as well as the number of blows from the first cracks to the final failure in the high percentage of the fiber increased up to  80%. Moreover, it can be concluded that, by adding fiber, the failure crack pattern was changed from a single crack to a group of narrow crack, which demonstrate the beneficial effect of fiber reinforced concrete when subjected to impact loading.
 

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The effects of tempering heat treatment on girth weld containing titanium oxide and titanium carbide nanoparticles (X-65 grade of the gas pipeline) were evaluated. The Charpy results show that it has been respectively increased by 26% and 15% in the tempered sample containing titanium oxide and titanium carbide nanoparticles compared to the no heat treatment sample (containing titanium carbide and titanium carbide nanoparticles). Also, the ultimate strength tempered sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the no heat treatment sample (containing titanium oxide and titanium carbide nanoparticles) has been respectively decreased by 6% and 4%. The results show that the fatigue life in both tempered nano-alloy samples has been increased. The fatigue life in the tempered sample of titanium carbide nanoparticles has increased more than the fatigue life in titanium oxide nanoparticles. The fatigue test results show that in the tempered sample containing titanium carbide nanoparticles compared to the tempered sample containing titanium oxide nanoparticles, fatigue life (150-N force) has been increased by 30%. In this loading, the fatigue life (tempered sample containing titanium carbide nanoparticles compared to the no heat treatment sample) has been increased by 19%. The hole drilling strain gage results show that in the tempered sample containing titanium oxide nanoparticles and titanium carbide nanoparticles, hoop residual stresses have been respectively decreased by 48% and 45% compared to the no heat treatment sample (containing titanium oxide and titanium carbide nanoparticles). 
 

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In this article, the effects of normalization heat treatment on girth weld with containing titanium oxide and titanium carbide microparticles (X-65 grade of the gas pipeline) were evaluated. The Charpy test results show that in the normalized sample containing titanium oxide microparticles and titanium carbide microparticles compared to the no heat treatment sample (containing titanium carbide microparticles and titanium carbide microparticles), has been respectively increased by 33% and 18%. Also, the ultimate strength of normalized samples containing titanium oxide microparticles and titanium carbide microparticles compared to the no heat treatment sample (containing titanium oxide microparticles and titanium carbide microparticles) has been increased by 9% and 11%, respectively. The results show that the fatigue life in both normalized micro-alloy samples has been increased. The fatigue life in the normalized sample of titanium carbide microparticles has increased more than the titanium oxide microparticles. The fatigue test results show that the fatigue life (150-N force) has been increased by 36% in the normalized sample containing titanium carbide microparticles compared to the normalized sample containing titanium oxide microparticles. In this loading, the fatigue life (normalized sample containing titanium carbide microparticles compared to the no heat treatment sample) has been increased by 27%. The hole-drilling strain-gage results show that in the normalized sample containing titanium oxide and titanium carbide microparticles, hoop residual stresses have been respectively decreased by 12% and 8%compared to the no heat treatment sample (containing titanium oxide microparticles and titanium carbide microparticles).

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Titanium is one of the most important microalloy elements used in the gas transmission industry. In this paper, titanium nano-oxide and titanium nano-carbide were added to two separate samples. Then the shielded metal arc welding (SMAW) was performed on high-strength low alloy steel according to welding procedure specification of the national Iranian gas company. The effects of annealing heat treatment on girth weld with containing titanium oxide and titanium carbide nanoparticles (X-65 grade of gas transmission pipeline) were evaluated. The Charpy test results show that in the annealed sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the no heat treatment sample (Containing titanium carbide nanoparticles and titanium carbide nanoparticles), energy absorbed has been respectively increased by %13 and %9. Also, the ultimate strength of the annealed sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the non-heat treated sample has been respectively decreased by %8 and %3. The fatigue life in both annealed nano-alloy samples has been increased. Also, the fatigue life in the annealed sample of titanium carbide nanoparticles has increased more than fatigue life in the titanium oxide nanoparticles. The fatigue life (Annealed sample containing titanium carbide nanoparticles compared to the no heat treatment sample) has been increased by %16. The hole drilling strain gage results show that in the annealed sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the non-heat treated sample, hoop residual stresses has been respectively decreased by %31 and %19. 

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In the present study, the usability of high-density polyethylene (HDPE) based composites in medical applications under impact loads was investigated. Due to the importance of biocompatibility of composites in the medical applications and body environment, zinc oxide nanoparticles (ZnO) were selected as reinforcements. ZnO nanoparticles are generally safe and have superior antibacterial properties. A finite element simulation process with a new approach were used to study the impact properties of the composites in the standard Charpy impact test; moreover, in the experimental procedure, a new method was introduced for the production of HDPE/ZnO composites without use of the compatibilizers. Fourier-transform infrared spectroscopy (FTIR) test was used to check the diffusion of particles in composites. Field emission scanning electron microscopy (FESEM) was utilized to examine the presence of particles in composites. The results of the simulation showed that the HDPE/1%ZnO composites have the best impact resistance in comparison to other composites. Experimental results also showed that HDPE/1%ZnO composites have the best performance in terms of impact strength with an error of about 11% compared to simulation results and are economical. Moreover, the results of antibacterial test of HDPE/1%ZnO composites confirm the excellent performance of this composites against gram-positive and negative strains.

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The importance of environmental issues has increased the use of biodegradable polymers which nowadays have become among main components in medical and biological applications. In the present study, a new combined method of fused filament fabrication (FFF) and batch foaming was introduced to improve the properties of poly lactic acid. For this purpose, FFF samples were produced with infill percentages of 100, 80 and 60 and then, foamed in batch process. Due to the importance and effect of the void fraction on structural and mechanical performance as well as the biodegradability of materials with porous structure, especially for medical purposes, void fraction and impact strength were evaluated. The results showed that the void fractions of FFF samples were 3%, 13% and 25% in infill percentages of 100, 80 and 60, respectively while after the foaming they reached to 14%, 19% and 30%. The findings revealed that the impact strength of FFF foamed samples was improved compared to FFF solid samples. For samples with 100 infill percentage, the impact strength improved from 207 to 506 J/m² due to the foaming procedure with nano-sized cells created by the batch foaming.