جستجوی مقالات مرتبط با کلیدواژه « Tensile properties » در نشریات گروه « مواد و متالورژی »

In this study, the effects of grain size on the tensile properties and the work-hardening behavior of 304 austenitic stainless steel was investigated. For this purpose, the thermomechanical processing was carried out by applying a 75% thickness reduction to the as-received 304 stainless steel sheet followed by annealing at two different temperatures of 750 and 1000 °C to produce sheets with two different fine- and coarse-grained microstructures. The average grain size decreased from 25 μm in the as-received matrix to 1.93 μm in the sample, which was annealed at 750 °C for 90 min (fine-grained sample). Also, the mean grain size of 35.52 μm (coarse-grained sample) was obtained after annealing at 1000 °C for 90 min. XRD and optical microscopy were used for characterizing the microstructure. The tensile tests were performed in the directions of 0°, 45°, and 90° to the rolling direction of the samples. The yield strength of as-received, fine-grained, and coarse-grained samples were obtained 405, 733, and 305 MPa, respectively. However, the total elongation decreased from 73% in the as-received sample to about 52% in the fine-grained sample. The work hardening behavior of both fine- and coarse-grained samples was observed in three stages: an initial sharp drop until a minimum value was reached, then an increase until a maximum value was reached, and finally a reduction in the work hardening rate until the beginning of necking. The work-hardening rate (dσ/dε) of the coarse-grained sample was higher than that of the fine-grained sample. This was due to the higher martensitic transformation rate in the coarse-grained sample.

The main of this paper is to determine the tensile properties of natural flexible composites. In order to fabricate the composites, the cotton fibers and the latex were used as the reinforcement and matrix, respectively. At the first step, the latex samples were manufactured and tested under tensile loading. In the next step, using the cotton fiber the latex was reinforced and then tested under tensile loading. In addition, the NiTi shape memory alloy (SMA) wire was used to improve the tensile properties of the pure latex and the cotton/latex laminated composites. Therefore, one, two or three NiTi wires were used in the pure latex and cotton/epoxy composites samples. The results of experimental study displayed that in the presence of cotton fiber, the ultimate tensile strength of pure latex was increased from 0.93 to 13.51 MPa. Moreover, it was observed that due to adding one, two or three NiTi wires, the ultimate strength of the pure latex was enhanced almost 70, 500 and 800%, respectively. However, the ultimate tensile strength of the cotton/epoxy laminated composites in the presence of one, two and three NiTi wires was increased almost 2, 20 and 40%, respectively. In addition, comparison of the current research results with the other researchers’ investigations manifests that the cotton/epoxy composites reinforced by NiTi wire, the tensile strength of this flexible material is greater than the tensile strength of natural and artificial leathers.

The medical cast CoCrMo ASTM F75 alloy is used in orthopedic implants such as artificial toggle and knee. In this alloy, due to the existence of defects such as chemical inhomogeneities and large grain size, heat treatment is performed. In this research the effect of solution annealing heat treatment on the microstructural evolution and mechanical properties of two ASTM F75 alloy (the free of carbon specimen and the specimen containing 0.21 wt% carbon) was investigated. The solution treatment done at 1175, 1225 and 1275oC for 0.5, 1, 2 and 4 hours. Subsequently the specimens quenched in water. The results show that in the specimen without carbon, the σ precipitates were formed. However, in the specimen containing carbon, the M23C6 carbides and σ were formed. Besides, by adding carbon the volume fraction of carbides increased and reached to 6.55 % leads to increase in strength. By increasing annealing temperature from 1175 to 1275 oC and the time from 0.5 to 4 hours, the volume fraction and the size of carbides have been decreased. In the specimen containing carbon, by annealing at 1225oC for 1 hours the distribution of precipitates became homogenous in the microstructure. Besides, most of carbides at the grain boundaries in the cast condition were disappeared by heat treatment. Finally, in the specimen containing carbon in the heat-treated condition, the mechanical properties such as the ultimate tensile strength raised up to 19% and the ductility increased twice in comparison to the one in the cast condition

Metastable beta titanium alloys have the ability to achieve different microstructures as a result of various heat treatment cycles. The aim of the present study was to create a combination of fine spherical and needle-shaped alpha phase in a metastable beta Titanium alloy (Ti-3Al-8Mo-7V-3Cr) using two-phase solution annealing and aging to improve tensile properties. In this regard, one strip of the alloy was solution annealed in the two-phase region (α+β) at 750°C. Then, some of the solution treated specimens were aged in one step and the others in two steps. The microstructural observation and phase analysis were studied by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively followed by investigating tensile properties using tensile test. The results exhibited that the microstructure of the alloy after annealing in the two-phase region (α+β) consisted of a spherical primary alpha phase of 1 μm in the beta matrix. One-step aging at 600°C resulted in a microstructure without secondary alpha layers. This heat treatment cycle resulted a yield strength of 980 MPa and fracture strain of 13.9%. Two-step aging at 300°C and 600°C led to formation of the secondary alpha layers with 0.1 μm thickness and increased the yield strength and fracture strain to 1007 MPa and 15.8%, respectively.

This study was undertaken to improve the tensile properties of Al-4.5Cu-xSi-yFe alloy through thermal modification (T6 heat treatment). To this end, different amounts of Si (0.1-2.5 wt.%) and Fe (0.05-2.5 wt.%) were added to the alloy composition in order to investigate the effect of Fe/Si ratio on the alloy tensile properties and quality index in as-cast and heat treated conditions. According to the results, adding Si up to 2.5 wt.% improved the base (Fe-free) alloy fluidity. However, the maximum fluidity in Fe-bearing alloys obtained at 1.5 wt.% Si. The optimum Si content for maximum tensile strength and fracture strain in low-Fe alloys was determined as 1.5 and 0.5 wt.%, respectively. However, in Fe-containing alloys the optimum Si was determined based on the Fe/Si ratio. At the Fe/Si≤1 the compacted α-FeMn compound is the dominant Fe-phase which is not detrimental to the tensile properties. At the Fe/Si>1 the fraction of detrimental β-platelets is increased at the expense of α-FeMn. In as-cast condition, the maximum tensile strength and ductility are obtained in 1.5 wt.% Si containing alloy at the Fe/ Si ratio of unity and 0.3, respectively. Applying heat treatment encouraged the precipitation hardening as well as dissolution/ fragmentation of hard eutectic Si and Fe-rich platelets. Under this circumstance, the maximum tensile strength belongs to the sample containing 2.5 wt.% Si and Fe/Si ratio of unity where its tensile strength is higher than that of the as-cast and heat treated base alloy by 40 and 15%, respectively.

The effects of 0.05, 0.1 and 0.15 wt% C on the microstructure, hardness and tensile properties of annealed Haynes 25 were investigated. The alloys were melted in a vacuum induction melting furnace and purified through electro slag remelting process then solution annealed at 1200˚C for 30 min. The results indicated that W-riched M6C carbides developed in the microstructure and its amount increase with increase of carbon. By increase of Carbon from 0.05 to 0.15wt%, grain size decrease from 44 to 35 µm. The carbides act as nucleator and also retard grain growth that cause to reduce grain size. Mechanical properties investigation shows that with increasing carbon, as a result of grain refinement and the proper size and morphology of carbides, hardness increases from 255 to 290 Hv, yield strength from 450 to 510 MPa and ultimate tensile strength from 946 to 1088 MPa but ductility decreases slightly.

Cast Al-15Mg2Si composites due to appropriate specific strength and tribological properties are ‎widely used in automotive and aerospace industries. The improved properties of these composites ‎are governed by the correct controlling of morphology, size, and distribution of primary Mg2Si ‎particles. In this study the effect of solidification cooling rate (chill modification) was investigated ‎on structure and quality index of Al-15Mg2Si composite. The casting operation was performed in ‎different molds with varying cooling rates of 2.7, 5.5, 17.1, and 57.5 °C/s. According to the ‎microstructural observation and image analysis results, increasing the solidification rate resulted in ‎refinement of primary Mg2Si particles and improvement of their distribution in the matrix. The ‎increased solidification cooling rate, moreover, refined the grains so that increasing cooling rate ‎from 2.7 to 57.5 °C/s resulted in 93% reduction in grain size. These microstructural variations ‎improved the composite tensile strength, fracture strain, and quality index. The quality index of ‎composite solidified at 2.7 °C/s was found to be lower than that of composite solidified at cooling ‎rate of 57.5 °C/s by 240%.

In this research, the microstructures and mechanical properties of DIN 16MnCr5 low alloy steel under ferrite-martensite dual-phase (with various martensite volume fraction) were compared to full martensitic condition. Dual-phase microstructures were developed by inter-critical annealing. For this purpose, the samples were heated at various inter-critical temperatures (from 740 to 840 °C) for 60 minutes and then water quenching to room temperature. Also, to develop full martensitic microstructure, steel samples were immediately quenched in water after austenitization at 900 ˚C for 60 minutes. The microstructure and mechanical properties of the specimens were analyzed by scanning electron microscope equipped with EDS analyzer, X-ray diffraction and tensile and microhardness tests, respectively. Metallographic observations showed that by increasing the inter-critical annealing temperature from 740 to 840 °C, the martensite volume fraction (Vm) increased from 23 to 87%. Comparison of mechanical properties of dual-phase samples showed that by increasing Vm from 23% to 87%, there was an abnormal tensile behavior at Vm=73%, so that the energy absorption capability (product of tensile strength and uniform elongation) for ferrite-martensite dual-phase samples is much higher than to full martensitic samples. This remarkable modification in the mechanical properties of the dual-phase samples is due to the different hardening responses of the ferrite and martensite microconstituents because of the interaction between them. By increasing the Vm from 23 to 87%, the martensite microhardness decreased continuously from 717 to 471 HV10g, while the ferrite microhardness showed a peak value at Vm=73%.

In present research, the effect of tool transverse speed on the microstructure and mechanical properties of friction stir welded DP700 dual-phase steel has been studied. Welding process conducted at a rotational speed of 800 rpm and tool transverse speeds of 50 and 100 mm/min. Optical and scanning electron microscopy were used for microstructural examinations, and mechanical properties were evaluated using microhardness measurements and tensile test. Microstructural investigation revealed that the stir zone consists of bainite, acicular ferrite and polygonal ferrite. It was also revealed that the heat-affected zone (HAZ), based on the peak temperature (Tp), can be subdivided into three different regions: 1) inner HAZ, where Tp is higher than Ac3, 2) Middle HAZ, where Tp lies between Ac1 and Ac3, 3) Outer HAZ in which Tp is lower than Ac1. It was also found that the martensite phase tempers in OHAZ and the degree of tempering decreases with the increment of tool transverse speed. This results confirmed by microhardness measurements where the hardness reduction of the softened zone decreased from 28 to 20HV with an increment of tool transverse speed. The highest hardness of the joints corresponded to the stir zone, and its value increased from 345 to 375HV with rising tool transverse speed. Tensile test results showed that the ultimate strength of the joints was lower than the base metal (723MPa) and it increases from 662 to 671MPa with rising tool transverse speed. It was also revealed that increasing transverse speed improves the total elongation by 2.6%.

Fused Depositional Modeling (FDM) is one of the common methods for 3D printing of polymers, which is expanding in various industrial applications and engineering applications due to its ability to make complex parts. The mechanical properties of 3D printed parts strongly depend on the correct selection of processing parameters. In this study, the effect of three important parameters such as infill density, printing speed and layer thickness are investigated on the tensile properties of PLA specimens. To this end, standard specimens with four infill densities of 20%, 40%, 60% and 80%, two speeds of 20 mm/s and 40 mm/s, and two thicknesses of 0.1 mm and 0.2 mm are printed and tested under quasi-static tensile test. In all printed specimens, the print angle is assumed ±45°. Experimental results showed that the increase of infill density up to 60% has significant increase on the modulus of elasticity, ultimate strength, and failure strain. But at infill density of 80% with the highest stiffness to weight and strength to weight ratios, the failure strain has decreased up to 31.9% in comparison to infill density of 60%. Reducing printing speed from 40 mm/s to 20 mm/s causes the increase of stiffness, ultimate strength and failure strain up to 7.8%, 9.7% and 1.6%, respectively. Moreover, it is observed by reducing the layer thickness from 0.2 mm to 0.1 mm, modulus of elasticity increases 18.7% and failure strain decreases 53.4%.

In this study, the effect of vascular self-healing orientation on tensile strength and healing efficiency of epoxy-glass composite has been experimentally studied. Hollow glass fiber (HGF) of 450±10 μm diameter and 50%-55% hollowness was produced by using an extruder. Following, the HGFs were filled with healing components, and subsequently employed as vascular healing system in composite laminate. The orientations of HGFs were selected at three levels of 0, 45 and 90°. The distance of HGFs was kept at 200 μm. The virgin, damaged and healed specimens were characterized in term of tensile behavior and subsequently the healing efficiency was studied. The results of tensile tests indicated that the presence of blank HGFs in composite lowered the tensile strength as high as 17, 14 and 21% for HGFs angles of 0, 45 and 90°, respectively. As a damage, a strain of 1.2% was initiated in the tensile specimen and afterward the self-healing process was accomplished at temperature of 70 ˚C for a time period of 48 hours. Subsequently, the healing efficiency was measured by tensile testing. The results indicated that the best orientation of the filled HGFs was 45°, where the healing efficiency was equal to 42%. The morphology of fractured HGFs and healed zones was studied by employing scanning electron microscopy.