جستجوی مقالات مرتبط با کلیدواژه « tensile properties » در نشریات گروه « مکانیک »

Considering the increasing use of high-speed presses, such as high-speed servo presses, in the automotive industry, it seems necessary to investigate the formability of sheet metals in this range of forming speed. Therefore, this study has been conducted to investigate the effect of medium strain rate forming on the formability of the St14 steel sheet. Tensile tests were done at various strain rates, and formability tests were performed to create forming limit curves at the quasi-static and impact forming. Finite element simulation was used to extract the numerical forming limit curves. The material model was entered into the simulation by considering the strain rate effect using the VUHARD subroutine. The results of tensile tests showed that some influential strain-hardening indicators reduce with strain rate enhancement. Also, using the material model, the tensile behavior was predicted with good accuracy at each strain rate. In impact forming, fracture and strain concentration was transferred to the dome center, and the dome height in biaxial stretching was reduced by 17.1% compared to quasi-static forming due to the variation of frictional conditions. The forming limit curve of impact forming was shifted to the lower values and right side of the forming limit diagram compared to quasi-static forming. In impact forming, the forming limit in plane-strain condition was reduced by 8.1% compared to quasi-static forming. Also, the simulation results, including fracture position, forming limit curve, and dome height in both forming processes, were in good agreement with the experimental results.

Metastable beta titanium alloys are suitable for use in the aerospace industry due to their high strength and good ductility, as well as their high strength-to-weight ratio. The aim of the current research is to investigate the microstructure and tensile properties of the alloy after single-step and two-step aging following thermal-mechanical cycles of single-phase β annealing and two-phase α+β annealing. For this purpose, on one strip of the alloy, solution annealing heat treatment in the single-phase β region, cold rolling and recrystallization and on the other strip, solution annealing heat treatment in the two-phase α+β region was performed. Afterwards, the specimens from the strips were subjected to single-step aging at 550⸰C. In addition, in order to perform two-step aging, specimens were subjected to heat treatment at 300 and 550⸰C for primary and secondary aging, respectively. Then the structural evolution of the alloy was investigated by SEM and X-ray diffraction pattern and the tensile properties of it by tensile test. It was found that the optimum heat treatment cycle of the Ti-3873 alloy was two-step aging after α+β solution treatment leading to 1190 MPa yield strength and 14.7% elongation. In this case, the obtained structure has no grain boundary alpha and the formed secondary alpha has a length of less than 0.5 µm and its average thickness is 0.15 µm.

Crack nucleation and propagation in engineering segments and structures are unavoidable. Replacing a damaged part is the easiest way to prevent failure, but it is not always cost-effective. Therefore, in many cases, by repairing a component, the life of defective working parts can be increased.  One of the effective strategies, is mending the cracked area using composite patches witch are glued in crack formation place. The purpose of this study was to investigate the effect of patch on crack growth behavior as well as the effects of patch geometry on the mechanical properties of repaired Al5251 aluminum alloy. For this purpose, a Kevlar-epoxy composite patch with rectangular and H-shaped geometry has been used. Tensile test was performed to evaluate the mechanical properties and the crack growth behavior in the samples. The influences of patch geometry and effective area on tensile force, specimen ductility, toughness and crack forming force have been investigated. The results showed that with the use of composite patch, ductility, force at the moment of cracking and the failure force increased compared to samples without repair. Also, comparison of patches with equal effective area showed that samples repaired with H-shaped patch have more load capacity than rectangular patch. In addition, the amount of toughness in the sample repaired with H-shaped patch has increased.

The aim of this study is to improve the strength properties of glass-aluminum multilayer hybrid composite using AA1050 aluminum sheets processed by the accumulative roll bonding (ARB) process. Also, the effect of different cycles of ARB process on the strength properties of hybrid composite has also been investigated. At first, the ARB process was applied on the AA1050 sheet. Afterwards, the microstructure and tensile properties of the ARB deformed sheets were investigated. Then, the ARB processed AA1050 sheets were used to make glass reinforced aluminum laminate (GLARE). In the end, the tensile properties of the GLARE composite were examined. By the progress of the ARB process, the hardness and strength of the sheet increased. The elongation of the first cycle processed specimens dropped drastically. But, by increasing the process cycles, the elongation increased gradually. The use of the ARB processed aluminum sheet in the manufacture of GLARE composite significantly improved the tensile strength of the GLARE. In the GLARE made of annealed aluminum, most of the elongation of the aluminum layer occurred after the breaking of the glass fibers and in conditions outside the GLARE composite; as a result, the reduction of the sheet elongation during the ARB process caused the simultaneous failure of the metal layers and the glass fibers during the tensile test of the GLARE. Hence, this event did not reduce the ductility of the composite. In other words, the total energy absorption and fracture toughness of the aluminum layers occurred when the GLARE had not failed.

In the present study, Cu/Zn/Al multi-layered composite was processed by accumulative roll bonding (ARB) through nine passes. Afterwards, heat treatment processes at various temperatures (750-950℃) and times (10-25min) were done on the prepared composites to fabricate CuZnAl shape memory alloys. The microstructure (composites and alloy) were investigated using scanning electron microscopy and X-ray diffraction. Tensile properties and shape memory effect of the composites and alloys were also investigated by tensile test. The microstructure investigations show that plastic instability and shear bands occurred in different layers in the composite. In addition, a composite with a uniform distribution of Zn and Al reinforcing layers was produced after nine passes. The tensile strength of the composite increased from the first cycle to the third ARB cycle and then decreased from the fifth to the ninth ARB cycle. Finally, the best UTS (about 330MPa) and elongation (about 31.52%) values were obtained on the third and first pass, respectively. The results showed that CuZnAl shape memory alloy was successfully fabricated by the accumulative roll bonding process and next heat treatment. It was also found that the alloys treated at 900°C and cooled in ice water consist of martensitic phase. Additionally, the alloy annealed at 900°C for 15 minutes exhibited a good shape memory effect and strength (about 503MPa).

In this study, nanocomposites based on epoxy, nano-silica and short glass fibers were prepared with hand molding method. The resin material consisted of epoxy resin and polyamine. Nano-silica and glass fibers, with average length of 6 mm, were added to epoxy polymer matrix in three levels 0, 0.75 and 1.5 wt.% for nano-silica and 5, 10 and 15 wt.% for glass fibers, respectively. After sample preparation, tensile tests are performed to study tensile properties of composites and results were compared and analyzed. Results showed that by adding 0.75 wt.% nano-silica, tensile strength, elastic modulus and elongation increased and by addition 1.5 wt.% of nano-silica the mentioned properties decreased. On the other hand, adding just glass fibers enhanced elastic modulus continuously and declined tensile strength of the nanocomposite. Furthermore, simultaneous presence of glass fibers and nano-silica caused an enhancement in elastic modulus and a reduction in tensile strength and elongation at break.