جستجوی مقالات مرتبط با کلیدواژه « خواص فشاری » در نشریات گروه « فنی و مهندسی »

Due to their cellular structure, metal foams have properties such as low density, strength to weight and high energy absorption under compressive stresses. Among the various metals used for foaming, aluminum and its alloys are the most widely used due to their relatively low density, availability, and ease of foam formation. In this research, A356 aluminum and composite foams with different amounts of silicon carbide (SiC) particles as a reinforcing and stabilizing agent and calcium carbonate powder (CaCO3) as a foaming agent were produced using direct foaming method from the melt. The density of the foam sample was measured between 0.493 and 0.863 g/cubic centimeter. Then, the microstructure of the foams was examined by OM and SEM microscopes and the compressive and flexural properties of the foams in both conventional and sandwich panels. The relationship between flat stress and density with the weight percentage of CaCO3 and SiC particles was investigated, which shows that the compressive behavior of foam products is not uniform. On the other hand, it was shown that at 10% by weight of the SiC boosting agent, plateau stress increases with decreasing CaCO3 powder content from 6.89 to 11.62 MPa.

Reactive composites are a new group of composite materials consisting of two or more metal materials that can not ignite or explode in the environment but can release a lot of energy due to shock and severe impact loads. This study aimed to investigate the effect of the ratio of constituent particles on the microstructure and thermal and mechanical properties of the Al-Ni composite. For this purpose, the Al-Ni compound with 2:1, 1:1 and 3:1 molar ratios was milled and mixed. Then the samples were cold pressed and sintered at 400 ˚C under argon atmosphere for one hour. The microstructure of samples was analyzed by microstructure field emission scanning electron microscopy (FESEM) and XRD. For the investigation of thermal and mechanical properties, DTA and ignition tests and compression and Hopkinson tests were used respectively. In the ignition test, due to the AlNi product, the highest value of heat released was related to a sample with 1:1 Al:Ni molar ratio. In the compression and Hopkinson tests, the highest values of compressive strength were 208.7 and 309.7 Mpa respectively, which belong to a 1:1 Al:Ni molar ratio. Also, the results showed that the compressive strength increased by changing the strain rate from 0.01 s-1 (in the pressure test) to 1000 s-1 (in the Hopkinson test).

Reactive composites are a new group of composite materials consisting of two or more materials that cannot ignite or explode in the Environmental conditions, but can release a lot of energy due to shock and severe impact loads. This study aimed to investigate the effect of milling time on the microstructure, thermal and mechanical properties of the Al-Ni composite. For this purpose, the Al-Ni compound with a 2:1 Al:Ni molar ratio was milled for 0.5, 1, 2, 4 and 6 hours in attrition mill and mixed. Then the samples were cold press and sintered at 400 ˚C under argon atmosphere for one hour. The microstructure of samples was analyzed by field emission scanning electron microscope (FESEM) and XRD. To investigation of thermal properties DSC and DTA analysis and for mechanical properties compression test and Hopkinson test were used. The DSC analysis results showed that by increasing the milling time, the reaction start temperature decreased from 650.34 °C in the sample milled to 0.5 hour to 645.84 °C the sample milled to 6 hour and the reaction heat (enthalpy) decreased from 26.87 J/g to 14.84 J/g. The results of compression and Hopkinson tests of samples after 6 hours milling time showed 21 and 42 percent increase in compressive strength, respectively compared to samples after 0.5 hours milling time. Also, the results showed that the compressive strength increased by changing the strain rate from 0.01 s-1 (in the pressure test) to 1000 s-1 (in the Hopkinson test).

In this study, the effect of calcium and boron addition has been investigated on the microstructure and compression properties of AZ91 alloy. Initially, in order to determine the optimal calcium amount to reduce the grain size and the presence of secondary phases, 0.1, 0.5, 0.8 and 1 weight percent of calcium were added to the AZ91 alloy. The microstructure evaluation showed that an increase of calcium up to 0.5wt. % decreased the average grain size from 105 μm to 65 μm without the formation of Al2Ca phase. The similar tendency on grain boundary phases are also observed when increasing quantity of Ca added.  The microstructure and mechanical properties of the alloy was then evaluated by adding 0.03, 0.09 and 0.12wt. % B in the form of Al-3B master alloy. The results showed that the optimum concentration of boron is 0.09wt.% in order to achieve the lowest average grain size. In addition, the measured compression properties of samples containing 0.5wt. %   calcium with different amounts of boron showed that the alloy with 0.9wt. % B   presented the best mechanical properties.

In this study, aluminium composite foams reinforced by different volume fractions of SiC particles as reinforcement and stabilizing agent were fabricated with the direct foaming route of melt using different contents of CaCO3 as foaming agent. The density of produced foams were measured to be from 0.38 to 0.68 g/cm3. The microstructural features and compressive properties of the AA356/SiCp composite foams were investigated. The relation between plateau stress, density and, weight percentage of CaCO3 and SiCp volume fraction with a given particle size was also investigated. The results showed that compressive stress-strain curves of the products were not smooth and exhibit some serrations. Also, it was shown that in the same density of composite foams, the plateau stress of the composite foams increases with increasing volume fraction of SiC particles and decreasing weight percentage of CaCO3.

Epoxy / ceramic micro balloon syntactic foams are used in marine and automobile industries because of their high specific strength and capability of absorbing energy. In this paper، the neat epoxy and 9 series of syntactic foams with 3 kinds of ceramic micro balloon with different diameters and crush strength in different volume fractions (20%، 40% & 60%) were fabricated. Effect of varying these parameters on the mechanical properties of syntactic foams is investigated. Besides of all، the effect of different loading rate is investigated، too. All of the samples were tested in 10-1، 10-2 and 10-3 strain rates. The results indicate that with increasing the strain rate from quasi-static to moderate rates، the strength of foams became more. Also the results show that the syntactic foam with bigger micro balloon was weak in compression. In syntactic foams of low volume fraction the size effects is more. On the other hand، with increasing the volume fraction، the crush strength of micro balloon is become effective. Plateau stress and absorbed energy results show these facts obviously. With increasing the strain rate، the strength is increased considerably.