Volume 15, Issue 1 (3-2015)
Abstract
Explosive welding is used for excellent bonding of similar and dissimilar materials with the wide variety of thicknesses,area dimensions and different thermal and mechanical properties. In this study, an Al/St/Al multilayer sheet was fabricated by explosive welding process and the effects of annealing temperature on the interfacial properties of explosively bonded Al/Cu bimetal have been investigated. For this purpose, hardness changes along the thickness of the samples have been measured, and the thickness and type of intermetallic compounds formed at the joining interface have been explored by means of optical microscopy (OM), scanning electron microscopy (SEM) and also energy dispersive spectroscopy (EDS). By heat treatment of the samples at 300, 350 and 400°C, it was observed that intermetallic layer was formed at the interfaces. The obtained results indicate that, with the increase of the annealing temperature, the thickness of intermetallic compounds has increased and the amount of hardness along the thickness of the joining interface has diminished. In the annealed sample at 300 °C for 60 min, it was observed that intermetallic layers have formed at the interface of Al/St bimetals. These layers consist of the intermetallic compound Al2Fe and its thickness gets to about 35 μm at some points.
Volume 19, Issue 2 (February 2019)
Abstract
Vibration of various types of structures such as beam, plate, shell, and rod have been investigated by researchers for their application in a wide range of mechanical systems. The longitudinal vibration of the rods is of great interest, so that the researchers have performed them numerically or analytically and precise or approximate. In this research, the nonlinear longitudinal free vibration of rod with variable cross-section under finite strain has been investigated. First, the governing equations of the rod with variable cross-section were obtained, which are partial differential equations; then, they were transformed to nonlinear ordinary differential equations, using the Galerkin method with considering one mode shape. The problem was investigated for two boundary conditions. Using the multiple scales method, the equations were analytically solved. The differential equations are solved by Runge-Kutta numerical method of order 4, and then compared with the analytical solutions. The effect of the amplitude and rate of changing cross-section on the ratio of linear to nonlinear frequency and also the effect of different initial condition, rate of changing cross-section and coefficient of damper were shown in figure. The results show that the tapered cross-sectional area has a significant effect on the ratio of linear to nonlinear frequency to vibrations amplitude. The coefficient of damper has a little effect and initial condition has a considerable effect on the process of problem.
Volume 24, Issue 1 (1-2022)
Abstract
Fire blight, caused by Erwinia amylovora bacteria, is one of the well-known plant diseases in the world including major diseases of the fruit trees, especially apples and pears. In recent years, due to chemical nature of the pesticides damaging human health and environment, the importance of biological control is considered as alternative measure to manage plant diseases. To investigate the possibility of biological control of the pathogens, healthy foliar samples of apple, pear, and quince trees were collected from different regions of Kerman Province, Iran, and then, biocontrol activity of antagonist agents was evaluated under laboratory conditions. On the basis of the results, some of the antagonists could decrease the symptoms of the disease by 14.28-79.59%. Laboratory evaluation included investigating the disease severity in immature pears, biocontrol activity of antagonist agents in the plate assay, inhibitory siderophore production, biofilm formation capacity, drought stress tolerance, and silver nanoparticle synthesis capability, which showed that these antagonist agents could potentially control the disease. Among the 9 well-performed antagonistic isolates from apples and pears, Vr87 isolate was selected. The studies were confirmed by amplifying part of 16S rDNA region of the isolate, using specific primers. By comparing the results on the NCBI website, the selected isolate was identified as Enterobacter sp. genus. Among all selected isolates as successful factors in controlling fire blight pathogen, including isolated isolates and isolates in the collection of Vali-e-Asr University, Bacillus subtilis strain BsVRU1 in the Vali-e-Asr University collection, with 73.5% inhibition, had higher inhibitory power than the other antagonist isolates against the pathogen of fire blight disease.
