Joining metal sheets by welding different materials is absolutely necessary in the automotive and other industries. However, different welding methods may be used depending on the applications and materials. Spot welding is one of the applicable methods, which includes resistance spot welding (RSW) and friction stir spot welding (FSSW). Each method has its individual characteristics and advantages or disadvantages. RSW is one of the most popular welding methods, but in joining light-metals such as aluminium alloys, the application of this method would lead to some major difficulties [1]. Recently, automotive, aerospace and other industries have begun to pay serious attention to the FSSW method for joining metal sheets [2] to [3]. This method could be considered as an upgraded variant of the friction stir welding (FSW) process. Both FSW and FSSW processes can be termed as standard methods of welding aluminium alloys. FSW is a solid-state joining process which means that the metal is not fully melted and instead it is just softened [4]. One of the most important features of the FSW process is that the main characteristics of the materials remain unchanged as much as possible. In order to apply the FSSW method correctly, it is necessary to provide a proper model, which would allow for a more exact study of the fatigue and dynamic properties of the welding. There are some studies that deal with modelling and prediction of fatigue life of metals welded by FSSW methods in various applications. Some of these studies will be described below.The fatigue life of FSSW in aluminium 6061-T6 sheets were investigated by Wang and Chen [5]. In this work, tool geometry, the rotational speed, the holding time and the downward force were considered the most important processing parameters. They modelled the three dimensional FSSW's crack as a twodimensional crack problem. The fatigue life for FSSW has also been investigated by Lin et al.[6] to [8] and by Ericsson et al. [9]. They used fracture mechanics to solve the modelling problem. In all of the abovementioned papers the weld nugget is modelled as a cone. For example, in [6] to [8], a fatigue crack growth model was adopted based on the Paris law and the local equivalent stress intensity factors. Kinked cracks were applied to predict the fatigue life of FSSW and the fatigue crack propagation; the modelling results were then compared with experimental ones. In [9] the global stress intensity factor was used to predict the crack growth rate of the FSSW. These stress intensity factors were calculated from FE models. The main purpose of the above-mentioned works was to predict fatigue life using proper modelling, but additional goal of other studies has been to model welding in order to study the dynamic and vibrational characteristics of the model, which are very important for designing proper welding techniques, especially in the automotive and aerospace industries. Shang [10], Wang et al. [11] and Shang et al. [12] and [13] investigated the effects of fatigue cracks on the frequen...
Knowing how a musical instrument vibrates can benefit the tonal characteristics shaping of the instrument. In this research, an approach for investigating the mode shapes and natural frequencies of Setar body is addressed. First, mechanical properties of wood used in the production of Setar are analyzed experimentally. Then a numerical modal test is performed to find the mode shapes and natural frequencies of Setar structure. To validate the results obtained by the numerical method, experimental modal testing is also done for the structure, and it is found that the results of both the methods are in good consistency. As the vibration pattern of plates is of utmost importance in the production of musical instruments, vibration patterns of a Setar plate are experimentally extracted and the results are compared with finite element analysis.
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