The bobbin tool is a new design of the friction stir welding tool that provides the opportunity of the simultaneous double sided welding. The present research aims to design and manufacture a Floating bobbin tool; the capability of which is examined through welding aluminum alloy 6061. The results indicated that the high quality and defect-free butt welds can be produced via this tool. Moreover, the strength of the welds is similar to the strength of welded samples done by the conventional friction stir welding method. Regarding the quality and strength, the obtained samples were investigated by mechanical tests including tensile strength test and hardness test. Obtaining 60. 7% joint efficiency is indicative of success in the friction stir welding process; and, thus the efficiency of the designed tool. Besides, the second major characteristic of welding is the hardness, which is due to the dissolution of sediments, is decreased in the stirred area. This finding is confirmed by the behavior reported by the other investigators in the literature.

Conventional fusion welding of aluminum alloys results in coarse-grained structure, inevitable defects, and significant softening in the welding region. Friction stir welding with bobbin tool is a technique of friction stir welding method that has a great potential for developing applications of friction stir welding method in marine, aerospace, and automotive industries due to having an extra shoulder. Sheets of 5083 aluminum alloy with a thickness of 3 mm were welded using the bobbin tool friction stir welding method to assess the feasibility of similar joining. The effect of different process variables such as shoulder pinching gap, transverse speed and tool rotation speed was investigated. The results showed that a sound joint is achieved at a transverse speed of 13 mm / min and a tool rotation speed of 1350 rpm. The results of tensile test showed that the obtained joint efficiency is 94. 5%, which is higher than the joint efficiency of fusion methods and comparable to the joint efficiency of conventional friction stir welding. Microscopic evaluation of the fracture surface of welded specimens showed that for similar joints, the dominant fracture mechanism is ductile fracture.

The purpose of this study is to investigate the effect of using bobbin tool on the mechanical properties of aluminum alloy 6061-T6 in friction stir welding. The friction stir welding method is one of the suitable process to welding aluminum alloys to reducing welding defects and increase joint strength. In this process, the welding parameters such as the rotational speed of tools and travel speed, beside the type and geometry of the tool also has a great effect on the quality and strength of the weld. In this study by using the typical tool and bobbin tool the effect of welding parameters on the mechanical strength of the welded joint are investigated. The results of this study show that the bobbin tool has a higher performance and capability in connection with this type of alloy. The main advantage of the bobbin tool is welding the both sides of the weld zone at one stage of the welding process compared to the typical tool. Also in terms of mechanical strength of connection, the use of bobbin tool has resulted in improving the tensile strength of the connection and resistance to a better impact. The effects of welding parameters show that by increasing the rotational speed of the device from 900 to 1100 rpm as well as increasing the travel speed of the tool from 25 to 32 mm/min of the joints shear strength has increased.

Three mm thick plates of commercial pure copper were welded via friction stir welding method using a Floating bobbin tool. The effect of different process variables such as the tool transverse speed and the tool rotation speed were examined in order to create a weld with the desired properties. A defect-free weld was obtained at a rotation speed of 1400 rpm and a transverse speed of 18 mm/min with a shoulder pinching gap of 2. 7 mm. After the welding process, the soundness of the welds was confirmed by non-destructive methods of visual inspection and X-ray radiography. The results of the transverse tensile test showed that the as-weld joint efficiency was 86. 4%, which was higher than the joint efficiency made by the fusion welding method. The strength of the welds was such that the fracture of the workpiece was in the heat affected zone after the tensile test. On the other hand, the grain size of the weld was significantly less than the base metal. The lowest hardness around 40VHN was attributed to the middle of the thickness of the weld, while the highest hardness was in the vicinity of the lower shoulder of the tool, which was about 80 VHN.

In this research the effect of different rotational speeds and different materials for producing the bobbin tool in friction stir welding process on hardness and impact resistance changes for Aluminum 6061-T6 alloy is studied. According to the results, the most desirable tool to accomplish this process should be from H13 hot-work steel and the pin length should be as long as the work piece thickness. The most optimized ratio between tool shoulders diameter and pin length is about 3 to 5. Accordingly, the designed tool for the mentioned process had 20 mm shoulder diameter, 6 mm pin diameter and 4 mm pin length. Results showed that increasing the rotational speed had desirable effect on connections appearance quality and also cause raising the amount of consumed energy for breaking the work pieces and naturally it decreases the return angle of the projectile. Microstructure hardness tests showed that welding speed increase caused welded zone grains size changing. So it will increase the weld hardness. Furthermore, joints macrostructure’s defects were studied and determined that increasing rotational speed has good effect in decreasing these defects. Also in this research, the effect of using HSS tool as the bobbin tool material checked was investigated finally H13 was selected as the bobbin tool material due to the better strength in most other speeds. 1500 rpms selected as the best rotational speed in terms of affect on mechanical properties.

In order to evaluate the possibility of the similar and dissimilar welding of 5019 and 7039 aluminum alloys, plates of 3 mm thick from this alloy were welded via Self-Reacting Friction Stir Welding (SRFSW) method. Floating bobbin tool was designed and manufactured from heat –treatable hot working steel to perform the welding process. The effect of various process variables such as the shoulders pinching gap, the tool transverse speed and the tool rotational speed were investigated to establish a defect-free joint. Following the visual inspection and X-ray radiography, it was found that a defect-free joint is obtained at the transverse speed of 22 mm/min and rotational speed of 1120 rpm. The results of tensile test, also, revealed that the joint efficiency of 5019-5019, 7039-7039 and 7039-5019 joints are 72, 76 and 91. 5%, respectively. Accordingly, these amounts were more than the joint efficiency of the fusion welding, and comparable with/more than the joint efficiency of Conventional Friction Stir Welding (CFSW). Microscopic evaluation of the fracture surface of welded pieces indicated that the dominant fracture mechanism for similar joints is the soft fracture, while the one for non-similar fracture is the brittle fracture. Assessment of the cross-sectional hardness of the welded pieces near the upper and lower shoulders showed that the degree of hardness near the lower shoulder of the tool is always higher, which can be attributed to the lower temperature of the work piece in this area.

The main purpose of this study is experimental and numerical investigation on failure of friction stir welded AA6061-T6 joint under tensile-shear test using damage model. In the past, due to the problem of development in high-strength welds, fatigue and corrosion resistance in aluminum, the use of welding in these industries was limited. However, with the advent of the friction stir welding process, aluminum alloys has been considered and their welding has become possible. The use of lightweight materials, especially aluminum alloys in the automotive, shipbuilding and aerospace industries is increasing rapidly and the operation of these alloys requires the development of joining and welding methods. Therefore, the study and analysis of friction stir welding is substantial. In this study Gurson-Tevergaard-Needleman (GTN) model is utilized to study the failure of welded joint. A finite element (FE) model is developed to simulate failure of the welded joint under tensile-shear test. To validate the model, 8 samples including 4 samples of friction stir welds with conventional tool and 4 samples with bobbin tool are welded with different welding parameters to obtain failure. The comparison between experimental and FE model results shows that the GTN model has a good reliability to predict the failure force. In addition, the results show that the FE model can predict truly the starting of failure in the welded joint.

Quantifiers basically occur adjacent to a nominal phrase. However, sometimes the quantifier and the nominal phrase appear apart in sentences. This phenomenon is referred to as quantifier Floating (Q-Floating). The most prominent approach to Q-Floating is stranding analysis, according to which the quantifier and the adjacent nominal phrase together make up a single constituent, and in the course of derivation, the nominal phrase moves from this constituent to a higher position, stranding the quantifier in situ; in other words, stranding analysis considers the Floating quantifier construction as the result of a transformation from non-Floating quantifier construction. This paper addresses the structure of Floating and non-Floating quantifier constructions, provides evidence from Persian to indicate the independence of their structures, and argues for the oblige toriness of each structure. The Floating quantifier is shown to be a late adjunct to a copy of its associated DP: in the derivation leading to quantifier Floating, a DP moves from its θ-position and then receives a QP as an adjunct, and then it moves again to a higher position and strands the quantifier in situ.  According to Chomsky’s (2013) Labeling Algorithm, when QP is an adjunct to DP, the movement of DP and it’s leaving the QP behind is obligatory; to put it another way, Floating quantifier construction is obligatory. As opposed to Floating quantifier construction, in non-Floating quantifier construction, QP is not an adjunct. In this construction, the DP is the complement of the quantifier head. Given Labeling Algorithm, this construction is obligatorily motivated, too. In addition, since quantifier phrase is the topmost nominal phrase in such constructions, it is a phase; and in order for the DP to move out of this phase, it needs to move first to the specifier position of the QP, but this movement is considered too short. For this reason, DP cannot move off the QP in non-Floating quantifier constructions