PSI - Issue 14

K. Vijayan et al. / Procedia Structural Integrity 14 (2019) 642–648

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K.Vijayan et. al. / StructuralIntegrity Procedia 00 (2018) 000 – 000

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1. Introduction Friction stir welding is a joining process patented by Thomas et al. (1991). This is a solid state welding process wherein the tool rotates and traverse along the length of a clamped and butted work piece to be weldedas described by Mishra & Ma (2005). As the tool traverses along the length depending on the prevailing condition of stick or slip, the friction and plastic deformation generates heat. The FSW tool consists of two parts the shoulder and pin. A proper deign of these can aid in the material flow.Welding techniques can alter the microstructure depending on the type of welding. Those welding process which involves melting such as arc welding significant changes in the microstructure might not be observed. However, for a process like friction stir welding there could be significant changes in the microstructure. The speed of rotation, the axial load, feed rate and the type of tool influencesthe structural properties of the weld. Various authors such as Colegrove & Shercliff (2004) and Reynolds (2008)have tried to model the plastic flow using solid and fluid mechanics. The purpose of this study is to understand the influence of FSW microstructure (microscopic property) on the damping (macroscopic property). 2. Experimental study Friction stir welding was carried out on Aluminum 1100. The study was carried out on a specimen of dimension 100x50x5 mm. A parametric study was carried out by varying the tools, carriage speed and tool ration. Three cases carriage speed 28, 40 and 58 mm/min and Spindle speeds 1000,1400 and 2000rpm were considered. For the given spindle speeds and carriage speed three tools with different pin configuration namely tapered cylindrical, trapezoidal and straight cylindrical were tested. The tools shown in Fig.1have the shoulder diameter of 35 mm and the contact surface is active till 30 mm beyond which a taper is provided.

Fig. 1. FSW tools used for study

Four K type thermocouples were placed across the width on the retrieving side. First thermocouple was placed at 15 mm from the tool shoulder and subsequent ones at a spacing of 15 mm.The retrieving side was considered since previous researchers indicated that failure during tensile test generally occurs on the retreating side. The specimen was clamped and a backing plate was chosen with low thermal conductivity for proper welding similar to procedure followedby Kumar et al. (2013).

2.1. Tensile testing

A tensile test was carried out on UTM on the welded specimen. The variation in Young's modulus and tensile stress at Yielding for the various combinations of the system parameters are shown in Fig.2. A wide scatter in the values can be observed which indicates that these system parameters have significant influence on the weld quality.