Study on Residual Stress of Friction Stir Welding by Moiré Interferometry and Hole-Drilling Method

Friction stir welding(FSW) is a new welding technique since 90's,which is especially suitable for materials of poor fusion weldability,such as aluminium alloy.Residual stress distribution of FSW has high gradient,which makes the conventional strain gauge hole drilling method unsuitable.A combined method of moiré interferometry and incremental hole drilling was conducted to study non uniform residual stresses,calculation formula and the experimental technique were presented.This method makes use of moiré fringe patterns of three measurement points to calculate the local residual stresses of the interested region around the hole.This paper studied the non uniform residual stresses of a friction stir welded aluminium alloy plate in plane and in depth using the presented method.Experimental results show that the dominant longitudinal residual stress field is tensile within the friction band,just outside the band where the field drops steeply.Further out there are regions of balancing compression residual stress falling to near zero.