Residual stresses and fatigue behavior of hybrid butt welded joints

Abstract

Ti6Al4V alloy combines mechanical strength, deformability, excellent fatigue and corrosion resistance and high strength to weight ratio. Furthermore, the mechanical behavior remains excellent at high temperature. Such characteristics make this material attractive for numerous applications (structural, aerospace and naval) because of recent improvements in welding techniques (laser, hybrid laser/MIG) that allow realizing high quality titanium welded joints. However some problems related to the welding, as deteriorated material properties, residual stresses and distortions, need further investigations. Residual stresses can have a significant influence on the fatigue life of structural engineering components. For the accurate assessment of fatigue life a detailed knowledge of the residual stress profile is required. This paper presents a study on residual stresses of Ti6Al4V butt plates welded by hybrid laser/MIG process. Residual stresses were measured by hole drilling method using electrical strain gage rosettes bonded at different position, in order to evaluate magnitude and distribution of residual stresses along the cord. Residual stresses curves obtained are presented and discussed in terms of transversal and longitudinal residual stresses. Residual stresses were also measured at surface by means of X-ray diffractometer. Besides residual stress measurements, this paper presents experimental fatigue results on titanium grade 5 butt welded joints. The fatigue curves expressed in terms of nominal amplitude of stress (according to the traditional global method) and in terms of local amplitude of strain (according to the local Wel.Fa.Re. method) have been plotted after the experimental tests. Electrical strain gauges bonded close to the weld toe have been used to calculate the local strain amplitude. The aim of this work is to present experimental data related to welding processes in order to confirm the validity of currently procedures or improve them.