Characterisation of steel welded joints by infrared thermographic methods

Despite the large number of proposals in the field of fatigue prediction of welded joints, there is no worldwide accepted and unified theory which can be easily applicable to any load condition. Real life components, in fact, differ in geometry and/or type of load from the structural design considered by the Standards, hence a lot of precautionary safety factors are used, leading to an underestimation of the actual fatigue life of joints. Infrared thermography has a great potential in this field. In fact, it enables a full-field stress analysis with an adequate spatial resolution so that the complexity of the stress state at the weld toe and its time evolution are taken into account, emphasising anomalies that may predict structural failure. This paper presents a new method for the evaluation of the fatigue limit, focusing on interesting results derived from the analysis of thermoelastic signal phase evolution. Variations in the value of signal phase indicate a non-elastic behaviour and plastic dissipation in the material.