Abstract
Despite the large number of proposals in the field of fatigue prediction of welded joints, a globally accepted and unified theory, which applies easily to any load condition, does not exist. Real life components, indeed, differ in geometry and/or type of load from the structural design for which they are regarded by Standards, so that a lot of precautionary safety factors are used that lead to an underestimation of the actual fatigue life of joints. Infrared thermography has a great potential in this field, both from structural and thermomechanical points of view. It enables a full field stress analysis with a sufficient spatial resolution so that the complexity of the stress state at the weld toe and its time evolution are taken into account, emphasizing anomalies that may predict structural failure. A new methods for evaluation fatigue limit damage is presented in this paper and in particular interesting results derived from analysis of the evolution of thermoelastic signal phase. Variations in the value of signal phase indicate a not elastic behaviour and plastic dissipation in the material.
Highlights
Despite the large number of proposals in the field of fatigue prediction of welded joints, a unified theory and global validity, which applies to any load condition, does not exist
The design components differ in geometry and/or type of load from the structural details for which are regarded by rules so recourse usually a lot of precautionary safety factors that lead to an underestimation of the actual fatigue life of the joint
There are already in literature [2,3] thermal methods that allow the determination of fatigue limit and even the entire Wöhler curve
Summary
Despite the large number of proposals in the field of fatigue prediction of welded joints, a unified theory and global validity, which applies to any load condition, does not exist. There are already in literature [2,3] thermal methods that allow the determination of fatigue limit and even the entire Wöhler curve Anyway these methods are available only for base material testing of standard specimens and show many problems for materials different from steel. Traditional methods require the determination of heat sources and of plasticised area A new method is presented based on the analysis of the evolution of the phase change over time during the same loading stepped procedure that is much simpler and with an higher signal to noise ratio and is entitled to give good results with difficult materials such as aluminium alloys
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