Study of the effect of toe grinding on fatigue response of cruciform welded joints of ASTM A131 grade AH36 steel

Failures of mechanical and structural components due to fatigue are unfortunately recurrent in industry and there is a special concern when these components contain welded joints. Over the years, studies have been carried out with the objective of developing procedures and techniques for fatigue life increasing of this type of joints. Among them, a set of techniques consisting of bead or fillet reworking after the welding process completion has been developed. Present work aims to evaluate the effect, in terms of life under cyclical load, of the toe grinding technique, which consists of a weld toe machining process employing a round tip tool. Such a process generates a shallow circular groove which allows the reduction of the stress concentration factor as well as microdefects removal. More specifically, the study focused on the influence of such process on the fatigue life of cruciform joints of ASTM A131 -Grade AH36 steel, welded by Flux Cored Arc Welding Process and subjected to transverse cyclic loading. Experimental procedures involving different manufacturing areas were applied for specimens preparation, including a prequalified welding process, as well as nondestructive weld bead inspection techniques. Even so, lateral cutting of the specimens evidenced lack of penetration at the root of the beads. After that, the sample was divided into two groups - with and without toe grinding application - and the fatigue tests were performed under similar conditions for both groups. The results obtained indicate that the failure mechanism, in the case of ordinary specimens, was the propagation of intrusion-type micro-cracks which were previously located at the weld toe. On the other hand, the specimens presenting toe grinding grooves suffered a failure site changing, from toe to the weld root, accompanied by an expressive increase in the number of cycles up to failure.