PSI - Issue 25

Pietro Foti et al. / Procedia Structural Integrity 25 (2020) 201–208 Pietro Foti, Filippo Berto / Structural Integrity Procedia 00 (2019) 000–000

202

2

material toughness

IC K

radius of the control volume

0 R

SED

strain energy density critical strain energy

C W

Greek 2 

opening angle of V-notch

supplementary angle of  :     



mode 1 and 2 Williams’ eigenvalues for stress distribution at V-notches

1 2 ,  

Poisson’s ratio



1. Introduction In order to improve the fatigue strength of a welded detail several techniques can be employed. The improvements led by these methods act mainly on the geometry of the welding or on the residual stress generated during the welding process. The methods based on the modification of the weld geometry operate on the weld toe defects while the residual stress methods impose beneficial compressive stresses in the critical zone to contrast the crack initiation and propagation. These methods have usually more effect in improving the fatigue behavior of high-strength steels than of construction steels. Among the methods acting on the welding geometry, there is the TIG-dressing process. In this technique, the standard equipment, used to realize the gas tungsten arc welding, is exploited without the use of filler material to smooth the sharp V-notch that is usually created at the welding toe during the welding process itself. The optimum conditions to TIG dressing have been proposed by Kado et al. (1975) with a depth of penetration of the arc ranging from 3 mm to 6 mm depending on the heat input. As noted by Fisher et al. (1993) this technique has been used to remove 4 mm deep fatigue cracks. However, this technique depends on the operator skill and requires proper operating conditions such as cleanliness of the welding but also welding speed, position and angle of the torch and as stated above welding deep in order to obtain an optimum weld toe shape that ensure a better fatigue behavior of the entire joint. 2. Materials and Methods 2.1. Fatigue tests data Table 1 reports the results of the fatigue tests, carried out by Bettarin (2015), re-analyzed in the present work in terms of averaged SED. The details analyzed are welded joints made of S275JR both in as welded condition and TIG dressed in order to have a radius ߩ ൌ ͷ݉݉ at the weld toe. The geometry of the joint is given in figure 1.