Prevention of HS-type crack in welding under pulsating loads

Repair and reinforcement works using welding on steel structures in service conditions are often done under pulsating loads. The hot crack, which was classified into that in solid-liquid state (solidification crack) and that in solid one (called as the HS-type crack) initiating at high temperature, sometimes occurred in the welding under the pulsating loads. The study examined the preventive condition of the HS-type crack by using the results of the weld hot cracking test under the pulsating loads. Then, prevention of the hot crack (including the solidification crack) was synthetically investigated in mechanics. The equation which describes the initiation of the HS-type crack produced in the welding under the pulsating loads was derived. Based on it, a practical equation to decide the initiation of the HS-type crack was shown, in which relative root gap opening displacement, Delta delta , that can be easily measured before the welding was used as a measure for the crack initiation. Applying it to the results of the hot cracking test, the validity of the practical equation proposed was concretely shown. The critical strain for the hot crack of the weld metal used in the study was shown. Concerning the solidification crack initiation, the main factor was the product of Delta delta by the external loads and repeated number. The main factor for HS-type crack initiation was the maximum strain rate (the root gap opening rate) by the external loads in a cycle. The procedure to apply the evaluating expression for the prevention of the hot crack produced in welding under pulsating loads, that is the solidification crack and the HS-type was shown. So far as the equation proposed in the study is used, the critical strain is not necessary to be obtained from a series of the weld hot cracking test in the whole frequency range.