Avaliação da propagação de trinca por fadiga em soldas subaquáticas molhadas

Abstract

The characteristic of fatigue cracks propagation of welds produced in underwater wet welding were evaluated out of water. Butt welds produced in a hyperbaric chamber at simulated depths of 10, 60 and 90m. A gravity welding system was used to deposit E6013 commercial electrode coated with vinylic varnish. Welding joints were prepared from an A-36 plate, 19 mm thick with 45 V-grooves filled with an average of 18 passes. The fatigue crack growth rate properties in the near-threshold and Paris regimes for the weld metal were determined by using compression pre-cracking followed by load reduction and constant-amplitude test procedures. Mechanisms of crack propagation were investigated on fracture surface by means of Scanning Electron Microscope and Confocal Laser Scanning Microscopy. Lateral surfaces observations, considering different loading conditions, were made using Optical Microscopy. The resulting fatigue crack growth rates were shown to depend on pore density that varies with underwater wet welding depth. Fatigue crack growth path shows a branched morphology, which is consequence of interaction between cracks and pores. The results of this study show that underwater wet welding procedures produce fatigue resistant weld metal that is adequate for use at low applied stresses in structures, in agreements within design codes.