Application of the SPI technique to study the effect of corrosion factors on the crack-tip deformation of metals

A computerized digital speckle-interferometry system (SPI) was set up so that the near-tip in-plane displacement and the strain field of precracked specimens can be determined experimentally in air and in solution. The effects of three corrosion factors on the crack tip were considered: 1. (1) the effect of an anodic current, 2. (2) the effect of hydrogen charging 3. (3) the effect of adding an inhibitor. The results in air and in solution show that the near-tip displacement field and strain field are far more complex than the results of the classic theoretical analysis. It was also found that an anodic current raises the level of strain and the size of the active plastic zone up to 3 or 4 times more than that under free corrosion conditions, that hydrogen charging makes the material at the crack tip harder and that the inhibitor controlling the anodic process decreases the dissolution rate at the crack tip and so decreases the extent of corrosion-enhanced deformation.