Final answer:
The defect referred to when the cross-sectional thickness of the base metal is reduced along the edge of a weld bead is called undercut. This defect weakens the weld area by causing stress concentration, potentially leading to cracks. Thus (option a) is right answer.
Step-by-step explanation:
When the cross-sectional thickness of the base metal has been reduced along the edge of a weld bead, this defect is referred to as undercut. Thus (option a) is right answer.
This is a type of weld defect that occurs when the weld does not fill in completely or the base metal is melted away along the edges of the weld. Not only does undercut weaken the weld, it can also lead to cracks forming due to stress concentration. Undercutting is commonly caused by incorrect welding parameters, such as too high a current or incorrect angle of the welding torch.
In welding, various defects can affect the integrity and strength of the weld, including overlap, porosity, and incomplete fusion.
Overlap occurs when the weld metal flows onto the surface of the base metal without bonding. Porosity is the presence of tiny cavities or holes within the weld caused by trapped gases. Incomplete fusion is a failure of the weld metal to properly meld with the base metal or between weld passes.