What part of the weld will crack first?

• A. The toe
• B. The root of the weld
• C. The crown
• D. The weld center

Answer: (A)

The weld toe is the most likely first crack location because it is where the weld bead meets the base metal, creating the sharpest change in geometry. That sharp transition concentrates stress, and any surface flaws, undercut, or residual stresses from welding amplify this concentration. Under cyclic or tensile loading, these factors make the toe the starting point for fatigue cracks that then propagate along the weld. The crown, being the top surface of the bead, generally has a smoother transition and lower local stress concentration than the toe, so cracks there are less likely to initiate first. The root can crack if there are fusion defects or hydrogen-related cracking at the weld root, but those conditions are specific and don’t occur as universally as the toe crack initiation. The weld centerline experiences more uniform stress and lacks the abrupt geometric discontinuity that drives early initiation, so cracks there are not the typical first failure mode.