Which of the following indicates localized failure in a weld caused by thermal stresses?

The correct choice highlights crater cracks as an indication of localized failure in a weld resulting from thermal stresses. Crater cracks typically occur at the end of a weld bead or at the center of a weld puddle when the weld metal solidifies. They are associated with the rapid cooling and contraction of the molten weld metal, which can generate significant thermal stresses. When the weld solidifies, these stresses can surpass the tensile strength of the material, leading to the formation of cracks.

Understanding the nature of crater cracks emphasizes the importance of managing thermal profiles and solidification processes in welding, as this can directly influence the quality and integrity of the weld. Proper techniques, including preheating and controlled cooling rates, can help mitigate the risk of such failures.