Incomplete fusion can form which of the following defects?

• A. Crack
• B. Undercut
• C. Porosity
• D. Stress point

Answer: (D)

Incomplete fusion leaves an unbonded seam at the joint, which acts as a flaw in the weld. That unfused area can’t carry load properly, so stresses concentrate at the fusion boundary. Under service conditions or thermal cycling, this concentration readily initiates and propagates a crack along or near the weld, making cracking the most likely defect you’d see from incomplete fusion. Undercut, porosity, and terms like “stress point” describe different issues: undercut is a groove at the weld toe from heat/technique, porosity comes from gas pockets during solidification, and a vague “stress point” isn’t a standard defect term for this situation.