In a fillet weld, the weakest section is the
- Asmaller side of the fillet
- Bthroat of the filletCorrect
- Cside perpendicular to force
- Dside parallel to force
Solution
Concept
A fillet weld fails across its minimum section, which is the throat, so strength is based on the effective throat thickness.
Formula
t = 0.7 × s (for equal-leg 90° fillet weld)
Step-by-step solution
1. A fillet weld has a roughly triangular cross-section. 2. The smallest distance from the root to the face is the throat. 3. The throat is the minimum area section, so stress there is highest. 4. So the weakest section is the throat, answer (B).
Explanation
The throat is the shortest distance from the root of the weld to its face. It has the smallest area, so failure happens along it. That is why weld design uses the effective throat thickness.
Why the other options are wrong
A: The sides (legs) are larger than the throat, so they are not the weakest. C: The direction of force does not change the minimum section. D: Same reason as C; failure is still through the throat.
Shortcut
Weld strength = throat × length × design stress, so the throat is the critical section.
Common mistake
Using the leg size instead of the throat thickness in strength calculation.
Correct answer: B) throat of the fillet