AWS AWS Distortion Control & Residual Stress 2 — Questions and Answers
Question 1: Residual tensile stresses in a weldment are most likely to be found:
- Far from the weld in unaffected base metal
- In the weld and HAZ region, parallel to the weld axis (Correct answer)
- Only in the base metal, never in the weld metal
- In presetting fixtures after welding
Correct answer: In the weld and HAZ region, parallel to the weld axis
Residual tensile stresses are highest in the weld metal and HAZ near the fusion line, acting parallel to the weld due to constrained thermal contraction.
Question 2: What is the concern with residual tensile stresses in a structure subjected to fatigue loading?
- They reduce hardness in the HAZ
- They reduce the effective fatigue life by adding to applied tensile stresses (Correct answer)
- They increase porosity in future welds
- They cause the weld to become magnetic
Correct answer: They reduce the effective fatigue life by adding to applied tensile stresses
Residual tensile stresses combine with applied cyclic stresses to accelerate fatigue crack initiation and propagation.
Question 3: How does 'shot peening' or 'hammer peening' of a weld toe improve fatigue life?
- It increases the weld cross-section area
- It introduces compressive residual stresses at the weld toe, counteracting applied tensile stresses (Correct answer)
- It removes the weld reinforcement entirely
- It remelts the weld toe to smooth the transition
Correct answer: It introduces compressive residual stresses at the weld toe, counteracting applied tensile stresses
Peening plastically deforms the weld toe surface, inducing compressive residual stresses that counteract applied tensile stresses and inhibit crack initiation.
Question 4: What is 'lamellar tearing' and which base metal condition makes it most likely?
- Tearing parallel to the weld face in butt welds due to high toughness
- Subsurface tearing parallel to the plate surface due to low through-thickness ductility and sulfide inclusions (Correct answer)
- Cracking at the weld root due to hydrogen
- Surface cracking caused by high welding speed
Correct answer: Subsurface tearing parallel to the plate surface due to low through-thickness ductility and sulfide inclusions
Lamellar tearing occurs beneath welds in the base metal when through-thickness strains fracture planes of low ductility caused by sulfide or silicate inclusions aligned parallel to the plate surface.
Question 5: Which technique for controlling distortion relies on using strong-backs, clamps, or fixtures to physically restrain the parts during welding?
- Pre-setting
- Back-step welding
- Mechanical restraint (fixturing) (Correct answer)
- Peening
Correct answer: Mechanical restraint (fixturing)
Mechanical restraint uses fixtures, clamps, or strong-backs to hold parts in alignment during welding, preventing distortion from occurring.
Question 6: Transverse shrinkage in a butt weld is approximately proportional to:
- The travel speed squared
- The amount of weld metal deposited (weld cross-sectional area) (Correct answer)
- The electrode diameter used
- The shielding gas flow rate
Correct answer: The amount of weld metal deposited (weld cross-sectional area)
Transverse shrinkage increases with the volume of weld metal deposited, because more weld metal means more thermal contraction across the joint.
AWS AWS Distortion Control & Residual Stress 2
Residual tensile stresses in a weldment are most likely to be found: