AWS Distortion Control & Residual Stress Flashcards
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Read the first 7 AWS Distortion Control & Residual Stress flashcards as text
Which post-weld treatment is most effective at redistributing and reducing residual stresses in carbon steel weldments?
Answer: Post-weld heat treatment (PWHT) / stress relief annealing
PWHT at appropriate temperatures (typically 1100–1200°F for carbon steel) allows plastic flow and creep to redistribute and reduce residual stresses.
A fabricator is welding two plates butt-welded together and wants to minimize transverse shrinkage. Which approach is most effective?
Answer: Minimize the weld cross-sectional area by using joint designs with the least required fill
Minimizing the volume of weld metal deposited directly reduces transverse shrinkage because less material contracts upon cooling.
What is the effect of peening on residual stresses in a weld?
Answer: Introduces compressive residual stresses at the surface, offsetting tensile residual stresses
Peening stretches the weld surface plastically, introducing compressive stresses that counteract the tensile residual stresses left by solidification shrinkage.
When welding a closed-section box structure, why is distortion particularly difficult to control compared to open sections?
Answer: Rigid restraint of all four sides increases residual stress without allowing stress relief through distortion
In closed box sections, all sides restrain each other, preventing visible distortion but causing very high residual stresses that can lead to cracking.
Which distortion type is characterized by a rotation of the joint members about the weld axis, causing the plates to form a V-shape when viewed from the end?
Answer: Angular distortion
Angular distortion produces a V-shape across the weld cross-section because the top of the weld shrinks more than the root due to the larger weld cross-section area at the top.
What is the relationship between joint restraint and residual stress magnitude after welding?
Answer: Higher restraint produces higher residual stresses because the metal cannot freely contract
When a weld is highly restrained, shrinkage forces cannot be relieved through movement, so they remain as high residual stresses within the weldment.
Which of the following welding variables, if increased, will most directly INCREASE longitudinal distortion (bowing) in a long weld on a beam?
Answer: Total heat input per unit length
Higher heat input per unit length increases the volume of metal that undergoes thermal expansion and contraction, causing greater longitudinal shrinkage and bowing.