Welding Flashcards
What is arc welding?
Power supply and electrode, transfer of electrons from electrode to work piece
What is submerged arc welding?
Uses flux layer to exclude oxygen from the weld
easily automated but only horizontal structures
but leads to entrapment of non-metallic inclusions
When does Widmanstatten ferrite grow?
when the cooling rate is too fast for pearlite and allotriomorphic ferrite
What is acicular ferrite?
A finer form of widmanstatten
What is MIG welding?
metal inert gas welding uses a consumable electrode
What is TIG welding?
tungsten inert gas welding uses a non-consumable tungsten electrode
How does welding cause residual stress?
As liquid cools it contracts and then further contracts into solid state
What are primary and secondary stresses?
Primary - normal or shear stresses imposed by a load
Secondary - normal or shear stresses developed by the constraint of adjacent material or self-equilibrating and self-limiting arising from geometric discontinuities and stress concentrations
What is a residual stress?
Stress that remains when a primary stress is removed, ie secondary
What are the length scales of residual stress?
Type 1 - macro stresses over the largest distance
Type 2 - Integranular over a few grains
Type 3 - intergranular over inner atomic distances caused by point defects and dislocations
How can residual stresses be analysed?
Welded bead on plate, FE
What is the FAD?
Failure assessment diagram - to predict whether a component will fail under given conditions, proximity to failure is approximated by K/K1c
Why are weld residual stresses an issue for nuclear plants?
boiler bifurcations suffer creep damage due to reheat cracking
What is creep?
Time dependent plastic flow under constant load
What are the main stages?
1 - transient creep
2 - steady state creep
3 - tertiary creep and fracture
