7.1 Tensile Testing
Key Takeaways
- Tensile testing measures UTS, yield strength, elongation, and reduction of area
- Transverse tensile tests are required for procedure qualification — must equal or exceed base metal minimum UTS
- Fracture location matters: base metal fracture at ≥ minimum UTS is acceptable
- Elongation and reduction of area measure ductility — low values indicate embrittlement
- The stress-strain curve shows elastic, yield, plastic, UTS, and fracture behavior
- Two transverse tensile specimens are required per PQR under AWS D1.1
Last updated: March 2026
7.1 Tensile Testing
Tensile testing is the most fundamental mechanical test in welding qualification. It measures a material's response to uniaxial pulling (tensile) force, determining key mechanical properties.
Properties Measured
| Property | Definition | Units |
|---|---|---|
| Ultimate Tensile Strength (UTS) | Maximum stress the material can withstand before fracture | psi or ksi |
| Yield Strength | Stress at which permanent deformation begins (0.2% offset method) | psi or ksi |
| Elongation | Percentage increase in gauge length at fracture (measure of ductility) | % |
| Reduction of Area | Percentage decrease in cross-section at fracture (measure of ductility) | % |
Tensile Test Specimens for Weld Qualification
| Specimen Type | Purpose | Loading Direction |
|---|---|---|
| Transverse tensile | Tests the entire weld cross-section (weld metal + HAZ + base metal) | Perpendicular to weld axis — load across the joint |
| All-weld-metal tensile | Tests only the weld metal properties | Parallel to weld axis — specimen from weld metal only |
| Longitudinal tensile | Tests the entire joint along the weld axis | Parallel to weld axis |
For procedure qualification (PQR) under AWS D1.1:
- Two transverse tensile specimens are required
- Each must have a tensile strength not less than the minimum specified UTS of the base metal
- If the specimen breaks in the base metal outside the weld and HAZ at a stress ≥ minimum UTS, the test is acceptable regardless of where fracture occurs
Stress-Strain Relationship
The stress-strain curve from a tensile test reveals important material behavior:
- Elastic region — material returns to original shape when load is removed (Hooke's Law: stress = E × strain)
- Yield point — permanent deformation begins
- Plastic region — material deforms permanently but still carries increasing load
- Ultimate tensile strength — maximum load before necking begins
- Fracture — material breaks
Interpreting Results for the CWI
| Result | What It Tells You |
|---|---|
| UTS meets minimum | Weld joint is as strong as the base metal — passes |
| UTS below minimum | Weld joint is weaker than required — fails |
| Fracture in weld metal | Weld metal may be understrength — evaluate carefully |
| Fracture in HAZ | HAZ may be embrittled — evaluate microstructure and heat input |
| Fracture in base metal | Weld and HAZ are stronger than base metal — generally acceptable |
| Low elongation | Material lacks ductility — may indicate embrittlement |
For the Exam: Know that transverse tensile test specimens must equal or exceed the minimum specified UTS of the base metal. If the specimen breaks in the base metal at or above minimum UTS, the test passes.
Test Your Knowledge
For a procedure qualification under AWS D1.1, the transverse tensile test specimen must have a tensile strength:
A
B
C
D
Test Your Knowledge
Which property measured in a tensile test indicates the ductility of the material?
A
B
C
D