Environmental Fatigue Crack Growth

Purpose 

Perform fatigue crack growth and fracture mechanics research on aerospace alloys, simultaneously mimicking service loads and environments; provide relevant information needed to characterize material performance in service-like environments, including crack growth rates, fracture loads, strain field data (digital image correlation), and high-fidelity characterization of the test environment.
Equipment/Test Method
Automated Fatcragrows

Automated fatigue crack growth and fracture test systems
-Computer-controlled servo-hydraulic test machines
-Load capacities: 20 kips (x3)
-Ability to run tests at elevated temperature (up to 600oC)
Environmental test Chamber

High-Purity Gaseous Test Chamber
-Environments- Vacuum (< 10-9 Torr)- Argon, Nitrogen, Helium, Water Vapor, etc.
Aquious Test Chamber
Aqueous Test Chamber- environments (e.g., salt water)
envircracgrsw
Small-crack testing (potential difference)

 

Typical/Recent Experiments 

  • Small crack tests on aluminum alloy coupons containing countersunk fastener holes

Geometry selected to mimic aircraft lap-splice joints
Cracks monitored using potential difference
Tests conducted in a saline solution created to be identical to fluid found in lap-splice joints during destructive teardowns.

  • Near-threshold fatigue crack closure

Tests conducted to isolate dominant near-threshold crack closure mechanisms
Testing in vacuum to eliminate oxide-induced crack closure
Digital image correlation used to characterize crack closure

  • Fatigue crack growth tests in vacuum to mimic space environments

Testing done in a Mars-like atmosphere by back filling with appropriate gases