Failure Analaysis

   Failure as a Design      Criterion

   Fracture Mechanics

 :: 
Tutorial Questions

 :: 
Griffith Equation


 :: 
Stress Intensity Factor and Fracture Toughness Testing
- Stresses Close to a Crack Tip
- Fracture of Glass
- High Strength Versus high Toughness
- Quenching and Residual Stress
- Missile Motor Case Fracture
- Fracture Toughness Tests
- Plastic Zone Effect
- Specimen Thickness Effect
- Growth of Semi-Elliptic Flaws
- Leak-Before-Break Concept
- Pressurised Vessels
- Fracture of a Beer Barrel
- Pin-Loaded Lug
- Materials Selection and Temperature
- Chemical Reactor Vessel
- Fracture of Ice

 :: 
Characterising Sub-Critical Growth
 -  Fatigue Life Prediction
 -  Stress Corrosion Cracking

 :: 
Theory Resource



Problem 5

This problem is based on the real failure analysis of ICBM motor cases in the 1960's, and was an early use of fracture mechanics. It should take about 5 minutes to complete.
Following the failure of a rocket motor casing at an applied stress of 1260 MPa during hydraulic proof testing, investigation revealed an internal elliptical flaw which had extended to 4.0 mm by 1.6 mm prior to fracture. The material had been heat treated to a proof strength of 1645 MPa and had a K1C value of 60 MPa m1/2.

Calculate the applied stress necessary to cause fracture, using the K-calibration shown below. Does the calculated value agree with the observed value of failure stress?
Ksol.jpg (177284 bytes) Where, for surface flaws:

and for embedded flaws:


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