Failure Analaysis

   Failure as a Design      Criterion

   Fracture Mechanics

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Tutorial Questions

 :: 
Griffith Equation


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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

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Theory Resource



Problem 8

This question is straightforward, and shows an application of the concept of stress state being determined by the ratio of crack tip plastic zone size to specimen thickness. This concept is used in plane strain fracture toughness tests to BS 7448 : Part 1 : 1991 in choosing specimen thickness and checking that plane strain conditions existed in the test (see Problem 6, i.e. Missile Motor Case Fracture). It should take about 10 minutes to complete.
Catastrophic fracture occurred in a thick steel plate during proof testing, at an applied stress of 700 MPa. The initiating defect was an embedded sharp penny-shaped flaw with a radius of 2.5 cm. Calculate the fracture toughness of this steel.

It is desired to check this value by determining the plane strain fracture toughness from standard tests. The yield strength of the steel is 1100 MPa. A sheet of nominally similar steel, 7.5 mm thick, is available. Is this sufficiently thick to obtain a valid K1C value? If not, what thickness of steel should you order?

The stress intensity solution for an embedded circular crack is:


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