Failure Analaysis

   Failure as a Design      Criterion

   Fracture Mechanics

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Tutorial Questions


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Griffith Equation
- Fracture of Glass Sheet
- Fracture of Maraging Steel
- Relative Magnitudes of Plastic Work and Surface Energy
- Fracture of Perspex Sheet
- Fracture of Cast Iron
- Failure Criteria : Yield Versus Fracture
- Griffith Fracture Criterion
- Fracture of Alumina Grinding Wheel

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Stress Intensity Factor and Fracture Toughness Testing

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

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Theory Resource




Problem 8

This question should take about 15 minutes to complete. It illustrates one use of fracture mechanics in materials processing, and requires some thought about the critical type of defect and its position in the component of interest.
Grinding wheels are fabricated, typically, from alumina powder, which is compacted and sintered at high temperature and pressure. The powder is sieved before compacting to remove impurities which may later act as defects in the grinding wheel. Hence residual impurities are related in size to the sieve mesh dimension.

One particular type of alumina wheel has a density of 3800 kg/m3, a bore diameter of 140 mm and an outer diameter of 1.0 m. It spins at 3000 rpm.

The maximum stress in the wheel is given by:

Calculate the allowable size of the sieve mesh if the wheel is to have a factor of safety of two on critical defect size when operating at 3000 rpm.

Note that, for alumina, the fracture toughness R = 0.10 kJ/m2 and E = 371 GPa.  You may assume plane strain conditions.

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