User:Roshanrahim92/sandbox

Fracture Toughness Testing

Fracture toughness is an indication of the amount of stress required to propagate a preexisting flaw. It is a very important material property since the occurrence of flaws is not completely avoidable in the processing, fabrication, or service of a material/component. Flaws may appear as cracks, voids, metallurgical inclusions, weld defects, design discontinuities, or some combination thereof. Since engineers can never be totally sure that a material is flaw free, it is common practice to assume that a flaw of some chosen size will be present in some number of components and use the linear elastic fracture mechanics (LEFM) approach to design critical components. This approach uses the flaw size and features, component geometry, loading conditions and the material property called fracture toughness to evaluate the ability of a component containing a flaw to resist fracture. A Parameter called the stress-intensity factor (K) is used to determine the fracture toughness of most materials.

Fracture Toughness Testing Methods

Fracture toughness is a critical mechanical property for certain applications. There are several types of test used to measure fracture toughness of materials. Some of these methods are :

1. Determination of Plane Strain Fracture Toughness, KIc

This method provides a quantitative measure of fracture toughness in terms of the critical plane strain stress intensity factor. The test must be validated once complete to ensure the results are meaningful. The specimen size is fixed, and must be large enough to ensure plane strain conditions at the crack tip. This limits the product forms to which the test can be applied.

2. Determination of Tear Resistance (Kahn Tear Test)

The tear test (e.g. Kahn tear test) provides a semi-quantitative measure of toughness in terms of tear resistance. This type of test requires a smaller specimen, and can therefore be used for a wider range of product forms. The tear test can also be used for very ductile aluminium alloys (e.g. 1100, 3003), where linear elastic fracture mechanics do not apply (see properties in practice).