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What is Fracture Toughness?

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  • Written By: Mary McMahon
  • Edited By: Nancy Fann-Im
  • Last Modified Date: 13 November 2016
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Fracture toughness is a measure of how well a material with an existing flaw performs under pressure. In materials testing, people use equipment to subject materials with known flaws to controlled pressure to see when something like a crack turns into a full fracture and causes the material to fail. Engineers assume that perfection is impossible, and thus need to design materials with fracture toughness appropriate to the application so they will resist pressure and retain their integrity.

In a measure of fracture toughness, the goal is to look at performance with different types of cracks and flaws like air bubbles deep inside the material. Equipment can subject to the material to sliding, tearing, or tensile forces to determine how it behaves. This provides a series of fracture toughness measurements engineers can use to determine when the material will fail and under what conditions.

The risk of fracture increases as pressure on the material increases. If the material is too brittle, it can be prone to fracturing under relatively low levels of pressure, but extremely flexible materials may deform, making them useless. Engineers need to strike the middle ground when developing materials, providing them with the flexibility to resist fractures and the brittleness to withstand deforming pressures. This can require modifications to the composition and design of product components.

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If the fracture toughness is too low, it means the material may be prone to failure. This is not desirable and engineers need to return to the drawing board to determine how to correct the problem. This can involve changing the composition of a metal alloy, altering the shape of a part, or redesigning a piece of equipment to change the distribution of pressure when it is operational. High fracture toughness is a good sign, showing that materials are resistant enough to meet the need, but it can come with other problems, like materials too heavy for the intended application.

The law may require a certain standard of fracture toughness for particular materials, due to safety concerns. In these cases, companies may need to show the results of testing to government inspectors so they can confirm that the company is meeting the standards. Companies may also have internal and industry standards they need to meet in order to remain competitive. Discussion of testing results is also important for activities like bidding on projects, as companies want to show how their end products will be superior to those of competitors.

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