Fracture toughness is a measure of a material's ability to resist fracture when a crack or defect is present. It is an important property for materials used in structural applications, as it determines the maximum stress a material can withstand before breaking.
Fracture toughness is typically measured using standardized tests, such as the Charpy or Izod impact tests. These tests involve subjecting a sample of the material to a sudden impact and measuring the energy absorbed before fracture occurs. The results are then used to calculate the material's fracture toughness.
Fracture toughness and strength are related but distinct properties. Strength refers to a material's ability to withstand stress without permanent deformation or failure, while fracture toughness specifically measures a material's resistance to fracture when a crack or defect is present. A material can have high strength but low fracture toughness if it is brittle and prone to sudden failure, while a material with lower strength may still have high fracture toughness if it is able to resist fracture even with defects present.
Temperature can have a significant impact on a material's fracture toughness. Generally, materials become more brittle at lower temperatures, which can decrease their fracture toughness. This is why materials like steel and aluminum are often tested for fracture toughness at different temperatures, to determine their performance in different environments.
Fracture toughness is an important consideration in materials selection and design for structural applications. Materials with high fracture toughness are preferred for structures that are expected to experience high stress or potential cracking, as they will be less likely to fail catastrophically. Fracture toughness data is also used in fracture mechanics calculations to determine the critical crack size and predict the likelihood of fracture in a given material under specific conditions.