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Fracture Mechanics

Definition - What does Fracture Mechanics mean?

Fracture mechanics refers to the mechanics of solids containing planes of displacement discontinuities (cracks) with special attention to their growth. Fracture mechanics is a failure theory that:

  • Determines material failure by energy criteria, possibly in conjunction with strength (or yield) criteria
  • Considers failure to be propagating throughout the structure rather than simultaneous throughout the entire failure zone or surface

It is a useful method of determining:

  • Stress and flaw size
  • Fracture toughness
  • Fatigue crack growth
  • Stress-corrosion crack growth behavior

Fracture mechanics has been used heavily in the aerospace, and ship industries with a recent extension to the ground vehicle industry.

Corrosionpedia explains Fracture Mechanics

Fracture mechanics is the field of mechanics concerned with the study of the propagation of cracks in materials. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the material's resistance to fracture.

Fracture mechanics is an important tool in improving the mechanical performance of components. It applies to the microscopic crystallographic defects found in materials in order to predict the macroscopic mechanical failure of bodies. Fractography is widely used with fracture mechanics to understand the causes of failures and also verify the theoretical failure predictions with real-life failures.

Interior and surface flaws arising from the manufacturing process are found in all metal structures. Not all such flaws are unstable under service conditions. Fracture mechanics analyzes flaws to determine which are safe and which are liable to propagate as cracks and cause failure of the flawed structure.

There are two types of fracture mechanics:

  • Linear-elastic fracture mechanics - the basic theory of fracture that deals with sharp cracks in elastic bodies
  • Elastic-plastic fracture mechanics - the theory of ductile fracture, usually characterized by stable crack growth (ductile metals)

Fracture mechanics can estimate the maximum crack that a material can withstand before it fails, taking into consideration:

  • Overall dimensions of the structure
  • Stress value where crack initiation takes place
  • Notch toughness value
  • Behavior of materials
  • Fatigue crack growth and stress corrosion crack growth

Fracture mechanics can be used in:

  • Design
  • Material selection and alloy development
  • Determining the significance of defects
  • Monitoring and control
  • Failure analysis
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