Fracture mechanics

Fracture mechanics studies how cracks initiate and grow under stress and how they cause materials and structures to fail. It relates crack behavior to material properties, geometry, and loading.

Stress intensity factor: A parameter describing the magnitude of the elastic stress field near a crack tip. It links applied loading and crack geometry to the intensity of crack-tip stresses.
Linear elasticity: A model in which stress is proportional to strain and deformation is recoverable. Linear-elastic fracture mechanics relies on this behavior outside a small crack-tip region.
Damage-tolerance design: An engineering approach that permits flaws while requiring them to remain detectable and safe until repair. Fracture calculations estimate whether assumed cracks can grow to critical size between inspections.
Fatigue: Progressive material damage caused by repeated or fluctuating loading, often leading to fracture. Fatigue describes a loading-driven failure process, while fracture mechanics analyzes crack behavior within it.
A. A. Griffith: A British engineer whose 1920 analysis connected crack growth in brittle materials to changes in elastic energy. His energy balance established a foundational explanation for why microscopic flaws weaken glass.
Energy release rate: The decrease in potential energy per unit increase in crack area during crack growth. It expresses the mechanical energy available to extend a crack.
Continuum mechanics: The mathematical study of material deformation and motion using fields such as stress and strain. Fracture calculations use continuum fields to represent stresses around flaws.
Fitness-for-service: An engineering assessment of whether equipment with damage can continue operating safely. Crack assessments help determine if flawed components require repair, replacement, or monitoring.
Creep: Time-dependent deformation under sustained stress, especially at elevated temperature. Creep can cause failure without the cyclic loading central to fatigue crack growth.
Griffith criterion: A condition for crack growth in brittle materials based on the balance between released elastic energy and surface energy. It is the early energy-based criterion later extended to practical engineering materials.

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