Frakturmekanikk

Frakturmekanikk, or fracture mechanics, is the field of study concerned with the initiation and propagation of cracks in solids and the conditions that lead to structural failure. It integrates concepts from elasticity, plasticity, fracture theory, and applied mechanics to predict crack growth under real-world loading, environments, and loading histories.

Key concepts include the stress-intensity factor K, which describes the singular stress field near a crack tip under different load modes. Mode I (opening), Mode II (sliding), and Mode III (tearing) define how cracks are loaded. The material’s resistance to crack growth is quantified by fracture toughness, commonly K_IC for brittle materials or J_IC for elastic-plastic behavior. The Griffith criterion links fracture to an energy balance, while the energy release rate G provides an alternative frame, with G_IC mapping to the onset of fracture in linear elastic conditions. Irwin extended LEFM to account for plastic zones, and the J-integral offers a path-independent measure for elastic-plastic cases.

Methods in frakturmekanikk include experimental testing and numerical modeling. Standard tests such as compact tension (CT), three-point bending, or single-edge notch bending characterize K_IC and crack-growth resistance. Fatigue fracture is described by Paris’ law, da/dN = C(ΔK)^m, linking crack growth to cyclic loading. Numerical tools, especially finite element analysis, support complex geometries and material behaviors.

Applications span aerospace, civil and mechanical engineering, energy, and safety-critical structures. The field also addresses limitations of linear elastic approximations, requiring elastic-plastic fracture mechanics or cohesive-zone models for highly ductile materials and large-scale yielding.