Fraktureenergi

Fraktureenergi, or fracture energy, is the energy required to create a new unit area of crack surface as a crack propagates through a material. It is typically denoted Gc and has units of joules per square meter (J/m^2). In fracture mechanics, Gc is the critical energy release rate at which crack growth becomes unstable. For brittle materials, Gc is close to the intrinsic surface energy, while for ductile and quasi-brittle materials it includes additional energy dissipated by plastic deformation or damage.

Gc is linked to the material’s fracture toughness. In linear elastic fracture mechanics, the relation Gc = (K_IC)^2 / E' holds, where K_IC is the fracture toughness and E' is the effective elastic modulus (depending on plane strain or plane stress conditions). This connects the energy-based description to the stress-intensity framework.

Measuring fracture energy typically involves tests that enforce crack growth, such as compact tension (CT) or three-point bending of a notched specimen. The energy dissipated during crack extension is obtained from the area under the load–displacement curve, and Gc is calculated by dividing this energy by the newly formed crack surface area. In cementitious materials like concrete, fracture energy (often denoted Gf) is a key parameter in cohesive crack models and is determined by size-effect tests or notched beam experiments.

Fraktureenergi is used to assess and compare the resistance of materials to crack propagation, guide design against fracture, and calibrate fracture models. Its value can depend on loading rate, temperature, moisture, and material heterogeneity.