Scheurmodi

Scheurmodi, or crack modes, refer to the three fundamental ways a crack surface displaces during propagation under load. The concept is standard in fracture mechanics and is used to predict crack growth and assess structural integrity.

Mode I is the opening mode: tensile stress normal to the crack plane causes the fracture faces to move apart, typically the dominant mode under opening loads. Mode II is in-plane shear, where the crack faces slide relative to one another within the crack plane. Mode III is anti-plane shear, with out-of-plane shear that tears the faces apart along the thickness direction.

Each mode is associated with a stress intensity factor: K_I for Mode I, K_II for Mode II, and K_III for Mode III, and corresponding energy release rates G_I, G_II, G_III. In real components, loading is often mixed-mode, involving more than one mode; crack growth is governed by a combination of K-values and material fracture toughness, K_IC, K_IIc, K_IIIc, or equivalent G-values.

Practically, scheurmodi are used in component design, failure analysis, and nondestructive testing. Tests such as compact tension or three-point bending are used to characterize Mode I, while other tests or finite-element analysis can reveal the relative contributions of Modes II and III. Modern techniques such as digital image correlation help map displacement fields near cracks to identify active modes.

See also: fracture mechanics, stress intensity factor, mixed-mode fracture.