Decohesion

Decohesion is a fracture mechanism in which separation occurs along interfaces within a material due to loss of cohesion at the interface. It is particularly relevant for polycrystalline metals, ceramics, composites, and rocks, where grain boundaries, phase boundaries, or particle–matrix interfaces can govern failure. It can present as intergranular cracking, interfacial debonding, or delamination.

Mechanisms and driving factors: The strength of an interface is characterized by interfacial fracture toughness or energy of separation. Decohesion occurs when the energy release rate for opening the interface exceeds this toughness. Environmental and microstructural factors—such as chemical reactions, corrosion, moisture, temperature, irradiation, residual stresses, lattice mismatch, and impurities—can weaken interfaces and promote decohesion.

Characterization and examples: Observed as intergranular cracks in metals, delamination in layered composites, or debonding at particle-matrix boundaries. Experimental methods include microscopy and fracture tests; modeling often uses cohesive-zone concepts with traction-separation laws to describe opening of the interface and calculation of Gc or interfacial K_IC.

Relation to other failure modes and mitigation: Decohesion is distinct from transgranular fracture within grains. Controlling decohesion involves strengthening interfaces, applying coatings, adding interfacial toughening mechanisms, processing to reduce residual stresses, and managing environmental exposure.