E399 Test Method for Plane-strain Fracture Toughness of Metallic Materials ASTM E740 Practice for Fracture Testing with Surface-Crack Tension Specimens ASTM E1820 Standard Test Method for Measurement of Fracture Toughness ASTM E1823 Terminology Relating to Fatigue and Fracture Testing ISO 12135 Metallic materials — Unified method of test for the determination of quasistatic fracture toughness ISO 28079:2009, the Palmqvist method, used to determine the fracture toughness for cemented carbides Crack deflection toughening Many ceramics with polycrystalline structures develop large cracks that propagate along the boundaries between grains, rather than through the individual crystals themselves since the toughness of the grain boundaries is much lower than that of the crystals. The orientation of the grain boundary facets and residual stress cause the crack to advance in a complex, tortuous manner that is difficult to analyze. Simply calculating the additional surface energy associated with the increased grain boundary surface area due to this tortuosity is not accurate, as some of the energy to create the crack surface comes from the residual stress. Model A mechanics of materials model, introduced by Katherine Faber and Anthony G. Evans, has been developed a to predict the increase in fracture toughness in ceramics due to crack deflection around second-phase particles that are prone to microcracking in a matrix. The model takes into account the particle morphology, aspect ratio, spacing, and volume fraction of the second phase, as well as the reduction in local stress intensity at the crack tip when the crack is deflected or the crack plane bows. The actual crack tortuosity is obtained through imaging techniques, allowing the deflection and bowing angles to be directly input into the model. The resulting increase in fracture toughness is then compared to that of a flat crack through the plain matrix. The magnitude of the toughening is determined by the mismatch strain caused by thermal contraction incompatibility and the microfracture resistance of the particle/matrix interface. This toughening becomes noticeable when there is a narrow size distribution of particles that are appropriately sized. Researchers typically accept the findings of Faber's analysis, which suggest that deflection effects in materials with roughly equiaxial grains may increase the fracture toughness by about twice the grain boundary value. See also Brittle–ductile transition zone Charpy impact test Ductile-brittle transition temperature Impact (mechanics) Izod impact strength test Puncture resistance Shock (mechanics) Three-point flexural fracture toughness testing Toughness of ceramics by indentation References Further reading