Fracture toughening mechanisms
Intrinsic toughening mechanisms
Intrinsic toughening mechanisms involve a fundamental change of material properties like ductility and plasticity. These changes can be achieved by creating a more stable microstructure, or by increasing precipitate particle spacing to improve ductility.
Extrinsic toughening mechanisms
Extrinsic toughening mechanisms act during crack propagation at the location of the crack, and these mechanisms come in two subcategories based on where they act.
Three zone shielding mechanisms act on the crack tip to interfere with crack propagation. The first is transformation toughening, which occurs when the crack actually changes the crystalline structure of the surrounding material to inhibit crack growth. The second and third mechanisms are microcrack toughening and crack field void formation, where either microcracks or microvoids form around the crack tip and reduce the crack tip stress concentration.
Contact shielding mechanisms act behind the propagating crack. Contact shielding mechanisms often induce some sort of crack closure, either by the roughness of the fracture surface, or by unbroken fibers bridging the crack. A sliding crack surface or a wake of plasticity behind the crack are also contact shielding mechanisms.
- Hertzberg, Richard W. Deformation and Fracture Mechanics of Engineering Materials, Fourth Edition. John Wiley and Sons, Hoboken, NJ: 1996.