Mechanics of Fracture

摘要: Calculations of the theoretical strengths crystalline solids are usually based on idealised forms atomic force-displacement curves, in which force is defined as differential with respect to distance inter-atomic or inter-ionic energy. The energy curve similar that for a diatomic molecule it represents resultant repulsions and attractions; nature strength attractive forces depending bond type: ionic, covalent, metallic, Van der Waals. Differences character between lattice occur at separations order one spacing, when Friedel oscillations screening charge cause long range component interaction potential undergo damped oscillation about zero. For small displacements, force/displacement linear, having slope equivalent Young’s modulus, E. A also has shear stiffness, denoted by modulus μ. Both E μ macroscopically, randomly-oriented polycrystals assumed be isotropic. In single crystals, both tensile stiffness vary orientation crystal axis these variations can substantial: iron, example, minimum value [100]direction (132 GPa room temperature) maximum [111] direction (260 GPa).