Category: Science & Engineering

1. Why are ceramics brittle and most metals not? Ceramics materials have very small and omnipresent flaws as minute surface or interior cracks (microcracks), internal pores, and grain corners, which are virtually impossible to eliminate or control. These flaws serve as stress raisers such that depending on crack orientation and geometry, applied stress may be amplified or concentrated at the tip of the crack. When the magnitude of a tensile stress at the tip of one of these flaws exceeds the value of this critical stress which is large enough to break apart the interatomic bonds, a crack forms and […]

The simplest of the point defects is a vacancy, or vacant lattice site, one normally occupied from which an atom is missing. Impurity point defects are found in solid solutions, of which there are two types: substitutional and interstitial. A dislocation is a linear or one-dimensional defect around which some of the atoms are misaligned. An edge dislocation moves in response to a shear stress applied in a direction perpendicular to its line; One type of dislocation is an extra portion of a plane of atoms, or half-plane, the edge of which terminates within the crystal. This is termed an […]

Resilience: is the capacity of a material to absorb energy when it is deformed elastically and then, upon unloading, to have this energy recovered.The associated property is the modulus of resilience, which is the strain energy per unit volume required to stress a material from an unloaded state up to the point of yielding. Toughness: is a mechanical term that is used in several contexts; loosely speaking, it is a measure of the ability of a material to absorb energy up to fracture. Specimen geometry as well as the manner of load application are important in toughness determinations. Furthermore, fracture […]