PEC材料工程英语证书考试-材料特性术语.docVIP

PEC材料工程英语证书考试-材料特性术语 Density Units: SI: Mg/m3; cgs: g/cm3; Imperial: lb/ft3 The density is the weight per unit volume. We measure it today as Archimedes did: by weighing the material in air and in a fluid of known density. Atomic Volume Units: SI: m3/kmol; cgs: 106cm3/kmol; Imperial: in3/kmol The atomic (or molecular) volume Vm is the average volume per 103N0?of atoms in the structure, where N0?is Avogadros number (6.022 x 1023/mol). For a pure element, it is simply: where A is the atomic weight in kg/kmol and?r?is the density in kg/m3. For compounds the average atomic volume is where M is the molecular weight and n is the number of atoms in the molecule. Thus for a compound with the formula AxBy?it is where AA?is the atomic weight of element A, and AB?is the atomic weight of element B. For a polymer (CxHyOz)n it is therefore where AC?is the atomic weight of carbon, and so on. The atomic volume is involved in many property correlations (and thus is crucial for?checking and estimating?properties) and, together with the density, it gives the atomic weight. Energy Content Units: SI: MJ/kg; cgs: kcal/g; Imperial: kcal/lb The energy content of a material is an approximate estimate of the energy used to make it from its naturally-occurring ores, feed stocks or sources, plus the energy content of the source material itself. (Usually the energy content of the source material is small, except, for example, when the source is oil.) Thus the energy content of Aluminium is dominated by the electric power absorbed in its extraction from Bauxite; that for polymers, for which the feed stock is crude oil is the energy contained in the oil itself plus that of the subsequent processing; and that for wood is the energy content of wood plus the energy required to harvest it. Youngs Modulus Units: SI: GPa; cgs: 1010dyne/cm2; Imperial: 106psi Youngs modulus, E, is the slope of the initial, linear-elastic part of the stress-strain curve in tension or compression. For isotropic material