Properties of materials
While in use, all materials are exposed to external stimuli that cause some kind of response. A property is a material characteristic that describes the kind and magnitude of response to a specific stimulus. For example, a specimen exposed to forces will experience deformation, or a metal surface that has been polished will reflect light. In general, definitions of property are made independent of material shape and size.
Virtually all important properties of solid materials may be grouped into six different categories:
– thermal (including melting and glass transition temperatures)
Mechanical Properties relate deformation to an applied load or force; examples include elastic modulus and strength.
Electrical Properties are, e.g. electrical conductivity, resistivity and dielectric constant. The stimulus is voltage or an electric field.
Thermal Properties of solids can be described by heat capacity and thermal conductivity. Poor thermal conductivity is responsible for the fact that space shuttle tiles containing amorphous, porous silica (SiO2) can be held at the corners, even when glowing at 1000 °C.
Magnetic Properties demonstrate a material’s response to the application of a magnetic field.
Optical Properties are a material’s response to electromagnetic or visible light. The index of refraction and reflectivity are representative optical properties.
Deteriorative Propertiesrelate to the chemical reactivity of materials. The chemical reactivity, e.g. corrosion, of a material such as an alloy, can be reduced by heat treating the alloy prior to exposure in salt water. Heat treatment changes the inner structure of the alloy. Thus crack propagation leading to mechanical failure can be delayed.
stimulus (единств число)- stimuli (множ. число)
7. Проверьте усвоенную информацию, ответив на следующие вопросы на английском языке:
1. What is a material’s property?
2. Do mechanical properties deal with deformation?
3. How can the thermal behavior of solids be characterized?
4. How to delay the crack propagation leading to mechanical failure?
8. Приведите примеры предметов, которые вы используете дома или в аудитории. Заполните таблицу по образцу и обсудите свойства материалов в группе:
Characteristics of materials
|| used for
|| made from
|| a good choice because
|| to heat food
|| it conducts heat well