compound

elements of the same kind bond with each other

alloy

different elements form a molecule together via bonds

mixture

different substances and molecules that are not bound to each other on an atomic level

crystalline structure

atoms or molecules bound together in a solid often form a strong, orderly, 3-dimensional pattern

amorphous structure

molecules don not follow a nicely repeating 3D pattern, long intertwined chains of molecules

chemical properties

material properties that are related to the atomic structure and the chemical composition of the material

composition

list of the elements or chemical compounds that make up the material, with an indication of the levels in which these components occur

crystal structure

the way the atoms or molecules of the material are arranged in repeating parts

microstructure

structure that becomes visible on the surface of the material when magnified by a factor of at least 10

corrosion resistance

ability of a material to resist chemical or electrochemical affection by substances in its environment

physical properties

properties are related to the physics of the piece, often related to the environment the material is in

melting point

temperature at which a solid material becomes liquid when heated and solidifies when cooled. Many materials do not have a precisely defined melting point, but rather a melting range.

specific mass

mass (or weight) of a substance per unit volume, also called density

specific weight

ratio of the mass of a given volume of substance to the mass of an equal volume of water.

refractive index

thermal properties

ratio of the speed of light in that substance to the speed of light in a vacuum

coefficient of thermal conductivity

λ (in W/m.K) amount of heat passing through a homogeneous material per unit of time, per unit of surface area, per unit of temperature gradient in the direction perpendicular to the surface

linear coefficient of expansion

α in (m/m.K) change in length per degree of temperature change

softening temperature

temperature at which a polymer exhibits a given degree of bend or deformation under a given load

water absorption capacity

percentage increase in weight of a substance when immersed in water under controlled conditions for a specified period of time

specific heat capacity

amount of heat required to raise one kilogram of a substance one degree Celsius in temperature

breakdown voltage

minimum voltage that causes a portion of an insulating material to experience electrical breakdown and become electrically conductive

specific electrical resistance

electrical resistance per unit length and per unit area of the cross-section, or the electrical resistance per unit length and per unit mass

mechanical properties

important when forces are applied to the material, mechanical properties depend on both chemical and physical properties of a material

tensile strength

ratio of the maximum load in a tensile test to the original cross-section of the test piece. Measured in N/m²

yield strength

maximum stress at which a material can stretch without plastic deformation

compressive strength

greatest pressure that a material can withstand without breaking

elasticity modulus

ratio of stress to strain in the elastic region. This is also a measure of the stiffness of a material

bend strength

tension in the outer edge of a uniaxially supported beam that undergoes a predetermined bending under the influence of a load

shear strength

stress at which breakage (shear) occurs in the plane of the cross-section of the material

hardness

resistance of a material to plastic deformation

notched impact strength

amount of energy required to cause a given volume of a material to break

stress

ratio between the force and the loaded area

strain

elongation, amount by which a material will stretch under a certain stress

tensile test

compression test, mainly used to determine the relationship between the average tensile stress and strain in many structural materials

conventional stress-strain diagram

elastic behavior (stress-strain diagram)

if test piece returns to its original shape or length when the load acting on it is removed

plastic behavior (stress-strain diagram)

yielding (stress-strain diagram)

slight increase in stress above the elastic limit results in a deterioration of the material and causes permanent deformation

strain hardening (stress-strain diagram)

When flow has ceased, increasing the load causes the curve to rise continuously, but to flatten out until a tension is reached, which is called the ultimate strength or tensile strength. The increase in this curve is called strain hardening. During the test, the area of the cross-section decreases as the test bar is elongated

necking (stress-strain diagram)

cross-sectional area begins to decrease at one location on the test bar, not over its entire length. This causes a narrowing

safety factor (stress-strain diagram)

safety factor when designing components that will experience a higher voltage. When designing these components, we will determine the maximum permissible stress as a factor of the yield stress. We call this the safety factor v (value greater than 1). The safety factor depends on the type of load (static, dynamic).

ductile materials

any material that can be substantially deformed before it cracks or breaks

brittle materials

Materials that have little or no yield before they collapse

Hooke's law

𝜎 = 𝐸𝜀 increase in stress causes a proportional increase in strain