Material Property Definitions

Thermal    |    Optical    |    Mechanical    |    Electrical

Listed below are property definitions related to charts on our material properties pages. See a complete list of materials we machine.

Thermal

Annealing Point
The temperature at which internal stresses are substantially removed in a short period of time.

Glass Transition Temperature
The temperature range in which a material transitions from a true solid to a very viscous liquid. This definition applies to non-crystalline solids.

Melting Point
The temperature at which a material turns suddenly from solid to liquid.

Softening Point
The temperature at which a glass deforms at a specific rate under its own weight.

Specific Heat
The amount of energy a body stores per unit mass for each degree increase in temperature (at constant pressure).

Strain Point
The temperature at which internal stresses in glass are substantially relieved in approximately 1 hour.

Thermal Conductivity
A material property that describes the rate at which heat flows through a unit area of homogeneous material for a given temperature difference.

Thermal Expansion
The change in length per unit length of a material corresponding to a unit change in temperature.

Thermal Shock
A parameter that characterizes the material cracking resulting from the temperature gradients caused by rapid change in temperature. A reduction in temperature is usually used for brittle materials.

 

Optical

Refractive Index
Ratio of the speed of monochromatic light in a vacuum to the speed of light through a material.

Transmission Range
Wavelength range light will transmit through a unit length of optical material without significant optical attenuation.

 

Mechanical

Brinnell Hardness
A hardness test that forces a hardened steel or tungsten-carbide ball against the smooth material surface for a standard dwell time to create an indentation. The hardness is expressed as a Brinell Hardness Number (BHN) computed by dividing the force by the projected area of indentation.

Bulk Modulus
Ratio of stress to change in volume of a material subjected to axial loading. It is related to the Modulus of Elasticity and Poisson's Ratio by the following equation: Bulk Modulus = (Modulus of Elasticity)/(3x(1-2xPoisson's Ratio)).

Compressive Strength
Compressive Strength is the maximum compressive stress a material can withstand before failure.

Density
Mass per unit volume.

Elastic Limit
Greatest stress that can be applied to a material without causing permanent deformation.

Flexural Strength
Maximum stress developed in a specimen just before it cracks or breaks in a flexure test.

Fracture Toughness
The measure of resistance a material has to the propagation of a crack. The higher the fracture toughness, the more resistant a material will be to rapid crack growth.

Hardness
The resistance a material surface offers to abrasion, scratching and indentation. Common measures of hardness are Mohs, Vickers, Brinell, and Knoop.

Knoop Hardness
A hardness test that forces a pyramid-shaped diamond tip against the smooth surface of a material for a standard dwell time to create an indentation. This test differs from the Vickers test in that only a small indentation is made so that the test can be used with brittle materials or thin sheets. The hardness is expressed as a Knoop Hardness Number (HKN) computed by dividing the force by the projected area of indentation.

Mohs Hardness
Scale of hardness that characterizes the scratch resistance of various materials through the ability of a harder material to scratch a softer material. Mohs hardness is based on a scale of ten minerals that are all readily available. As the hardest known naturally occurring substance, diamond is at the top of the scale. Talc is at the bottom of the scale.

Poisson's Ratio
The negative ratio of the thickness decrease divided by the length increase resulting from a tensile stress applied to a material.

Porosity
The proportion of the non-solid volume to the total volume of material.

Shear Modulus
The proportionality constant between elastic shear stress and elastic shear strain of a solid material subjected to shear loading.

Shore Durometer
Shore Durometer is a measure of hardness commonly used with rubbers, elastomers and polymers.    Like all hardness testers, the Shore Durometer test measures the depth of an indentation under a given test force. There are no less than 12 Shore Durometer scales, with the two most common being the Durometer Shore A and D scales.  The Shore A scale used for softer materials and the Shore D scale is for harder ones. The primary differences between the two scales are  the force range and indenter shape used during the tests.  

All scales range in numbers from 0 to 100, with higher numbers indicating harder materials.  For reference, provided below are the Durometer values for a few common materials:

  • Rubber Band:  25 Shore A
  • Automotive Tire Tread: 70 Shore A
  • Hydraulic O-Rings: 70 – 90 Shore A
  • Hard Hat:  75 Shore D

Tensile Strength
The maximum tensile stress a material can withstand before rupture.

Torsional Strength
The maximum torsional stress that a material can withstand before rupture.

Vickers Hardness
A hardness test that forces a pyramid-shaped diamond tip against the smooth surface of a material for a standard dwell time to create an indentation. The size of the indentation determines the hardness value. The Vickers Number (HV) is then determined by the force applied to the diamond and the projected surface area of the resulting indentation.

Yield Strength
Maximum stress that can be developed in a material without causing plastic deformation. It is the stress at which a material exhibits a specified permanent deformation and is a practical approximation of elastic limit. The amount of permanent deformation used depends on the material (for metals it is 0.2% strain).

Young's Modulus
The proportionality constant between elastic stress and elastic strain for a solid material subjected to uniaxial loading. This property describes the inherent stiffness of a material.

 

Electrical

Dielectric Constant
The property of the dielectric material that indicates the ability of a material to store electrical energy. It is expressed as a ratio relative to the dielectric constant of a vacuum.

Dielectric Strength
The minimum electric field that produces a breakdown of the insulating properties of a dielectric material.

Resistivity
A measure of a material's resistance to electrical current per unit length for a uniform cross section.

Dielectric Loss Tangent
Product of the dielectric constant of a material and the tangent of its dielectric loss angle.

Dielectric Loss Angle
90 degrees minus dielectric phase angle.

Dielectric Phase Angle
Angular difference in phase between the sinusoidal alternating potential difference applied to a dielectric material and the component of the resulting alternating current having the same period as the potential difference.