Frequently Asked Questions / Glossary

Compressive stress - Is the stress state when the material tends to compact (volume decrease). A simple case of compression is the uniaxial compression induced by the action of opposite, pushing forces. Most materials can carry compressive stress,

Ductility - Being capable of sustaining large plastic deformations without fracture. It is characterized by the material flowing under shear stress.

Elastic deformation - Is the spring-like deformation, where a material will return to its original shape - see also Plastic deformation

Elastic limit - Maximum stress to which a material may be subjected without permanent set.

Endurance limit - Maximum stress at which any given material may operate indefinitely without failure for a given minimum stress.

Fatigue - Is a process by which a material is weakened by cyclic loading. The resulting stress may be below the ultimate tensile stress

Fracture - Is the separation of a body into two, or more, pieces under the action of stress.

Hydrogen embrittlement - Hydrogen absorbed in electroplating or pickling of carbon steels, tending to make the spring material brittle and susceptible to cracking and failure.

Mechanical spring - Elastic body, whose primary function is to deflect or distort or absorb energy under load and which recovers its original shape when released.

Metric system - See SI

Modulus of elasticity - See Young's modulus

Modulus of rigidity - See Shear modulus

Passivating - Acid treatment of stainless steel to remove contaminants and improve corrosion resistance.

Permanent set - A material that is deflected so far that its elastic properties have been exceeded and it does not return to its original condition upon release of load.

Plastic deformation - The non-reversible change of shape in response to an applied force

Relaxation - The opposite of stress or tension

Shear modulus G - Is defined as the ratio of shear stress to the shear strain.

Shear strain - Is the components of a strain at a point that produce changes in shape of a body (distortion) without a volumetric change

Shear stress - Is caused when a force is applied to produce a sliding failure of a material along a plane that is parallel to the direction of the applied force e.g. when cutting paper with scissors or a lock with a bolt cutter.

Shot peening - A cold-working process in which the material surface is peened to induce compressive stresses and thereby improve fatigue life.

Shot peening - Is a process used to modify mechanical properties of metals, It entails impacting a surface with shot (round metallic particles) with force sufficient to create dimples and with enough shot that those dimples overlap

SI - International System of Units. SI is sometimes referred to as the metric system.

Stiffness - Is the resistance of an elastic body to deflection by an applied force. Stiffness is typically measured in Newton’s per meter.

Strain - Deformation caused by the action of stress on a solid material. Strain therefore expresses itself as a change in size and/or shape.

Stress - The force that is exerted on a solid material from the outside. The SI unit for stress is the Pascal (symbol Pa); in US Customary units, stress is expressed in pounds per square inch (PSI). See also"

Stress range - The difference in operating stresses at minimum and maximum loads.

Tensile strength (Rm) - Te maximum amount of stretching stress a material can withstand before it tears. Materials rated at a high tensile strength are durable and difficult to tear.

Tensile stress - Is a loading that tends to produce stretching on a material by the application of axially directed pulling forces. Materials can withstand some tensile loading, but if enough force is applied, they will eventually break into two pa

Yield strength - The amount of strain that a material can undergo before moving from elastic deformation into plastic deformation. The stress felt by a material given a certain strain is defined by linear relationship, with a slope defined by the m

Young's modulus - Is a measure of the stiffness of a given material, That is how hard it is to stretch chemical bonds that bind the atoms of a material together. Also known as Elastic modulus