Edge Density Ratio of the total length of all sides or edges to the area or volume enclosed by the sides or edges.

Elastic Able to return to its original size and shape after removal of stress.

Elastic hysteresis Difference between strain energy required to generate a given stress in a material and elastic energy at that stress. It is the energy dissipated as heat in a material in one cycle of dynamic testing. Elastic hysteresis divided by elastic deformation energy is equal to damping capacity.

Elastic limit Greatest stress that can be applied to a material without causing permanent deformation. For metals and other materials that have a significant straight-line portion in their stress/strain diagram, elastic limit is approximately equal to proportional limit. For materials that do not exhibit a significant proportional limit, elastic limit is an arbitrary approximation (the apparent elastic limit).

Elastic limit, apparent Arbitrary approximation of the elastic limit of materials that do not have a significant straight line portion on a stress/strain diagram. It is equal to the stress at which the rate of strain is 50% greater than at zero stress. It is the stress at the point of tangency between the stress- Elastic Hysteresis strain curve and the line having a slope, with respect to the stress axis, 50% greater than the slope of the curve at the origin.

Elasticity/plasticity The ability of a material to return to its original state after deformation: the yield point is not exceeded: this is elastic behavior. For example, plastics in general respond elastically. If a material’s yield point is exceeded when stressed, it does not return to its original state after removal of the stress: this is permanent deformation by plastic behavior. Plasticity is the inverse of elasticity. Another way of explaining this is the following. During the first part of the pulling process in the tensile test, both tensile stress and tensile strain continue to increase, and in proportion. When this takes place, the material acts like a spring, and is said to have elastic behavior. Some materials will be broken when they have been strained only a small amount, and while still showing essentially elastic behavior. Other materials can be stretched many times their original length before they break. The latter have a yield point, and a corresponding yield stress.

Element One of a class of 103 substances that cannot be separated into simpler substances by chemical means (see Periodic Table).

Elongation (1) The fractional increase in length of a material stressed in tension. (2) Measure of the ductility of a material determined in a tension test. It is the increase in gage length (measured after rupture) divided by original gage length. Higher elongation indicates higher ductility. Elongation cannot be used to predict behavior of materials subjected to sudden or repeated loading.

Embossing Techniques used to create depressions of a specific pattern in plastics film and sheeting.

Embrittlement Reduction in ductility due to physical or chemical changes.

Employment The act of using or applying, as in the optimal employment of mass to resist the forces of loading.

Endurance Alternate term for fatigue limit.

Engineering stress Load applied to a specimen in a tension or compression test divided by the cross-sectional area of the specimen. The change in cross-sectional area that occurs with increases and decreases in applied load, is disregarded in computing engineering stress. It is also called conventional stress.

Engineering symbols

Environmental resistance A mechanical material property related to how a material responds to environmental conditions, such as heat and moisture.

Equiangular Having equal angles.

Equilateral Having sides of equal length. For example, an equilateral triangle has three sides of equal length (and equal interior angles of 60°).

Equilibrium State of a system in which the properties do not change with time; state of rest or balance due to the equal action of opposing forces.

Equiradius Equal or common radius.

Equivalent Equal in value, measure, force, effect, significance, etc., as in one-to-one correspondence.

Extrusion The process of foaming continuous shapes by forcing a molten plastic material through a die.