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  • 1. The quality or condition of being strong. a. Power of action in body or limbs; ability to exert muscular force. In 15-18th c. the plural was often used after a plural possessive.
b. Bodily vigour in general; efficiency of the bodily powers; esp. in contrast with the weakness due to illness, fatigue, age, immaturity, etc. Also collect. pl. for sing.: cf. L. vires.
c. Power in general, whether physical, mental, or due to the possession of resources; ability for effective action; efficiency, vigour (of mental faculties, etc.).
d. Capacity for moral effort or endurance; firmness (of mind, character, will, purpose); power to resist temptation or fulfil a difficult duty; fortitude as one of the cardinal virtues. Freq. in phr. strength of character. in one's own strength: in reliance on oneself and not on divine grace.
e. Power of contending in warare; now chiefly, military power derived from numbers, equipment, or resources.
f. In a fortification, fortified place, etc.: Power of withstanding assault or capture.
g. In things, material or immaterial: Operative power; capacity for producing effects.
h. Validity, legal force. to bear strength: to be in force. to stand in its strength: to remain valid. Obs.
i. Power to sustain the application of force without breaking or yielding.
j. Intensity and active force (of movement, wind, fire, a stream, current of electricity, or the like); intensity (of a physical condition, colour, sound, etc.). In Telecommunications also with following numeral, indicating signal strength as shown on a meter. with strength: violently.
k. Vigour, intensity (of feeling, conviction, etc.). Also, emphasis, positiveness (of refusal).
l. Intensity of the specific property, or proportionate quantity of the active ingredient in a substance; potency (of drugs, liquors). Also, in particularized sense, a definite degree of strength.
m. Of soil: Firmness.
n. Demonstrative force or weight (of arguments, evidence); amount of evidence for (a case).
o. Energy or vigour of literary or artistic conception or execution; forcefulness (of delineation, versification, expression).
For lessons on the topic of Strength, follow this link.

Description (Materials Science)

In materials science, the strength of a material refers to the material's ability to withstand an applied stress without failure. Yield strength refers to the point on the engineering stress-strain curve (as opposed to true stress-strain curve) beyond which the material begins deformation that cannot be reversed upon removal of the loading. Ultimate strength refers to the point on the engineering stress-strain curve corresponding to the maximum stress. The applied stress may be tensile, compressive, or shear.

A material's strength is dependent on its microstructure. The engineering processes to which a material is subjected can alter this microstructure. The variety of strengthening mechanisms that alter the strength of a material includes work hardening, solid solution strengthening, precipitation hardening and grain boundary strengthening and can be quantified and qualitatively explained. However, strengthening mechanisms are accompanied by the caveat that some mechanical properties of the material may degenerate in an attempt to make the material stronger. For example, in grain boundary strengthening, although yield strength is maximized with decreasing grain size, ultimately, very small grain sizes make the material brittle.

In general, the yield strength of a material is an adequate indicator of the material's mechanical strength. Considered in tandem with the fact that the yield strength is the parameter that predicts plastic deformation in the material, one can make informed decisions on how to increase the strength of a material depending its microstructural properties and the desired end effect.

Strength is considered in terms of compressive strength, tensile strength, and shear strength, namely the limit states of compressive stress, tensile stress and shear stress, respectively. The effects of dynamic loading is probably the most important practical part of the strength of materials, especially the problem of fatigue. Repeated loading often initiates brittle cracks, which grow slowly until failure occurs.

However, the term strength of materials most often refers to various methods of calculating stresses in structural members, such as beams, columns and shafts. The methods that can be employed to predict the response of a structure under loading and its susceptibility to various failure modes may take into account various properties of the materials other than material (yield or ultimate) strength. For example failure in buckling is dependent on material stiffness (Young's Modulus).[1]