Strength of materials

Total stress

Total stress is the resultant internal force that resists change in the size or shape of a body acted on by external forces.

Unit stress

Unit stress or intensity of stress is the stress per unit area

Normal stress

Normal stress on a section is one that acts in a direction perpendicular to section considered.

Ultimate stress

Ultimate stress is the ratio of the maximum load that a specimen sustains to its original area of the cross- section

Strain

Strain is defined as the change in length per unit length According to Hooke's law, a body acted on by external forces will deform in proportion to the stress developed as long as the unit stress does not exceed a certain value, known as proportional limit.

Proportional limit

Proportional limit is the highest unit stress at which the stress is proportional to deformation ie. when curve between stress and deformation departs from a straight line.

Elastic limit

Elastic limit is the maximum unit stress to which a material may be subjected and still be able to return to its original form upon removal of stress

Yield point

Yield point of a material is the unit stress at which the deformation first increases markedly without any increase in the applied load It is always above the proportional limit.

Ultimate strength

Ultimate strength is the highest unit stress it can sustain before rupturing. Breaking strength is the unit stress at which the material tested ruptures. Modulus of elasticity (E) in tension or compression is the constant which expresses the ratio of unit stress, to unit deformation for all values of unit stress not exceeding the proportional limit of material.

Modulus of elasticity in shear is sometimes called the modulus of rigidity.

Factor of safety

Factor of safety is the ratio of ultimate atrength the material to the allowable stregg,

Elasticity

Elasticity is ability of a material to deform and return to its original shape upon removal of the load

Ductility

Ductility is bility of a material to undergo large permanent deformations in tension, ie property which enables a material to be drawn into a wire,

Malleability

Malleability is the ability to undergo large permanent deformation in compression, or property which permits material to be beaten or rolled into thin sheeta.

Plasticity.

A material is plastic if the smallest load produces a permanent deformation. Brittleness. A material which can be only slightly deformed without rupture is termed as brittle.

Brittleness

Brittleness and plasticity are opposite terms

Toughness

Toughness is the ability to withstand high unit stress together with great unit deformation without complete fracture. Difference between ductility and toughness is that ductility deals only with the ability to deform, whereas toughness considers both the ability to deform and the stress developed during deformation.

Stiffness

Stiffness is the ability to resist deformation under stress.

Hardness

Hardness is the ability to resist very small indentation, abrasion and plastic deformation. It is a combination of several properties.

Creep stresses

These occur when either the load or the deformation progressively varies with time. They are usually associated with non-cyclic phenomena.

Fatigue stresses

These occur when the cyclic variation to either load or strain is coincident with respect to time.

Impact stresses

These occur from loads which are transient with time, the duration of the load application being of the same order of magnitude as the natural period of vibration of the specimen.