Strength of materials

The strength of materials is determined using various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts.

The methods employed to predict the response of a structure under loading and its susceptibility to various failure modes takes into account the properties of the materials such as its yield strength, ultimate strength, Young's modulus, and Poisson's ratio.

The theory began with the consideration of the behavior of one and two dimensional members of structures, whose states of stress can be approximated as two dimensional, and was then generalized to three dimensions to develop a more complete theory of the elastic and plastic behavior of materials.

The applied loads may be axial (tensile or compressive), or rotational (strength shear).

The ultimate strength of the material refers to the maximum value of stress reached.

The chewed bubble gum, on the other hand, will plastically deform enormously before finally breaking.

The ultimate strength is the maximum stress that a material can withstand before it breaks or weakens.

For example, to achieve a factor of safety of 4, the allowable stress in an AISI 1018 steel component can be calculated to be

Design stresses that have been determined from the ultimate or yield point values of the materials give safe and reliable results only for the case of static loading.

Many machine parts fail when subjected to a non-steady and continuously varying loads even though the developed stresses are below the yield point.

Generally, higher the range stress, the fewer the number of reversals needed for failure.

Of the latter three, the distortion energy theory provides the most accurate results in a majority of the stress conditions.

The strain energy theory needs the value of Poisson's ratio of the part material, which is often not readily available.

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 on its microstructural properties and the desired end effect.

The effects of dynamic loading are probably the most important practical consideration of the theory of elasticity, especially the problem of fatigue.

Repeated loading often initiates cracks, which grow until failure occurs at the corresponding residual strength of the structure.