Stress And Stain

Simple Stress and Strain

The strength of materials are expressed from the point of view of machine designer. A machine designer needs to know the properties of different materials so that he can select the most suitable material for each part of a machine. A machine designer uses his information of stress to make sure that the stress is reasonable and that each part of the machine is sufficiently strong. Strength of materials is the scientific area of applied mechanics for the study of the strength of engineering materials and their mechanical behavior in general (such as stress, deformation, strain and stress-strain relations). 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.

One can see the importance of stress and strain. They are an indication of how severely the part in machine is loaded and how it is a factor that determines whether the forces applied are reasonable. Stress and strain always occur together. When a material is subjected to stress, it deforms, and when a material is deformed there must be strain. If the stress and strain are not the same for all materials, then it is found by experiments There is a relation between the stress and the strain for any given material. It said, when the relationship between the two are given, the stress and the strain can be found in one another. All materials deform when subjected to stress and it is necessary to be able to calculate the deformation of a body under load, because in most cases the deformation is more momentous than the stress.

Stress is in all probability the most imperative word in the subject matter of strength of materials. Stress is defined as force per unit area. It has the same units as pressure, and in fact pressure is one special variety of stress. However, stress is a much more complex quantity than pressure because it varies both with direction and with the surface it acts on. The simple stress are: compression (stress that acts to shorten an object), tension (stress that acts to lengthen an object), and shear (stress that acts parallel to a surface). Shear can cause one object to slide over another. It also tends to deform originally rectangular objects into parallelograms. The most general definition is that shear acts to change the angles in an object.

Strain is defined as the amount of deformation an object experiences compared to its original size and shape. For example, if a block 10 cm on a side is deformed so that it becomes 9 cm long, the strain is (10-9)/10 or 0.1 (sometimes expressed in percent, in this case 10 percent.) Note that strain is dimensionless. Strain in addition can be express further in these familiar terms: compression (longitudinal strain that shortens an object), tension (longitudinal strain that lengthens an object) and shear (strain that changes the angles of an object). Shear can also causes lines to rotate in strain. These stresses can further be said to be a member of a machine or structure that indicates how severely it is loaded; a stress is said to be a failure if the machine part is loaded to heavy.

Tensile stress is the stress that can be applied to an object by pulling on it, or attempting to stretch it. Further, it 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 parts. Steel is an example of a material with high tensile strength. Its opposite is compressive stress and compression stress. Compressive is the stress applied to materials resulting to their compaction (decrease of volume). When a material is subjected to compressive stress then this material is under compression. Usually compressive stress applied to bars, and columns. In architecture and structural engineering, a column is that part of a structure whose purpose is to transmit through compression the weight of the structure. Other compression members are often termed columns because of the similar stress conditions. Columns can be either compounded of parts or made as a single piece. In addition, a material is compression stress when the forces acting on it tend to shorten it. The forces have a propensity to squeeze the material together and this predisposition is resisted by interior forces or stresses.

Stress is plotted vertically and strain is plotted horizontally. After it is plotted, the line then is drawn trough the plotted points to give the stress-strain curve. It is understood that it is not always a straight line but straight enough for practical purposes. The stress is related to the external force you put on an object. The strain is resulting deformation of the object's shape or size. Stress and strain can be thought of as cause" and effect". If you put a force on something, it changes. This sort of deformation is called elastic deformation. The word elastic"