Stress analysis
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Stress analysis is an engineering discipline that determines the stress in materials and structures subjected to static or dynamic forces or loads (see statics and dynamics). The aim of the analysis is usually to determine whether the element or collection of elements, usually referred to as a structure, can safely withstand the specified forces. This is achieved when the determined stress from the applied force(s) is less than the ultimate tensile strength or ultimate compressive strength the material is known to be able to withstand, though ordinarily a safety factor is applied in design.
Sometimes the term stress analysis is applied to mathematical or computational methods applied to structures that do not yet exist, such as a proposed aerodynamic structure, or to large structures such as a building, a machine, a reactor vessel or a piping system.
A stress analysis can also be made by actually applying the force(s) to an existing element or structure and then determining the resulting stress using sensors, but in this case the process would more properly be known as testing (destructive or non-destructive). In this case special equipment, such as a wind tunnel, or various hydraulic mechanisms, or simply weights are used to apply the static or dynamic loading.
When forces are applied, or expected to be applied, repeatedly, nearly all materials will rupture or fail at a lower stress than they would otherwise. The analysis to determine stresses under these dynamically forced conditions is termed fatigue analysis and is most often applied to aerodynamic structural systems.
[edit] Load Transfer Path
The evaluation of loads and stresses within a complex assembly of parts is directed to finding the load transfer path. Loads will be transferred by physical contact between the various component parts, and can often be identified visually, or by simple logic. The object of the exercise is to isolate the maximum stress on each part, and compare it with the strength of the material used in the parts. It is a method used in Forensic engineering, where broken parts are analysed for the cause or causes of failure. The method seeks to identify the weakest component in the load transfer path. If this is the part which actually failed, then it may corroborate independent evidence of the failure. If not, then another explanation has to be sought, such as a defective part which lowers the tensile strength for example.
[edit] Stiffness Matrix
Many typical analyses can utilize a method called Direct Stiffness Method or matrix stiffness method. For example, if k is the stiffness of a spring that is subject to a force Q, the spring's stiffness relation is
Q = k q
where q is the spring deformation. This relation gives q = Q/k as the resulting spring deformation.
This is also referred to as the Finite element method. However, the structural mechanics, strength of materials, 2-D and 2-D matrix mathematics involved are not discussed here, but rather on other linked topics.
