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YOU ARE HERE: Home >> Analysis Basics >> Stress Analysis |
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Stress Analysis - a definition |
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STRESS ANALYSIS
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What is Stress Analysis? Stress analysis is used to ensure a component or assembly achieves its expected life. In most cases, where the loads are applied many times, we often speak of durability and fatigue strength, the latter being a material property. Stress analysis calculations require materials data, component geometry and applied loads. These calculations attempt to determine a suitable structural design for a component. Engineering stress is fundamentally expressed as load divided by area, with SI units of Newtons per metre squared [N/m2]. This can be compared with the physical quantity pressure. It expresses the severity of loading experienced by the material from which a part is made. For every engineering material, the strength (or more specifically ultimate tensile strength (UTS), yield strength or fatigue strength) defines a particular value of stress (i.e. how much force can occur over a unit area of the material) that can be sustained before failure. Stress is never uniform in engineering components, and there often can be small regions of stress in a component that are in excess of the strength of the material, whereas elsewhere the stresses are relatively low. Stress analysis or calculations determine the magnitude and locations of these stresses. A typical stress analysis hand calculation could use a beam bending or similar equation (Read about this equation on the Introduction to FEA 1 page here), or empirical data available from the famous 'Roark' book for example (Warren C Young, Roark's Formulas for Stress and Strain, 6th Edition, Mc Graw Hill International, 1989). Alternatively, formulas for stress concentration factors or SCFs can be obtained from 'Peterson' (R E Peterson: 'Stress Concentration Factors', Wiley Interscience, New York, USA; 1974). (Read about SCFs here. In practice, stress analysis ranges in complexity (or cost) from simple hand calculations to finite element analysis. Hand calculations can be performed to national or international standards for a particular industry or component type. Spreadsheets and computer programs are used where appropriate, and these can provide useful insights into the structural performance of a design. Common standards for analysis of general fabrications include BS7608 and Eurocode 9, for the analysis of welded and bolted steel structures. In any structure, most of the attention of the stress analyst is focussed on the welds or bolted joints themselves as this is where the stress concentrations are highest and the material, if welded, can have a much reduced fatigue strength. Other standards include BS 5950 for structural steelwork, BS PD 5500 for pressure vessels and BS 8118 for aluminium. An increasingly important approach to the stressing of general structures is using results from finite element analysis (FEA) to assess welded or bolted joints, using fatigue data and techniques from the above standards. These standards were not originally intended to be used in conjunction with FEA but they can be, providing a suitable approach is adopted. We have particular expertise in this field. Read our newsletter for an example of this approach. |
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