TWI Knowledge Summary

Stress analysis

Man-made objects have a purpose and a nominal specification. Durability is an important aspect of the specification of built or manufactured items. Designers and engineers use materials data and expected load levels to create suitably sized components through the use of stress analysis.

Stress is most fundamentally expressed as load divided by area. It expresses the severity of loading experienced by material in equipment (hence, higher loads can be sustained by larger cross-sections of the same material). A variety of reasons, however, mean that stress is never uniform in engineering components. Stress distributions are frequently complex. The methods of stress analysis have been developed to give engineers practical methods for assessing the level of stresses.

Stress distributions are usually classified as either linear or non-linear by engineers. In general, a distribution will be composed of both types. The linear portion can often be calculated analytically with relative ease. Non-linear distributions of stress can be predicted by analytical methods, but the techniques used are complex. Encyclopaedias of the peak stresses from non-uniform stress distributions have therefore been prepared to help the stress analyst (e.g. R E Peterson: 'Stress Concentration Factors'. Publ: New York, USA; Wiley Interscience; 1974. ISBN Q-471-68329-9).

Computer based numerical stress analysis methods (e.g. finite element analysis or FEA) have permitted the complex distributions of stress in engineering components to be more routinely calculated. These allow linear elastic and non-linear (e.g. elastic-plastic) stress analyses to be performed for static and dynamic loads. The computer-based engineering office is now integrating the processes of component drawing and component stressing through the use of Computer Aided Design (CAD) systems. Information transfer should therefore be more straightforward. However, advanced software is needed to interpret and process the data. Further development of the software and the file format protocols is needed.

Existing engineering components can be assessed using experimental stress analysis. The results will then be applicable to the real material characteristics of the component and the correct in-service loads.

Further information

A stress intensity factor solution for root defects in fillet and partial penetration welds. (Technology Briefing 575 - October 1996)

FAQ: What element type should be used in finite element modelling of welded structures?

FAQ: How are welds included in models of structures?