Although the finite element method can provide accurate stress analysis when used properly, other techniques remain useful and include hand calculations, brittle coating and photoelastic methods.  Hand calculations are routinely used during the design of a component to quickly check allowable loads and determine required thickness.  Brittle coating techniques provide a simple method of identifying locations of high stress when examining large areas.  Photoelastic models provide easy demonstration of the influence of loading on component stresses and are ideal for the purpose of qualitative visualization.  This method can also be quantitative if necessary.

Hand calculations remain the cornerstone of stress analysis.  For simple problems and where checking of more complex analysis is desired, the use of established engineering calculations is essential.  Calculations carried out by hand provide the analyst with an opportunity to obtain a “feel” for the important considerations in a design and help identify critical areas of concern.  Calculations are also required for the sizing and selection of mechanical components such as roller bearings, springs, bushings and interference fit parts.

The brittle coating method is a unique technique where a special coating is sprayed onto the exterior surface of an unloaded component.  Just prior to testing, the sensitivity of the coating is established using a cantilever beam calibrator.  Once loaded the resulting crack pattern provides a qualitative or quantitative evaluation of the strain field over a large area.  This method is accepted by ASME section VIII UG-101(l) for use during pressure vessel proof testing.

The photoelastic method of stress analysis employs a 2 dimensional transparent model of the component being investigated.  Using cross-polarized lenses, coloured fringes appears in the plastic model when it is subjected to given loading.  The fringes are related to the prevailing strain in the part.  This method is excellent for demonstration purposes and where the effect of minor geometry changes is required.

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