Photoelastic stress analysis is a powerful full-field non-contact optical method for determining stresses and load paths in components or structures. It is also widely used for measuring residual stresses in transparent materials - particularly glass. The technique utilises an effect known as bi-refringence. This means that when a transparent material is stressed and observed under polarised light, interference fringes are formed which coincide with lines of shear stress. VisEng uses and sells the latest automatic measurement equipment which provides real-time results very rapidly.
2-D Photoreflective Coating
Photoreflective Coating on a Weld
Sheer Stress Around a Coated Weld
A quick and simple approach to photoelastic analysis. This method involves applying a thin epoxy coating to a metal, glass or plastic component or even a model of a component. When the component is loaded, stresses are transmitted into the coating and when viewed under polarised light, the photoelastic fringes can be observed and analysed to determine shear stresses. This method can be used to very quickly identify load paths within a structure as well as determining areas of stress concentration which could lead to a potential fatigue failure.
3-D Photoelastic Analysis
Stress Distribution on a Joint
The 3-D technique is carried out by making a transparent model of a component or structure, and applying scaled-down loads to simulate real loading conditions. By interpreting the generated fringe patterns, the full-field, external and internal stress distribution in the part can be determined. With the use of rapid prototyping technology it is possible to construct photoelastic models direct from CAD data, hence allowing full stress analysis of parts to be performed at the concept stage of design, alongside or instead of finite element analysis producing fast and accurate product validation.
Glass Analysis
Stress Concentration on a Windscreen Edge
Knowing the residual stress levels in glass products is vital to ensure their long-term durability. VisEng has the capability to measure residual stresses in glass and also, by applying a thin photoreflective coating, assembly or loading stresses. Using the GFP 2000 automated polariscope, glass problems can be quickly identified and eradicated (e.g. windscreen analysis).
Toughened Glass Residual Stresses
Stress Patterns as a Result of Tempering in Toughened Glass
Using the GFP 1000 or GFP 2000, safety glass may be rapidly checked for correct tempering. Problems at the glass manufacturing stage can be identified and resolved. The equipment will work on most transparent materials and can give quantitative as well as qualitative results.
Photoreflective Coating Applications on Glass
Application of Photoreflective Coating
The photoreflective coating technique allows any additional stresses experienced by the glass to be quickly found and analysed. The coating is easily applied by simply mixing a two part epoxy resin which is then spread onto the glass using a special spreader tool. The coating thickness is typically only 0.5mm and so cures very quickly.
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VisEng Ltd
PO Box 2623
Warwick
CV34 6ZX
United Kingdom
