Photo‐Elastic Stress Patterns

TO define the science of photo‐elasticity we need but say that, with the aid of certain optical equipment, it enables us to see the pattern of stress simultaneously over the entire extent of a scale model under test. If desired, the pattern may be seen in all the delicate hues of the spectrum, but for exact analytical measurement it is sometimes preferable to obtain the sharp‐edged black and white tracing by means of monochromatic light. We might with reason add that the pattern so depicted is complete down to the last detail and represents, in many cases, a unique solution of a complex mathematical problem in elastic deformation. Its application to mechanical engineering design has been widespread and is still reaching out into new fields. By its use it is now possible to trace and measure the intensity and internal distribution of stress in loaded components far more speedily and accurately than can be achieved by any other method.