Stereolithography for 3D photoelasticity

Abstract

Recently, the use of photoelasticity has become more widespread due to the development of digital methods of fringe analysis [1] that allow a significant reduction in the time taken to achieve a stress map for any given model, particularly when only fractional fringe orders are displayed. However, in order for the full potential of the photoelastic method to be realised, a technique for rapidly producing complex 3-dimensional photoelastic models must be developed. Stereolithography is one so-called ‘rapid-prototype’ method that works by building a laminar model from a tank of photo-curing resin. A perforated metal plate is submerged in the liquid resin to a depth of typically around 0.1mm. A laser then traces the shape of the first layer of the component onto the plate, curing a thin layer of the resin. The plate is lowered by 0.1mm, and a further layer of resin cured by the laser. By this method, complex structures may be ‘laid-up’ in a matter of hours. Previous studies concerned with the use of stereolithography for the production of photoelastic models [2] have noted that unacceptable levels of residual birefringence and stress have remained in the photoelastic model even after conventional annealing methods. Thus the use of such methods has been limited. If the stereolithographic method were developed for photoelasticity, one possible area of interest would be the design and analysis of orthopedic implants. This paper outlines a series of studies looking at the requirements of photoelastic materials for three-dimensional stress analysis