in accordance with the applicable manufacturer 39 s recommendations using standard procedures and were then instrumented with pairs of electrical resistance strain gauges and electrical resistance temperature transducers the free post curing shrinkages ranged from 2000 to 6000 micro strain having determined these free shrinkage values simple theory of mechanics of solids allows the prediction of residual stress values that would prevail in post cured fabrications consisting of any combination of these resins depending upon the reinforcement types and contents in the inner and outer layers in a composite using two distinct resin types these values suggest that residual compressive stresses as high as 10 mpa typically between 4 and 10 mpa could be generated in the inner layer 18 however to determine whether the actual residual stresses in a fabrication were of the same order as those predicted testing was carried out whereby a number of specimens were constructed making use of the potentially most suitable resin types from the candidate families judged on the basis of their recorded free shrinkages these specimens thus made use of resin types likely to introduce a reasonable level of compressive stress into the material intended for exposure to the corrosive liquor whilst maintaining an adequate degree of resistance to general corrosion and high temperature attack the generated residual stresses were measured by incremental hole drilling based upon the measured relaxation which accompanies the removal of stressed material compressive residual stresses between 5 and 7 mpa were measured these values being in reasonable agreement with the theoretically predicted values and more importantly of sufficient level to retard crack propagation rate by three to four orders of magnitude 1000 to 10000 times in comparison with rates in material in.