Static and dynamic pre-stressing of metal discs.

In order to develop a technique of controlled prestressing of metal components, mild steel discs were dynamically loaded using explosives. Subsequently, mild steel discs of similar dimensions were loaded statically. The following loading conditions were studied:(i) at fixed radius and varying load (ii) at varying radial positions and fixed load (iii) at constant load and fixed radius but varying outer diameter of disc (dynamic tests only).For the dynamically loaded discs, residual radial stresses have been obtained by an experimental technique, based on strain gauge readings, which permitted the estimation of the residual stresses at the incremental radius of the successively cut sections of the discs for both outer and inner sections. Further analysis of the experimental results has produced values for the residual radial and hoop stress at radii close to the explosive loading radius. Correlation from results obtained from the statically loaded discs was provided by strain gauges fixed at varying fixed radii on each-loaded disc. The experimental analysis for the statically loaded discs was of simpler form than that required for the dynamically loaded discs.In order to establish the validity of the method for estimating the residual radial stresses, certain other experimental measurements have been made viz: planedeformation, hardness, microstructural examination and buckling tests. A theoretical model based on plastic deformation of the loaded annulus has been developed which requires an estimation of the energy transferred from the loading ring or annulus to the surface of the disc. In the majority of cases, agreement between experimental and theoretical values of residual radial and hoop stress have been found in both magnitude and sign. A further theoretical approach was applied using finite element technique to validate the equivalent stress values obtained from the experimental results of the statically loaded discs. Comparison of the results again showed good agreement in magnitude and sign.