Analysis of residual stress profiles in plastic materials using the hole drilling method - Influence factors and practical aspects

The current work introduces a procedure to locally measure residual stresses in polymers. For this purpose, the hole drilling method was adapted to the prevailing boundary conditions. Particular attention is given to the analysis of the measured strain signal which is time dependent and strongly influenced by local temperature fluctuations. The different sources of heat prevailing during the measurement and their impact are outlined. By thorough analysis of the viscoelastic and thermal deformation occurring during and after drilling the material, a procedure is proposed to measure the correct strain relaxation from which residual stresses can be calculated. Using quenched polycarbonate samples with known residual stress profiles, the potential of the proposed approach was demonstrated and is discussed.