Investigation of the warm prestress effect

Experimental assessment of fracture toughness behavior was performed using CT- and precracked Charpy-V specimens of two reactor pressure vessel steels in different warm prestressed conditions. By means of X-ray analysis, a butterfly-like compressive residual stress field was evaluated at the prestressed crack tip. Fractographic features indicated an increase in the critical distance for cleavage initiation after prestressing. Based on the experimental results, the warm prestress effect may be seen as a complex phenomenon in which the loss of constraint due to compressive residual stresses and a microstructural predamaging at the blunted crack tip are interrelated to an apparent enhancement of fracture toughness.