Further Analysis of Warm Prestressing (WPS) Effects: Role of Local Stress and Strain
Effect of WPS in ferritic alloys 15Kh2MFA (CrMoV) and 18MND5 increases with prestress level more rapidly than Chell’s model predicts; this observation had not been understood until now. In this work, experimental data are presented concerning behaviour of steels under simple Load – Unload – Cool – Fracture history. Chell’s model uses as input quantity true fracture toughness and predicts, for simple temperature and loading histories, apparent fracture toughness. A new proposed model based on local approach corrects value of true fracture toughness as an input quantity for Chell’s formulas. Idea of the true fracture toughness increase consists in deactivation of fracture initiation particles during preload. But another interpretation is also possible: Retarding influence of dislocation substructure formed during preload (phase L) on the cleavage microcrack growth at low temperature during loading to fracture (phase F) may cause similar effect. Universal behaviour found in both steels indicates that the second interpretation is more realistic one.