Load history effects on fracture toughness of RPV steel

摘要

Fracture toughness is required for assessing structural integrity of reactor pressure vessels (RPV).However,it has been long recognized that load history effects can increase the apparent toughness,which is not considered in practical rules assessment.This could lead to over pessimistic assessment in case of thermomechanical transient.The so-called warm prestress (WPS) effect corresponds to the absence of crack propagation after prestressing if the load is held constant or decreased as the temperature is decreased.This study investigates the WPS effect on A508 Cl3 RPV steel,focusing on transient loadings in which the load is increased during cooling,with a twofold aim.Firstly to investigate experimentally to which extent it is possible to go beyond the WPS effect by progressively increasing the slope of the transient.Secondly,to assess numerically the ability of local approach to fracture (LAF) models to quantitatively predict the experimental results.The evolution of local quantities such as opening stress,cumulated plastic strain,triaxiality close to the crack tip are finally described in details.