A method for predicting fracture resistance of material in cyclic loading under viscoelastoplastic deformation and neutron irradiation conditions

Abstract

We analyze the available methods for prediction of fatigue fracture resistance, which allow for material creep in a deformation cycle and neutron irradiation. Benefits and drawbacks of the available methods are discussed. We present a new method for the fatigue fracture strength prediction, which suffers no disadvantages inherent to the well-known methods. The proposed method has been verified on austenitic steels tested at elevated temperatures.Keywords: fatigue fracture resistance, creep, neutron flux level.Introduction. Various parts of a fast neutron reactor plant operate in a wide temperature range -from 220 to 580°C. Moreover, some of them are subjected to intensive neutron irradiation. During the reactor transient modes, such as reactor going-up, shutdown cooling, fast emergency protection conditions, the temperature distribution in structural elements is highly nonuniform, resulting in thermal stresses and strains. The transient processes, when repeated many times, may lead to fatigue damage. Since the structural elements operate at temperatures above the temperature threshold of creep, damage should be considered as a case of interplay between fatigue and creep. The problem becomes even more complicated as this process is accompanied by an intensive neutron irradiation of the structural elements, which contributes to a considerable deterioration of ductility and creep rupture strength of material. The static strength and ductility characteristics of a material correlate with its resistance to fatigue fracture; therefore, neutron irradiation has a significant effect on the cyclic strength of the material.The objective of the present work has been to review the currently available methods and to further develop them to enable prediction of fracture resistance in cyclic loading under viscoelastoplastic deformation and neutron irradiation conditions. 1. Current Status. Let us discuss the currently available methods for predicting fatigue damage in a material under creep and neutron irradiation conditions.In [1][2][3][4], the researchers used a so called strain range partitioning method which essentially consists in dividing the damage into components induced by the time-dependent and time-independent strains. Generally, alternating inelastic deformation is split into the four components: a) plastic tensile strain followed by plastic compression strain Δε pp ;

Study of the effect of thermal aging on durability and plasticity of Kh18N9 steel

“…In summing the damage under conditions of simultaneous action of creep and fatigue, the calcula tion will be conservative if the damage caused by creep is calculated on the basis of properties of the austen itized material and fatigue curves Δε(N f ) are plotted using the Coffin-Manson equation [9][10][11] with the following conditions:…”