Interaction of Cyclic Loading (Low-Cyclic Fatigue) with Stress Corrosion Cracking (SCC) Growth Rate

He Xue,Muhammad Usman,Rui Guo,Yueqi Bi,Rehmat Bashir

doi:10.1155/2020/8026372

Abstract

The structural integrity analysis of nuclear power plants (NPPs) is an essential procedure since the age of NPPs is increasing constantly while the number of new NPPs is still limited. Low-cyclic fatigue (LCF) and stress corrosion cracking (SSC) are the two main causes of failure in light-water reactors (LWRs). In the last few decades, many types of research studies have been conducted on these two phenomena separately, but the joint effect of these two mechanisms on the same crack has not been discussed yet though these two loads exist simultaneously in the LWRs. SCC is mainly a combination of the loading, the corrosive medium, and the susceptibility of materials while the LCF depends upon the elements such as compression, moisture, contact, and weld. As it is an attempt to combine SCC and LCF, this research focuses on the joint effect of SCC and LCF loading on crack propagation. The simulations are carried out using extended finite element method (XFEM) separately, for the SCC and LCF, on an identical crack. In the case of SCC, da/dt(mm/sec) is converted into da/dNScc (mm/cycle), and results are combined at the end. It has been observed that the separately calculated results for SCC da/dNScc and LCF da/dNm of crack growth rate are different from those of joint/overall effect, da/dNom. By applying different SCC loads, the overall crack growth is measured as SCC load becomes the main cause of failure in LWRs in some cases particularly in the presence of residual stresses.

Highlights

Mechanical fatigue and SCC are two important types of failure in the light-water reactors (LWRs) [1, 2]. e word fatigue was firstly originated from the Latin word Fatigare which means “to tire” and commonly associated with mental and physical weariness in the people
Resistance to the fatigue by the material can be classified into following regimes: low-cycle fatigue or limited resistance (104and 105 cycles), high-cycle fatigue (106 to 107cycles), and gigacycle fatigue [5]. e fatigue caused by the small elastic strains under a high number of load cycles before failure occurs is called high-cycle fatigue. e stress in case of high-cycle fatigue comes from a combination of mean and alternating stresses. e mean stress is caused by residual stress, the assembly load, or strongly nonuniform loading [6]
Low-cyclic fatigue (LCF) is the cause of failures, so the LCF is considered in this research

Summary

Introduction

Mechanical fatigue and SCC are two important types of failure in the LWRs [1, 2]. e word fatigue was firstly originated from the Latin word Fatigare which means “to tire” and commonly associated with mental and physical weariness in the people. E fatigue caused by the small elastic strains under a high number of load cycles before failure occurs is called high-cycle fatigue. E stress in case of high-cycle fatigue comes from a combination of mean and alternating stresses. E mean stress is caused by residual stress, the assembly load, or strongly nonuniform loading [6]. LCF is fatigue in which the plastic deformation is considered in each cycle. LCF has two characteristics: plastic deformation in each cycle and low-cycle phenomena [7, 8]. E failure due to the crack propagation in the case of LCF is more prominent as compared to that in case of high-cyclic fatigue (see Figure 1). LCF is the cause of failures, so the LCF is considered in this research

Methods

Results

Conclusion