13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Atomistic simulation of fatigue crack growth in α-Fe under high temperature Tong Liu1,*, Minshan Liu1 1 Thermal energy engineering research center of Zhengzhou University, Zhengzhou 450002, China * Corresponding author: liutung@zzu.edu.cn Abstract The crack growth behaviors loaded in mode I under strain and stress control at different temperatures were presented in α-Fe by atomistic simulations using LAMMPS code. The interatomic bonds of atoms were characterized using the embedded atom method interatomic potential. The simulation models were built with initial edge crack subjecting to cyclic uniaxial constant strain rate and constant stress. A temperature range from 100 K to 1200 K was considered to probe the influence of the temperature on crack growth. The crack growth mechanism and the radial distrinution function (RDF) during crack growth were investigated. The results indicated that the crack propagation mechanisms were sensitive to temperature and the boundary conditions. By proposed image adjusting technology the dislocation slip bands can be more clearly displayed on screen. In order to include the effect of temperature on crack growth, a temperature factor defined as a function of temperature in exponential form was introduced to modify the theoretical expressions based on thermal activation theory. Its coefficent and index can be determined by the RDF peak value obtained from atomistic simulations. For cyclic loading the crack growth process was dependent on both temperature and cyclic loading period in terms of simulations. Keywords Molecular simulation; Fatigue crack growth; High temperature; Iron; Thermal activation. 1. Introduction Ferritic steels are widely used in process industry, modern nuclear power plants, military industry and others. The main crystal structure of steels is body-centered cubic (bcc) lattice of iron and it is comonly called α-Fe[1]. It is unavoidable for steels with defects so safety assessment on strucure integrity with defects is essential for engineering application. While in critical components of nuclear facilities, the radiation, high temperature and presssure, start and stop operations influence behavior of steels significantly and imply high potential failure risks for the integrity of reactor components with crack-like defects. The detail understanding of the processes occurring near the crack tip during the crack nucleation and growth can largely help in the material development and safety assessment under service in particular high temperature environments[2]. As the fatigue fracture is the primary cause of failure for almost all engineering structures subjecting to repeated cyclic loading, so many people have been do much research efforts on this scope. Most investigations on fatigue fracture have been performed at the macroscale and the theory on analysis methods and experimental approaches related to fatigue strength and fracture mechanics has been well established based on mechanics of continua and test at the macroscale with the crack lengths ranging from a few decades of microns to centimeters. However, on the kernel mechanism of fatigue crack initiation and growth are maily determined by interatomic bond rupture,crystal plastic deformation and the associated material defects in the vicinity of the crack tip. Recent developed atomistic simulations provide a high efficient approach to investigate fatigue fracture behavior at the nanoscale. With the knowledge of nanoscale fatigue, more accurate macroscale predictive tools can be got, mechanism understanding of grain boundary effects, crystal orientation effects, and driving force versus material resistance effects can be clearly obtained. The material deformation and fracture mechanism of a structure with cracks have been paid close attention in worldwide. The fracture response of a material under mechanical load and temperature is a multiscale problem. It is the result of dislocation slip, grain boundary motion, plastic deformation and interplanar cleavage. The literature indicates that the atomistics of the crack
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