[SY-J2] Symposium J-2

[SY-J2] Cracking behavior of ferrite-pearlite pipeline steel with hierarchical and concurrent multiscale modeling schemes

^○Taolong Xu^1,2, Wei Wang¹, Xiaojiao Deng¹, Anlin Yao¹, Jinghong Fan^3,2 (1.Southwest Petroleum University of China, China, 2.International Institute of Material Multiscale Modeling, United States of America, 3.Alfred University, United States of America)

Attempts of two schemes with atomistic-based multiscale simulations for lamellar ferrite-pearlite pipeline steel are evoked in this work. They are hierarchical multiscale method by atomistic-based Cohesive Zone Model (CZM) and concurrent multiscale method by extended Generalized Particle Dynamics Method (XGP), where XGP proposed recently by author and coauthors (Fan, Eng. Fract. Mech., 2017) is an extension of the GP method (Fan, Multiscale Model. Simul., 2009) in which finite element (FE) nodes are connected with the outermost particles, thus encouraging accurate crack-tip parameters are obtained due to reduce artificial effects on the atom-node boundary. The former one bridging crack propagation at the atomistic and mesoscopic scale by local energy release rate G_c extracted from ferrite-cementite grain boundary, where G_c characterized by exponential and trilinear traction-separation law (TSL) complied into VUMAT in finite element software, using the unique cohesive element length (Xu, Eng. Fract. Mech., 2016), tension specimen FE models are designed to reveal the accuracy of the intrinsic correlation between the atomistic and mesoscopic scale under a stress intensity factor, and will be verified by the fracture test result, which proves the practicability of concurrent multiscale method to solve the cracking behavior of engineering material. The latter one investigates the lamellar ferrite-cementite micro-structure with extra size compared to conventional multiscale method such as the quasicontinuum (QC) method, for crack-tip behavior, the GP method provides the possible way to qualify the layer thickness characterize of ferrite, as well as the model size effect via XGP multiscale analysis under one-order larger than GP model, XGP method develops a sufficiently large model bases on proven accuracy may open a new avenue to study the cracking behavior in lamellar structure, also explore a new types of multiscale methods which can improve the accuracy in bridging atomistic and continuum scales. However, each simulation scheme, Bagaryatskii orientation relationship between ferrite and cementite within pearlite is developed by Voronoi geometric method, and then the crystal boundary of lowest energy state is obtained by using conjugate gradient method and annealing under NPT ensemble.