FE Analysis of Evolution of Defects during Rolling

Abstract

Defects might appear in materials, such as cracks, inclusions. The evolution behavior of defects in steels during rolling severely affects the rolled products quality. In this chapter, the author summed up the previous researches on the evolution of cracks and inclusions during rolling, mainly contains the researches on the evolution of surface cracks by 2D thermo-mechanical FEM, the evolution of surface cracks during vertical-horizontal (V-H) rolling by 3D FEM, the evolution of internal cracks during V-H rolling, the evolution of inclusions during flat rolling. Evolution of surface cracks by 2D thermo-mechanical FEMSince the brittle fracture model proposed by Griffith last century, a large number of researchers and engineers have carried out a lot of work that focuses on the behavior of cracks. The research reports on the appearance and the propagation of cracks in rolled steels during rolling were investigated [22~25]. Considerable investigations have been carried out on applying FEM for simulation of the propagation and closure of cracks in materials during rolling. A self-healing shape memory alloy (SMA) composite was simulated via a finite element approach that allows crack to propagate in a brittle matrix material by Burton, et al [26]. The SMA wires were carefully (1) where  is density; c is specific heat; k is coefficient of heat conductivity; q  is internal heat source strength, which is the plastic work done of slab deformation during rolling.where m is coefficient of heat transform by plastic work done, 95 .During hot rolling, the thermal transfers between the slab surface and the external environment contain two ways: heat emission and convection current. When the slab is not in the deformation zone, the heat radiation is much larger than the heat convection which could be neglected. According to the Stefan-Boltzman equation,S is the coefficient of Stefan-Boltzman; S B is the blackness on slab surface, T is the slab surface temperature;  T is the temperature of environment. The heat transfers between the slab surface and the work roll is calculated by the Eq. (4). ) (where h i is the coefficient of convective heat transfer between the slab and the roll; T R is the temperature of roll. The coupled thermal-mechanical method is solved by dynamic explicit approach [35]. The heat transfer equations are integrated using the explicit forward-difference time integration rule:

Building a predictive soft armor finite element model combining experiments, simulations, and machine learning

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