Crack initiation ahead of piled-up of dislocations emitted from a mode Ⅱ blunt crack

Caifu Qian, Wuyang Chu, and Lijie QiaoDepartment of Mechanical Engineering, Beijing University of Chemical Technology, Beijing 100029, ChinaDepartment of Materials Physics, University of Science and Technology Beijing, Beijing 100083, China

摘 要：<正>In situ tensile tests in a transmission electron microscope （TEM） show that dislocations emitted from a mode II crack tip will form a inverse piled-up group after equilibrium or a double piled-up group when they meet a obstruction, e.g., grain boundary or second phase. A microcrack can initiates in front of the piled-up group of dislocations. Micromechanics analysis shows that dislocations emitted from a mode II blunt crack tip can form a inverse piled-up or double piled-up group, depending upon the applied stress intensity factor K_lla, lattice friction stress τ f and the distance of the obstruction from the crack tip L. The maximum normal stress in front of the double piled-up group which is located at the direction of α = -64° increases with the increase in the stress intensity K_lla and the obstruction site L, and the decrease in the friction stress τ_f When it increases to equate the cohesive strength, a microcrack will initiate in front of the piled-up group.

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