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Published online by Cambridge University Press: 15 March 2011
In the polycrystalline Fe-Si alloy when a cleavage front transmits from one grain to another, it first penetrates stably through the grain boundary at a number of break-through points that distribute along the front quasi-periodically. As the critical energy release rate is reached, the unstable crack jump occurs and the recalcitrant grain boundary islands (RGBI) between the break-through points are left behind the verge of propagating, bridging across the crack flanks. Eventually, the RGBI are sheared apart, which leads to a 10%-30% increase in fracture resistance. In this paper, this process is investigated through an energy analysis. The influence of the size/spacing ratio of RGBI on the grain boundary toughness is discussed in detail.