It is a great challenge to extract the crack-tip intensity factors of ferroelectrics due to domain switching,especially for large-scale switching.An success attempt is the I-integral method(Yu et al.,2016.J.Mech.Phys.Solids 94,207-229).This paper extends the I-integral to ferroelectric polycrystals and establishes an area-independent I-integral,which has several merits over the switching-toughening model in determining the crack-tip stress intensity factors.First,restriction to small-scale switching is overcome.Second,the intensity factors are decoupled.Third,it is independent of integration area size,regardless of the presence of grain boundaries and domain walls.These advantages ensure the successful utility of the area-independent I-integral in ferroelectric polycrystals under large-scale domain switching.The phase field model is combined with the I-integral method to form an effective approach to predict the polarization distributions and to evaluate the crack-tip intensity factor.A tensile test of a cracked PbTiO3 ferroelectric polycrystalline plate is simulated through increasing the tensile strain step by step.The stable domain structures are given in Fig.1(a)-(c).For single-crystal,domain switching initiates from the crack tip,while for polycrystals,domain switching initiates not only from the crack tip but also from the grain boundaries due to high polarization gradient and stress concentration.As shown in Fig.1(d),domain switching is triggered by a critical load,which greatly reduces the mode-Ⅰ stress intensity factors.The critical load for polycrystals is much lower than for single crystals,and even vanishes due to grain orientations.The mode-Ⅰ stress intensity factor of the polycrystal is smaller than that of the single-crystal under the same applied load.