Numerical results indicated that plane strain state ( approximately ) was the main feature around the 3D crack front in the midsection of Mode I specimen, but the maximum values of stress triaxiality ( R σ ) were found only in the vicinity of ligament. 结果表明:在试样中面附近围绕Ⅰ型裂纹前缘,应力状态均具有明显的平面应变特征,而应力三轴度(Rσ)仅在韧带附近为最大。