为预测缺口裂纹对加工表面形成的影响,研究了切削脆硬材料时缺口裂纹的扩展.根据切削力作用性质,缺口裂纹属于Ⅰ-Ⅱ复合型荷栽裂纹,呈Ⅰ型开裂.基于广义合成偏应力强度理论,通过对复合型荷载作用下缺口裂纹裂尖处应力场的研究,分析了该处的开裂扩展机理,得到了缺口裂纹的扩展判据、起裂方向角解析表达式.分析结果表明:脆硬材料加工时缺口裂纹初始扩展方向总是指向工件内部,导致被加工表面粗糙度增大;在确定的刀、屑摩擦因数及工件泊松比条件下,起裂方向与刀具前刀面的夹角是不变的,且刀具前角越小,缺口裂纹向工件内部方向扩展的倾角越大.%In order to predict effects on machined surface by developed notch-crack, crack extension mechanism of notch-crack-tip was investigated in cutting brittle materials. The notch-crack was in I - II mixed mode according to loads exerting on the chip. Based on the strength theory of generalized composed deviator stress, this paper analysed notch-crack extension mechanism for brittle fracture process through analyzing the stress field in the neighborhood of crack tip under loading mixed-mode. Three major contributions here are summarized as follows: ①The criterion for the expansion of crack and the analytical expression of direction angle are presented here. ②It is deduced that the notch-crack always expands initially towards the interior direction of machined workpiece, and this leads to roughness enhancement of machined surface. ③The angle between crack expansion direction and the tool face is equivalent under the same cutting conditions. And the obliquity of expansion direction to workpiece surface increases with the tool orthogonal rake decreasing.
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