中文摘要：

对锯齿形切屑集中剪切带处的断裂现象进行了观察实验和几何描述,研究表明随着切削速度（变形速度）的提高,材料的脆延性将发生重要变化,这将导致齿形切屑形成机理逐渐由热塑性剪切失稳（绝热剪切）向周期性断裂机理过渡。

英文摘要：

In this paper a photographical study was carried out and the geometry of the crack was dispatched. The results show that with the increase of cutting speed the material dynamic properties change very much,which leads to chip formation mechanism shifting from thermal shear instability mechanism to the periodical cracking mechanism.