Defect-free Machining of Brittle Materials by Restraint of Crack Propagation with Ion Absorption

讨论了脆性材料加工过程中脆性裂纹的产生和扩展，以及裂纹扩展的抑制/控制方法。为了阐明玻璃加工中切屑形成过程的力学特征，对该过程进行了有限元模拟。在良好的切割条件下，可以看到无缺陷的流动型切屑。通过引入概率断裂准则的有限元方法，模拟了裂纹型切屑形成向流动切屑形成的转变过程。裂纹的产生及其扩展通道在很大程度上取决于切割深度。在细切削条件下，也可以看到无缺陷的切屑生成过程。定量地讨论了环境对脆性材料力学特性的影响。加工液中的特殊离子对材料的断裂应力影响很大，离子使材料表面光滑，但在加工过程中，断裂应力降低。由于脆性材料的表面能或断裂韧性对裂纹的产生/扩展有很大的影响，本文讨论了在裂纹尖端吸收特殊离子来控制韧性的新方法。最后，构建了一台用于脆性材料微纳米加工的微型数控机床，并对其性能进行了测试，从而实现了无缺陷加工。

A brittle crack generation and its propagation are discussed in machining process of brittle materials, and the restrain/control method of crack propagation is also discussed. In order to clarify a mechanical feature of a chip formation process in glass machining, the process is simulated by FEM. A flow type chip without defect can be seen under a fine cutting condition. A transition from a crack type chip formation to a flow type one is also simulated through FEM introducing a probabilistic fracture criterion. A crack generation and its propagation pass in a work are greatly dependent with a depth of cut. A defect free chip generation process can be also seen under a fine cutting condition. The effects of environment on mechanical characteristics of the brittle materials are quantitatively discussed. A fracture stress of the materials are greatly affected by special ions in machining fluids and the ion gives a fine finishing surface, but the fracture stress decreases of machined work in the ion. Since a surface energy or fracture toughness of brittle material affects greatly on crack generation/propagation, the new methods to control the toughness are discussed, where the special ion is absorbed in a crack tip. Finally a micro NC machine for micro/nano machining on brittle materials is constructed and its performance is examined, where a defect free machining is possible.