Simulation of Adiabatic Shear Bands in Orthogonal Machining of Ti6Al4V Using a Rigid-Viscoplastic Finite Element Analysis
Simulation of Adiabatic Shear Bands in Orthogonal Machining of Ti6Al4V Using a Rigid-Viscoplastic Finite Element Analysis
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DOI：
10.3390/met10030338
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发表时间：
2020-03-01
期刊：
影响因子：
2.9
通讯作者：
Korlos, Apostolos
中科院分区：
文献类型：
--
作者：
Friderikos, Orestis;Sagris, Dimitrios;Korlos, Apostolos
突变剪切失稳是Ti6Al4V正交切削的主要机制。即使在低速下的切屑分割也证明了在材料的塑性变形期间出现了某种不稳定性。在这些理论模型中，灾难性的热塑性滑移被提出作为一种机制来解释均匀塑性变形的失稳，这导致局部化的带状绝热剪切变形。另一方面，断裂模型，考虑加工作为一种机制的韧性或脆性断裂被用来解释作为一个周期性的裂纹产生机制的分段芯片的形成。本文旨在通过热力耦合刚粘塑性有限元分析阐明上述理论模型的基本机理。引入韧性损伤的能量准则，数值结果表明，绝热剪切带（ASB）内的破坏是发生在强烈剪切局部化之后的后局部化机制。模拟结果显示，一个空洞的启动和合并机制，类似于一个阵列的不连续退化元素的近椭球形的增长和逐步合并，形成一个宏观裂纹内的ASB。ASB形成的几个方面，其中包括微尺度空间温度分布，临界损伤能量，芯片分割频率等的参数研究。ASB形成有关芯片形态和切削力的实验结果进行编译和分析，以评估在低速制度的有限元模型。
Catastrophic shear instability is the dominant mechanism during orthogonal cutting of Ti6Al4V. Chip segmentation even at low speeds testifies to the emergence of some kind of instability during plastic deformation of the material. Among the theoretical models, catastrophic thermoplastic slip is proposed as a mechanism to explain the destabilization of homogeneous plastic deformation, which results in localized, band-like adiabatic shear deformation. On the other hand, fracture models which consider machining as a mechanism of ductile or brittle fracture are used to explain the segmented chip formation as a periodic crack generation mechanism. This work aims at elucidating the fundamental mechanisms of the above theoretical models using a coupled thermomechanical rigid-viscoplastic FEM analysis. Introducing an energy criterion for ductile damage, numerical results showed that failure within the adiabatic shear band (ASB) is a post-localization mechanism occurring after intense shear localization. Simulations revealed a void initiation and coalescence mechanism which resembles an array of discontinuous degraded elements of nearly ellipsoidal shapes that grows and progressively coalesces forming a macro crack inside the ASB. Several aspects of ASB formation are addressed, among others, the micro-scale spatial temperature profile, parametric studies of critical damage energies, chip segmentation frequency, etc. Experimental results of ASB formation pertaining to chip morphology and cutting forces are compiled and analyzed to evaluate the FEM model at the low speed regime.