A shear modified coupled damage criterion based on continuum damage mechanics has been proposed in this study. Khan-Huang-Liang (KHL) model is implemented to predict the constitutive behavior of Ti-6Al-4 V (Ti64) alloy. A VUMAT subroutine has been developed for the damage model using a stress integration algorithm. Multiple simulations with tensile, compression and shear geometries are carried out in Abaqus/Explicit and compared with the experimental results to benchmark the hardening and damage criteria. The flow forming process involves a complex triaxial state of stress. This study is focused on understanding the contribution of triaxiality and shear during deformation and fracture in the flow-forming process with different roller arrangements. For this purpose, the flow-forming processes with three different roller arrangements, single roller, three roller, and wedge roller, are modeled, and their formability is compared by implementing a shear modified continuous damage model. A single roller flow-forming (SRF) arrangement undergoes high triaxiality due to excessive material displacement by the roller and high strain gradient in the axial direction. The fracture occurs near the interface of the reducing and thinning zone. The three-rollers flow-forming (TRF) provided maximum reduction till fracture and material fails due to excessive strain in the thinning zone at a relatively large percentage reduction. The wedge roller flow-forming (WRF) suffers a lack of uniform material softening, and fracture occurs near the interface of the uplift and reducing zone under high triaxiality. 3-D process maps have been developed for predicting fracture strain as a function of stress triaxiality/Lode parameter and stress triaxiality/thermal softening factor $(E/{\overline{\sigma }}^2)$. Finally, a summary chart correlating the parameters, and flow-formability has been developed.

这项研究提出了基于连续损伤力学的剪力修正耦合损伤准则。采用Khan-Huang-Liang（KHL）模型来预测Ti-6Al-4 V（Ti64）合金的本构行为。已经使用应力积分算法为损坏模型开发了VUMAT子例程。在Abaqus / Explicit中进行了具有拉伸，压缩和剪切几何形状的多次模拟，并将其与实验结果进行比较，以此作为硬化和破坏标准的基准。流动形成过程涉及复杂的三轴应力状态。这项研究的重点是了解三轴性和剪切在不同辊排列的流动形成过程中变形和断裂过程中的贡献。为此，采用三种不同的辊布置（单辊，对三个辊和楔形辊进行了建模，并通过实施剪切修正的连续损伤模型比较了它们的可成形性。单辊流动成形（SRF）装置由于辊的过多材料位移和轴向上的高应变梯度而承受高三轴性。断裂发生在缩小和变薄区域的界面附近。三辊流成型（TRF）可以最大程度地减少压力，直到由于相对较大的减少百分比导致的变薄区域中的过度应变而导致断裂和材料破裂为止。楔形辊流成形（WRF）缺乏均匀的材料软化，并且在高三轴度下，在隆起和减小区域的界面附近发生断裂。$（Ë/{\overline{\sigma }}^2）$。最后，建立了一个与参数相关的汇总表，并开发了可流动性。