A new methodology for prediction of fracture initiation in hot compression of Ti40 titanium alloy

It is well known that once plastic deformation reaches a certain limit, metal materials may undergo ductile fracture, which will affect the workability of engineering materials. The accurate prediction of a material ductile fracture is thus of practical importance in the optimization of processes and improvement of products. The knowledge of the strain paths at a critical fracture site of a deforming material is helpful to study the detailed mechanics in the workability. Therefore, an accurate determination of the critical fracture reduction is a prime requirement for proper design and control of any metalworking process. However, it is always a difficult problem on a hot deformation field. In this work, a new high-speed photography was proposed for capturing the initiation and propagation of ductile fracture of Ti40 alloy during hot compression. The results suggest that the high-speed photography technology can clearly display the nucleation site and propagation process of cracking, and thus is an excellent method to represent dynamically the hot-deformation fracture. Based on the Oh fracture criterion, a new hot-deformation fracture criterion, which considered the effect of temperature and strain rate, was built. Then, by combining the DEFORM-3D simulation software and FROTRAN language, hot workability of Ti40 titanium alloy in metalworking processes can be predicted which shows that the proposed prediction model can precisely predict the fracture initiation in the upsetting of Ti40 ingot. Even better, this model can be further applied for optimizing the canned upsetting and indicates that the canned forging is effective for avoiding the oxidation cracking.