Ti Research
A study on deformation characteristics of CP Ti sheet
In Jeonghun, Young-Suk Kim*
Introduction
- CP Ti(commercially pure titanium) has been actively used in plate heat exchangers(left picture)
due to its light weight, high specific strength, and excellent corrosion resistance.
- This material is allotropic metal. It has a hexagonal closed packed crystal structure(HCP) at low
temperatures.
- Particularly, it is difficult to forming in a press compared with typical steels due to limited slip system, low young’s modulus, and strong in-plane anisotropy.
- Its plastic deformation mainly happens by twin deformation, and strain-stress curves are different in rolling direction and transverse direction.
Material properties
- Strain-stress curves of CP Ti sheet is different in variable directions because of anisotropy property.
- The surface characteristics and the fracture made by tensile deformation also are different by each direction.
- For example, the fracture mode of rolling direction tensile specimen is cleavage fracture and that of transverse direction tensile specimen is dimple fracture.
Forming limit curve
- Forming limit curve(FLC) is important to evaluate formability about CP Ti sheet.
Because CP Ti sheet has different r-value(anisotropy value) by each direction, FLC of
rolling direction and transverse direction tends to different each other.
- FLC of rolling direction is evaluated lower than transverse direction. It is critical to
real factory due to formability.
Finite element simulation
- Finite element method(FEM) has been effectively used to solve the elastic and plastic analysis.
- The finite element simulation is conducted to evaluate formability of CP Ti sheet.
- The simulation was carried out using the explicit analysis of ABAQUS 6.12. Hardening curve is used from Kim-tuan equation in simulation.
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