Abstract
Formability of pure molybdenum in thermal forming process has been greatly improved, but it is still hard to avoid the generation of rupture and other quality defects. In this paper, a ductile fracture criterion of pure molybdenum sheet in thermal forming was established by considering the plastic deformation capacity of material and stress states, which can be used to describe fracture behaviour and critical rupture prediction of pure molybdenum sheet during hot forming process. Based on the isothermal uniaxial tensile tests which performed at 993 to 1143 K with strain rate range from 0.0005 to 0.2 s−1, the material parameters are calculated by the combination method of experiment with FEsimulation. Based on the observation, new fracture criteria can be expressed as a function of Zener-Hollomon parameter. The critical fracture value that calculated by Oyane-Sato criterion increases with increasing temperature and decreasing strain rate. The ductile fracture criterion with Zener-Hollomon parameter of pure molybdenum in thermal forming is proposed.
Highlights
Molybdenum is a refractory metal which is widely utilized in lighting-technology, high performance electronics, furnace construction and sputter targets since it possesses a combination of physical properties including excellent strength at elevated temperature, high corrosion resistance except oxidation resistance, high thermal conductivity, a high elastic modulus and a low thermal-expansion coefficient
A ductile fracture criterion of pure molybdenum sheet in thermal forming was established by considering the plastic deformation capacity of material and stress states, which can be used to describe fracture behaviour and critical rupture prediction of pure molybdenum sheet during hot forming process
The application of the ductile fracture criteria for the prediction of the forming limit diagram (FLD) of sheet metal was investigated by Ozturk [2] et al Lou [3] et al developed a ductile fracture criterion which is proposed to model fracture behaviour of sheet metals for nucleation, growth and shear coalescence of voids during plastic deformation
Summary
Molybdenum is a refractory metal which is widely utilized in lighting-technology, high performance electronics, furnace construction and sputter targets since it possesses a combination of physical properties including excellent strength at elevated temperature, high corrosion resistance except oxidation resistance, high thermal conductivity, a high elastic modulus and a low thermal-expansion coefficient. It is difficult to work in hot forming processes due to extensive surface and edge cracking. The extension of the fracture criteria to hot forming processes is difficult because ductile fracture is a complicated phenomenon that is dependent upon process parameters, such as stress, strain and forming temperature. He [5] et al, built a new ductile fracture criterion taking into account the plastic deformation capacity of material and stress states, which can be used to describe fracture behaviour and critical rupture conditions of 30Cr2Ni4MoV ultra-super-critical rotor steel during hot forging process. For hot forming processes, a reliable fracture criterion should at least account for temperature and strain rate
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