BEHAVIOUR AND MECHANISM OF STRAIN HARDENING FOR DUAL PHASE STEEL DP1180 UNDER HIGH STRAIN RATE DEFORMATION

Some results of an experimental study on high strain rate deformation of TC21 alloy are discussed in this paper. Cylindrical specimens of the TC21 alloys both in binary morphology and solution and aging morphology were subjected to high strain rate deformation by direct impact using a Split Hopkinson Pressure Bar. The deformation process is dominated by both thermal softening effect and strain hardening effect under high strain rate loading. Thus the flow stress doesn’t increase with strain rate at the strain hardening stage, while the increase is obvious under qusi-static compression. Under high strain rate, the dynamic flow stress is higher than that under quasi-static and dynamic flow stress increase with the increase of the strain rate, which indicates the strain rate hardening effect is great in TC21 alloy. The microstructure affects the dynamic mechanical properties of TC21 titanium alloy obviously. Under high strain rate, the solution and aging morphology has higher dynamic flow stress while the binary morphology has better plasticity and less prone to be instability under high strain rate condition. Shear bands were found both in the solution and aging morphology and the binary morphology.

Download Full-text

Analysis of Failure in Dual Phase Steel Sheets Subject to Electrohydraulic Forming

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4027940 ◽

2014 ◽

Vol 136 (5) ◽

Cited By ~ 15

Author(s):

Javad Samei ◽

Daniel E. Green ◽

Sergey Golovashchenko

Keyword(s):

High Strain Rate ◽

Strain Rate ◽

Dual Phase Steel ◽

High Strain ◽

Dual Phase ◽

Dual Phase Steels ◽

Electrohydraulic Forming ◽

Steel Sheets ◽

Conical Die ◽

The Impact

In previous work, the formability of dual phase steel sheets formed under quasi-static and high strain rate conditions was investigated in macroscale (Golovashchenko et al., 2013, “Formability of Dual Phase Steels in Electrohydraulic Forming,” J. Mater. Process. Technol., 213, pp. 1191–1212) and microscale (Samei et al., 2013, “Quantitative Microstructural Analysis of Formability Enhancement in Dual Phase Steels Subject to Electrohydraulic Forming,” J. Mater. Eng. Perform., 22(7), pp. 2080–2088). The Nakazima test and electrohydraulic forming (EHF) were used for quasi-static and high strain rate forming, respectively. It was shown that dual phase steel sheets exhibit hyperplastic behavior when subject to EHF into a conical die and the micromechanisms of formability improvement were discussed (Samei et al., 2014, “Metallurgical Investigations on Hyperplasticity in Dual Phase Steel Sheets,” ASME J. Manuf. Sci. Eng. (in press)). In this paper, mechanisms of failure in dual phase steels formed under quasi-static and EHF conditions are discussed. For this purpose, the nucleation, growth, and volume fraction of voids were studied. Also, fractography was carried out to understand the different types of fractures in the three grades of dual phase steels. The main objective of this work was to determine how failure was suppressed in the EHF specimens formed in the conical die compared to the Nakazima specimens. The impact of the sheet against the die was found to be the major reason for the delay in failure in the EHF specimens.

Download Full-text