فهرست مطالب

Iranian Journal of Materials Forming - Volume:4 Issue: 1, Spring and Summer 2017

Iranian Journal of Materials Forming
Volume:4 Issue: 1, Spring and Summer 2017

  • تاریخ انتشار: 1395/12/22
  • تعداد عناوین: 5
|
  • M. Zeinali, E. Shafiei *, K. Farmanesh, R. Hosseini, R. Sooltanipor Pages 1-11
    To investigate the hot deformation behavior of 17-7 PH stainless steel, hot compression tests were carried out at the temperatures of 950, 1050 and 1150 oC and strain rates of 0.001 s-1 to 0.1 s-1. Accordingly, the hot working behavior was studied by the analyses of flow stress curves, work hardening rate versus stress curves, exponent- type constitutive equations and deformed microstructures. Meanwhile, the average normalized critical stress for initiation of dynamic recrystallization (DRX) was determined using a 3rd order polynomial curve fitting. The results show that the flow stress depends strongly on the deformation temperature and the strain rate, and it increases with the deformation temperature decreasing and the strain rate increasing. Furthermore, it was found out that the co- existence of δ- ferrite lowers the softening rate at high Z (Zener- Holloman parameter) conditions. The experimental results were then used to determine the constants of constitutive equations. There is a good agreement between the measured and predicted results indicating a high accuracy of exponent- type constitutive equations.
    Keywords: Hot deformation, Dynamic recrystallization, Constitutive analysis, 17-7 PH stainless steel
  • M. Rakhshkhorshid* Pages 12-20
    In this research, a radial basis function artificial neural network (RBF-ANN) model was developed to predict the hot deformation flow curves of API X65 pipeline steel. The results of the developed model was compared with the results of a new phenomenological model that has recently been developed based on a power function of Zener-Hollomon parameter and a third order polynomial function of strain power m (m is a constant). Root mean square error (RMSE) criterion was used assess the prediction performance of the investigated models. According to the results obtained, it was shown that the RBF-ANN model has a better performance than that of the investigated phenomenological model. Very low RMSE value of 0.41 MPa was obtained for RBF-ANN model that shows the robustness of it to predict the hot deformation flow curves of tested steel. The results can be further used in mathematical simulation of hot metal forming processes.
    Keywords: Hot deformation, Neural Computing, Radial Basis Function, Constitutive equations, Flow stress
  • S. Pasebani, M. R. Toroghinejad *, G. Dini Pages 21-27
    Accumulative roll-bonding (ARB) is a severe plastic deformation process that is using rolling to produce ultrafine grains in coarse grained metallic materials. In this study, ARB has been applied on 70/30 brass up to 6 cycles at ambient temperature and non-lubricated conditions to apply a true strain up to 4.8 Von Mises strain. Microstructures of ARBed brass samples were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that during ARB cycles, the grain size decreased from micron-size to nano-size and mechanical twins were widely observed throughout the microstructure after cycle 1. However after cycle 3, the twinning activity became significantly limited and deformation occurred via shear bands formation. After cycle 6, the measured average grain size was about 50 nm and nanotwins were observed originating from grain boundaries and gain boundary junctions. With the reduction in the grain size down to nanometer, the pole mechanism was not the dominant mechanism of nanotwin formation and nanotwins were mainly produced via partial dislocation emission from grain boundaries and grain boundary junctions.
    Keywords: Accumulative roll-bonding, nanotwins, nanostructured, 70, 30 brass
  • M. Seyed Salehi, N. Anjabin * Pages 28-38
    In the present study, the mechanical behavior of AA5052 aluminum alloy during cold deformation and subsequent isothermal annealing in a temperature range of 225-300oC was investigated using the uniaxial tensile test data. It is found that by increasing the annealing time and temperature the material yield strength is decreased. The microstructural investigations of the annealed samples show that the grains are elongated and there is no evidence of recrystallization. Hence, recovery is the main restoration phenomenon during the annealing treatment. The work hardening behavior of the alloy during cold work is modeled using a dislocation density based modeling approach and the softening behavior of deformed samples during subsequent annealing is modeled by applying a kinetics equation relating the yield strength to the annealing parameters. The kinetics equation is a nonlinear differential equation and it’s solved numerically by employing Runge-Kutta-Fehlberg (RKF) integration scheme which is coupled with Gauss-Newton nonlinear optimization technique to obtain the material constants of the model. The numerical results are validated using the experimental flow data.
    Keywords: Kinetics of static recovery, AA5052 aluminum alloy, Cold working, Isothermal annealing, Nonlinear regression
  • H. Deilami Azodi *, R. Darabi Pages 39-51
    Two-layer metallic sheets have wide applications in aerospace, marine, automotive and domestic industries due to their superlative characteristics. In this paper, the formability of two-layer sheet is investigated through analytical, experimental and numerical approaches. An analytical model is developed based on Marciniak-Kuczynski method associated Hill’s non-quadratic yield criterion. Forming limit diagrams are also obtained numerically based on finite element method using Bifurcation theory and ductile fracture criteria. Furthermore, experiments are carried out on Al3105-St14 two-layer sheet. Theoretical results from various methods are compared with results obtained from experiments to evaluate the competency of discussed analytical and numerical methods to predict the formability of two-layer sheets. The results show that analytical and numerical approaches discussed in this paper have good capabilities to predict the formability of two-layer sheets. However, the analytical method based on M-K model and numerical approach based on bifurcation theory are more suitable to determine the forming limit diagram of Al3105-St14 two-layer sheets.
    Keywords: Forming Limit Diagram, Two-layer Sheet, Marciniak-Kuczynski (M-K) Method, Bifurcation Theory, Ductile Fracture