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A phenomenological model presented by the authors in the previous study, which is a kind of two-region exponential function model, is used to describe flow stress behaviors of bearing steel, STB2. In this model, flow stress is calculated using two separated equations for hardening and softening regions. Peak stress, peak strain, hardening coefficient, steady state stress and softening coefficient are the required parameters for the model. These parameters are then either interpolated using linear regression or used to find some fitted functions of strain rate and temperature to identify the flow stress. The former is called the piecewise bi-linear function model (PLF model) while the latter the closed-form function model (CFF model). It has been shown that the flow stress curves of STB2 steel obtained by these two models are in good agreement with experimental results.

The material constants of a phenomenological model for predicting the grain size evolution during hot deformation are determined using first and second stages of a hot forging process. The constants including initial grain size exponent, strain exponent, strain rate exponent and dynamic recrystallization activation energy for SCR420HB bearing steel were obtained through finite element optimization technique introduced by the same authors in literature. In the optimization, the error between the experimental and predicted grain sizes at some sample points were minimized by adjusting the material constants as the design variables. The predicted grain size after the third stage using the optimized material constants was compared with the experimental values to validate the obtained material constants. The comparison showed that the model predicts the grain size with tolerable error when the obtained material constants are applied.

A practical method for determining dynamic recrystallization (DRX) parameters, consisting of finite-element analysis, optimization techniques, and experimental studies, is presented. The method iteratively minimizes the error between target values and the corresponding finite-element solutions using a general-purpose optimization tool. An isothermal hot compression test of AA6060 aluminum alloy was used to investigate the validity of the method. Three main DRX parameters in the Johnson-Mehl-Avrami-Kolmogorov model were obtained using the method, and good agreement was observed between the optimized parameters and reference values from the literature. The effects of mesh size and the number of sample points on the accuracy of the responses were also studied to show the numerical characteristics of the method, revealing that the greater the number of elements and sample points, the more accurate and reliable the results. Parameters acquired using fewer elements also provided acceptable optimized parameters for predicting DRX grain size.

We present a practical approach that improves the accuracy of finite element predictions of hot forging; we emphasize the importance of tribological characterization. We analyze three-stage hot forging of high-strength S45C bearing steel in terms of metal flow lines sensitive to friction. An optimized friction condition is determined by comparing the predicted and experimental flow lines under various conditions. We use a phenomenological approach to predict grain size after dynamic recrystallization when investigating the effects of friction. We explored the relationship between macroscopic and microscopic phenomena with an emphasis on the tribological effect. Friction coefficient optimization improved the predicted metal flow lines and also reduced the error between predicted and measured grain sizes after dynamic recrystallization at all sample points.

In the present study, the effects of back pressure on the filling fraction of die and the effective strain distribution throughout severely deformed material during pure shear extrusion, a novel severe plastic deformation process, are investigated by finite element analysis. A pure shear extrusion process found in the literature is employed and the predicted forming load is compared with experiments. A good agreement is observed between the results of the simulation with Coulomb friction of 0.12 and experiments. Various back pressures are applied to plunger at the exit channel of the die, and their influence on the filling fraction of the die and the effective strain in severely deformed billets are studied, indicating that the homogeneity of the effective strain on the cross-section of the deformed billet is decreased slightly. It is also found that the filling fraction of the die exit channel as well as average strain on the cross-section of the billet are increased.

Multilayered fibre–metal laminates (FMLs) are composed of metal semifinished products and fibre-reinforced plastics, and benefit from the advantages of both material classes. Light metals in combination with fibre-reinforced thermoplastics are highly suitable for mass production of lightweight structures with good mechanical properties. As the formability of light metal sheets is sometimes limited at room temperature, increasing the process temperature is an appropriate approach to improve formability. However, the melting of thermoplastic materials and resulting loss of stiffness limit the processing temperature. Since single-ply layers have different through-thickness stiffnesses, the forming process changes the ply thickness of the multilayered laminate. In the present study, the deformation behaviour of multilayered FMLs was investigated using a two-dimensional finite-element model assuming plane strain. The thermoelastic-plastic finite-element analysis made investigation of the variation in thickness made possible by incorporating sufficient mesh layers in the thickness direction. The results indicate that a thermoelastic-plastic finite-element model can predict the delamination of plies during deformation, as well as in the final product. Additionally, the predicted changes in thickness of the plies are in good agreement with experimental results when a temperature-dependent friction coefficient is used.

Shot peening is a surface engineering process acknowledged for its potential to develop fatigue strength and erosion-corrosion resistance of metallic materials. In the present study, a 3-D finite element model is employed to predict the effective parameters through a single shot impact and the accuracy of the simulation is validated using previous literatures. In order to induce uniform compressive residual stress patterns across the specimen, processing parameters such as shot velocity, impact angle and friction coefficient should be controlled. It is observed that by increasing the shot velocity and the friction coefficient, the depth of compressive residual stress increases. Moreover, a comparative study between isotropic and kinematic hardening models is performed to evaluate the significant role of the hardening models on the compressive residual stress. It is observed that the kinematic hardening model shows better compatibility with the experimental results compared to the isotropic hardening.

A practical method for adjusting and optimizing isothermal transformation (IT) diagrams using the Jominy test is presented. The method is based on a finite-element optimization procedure, which iteratively minimizes the error between the target phase fractions and the corresponding finite-element solutions at the sample points using an optimization tool. A standard Jominy test of AISI 52100 bearing steel is used to investigate the feasibility and reliability of the method. Three optimization parameters for each IT diagram curve are mathematically applied to the modified Kirkaldy model. These parameters are the design variables in the optimization. The curves obtained from the modified Kirkaldy model are used as the initial guesses in the optimization and they approach the experimental IT diagram by minimizing the error. Good agreement is observed between the optimized diagram and the experimental diagram reported in the literature. The predicted phase fractions using the experimental IT diagram, the IT diagram obtained from the modified Kirkaldy model, and those obtained from the optimized model are compared and demonstrate that the adjustment or optimization procedure significantly improves the accuracy of the predicted phase fraction of the model. The applicability of the method is investigated in a practical case study.

The results of electrochemical research on Zn5Al and Zn55Al alloys, doped with Calcium in the different concentration of natural ambient using Potentiodynamical method, indicate that, adding Calcium Ree due to move pitting and repassivation potentials to the positive area, and increasing concentration of chloride ions moves curves to the negative region. It is estimated that the small amount of Ca (0.005-0.05 wt %) reduce Corrosion rate of original alloy about 2-3 times. It means that the corrosion resistance of the Zn5Al and Zn55Al alloys improves considerably. Zn-Al-Ca alloy could be used as anode coatings to protect steel products and structures from corrosion.