Study on a New Forming Method—Thread Rolling by Crystal Plasticity Finite Element Simulation

In order to study a new thread rolling forming process from a microscopic perspective, a polycrystalline model was established, based on the crystal plasticity finite element method (CPFEM) and Voronoi polyhedron theory. The fluidity of metals was studied to explain the reason for the concave center. The simulation results show that the strain curve of the representative element can more truly reflect the deformation behavior of the material. The grain orientations after deformation are distributed near the initial orientation. The evolution of each slip system is determined by the initial grain orientations and grain locations. The pole figures obtained from the experiment show high consistency with the pole figures obtained by simulation, which verifies the accuracy of the texture prediction by CPFEM. The experimental results show that thread rolling is more uniform in deformation than ordinary rolling.

A Preisach Model for Monotonic Tension Response of Structural Mild Steel with Damage

This paper presents the new type of Preisach model that describes the elastoplastic behavior of structural mild steel under axial monotonic tension load with damage. Newly developed model takes into account elastic region, horizontal yield plateau, plastic hardening region, and softening region due to material damage under tension. In order to study the monotonic behavior of structural mild steel and find suitable material properties for the model, monotonic axial tensile tests up to the failure are carried out. Tests are conducted on specimens of the three most common types of European structural steel S235, S275, and S355. The basis of the model represents a mathematical description of material single crystal monotonic axial behavior. In the multilinear mechanical model, a drop in stress, after achieving ultimate stress under tension is achieved by a negative stiffness element. The good agreement with experimental results is accomplished by parallel connection of infinitely many single crystal elements, forming the polycrystalline model. The model represents a good solution for common engineering practice due to its geometrical representation in form of Preisach triangle.

Model Estimasi Karakteristik Modul Photovoltaic Polycrystalline dan Monocrystalline 50 Wp

Rasio elektrifikasi di Kabupaten Kupang masih 60%. Rata-rata rumah tangga yang belum mendapatkan pasokan listrik berada di perdesaan terpencil yang sulit dijangkau oleh jaringan PLN. Alternatif yang paling baik dalam penyediaan sumber energi listrik di perdesaan Kabupaten Kupang yang belum terjangkau oleh jaringan PLN adalah menggunakan modul PV. Tujuan penelitian ini adalah untuk membandingkan efisiensi modul PV bahan monocrystalline dengan polycrystalline dan menemukan model estimasi karakteristik modul PV pada saat musim kemarau. Metode yang digunakan dalam penelitian ini adalah metode observasi yaitu melakukan pengukuran variabel SR, S, ISC dan VOC. Hasil penelitian menunjukkan bahwa modul PV monocrystalline lebih efisien dibandingkan dengan modul PV polycrystalline. Pada penggunaan modul PV monocrystalline, model estimasi persamaan regresi adalah Isc = 0.0009 SR + 1.9497 dan Voc = 28.02 - 0.2683 S. Pada penggunaan modul PV polycrystalline model estimasi persamaan regresi adalah Isc = 0.001 SR + 1.6649 dan Voc = 25.644 - 0.2196 S.

Predicting the Tensile Behavior of Ti-6.6Al-3.3Mo-1.8Zr-0.29Si Alloy via the Temperature-Dependent Crystal Plasticity Method

Uniaxial tensile flow properties of a duplex Ti-6.6Al-3.3Mo-1.8Zr-0.29Si alloy in a temperature range from 213 K to 573 K are investigated through crystal plasticity modelling. Experimental results indicate that the initial yield stress of the alloy decreases as the temperature increases, while its work-hardening behavior displays temperature insensitivity. Considering such properties of the alloy, the dependence of the initial critical resolved shear stress (CRSS) on temperature is taken into account in the polycrystal plasticity modelling. Good coincidence is obtained between modelling and the experimental results. The determined values of CRSS for slip systems are comparable to the published data. The proposed polycrystalline model provides an alternative method for better understanding the microstructure–property relationship of α + β titanium alloys at different temperatures in the future.

Simulation of Crack Initiation and Propagation in the Crystals of a Beam Blank

Surface cracking seriously affects the quality of beam blanks in continuous casting. To study the mechanism of surface crack initiation and propagation under beam blank mesoscopic condition, this study established a polycrystalline model using MATLAB. Based on mesoscopic damage mechanics, a full implicit stress iterative algorithm was used to simulate the crack propagation and the stress and strain of pores and inclusions of the polycrystalline model using ABAQUS software. The results show that the stress at the crystal boundary is much higher than that in the crystal, cracks occur earlier in the former than in the latter, and cracks extend along the direction perpendicular to the force. When a polycrystalline model with pores is subjected to tensile stress, a stress concentration occurs when the end of the pores is perpendicular to the stress direction, and the propagation and aggregation direction of the pores is basically perpendicular to the direction of the tensile stress. When a polycrystalline model with impurities is subjected to force, the stress concentrates around the impurity but the strain here is minimal, which leads to the crack propagating along the impurity direction. This study can provide theoretical guidance for controlling the generation of macroscopic cracks in beam blanks.

Comparing Two Selection Laws of Active Slip Systems in Finite Element Polycrystalline Model for Numerical Material Testing

To meet the demand for high accuracy in metal forming simulation including difficult problems such as anisotropy, many material models have been developed. Since the recent material models usually possess many parameters and require cumbersome experiments, a reliable numerical material testing would be helpful to reduce the number of experiments. Therefore, we have engaged in development of a numerical material testing based on the finite element polycrystalline model in which the successive integration method is used for modeling slip systems. However, implementation based on the strain-rate dependent model, which is considered as the mainstream of such model, has not been rigorously considered in our research. In this study, two polycrystalline models were compared to establish better microstructural modeling for constructing a scheme of numerical material testing to predict material behavior that is not obtained by experiments. Numerical rolling, uniaxial tensile tests were conducted on aluminum alloy sheet with the strain-rate dependent model and the successive integration method. The crystal orientation calculated by the successive integration method exhibited close agreement with the experimental value of the rolled aluminum alloy sheet. On the other hand, the calculated crystal orientation by the strain-rate dependent model exhibited less close agreement with the experimental value of the same material than the successive integration method. To ascertain the characteristics of each model in terms of slip deformation quantitatively, the other tensile tests were conducted to calculate Lankford values caused by crystal orientation. Lankford values, calculated by the successive integration method, exhibited better agreement with experimental values than the strain-rate dependent model. These comparisons indicate that the successive integration method represented slip deformation more physically valid than the strain-rate dependent model and resulted in better calculation.

Crystal Plasticity Simulations of Haynes 230, an Analysis of Single Crystal and Polycrystalline Experiments

The behavior of a Ni-based superalloy, Haynes 230, was investigated at macro and micro scale level by means of a Crystal Plasticity (CP) model implemented in an open source Finite Element code, Warp3D. Single Crystal and polycrystalline specimens have been experimentally characterized with Digital Image Correlation (DIC) to identify the local strain field evolution. The results of single crystal’s tensile tests were used to obtain an estimation of the constitutive model parameters. Then a polycrystalline model, reproducing a tensile test with loading/unloading steps, was created starting from the microstructural data obtained with EBSD (electron back-scatter diffraction), which allowed the identification of grains geometry and orientations. The polycrystalline simulations were used to verify the prediction of the CP model over the experiment. The results of this study show that the comparison between experiments and numerical analysis is in good agreement on both global and local scale levels.

Micromechanical Modeling of the Ratcheting Behavior of 304 Stainless Steel

Numerical simulations of 304 austenitic stainless steel (SS304) cyclic and ratcheting responses are performed using polycrystalline plasticity models. On the basis of the polycrystalline model of Cailletaud and Pilvin (1994, “Utilisation de modèles polycristallins pour le calcul par éléments finis,” Rev. Eur. Élém. Finis, 3, pp. 515–541), a modification of the β rule that operates the transition between the macroscopic level and the grain level is proposed. The improvement of the transition rule is obtained by introducing a “memory variable” at the grain level, so that a better description of the local stress–strain behavior is provided. This new feature is calibrated by means of previous simulations using finite element (FE) aggregate models. The results of the updated polycrystalline plasticity model are in good agreement with the macroscopic responses.