Serkan Toros

Tensile and spring-back behavior of DP600 advanced high strength steel at warm temperatures

In recent years, the use of advanced high strength steels in automotive industry has been increased remarkably. Among advanced high strength steels, dual phase (DP) steels have gained a great attention owing to a combination of high strength and good formability. However, high strength usually increases the spring-back behavior of the material, which creates problems for the parts during the assembly. Thus, the uniaxial tensile deformation and spring-back behaviors of DP600 advanced high strength steel were investigated in rolling (0°), diagonal (45°), and transverse (90°) directions in the temperature range from room temperature (RT) to 300 °C. All tests were performed at a deformation speed of 25 mm/min. A V-shaped die (60°) was used for the spring-back measurements. The results indicated that the formability and spring-back of the material were decreased with increasing the temperatures. The material showed complex behaviors in different directions and at different temperatures.

Flow curve prediction of Al-Mg alloys under warm forming conditions at various strain rates by ANN

This paper describes an approach based on artificial neural network (ANN) to identify the material flow curves of strain hardened 5083-H111 and 5754-O Al-Mg alloys at the temperature ranges from room temperature (RT) to 300^oC and a strain rate of 0.0016-0.16s^-^1. The tensile tests were performed to determine the material responses at various temperatures and strain rates. An ANN model was developed to predict the flow curves of the materials in terms of experimental data. The input parameters of the model are strain rate, temperature, and strain while tensile flow stress is the output. A three layer feed-forward network was trained with BFGS (Broyden, Fletcher, Goldfarb, and Shanno) algorithm. The amount of the neurons in the hidden layer was determined by determining of the root mean square error (RMSE) values for each material. Results reveal that the predicted values in the ANN model are in very good agreement with the experimental data. The ANN model, described in this paper, is an efficient quantitative tool to evaluate and predict the deformation behavior of 5083-H111 and 5754-O Al-Mg alloys for tensile test at prescribed deformation conditions.

Strain Hardening and Strain Rate Sensitivity Behaviors of Advanced High Strength Steels

The mechanical properties of commercial dual phase (DP), transformation induced plasticity (TRIP), and high strength low alloy (HSLA-340) steel sheets are investigated and compared at various strain rates ranging from 0.0017 to 0.17 s−1 at ambient temperature. TRIP steel outperforms the other two materials, having comparable ductility and twice as large strength relative to DP steel. TRIP has larger strength and much larger ductility than HSLA-340. The exceuent ductility of TRIP800 is due to its high strain hardening capability, which promotes stable plastic deformation. It is observed that the strain hardening rate in TRIP800 does not decrease to zero at failure, as common in most materials in which failure is preceded by necking.

Tensile deformation behavior of AA5083-H111 at cold and warm temperatures

Abstract The effects of strain rate and temperature on the deformation behavior of hardened 5083-H111 aluminum magnesium alloy sheet were investigated by performing uniaxial tensile tests at various strain rates from 0.0083 to 0.16 s−1 and temperatures from – 100 to 300 °C. Results from the prescribed test ranges indicate that the formability of this material at cold and warm temperatures is better than at room temperature. The improvement in formability at cold temperatures is principally due to the strain hardening of the material. However, the improvement at warm temperature and low strain rate is specifically due to the high strain rate sensitivity characteristic of the material. Results indicate that this alloy should be formed at temperatures higher than 200 °C and at low strain rates.

Parameters Determination of Yoshida Uemori Model Through Optimization Process of Cyclic Tension-Compression Test and V-Bending Springback

IN RECENT YEARS, THE STUDIES ON THE ENHANCEMENT OF THE PREDICTION CAPABILITY OF THE SHEET METAL FORMING SIMULATIONS HAVE INCREASED REMARKABLY. AMONG THE USED MODELS IN THE FINITE ELEMENT SIMULATIONS, THE YIELD CRITERIA AND HARDENING MODELS HAVE A GREAT IMPORTANCE FOR THE PREDICTION OF THE FORMABILITY AND SPRINGBACK. THE REQUIRED MODEL PARAMETERS ARE DETERMINED BY USING THE SEVERAL TEST RESULTS, I.E. TENSILE, COMPRESSION, BIAXIAL STRETCHING TESTS (BULGE TEST) AND CYCLING TESTS (TENSION-COMPRESSION). IN THIS STUDY, THE YOSHIDA-UEMORI (COMBINED ISOTROPIC AND KINEMATIC) HARDENING MODEL IS USED TO DETERMINE THE PERFORMANCE OF THE SPRINGBACK PREDICTION. THE MODEL PARAMETERS ARE DETERMINED BY THE OPTIMIZATION PROCESSES OF THE CYCLING TEST BY FINITE ELEMENT SIMULATIONS. HOWEVER, IN THE STUDY BESIDES THE CYCLING TESTS, THE MODEL PARAMETERS ARE ALSO EVALUATED BY THE OPTIMIZATION PROCESS OF BOTH CYCLING AND V-DIE BENDING SIMULATIONS. THE SPRINGBACK PREDICTIONS WITH THE MODEL PARAMETERS OBTAINED BY THE OPTIMIZATION OF BOTH CYCLING AND V-DIE BENDING SIMULATIONS ARE FOUND TO MIMIC THE EXPERIMENTAL RESULTS IN A BETTER WAY THAN THOSE OBTAINED FROM ONLY CYCLING TESTS. HOWEVER, THE CYCLING SIMULATION RESULTS ARE FOUND TO BE CLOSE ENOUGH TO THE EXPERIMENTAL RESULTS.

3D Microstructural Finite Element Simulation of Martensitic Transformation of TRIP Steels

In this paper the effects of deformation modes on martensitic transformation for TRIP steels which are composed of Ferrite, Bainite and Retained austenite are investigated in the view of the microstructural level. For this porpose the simulations are run for a synthetically generated microstructure which have 55% Ferrit, 35% Bainite and 10% Retained austenite. In the simulations tensile, biaxial and shear type deformation modes are considered. The results reveal that biaxially loaded microstructure has the maximum amounts of martensite phases at the end of the given deformation and the less martensite is occurred in the shear type loading condition.

Evaluation of Anisotropy by Two Different Tests for TRIP800 Steel

For the process modeling, material properties such as anisotropy values at different orientation are very important. The most commonly used method for the determining of the anisotropy values is the tensile test that is performed for samples are prepared at different orientation. Besides the tensile test, the anisotropy parameters of TRIP 800 steel are measured with the hole-expansion test. The effects of the test methods on the yield surfaces are determined for using two different anisotropic yield criteria are Hill-48 and Barlat-89. Results illustrated that a significant difference is observed in the yield surfaces for the two test methods. The material under biaxial deformation is deformed plastically faster than the uniaxial deformation mode.

Modeling Uniaxial, Temperature, and Strain Rate Dependent Behavior of AZ31 Alloy by Softening Model

In the present study, a softening model proposed for warm forming behavior of Al-Mg alloys is applied to AZ31 alloy in order to determine the applicability of the model to magnesium alloys AZ31 alloy is tested at several temperatures (room temperature to 300 oC) and strain rates (0.0083-0.17 s-1). The results indicate that the model shows good agreement with experimental flow curves for different temperatures and strain rates for AZ31 alloy.

The Effects of Material Thickness and Deformation Speed on Springback Behavior of DP600 Steel

In the present study, the effects of deformation speeds, sheet thickness, and widths on the springback were investigated experimentally and numerically using a 60o V-shaped bending for DP600 steel. Results reveal that the springback was significantly decreased with increasing thicknesses and deformation speed including 125 mm/min in the range of 5-500 mm/min. The effects of widths on springback were found to be inconsiderable.