Papers by Keyword: Sheet Steel

Abstract: In the one bar method, one of the standardized high velocity tensile testing techniques for thin steel plate, sometimes it shows an apparent effect of transverse vibration of an output bar on dynamic behavior of the plate. Suppressing the lateral vibration of the loading end of the bar is the most important factor to decrease the apparent effect, as pointed by Yoshida, Kuriyama, Uenishi and Takahashi in 2002, and the present author in 2011. He proposed an output-bar supporting technique with a polytetrafluoroethylene (PTFE) collar. In the former work, the lateral vibration was not fully suppressed, because the collar had some clearance to the output bar. He convinced that, in order to eliminate the clearance, it was worthy to give some transverse pre-load on the bar from the outer surface of the collar. However, the output bar is a load-sensing elastic body with strain gages adhered on it. The axial strain signal is a source of load detection. If such transverse compression is applied to the output bar, the axial skin strain of it is reduced to some extent. The key factor is the collar material, PTFE. This solid polymer possesses the lowest coefficient of friction in the situation of PTFE on steel, typically 0.05-0.10. The present author has modified an output-bar supporting stand to apply the lateral compressive load to the output bar with the divided PTFE collars which allow the smooth axial movement of the bar. The transverse compressive load is varied as 0, 70, 200 and 420 N. Obtained dynamic stress-strain curves at the strain rate of 500 s^-1 are compared each other to indicate the effect of the lateral compression on the bar. As a result, the lateral compression of 200 N is found as the most suitable condition.

Abstract: During the annealing heat treatment following cold rolling of a 304L austenitic stainless steel sheet material, the material goes through changes in microstructure and mechanical properties. The cold rolling history together with the time/temperature trajectory in the annealing furnace can be used to model the final microstructure. In this work, physically based models for recrystallization and the following grain growth was created for the prediction of the microstructure evolution-both grain size and grain size distribution-, and an artificial neural network, ANN, was added for secondary effects. This is more commonly referred to as a hybrid model. The microstructure hybrid model was tested and validated against cold rolled and annealed production sheet material of various thicknesses and reductions, where the grain size and grain size distribution was measured by Electron Back Scatter Diffraction, EBSD. The recrystallization and grain growth parameters and functionality were fitted for non-isothermal conditions, against experimental tests of cold rolled material. Given process history and time/temperature data from the annealing heat treatment, the model can predict the microstructure, average grain size and grain size distribution with high accuracy and the executing time is short which makes it suitable for in-line use.

Abstract: Automobile body sheets mainly resist impact and pressure. However, the fatigue property is one of the main factors with regard to properties of sheet steels. Continuous vibration happens all over the sheet steels (especially chassis) while the vehicle is in motion. And the fatigue property becomes particularly important in the condition above. Fatigue tests are conducted to four kinds of thin sheet steels for automobile in this paper. The fatigue lives of samples from sheet steels are obtained according to the various stresses. The inferior limits of fatigue life and the inferior limits of fatigue strength under the higher stresses are acquired by the computation of fatigue data. Furthermore, the test results show that there is a certain relationship among the tensile strength, yielding strength and inferior limit of fatigue strength for these sheet steels. This paper is of certain reference significance for other similar test.

Abstract: At present there is no understanding referring to the full picture of processes, that take place in the structure formation and improvement of required level of physical-mechanical properties for IF steel. That is why this paper is devoted to investigations of the texture and the quantity of the special grain boundaries to enable IF steel to high drawability.