Papers by Keyword: Adiabatic Heating

Abstract: In this study, dynamic temperature field in a dissimilar steel joint specimen was numerically analyzed by means of three-dimensional explicit finite element analysis. Fully coupled thermal stress analysis was performed by using FE-code Abaqus/Explicit ver. 6.12. It was assumed that 90% of the plastic work was transferred to heat. Furthermore, dynamic loading tests were conducted with three-point bending specimen extracted from the dissimilar steel joint between a mild steel and a high tensile strength class steel. The specimen included a U-shape notch in the bonded interface. A high-speed infrared camera was used to measure the temperature field near the bonded interface. The temperature field was recorded at a frame rate of 200 Hz during the dynamic loading test. The numerically calculated temperature field near bonded interface showed reasonable agreement with the temperature field measured by the high-speed infrared thermography. The temperature in the soft steel particularly increased during the dynamic loading. On the other hand, the increase in temperature in the hard steel area was relatively few.

Abstract: Within this study, a new method for the determination of the Taylor-Quinney coefficient is presented. The coefficient was identified by measuring the force-displacement-behavior as well as the temperature change resulting from an adiabatic compression test. In order to deduce the global temperature increasing of the specimen from the local measured temperature a suitable specimen geometry was designed with the use of numerical simulation. The resulting specimen allows a friction-free compression and therefore precludes a temperature increase through friction. Finally, the Taylor-Quinney coefficient of C35 steel (1.0501) was experimentally determined in the initial state as well as after a heat treatment.

Abstract: In this study, results are presented of an extensive experimental program to investigate the strain rate dependent mechanical properties of various Transformation Induced Plasticity (TRIP) steel grades. A split Hopkinson tensile bar setup was used for the high strain rate experiments and microstructural observation techniques such as LOM, SEM and EBSD revealed the mechanisms governing the observed behavior. With elevated testing temperatures and interrupted tensile experiments the material behavior and the austenite to martensite transformation is investigated. In dynamic conditions, the strain rate has limited influence on the material properties. Yet an important increase is noticed when comparing static to dynamic conditions. The differences in strength, elongation and energy absorption levels observed between the investigated materials can be attributed to their chemical composition. Adiabatic heating during high strain rate deformation tends to slow down the strain induced martensitic deformation. The elongation of the ferritic and austenite constituents is found to be strain rate dependent and the strain induced martensitic transformation occurs gradually in the material.

Abstract: Magnesium alloy sheets had to be rolled at elevated temperature to avoid cracking. The poor workability of magnesium alloy is ascribed to its hcp crystallography and insufficient activation of independent slip systems. Present authors have succeeded in 1-pass heavy rolling of AZ31 magnesium alloy sheet below 473K by raising rolling speed above 1000m/min. Heavy reduction larger than 60% can be applied by 1-pass high speed rolling even at room temperature. The improvement of workability at lower rolling temperature is due to temperature rise by plastic working. The texture of heavily rolled AZ31 magnesium alloy sheet is investigated in the present study. The texture of sheets rolled 60% at room temperature was <0001>//ND basal texture. At the rolling temperature above 373K, the peak of (0001) pole tilted ±10-15 deg toward RD direction around TD axis
to form a double peak texture. The texture varied through thickness. At the surface, the (0001) peak tilted ±10-15 deg toward TD direction around RD axis to form a TD-split double peak texture. The direction of (0001) peak splitting rotated 90 deg from the surface to the center of thickness. Heavily rolled magnesium alloy sheets have non-basal texture. The sheets having non-basal texture are expected to show better ductility than sheets with basal texture.