جستجوی مقالات مرتبط با کلیدواژه « Austenite » در نشریات گروه « مکانیک »

In the present study, the effect of heat treatment temperature and time on the microstructural and mechanical properties of medium manganese advanced high strength steel with 5 wt% Mn and 0.1 wt% B were investigated. Three temperatures were selected as annealing temperatures based on the stability of the austenite phase (stability temperatures of 50, 70 and 90% of the austenite phase). Mechanical characterization was performed using a uniaxial tensile test and phase and microstructural studies were performed by XRD and SEM. Alloy ingots were hot rolled, followed by cold rolling. The cold rolled sample had a martensite structure before the annealing process and the annealing process at all three temperatures resulted in the annealing of the initial martensitic structure. With raising annealing temperature from 680 °C to 710 °C, and consequently increase in residual austenite, tensile strength and ultimate elongation increased. Due to the additional annealing of martensitic matrix, yield stress decreased. The superior properties were resulted from the sample annealed at 710 °C for 20 min which led to tensile strength and ultimate elongation of 960 MPa and 22%, respectively. Increasing the time from 10 min to 20 min at annealing temperature of 710 °C, led to the rising of ultimate elongation and residual austenite. However, further annealing time (30 min at 710 °C) brought about reduction in austenite stability due to the dissolution of Precipitate phases Accordingly, the austenite phase turned into martensite during cooling and the mechanical properties of the sample significantly worsened.

The procedure of modeling+of shape memory alloy (SMA) dynamics and the corresponding computerized algorithm are described extensively in this paper. In shape memory alloys, due to the existence of the Martensite and Austenite phases in the microscopic structure of the alloy and also conversion between the phases, the elasticity modulus of the material shows a time varying behavior, while the structures of the equations describing the dynamics of the system remain similar to the ones with constant elasticity modulus. To evaluate the effect of conversion between phases on the elasticity modulus, the Martensite to Austenite volume fraction is of the main concern. Therefore, the mentioned elasticity modulus can be modeled as an oscillating spring-damper-mass system with variable parameters. Then, a new chattering alleviation algorithm for sliding mode control (SMC) of non-linear systems is presented. In the new method, a mathematical function for regulating parameter is introduced. Due to the initial choice of this parameter by designer, the state vector of the system approaches the sliding surface with any arbitrary speed and enters the boundary layer surrounding the sliding surface, while the state vector does not include fast behaviors through the boundary layer. To show the abilities and the merits of the aforementioned regulating routine on the vibration control of a SMA system, simulations are carried out within Simulink environment. The results show that our proposed algorithm has positive effects on the control system performance, while the 5% uncertainity in the elasticity module has no effect on it.