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Effect of Laser Preheating AISI 4140 Specimens for Micro-Forging

Jung C., Lee M. G., Jeon Y.

Archives of Metallurgy and Materials

2017

Vol. 62, iss. 2B

1209--1213

Many high performance and permanent service parts require suitable material characteristics-high fatigue strength is one of the most important characteristics. For this reason, surface treatment processes are essential to increase the material performance and avoid the use of costly ineffective material. There exist various surface treatment processes for various applications. Each process has advantages and disadvantages and hybridization can solve various problems. The micro-forging process delivers a controlled and uniform surface hardness, but the depth of the forged surface is limited. On the other hand, laser heat treatment can increase the hardness drastically, but the surface may become brittle, which reduces the fatigue life. Laser-assisted micro-forging is a novel hybrid process of laser heat treatment and micro-forging that has the potential to increase the forging depth and relax the stress caused by the high temperature of the forging process. This study examines the effect of laser preheating in the micro-forging of AISI 4140. The processes were varied as follows: no treatment, micro-forging only, and laser-assisted micro-forging. The fatigue strength of the specimens was examined by means of an ultrasonic fatigue tester and then compared. The microstructural changes were investigated with respect to the processes by using scanning electron microscopy. In conclusion, it was confirmed that the laser preheating auxiliary forging affects the fatigue life. It was confirmed that the fatigue life was the mostly increased in 550°C temperature laser preheating micro forging process and the temperature was identified as the most important factor.

A fuzzy controller with a real-time tuning algorithm and its application to a steam generator water level control

Jung C., Kwon K.

Control and Cybernetics

1998

Vol. 27, no 4

545-564

It is nesessary to tune the fuzzy rules and the scalling factors in real-time control of a large scale system, the steam generator of a nuclear power plant, as it is related to safety and availability of the plant. A novel real-time tuning algorithm of fuzzy controller based on the scaling factors is proposed and applied to the steam generator water level control system of the nuclear power plant. The new real-time tuning algorithm adopts a variable reference tuning index for a good system tuning response and an instantaneous system fuzzy performance for scaling factor tuning. For the fuzzy steam generator controller, an image signal of feedwater flow error at low power is proposed and pressure compensation rules and a gain scheduler of feedwater temperature are designed also. The fuzzy controller of the steam generator water level is simulated by the proposed method. The simulation results show that the improved performance of the steam generator water level controller by the proposed method.