Model-based correlation between change of electrical resistance and change of dislocation density of fatigued-loaded ICE R7 wheel steel specimens

2018 ◽  
Vol 60 (7-8) ◽  
pp. 669-677 ◽  
Author(s):  
Peter Starke ◽  
Frank Walther ◽  
Dietmar Eifler
Keyword(s):  
Dislocation Density ◽  
Electrical Resistance ◽  
Wheel Steel ◽  
Model Based

Implementation and Investigation of a Compact, Powerful System for Diagnosis and Control of Shape Memory Alloys in Technical Applications

2019 ◽  
Author(s):  
Max Kaiser ◽  
Nils Neblung ◽  
Martin Gurka
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Electrical Resistance ◽  
Control Strategies ◽  
Memory Systems ◽  
Constant Load ◽  
Resistance Change ◽  
Model Based ◽  
And Control

Abstract In this paper we present the development, implementation and testing of a compact system for diagnosis and control of actuators based on metallic shape memory alloys (SMA). Using NiTi-SMA, very compact, cost-effective and lightweight actuation systems can be realized. In applications where the SMA is activated by internal Joule heating or its condition is diagnosed by the self-sensing of its electrical resistance, an electrical system capable of reliably measuring very small resistance changes (< 1 ohm) without affecting the phase-state of the SMA is required. In addition, the system must offer the possibility to evaluate the nonlinear, hysteresis-afflicted behavior of the SMA and to handle this difficulty, e.g. utilizing a model-based control. This paper presents a simple compact and adaptive system based on a microcontroller that meets these requirements. Detailed functional tests were carried out with the system to establish a correlation between the change in electrical resistance in the range < 200 mOhm and the current strain state of the actuator. For this purpose, a first series of tests was performed, with the SMA wires working against a constant load. In a second tests series, the SMA wires worked against springs of different stiffness. The use of a microcontroller enables simple implementation of different control strategies. The control system for the non-linear resistance change utilizes a fuzzy logic which divides the control algorithm into three regimes. In the regime of the martensitic phase transformation a PI-controller is used. The state of actuators with an absolute electrical resistance < 1 Ohm and a resistance change < 200 mohm associated with the phase transformation can be precisely measured and controlled with an accuracy < 10 mohm. The system can be configured with little effort for different tasks and shape memory systems of different sizes. Furthermore, it is possible to implement more complex control algorithms up to model-based controllers.

scholarly journals EBSD Study on Proeutectoid Ferrite and Eutectoid Ferrite Refinement Mechanism of D2 Wheel Steel Under a Rolling Condition

2021 ◽  
Author(s):  
Jun Hua ◽  
Pengtao Liu ◽  
Xiujuan Zhao ◽  
Chong Su ◽  
Ruiming Ren
Keyword(s):  
Dislocation Density ◽  
Shear Strain ◽  
Dislocation Cell ◽  
Rolling Contact ◽  
Wheel Steel ◽  
Size Difference ◽  
High Angle ◽  
Average Grain Size ◽  
Proeutectoid Ferrite ◽  
Refinement Mechanism

Abstract In this paper, the SEM (with EBSD system) is used to study the refinement mechanism of proeutectoid ferrite (Pro-f) and eutectoid ferrite (Eut-f) of D2 wheel steel in a rolling contact. The results indicate that with the increase of the shear strain (γ<0.21), the dislocation density in the proeutectoid ferrite increased continuously, and the dislocation cells formed were uniformly distributed in the grains. Subsequently, the dislocation cell boundaries were changed into low-angle boundaries (LABs), and then the low-angle boundaries were gradually changed into the high-angle boundaries (HABs), and the average grain size was refined from the original 8 μm to 710 nm. When the shear strain is at 0.21≤γ≤0.84, dislocation piled up occurred at the ferrite side of the interface of eutectoid ferrite/cementite, and the spatial misorientation between adjacent two eutectoid ferrites increased gradually, then the ferrite lamellar is divided into bamboo-like by the low-angle boundaries, and proeutectoid ferrite the grains are gradually refined into equiaxed grain. When the shear strain is at 0.84<γ<3.314, the number of high-angle boundaries inside the eutectoid ferrite lamellar increased, and it is refined into bamboo-like grains. The two kinds of ferrite grains are repeatedly refined many times by the equiaxial grains "elongation- bamboo like refinement-elongation", which gradually reduced the size difference. As the shear strain further increases, the two kinds of ferrite are completely mixed into the same morphology, the dislocation density is dramatically reduced, and ultra-fine equiaxed grains about 110 nm is formed.

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