Nondestructive Evaluation for Small Plastic Deformation and Deformation Histories in Reduced-activation Ferritic/Martensitic Steels
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カテゴリ: 第15回
Nondestructive Evaluation for Small Plastic Deformation and Deformation Histories in Reduced-activation Ferritic/Martensitic Steels
東北大学 流体科学研究所西安交通大学
何 曼如Manru HEStudent Member
東北大学 流体科学研究所内一 哲哉Tetsuya UCHIMOTOMember
東北大学 流体科学研究所高木 敏行Toshiyuki TAKAGIMember
西安交通大学? 振茂Zhenmao CHEN
Abstract: Magnetic Barkhousen Noise, Magnetic Incremental Permeability and Magnetic Flux Leakage methods are non-destructive evaluation methods for ferromagnetic materials. Reduced Activation Ferritic/Martensitic (RAFM) steel is a new kind of ferromagnetic material considered to be an important candidate structural material for thermal nuclear fusion reactors. The feasibility to use magnetic non-destructive evaluation techniques of MBN, MIP and MFL methods to evaluate the plastic strains in RAFM steel is experimentally investigated in the previous work of authors. Results show that signals of these three method change dramatically in small plastic deformation. In order to enhance high detection precision for RAFM steel, the change of NDT signals in samples with small plastic deformation and plastic deformation history is studied experimentally in this study.
Keywords: RAFM, Small plastic deformation, Deformation history, NDE, Fusion reactors
１．INTERDUCTION
Reduced-activation Ferritic/Martensitic (RAFM) steel is considered to be an important candidate structural material for thermal nuclear fusion reactors because of its low activation, excellent mechanical property, and good microstructure stability[1]. The plastic deformation inevitably occurs during the operation of the reactor for reason of unexpected giant loading process, such as a large earthquake. Therefore, reliable Non-Destructive Evaluation(NDE) is needed. Magnetic Barkhausen Noise (MBN), Magnetic Incremental Permeability (MIP) and Magnetic Flux Leakage (MFL) as three typical electromagnetic NDE techniques for ferromagnetic materials were studied to evaluate the plastic deformation of RAFM steel in previous works[2]. The validity of these three methods is proved while the precision of small plastic deformation is still need to be improved. Therefore, the relationship between NDT signals and small plastic deformation in RAFM steel and the influence of plastic deformation history is studied experimentally in this work.
高木 敏行、〒980-8577 仙台市青葉区片平2-1-1
東北大学流体科学研究所未到エネルギー研究センター システムエネルギー保全分野
E-mail: takagi@ifs.tohoku.ac.jp
２．EXPERIMENTS
Experiment systems
MBN, MIP and MFL methods describe the change of different magnetic properties during a magnetic procedure. An U shaped permalloy yoke, a group of excitation coils wounded on the yoke, a function generator and a power amplifier are used to generate integrated magnetization processes for the specimens. A high frequency sinusoidal excitation is also generated to get the signal of MIP in each time step by a lock-in amplifier. MBN and MIP signals are measured using a bottom coil of the ECT probe nearby the TP surface. MFL signals are collected by a Hall sensor which is set at the TP surface along the tensile direction. The functional block diagram of the experimental system is described in Fig.1.
Fig.1 Integrate measurement system
Experiment procedures
Strain gages with the max value of 5% were used to control the deformation of specimens. Tensile machine INSTRON 5582 was used with displacement control in speed of 0.3mm/min. The specimens were divided into two groups to investigate the relationship between NDT signals and small plastic deformation in RAFM steel and the influence of plastic deformation history in small deformation. Different levels of residual plastic strains (0%, 0.1%, 0.3%, 0.5%, 1%) were applied to Group.1 (No.1- No.5 Specimens). For each specimen NDT signals of three points were acquired after unloading. Group.2 (No.6 Specimen) was stretched 4 times and NDT signals of three points were detected before each tensile test.
No.1-No.5
(a) MBN
N.6
No.1-No.5
(a) MFL
N.6
３．RESULTS
The correlation between the NDT signals and the residual strain is shown in Fig.2. K factor defined as formula (1) is taken as the feature parameter of MFL signals. Here A1，A3，A5， and A7 denote the amplitudes of high harmonics of the MFL signals.
K ?(1)
The results of MBN show different tendency to specimens with and without deformation history. The root mean square(RMS) of MBN signals specimens stretched only once are firstly increasing then decreasing with plastic deformation, the peak value is at around 0.1%. While the signals of specimens with deformation history show a rising trend. The K factor of MFL signals are not influenced by deformation history and decreasing monotonously with increasing plastic deformation. The Height of Imaginary Part (HIP) of MIP signals is not influenced by deformation history and have the same tendency with RMS signals.
４．SUMMARY
In this work, several NDE methods for small deformation were investigated experimentally. The relationship between NDT signals and strains was drawn. Plastic deformation history have influence on MBN signals in small plastic deformation while it does not affect MIPand MFLsignals.
No.1-No.5(a) MIPN.6
Fig.2 The relationship between NDT signals and strains
a. Root mean square, b. K Factor, c. Height of imaginary part.
Acknowledgement
This study was partly supported by the JSPS Core-to-Core Program, A. Advanced Research Networks, “International research core on smart layered materials and structures for energy saving”, the National Magnetic Confinement Fusion Program of China, and Natural Science Foundation of China. The authors would also like to thank the China Scholarship Council for their financial support and the kind help of Mr. T.Sato and Mr. Matsumoto for the measurement
REFERENCES
L. Huang, X. Hu, W. Yan. Effect of heat treatment processes on microstructure and mechanical properties of ton-scale China low activation martensitic steel. Atomic Energy Science and Technology, 47(2013), 412-416.
M. He, Hn. Chen,S. Xie, Nondestructive Evaluation of Plastic Deformation in Reduced Activation Ferritic/Martensitic Steels for Structure of Fusion Reactors., Studies in Applied Electromagnetic and Mechanics, 41(2015),171-178.