| With the increasingly stringent emission standards, the major car manufacturers pay more attention on automobile lightweight which are an important energy-saving and emission reduction means. Especially, the use of new lightweight materials is the most effective means of lightweight vehicle. Advanced high strength steel and hot stamping high strength steel with the advantages of economy, safety and light weight, are the most widely used metal materials in the automotive body structure. To ensure mechanical properties of the formed high strength steel parts, the on-line testing is need. However, the traditional detection methods, such as metallographic observation and hardness measurement, are not only time-consuming, but also cause the irreversible damage of parts. Therefore, in order to realize the rapid and efficient measurement of mechanical properties of hot stamping high-strength steel automobile structure and the nondestructive testing of intensification of advanced high strength steel in forming process, a nondestructive detection method base on Barkhausen noise(Magnetic Barkhausen Noise, MBN) was put forward in this paper.The interior magnetic domains in ferromagnetic material will revolve under the external alternating magnetic field. The movement of domains becomes the form of a variety of flip like step-style under the hindering of pinnings, such as dislocations, grain boundaries and so on. The voltage signals captured by detection which are similar to periodic noise are called as Barkhausen noise. To realize nondestructive testing based on Barkhausen noise, it's necessary to research the relationship between stress state, microstructure and MBN signal characteristic values. Thus the MBN signal in time and frequency domain will be studied in the fields of deformation process, hardness and microstructure form macro view in this paper.According to the mechanism and characteristics of the MBN signal, the nondestructive testing system was developed. In consideration of the complex frequency components and multi influencing factors of MBN signal, the superposed average noise and power spectrum density calculation base on AR model were used to reduce noise and provide the technical foundation for the time-frequency analysis.In this paper, the MBN signal of the typical advanced high strength steel –TRIP steel was tested during the tensile process. The influence of TRIP effect on signal compared with the low steel-DC steel is obvious during elastic-plastic deformation. The results provide a new electromagnetic nondestructive testing method to observe continuous process of TRIP effect.For the detection of mechanical properties of hot stamping high strength steel, the relation of hardness and time-frequency characteristic value was studied. The research indicates that the MBN signal including peak value and RMS gradually decreased with the increase of hardness. Meanwhile, the peak value of low frequency component decreased and the high frequency increased. The essential reason is that the revolving of domain became more difficult and the release of MBN is harder. Moreover, it is found that the increase of heating rate and the reduction of holding time and heating temperature weaken the MBN with the same microstructures in the study of the influence of rapid electric heating parameters on MBN signal. The fitting function relation between the hardness, heating parameters and the time-domain characteristic value could provide the quantitative basis for the on-line detection. And the analysis of frequency components brings the foundation for the qualtitative analysis of the microstructures.Finally, the hardness testing method base MBN was designed and the portable MBN detector was developed for the on-site production. The hardness routing inspection system integrated hardness measurement system base MBN hardness and industrial robot can effectively improve the efficiency quality control and extend the application scenarios. |
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