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Ratcheting behavior and dislocation evolution of non-oriented electrical steel

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  The system cycle test of 30WGP1600 non-oriented electrical steel under uniaxial stress control was carried out. The effects of average stress, stress amplitude and peak stress on the ratcheting behavior of the material were analyzed. The dislocation configuration during ratchet deformation was observed by TEM transmission electron microscope. The law of evolution reveals the nature of the ratchet deformation of electrical steel.
  The structural member generates an irreversible accumulation phenomenon under the cyclic stress, that is, a ratchet effect. The ratchet effect can cause structural members to fail in size or fatigue deformation, with catastrophic consequences. For example, the rotor of an electric vehicle driving motor will produce a ratchet deformation under the action of centrifugal force. On the one hand, the ratchet deformation increases the probability of contact between the rotor and the stator, resulting in the scrapping of the motor; on the other hand, the irreversible plastic deformation deteriorates the magnetic properties of the motor, seriously impairs its function, and reduces the service life of the motor. Therefore, in order to optimize the motor structure and correct safety assessment, the motor design must fully understand the ratchet deformation behavior of the non-oriented electrical steel for the rotor under high frequency and low stress.
  In recent decades, a large number of experiments and theoretical studies have been carried out on the ratcheting effect of materials at home and abroad, but most studies on the ratcheting behavior of materials have low loading frequency, high applied stress (greater than the yield strength of the material), and the number of cycles. Within a few thousand weeks, there is still no experimental understanding of the ratcheting behavior of materials under low stress (peak stress less than or equal to yield strength), high loading frequency and over 100,000 cycles, and the study of ratcheting behavior of non-oriented electrical steel is more Rarely reported. Therefore, for 30WGP1600 non-oriented electrical steel, the evolution process of ratcheting strain of non-oriented electrical steel under low stress and high cycle time, and the influence of average stress, stress amplitude and peak stress on ratcheting behavior are studied. System description and analysis The strain change process of materials under low stress and the evolution of dislocation structure.
  The ratcheting behavior of 30WGP1600 non-oriented electrical steel under low stress and high cycle time was studied. The ratcheting behavior of electrical steel was analyzed. The evolution law of dislocation configuration during ratchet deformation was systematically studied, and the following main conclusions were obtained.
  (1) Regardless of the change in stress amplitude and average stress, the ratchet strain of electrical steel increases with the increase of peak stress. Therefore, the peak stress is the dominant factor affecting the deformation of the electrical steel ratchet.
  (2) When the applied peak stress is less than 300 MPa, the ratchet deformation is hardly occurred, and the electrical steel is in the elastic deformation stage; when the peak stress is greater than 300 MPa and less than 340 MPa, the electrical steel ratchet deformation is small, and the ratchet saturation state is reached at the beginning of the cycle; When the peak stress is greater than 340 MPa and less than or equal to the yield strength, the ratchet strain increase rate is first large and then small, and can be stabilized when the cycle is about 100,000 times.
  (3) When the peak stress is between 300 and 340 MPa, the dislocation density is low, and the dislocation configuration is mostly dislocation line. When reverse unloading, the dislocation motion is easier, the deformation recoverability is good; when the peak stress is At 340-400 MPa, multiple slip systems are easy to start, the dislocation density increases and the interaction increases, the dislocation motion resistance increases, and the irreversibility of deformation increases. The amount of ratchet deformation increases significantly during this period.
  (4) When the peak stress is the yield strength, at the initial stage of the cycle (ie, stage I), the dislocation motion and the proliferation rate are very fast, and the ratchet strain rate is also large; in the second stage of the ratchet deformation, the dislocation configuration is made of low density. The dislocation entanglement shifts to the high-density dislocation wall and the primary dislocation cell. Compared with the first stage, the dislocation proliferation rate is lower and the ratchet strain rate is correspondingly reduced. In the third stage of the ratchet deformation, the high-density dislocation group The state of the incomplete dislocation cell structure evolves, the cell structure is relatively stable, and the ratchet strain rate increases at a constant rate.