Research On Crack Monitoring Using GMR Test Array Based On Vertical Alternating Excitation

Compared to other nondestructive testing techniques,eddy current nondestructive testing has broad prospects with advantages of without contacting with the work piece,without coupling medium,fast detection speed,simple operation,low cost,easy to implement industrial automation measurement and so on.Metallic materials generate defects such as cracks in the production and application,and the cracks which grow to a certain extent will result in the fracture of materials,so the detection of the generation and expansion is of great importance to guarantee reliable operation and personal safety of the equipment.The eddy current testing technology for crack detection has already got a preliminary application,but due to the small size and complex expansion direction of the crack,the eddy current signal detection interference and the complex detection signal analysis process,the detection effect is not good.Mostly eddy current defects detection use the way of single exciting direction,however,the detection sensitivity is always uncertain since direction of defects detection is unknown in actual.In this paper,an eddy current testing probe based on GMR is designed according to the comparison of simulation of magnetic induction intensity variations under the same exciting direction and different defects direction,both qualitatively and quantitatively.Also the test data is used to determine the relative position of the GMR and the coil,and the difference of the ability of the experimental scanning curve on different defects directions to reflect defects.To achieve better defect detection using the features of vertical magnetic induction Bz,the simulation of amplitude distribution of Bz,the ability of the Bz curve reflecting the defect dimensions and the extent of the influence of the lift-off is presented,and the defect scan experiment is conducted to verify the features and benefits of in the Bz curve.In actual detection,the angle between the exciting direction and defects is unknown,the optimal detection direction can not be pre-configured,the detection sensitivity is uncertain,and the single exciting direction may not be able to achieve the highest detection sensitivity,so vertical alternating excitation are used to overcome these problems The simulation of the residual magnetic induction and syncretic distribution of Bz in different directions under vertical alternating excitation is analyzed,and the vertical alternating excitation advantages in the detection of defects in different directions is verified.On this basis,the GMR array detection probe under vertical alternating excitation is designed and the detection circuit is optimized.According to the experiment of cracks monitoring under vertical alternating excitation,vertical alternating excitation and GMR test array are found to have better detection results.