In order to study the ability of terahertz nondestructive testing technology to detect the bonding defects of multilayer heat-resistant structures, artificial defects were preset in the two-layer adhesive of composite material-adhesive-composite material-adhesive-metal bonding structure, and pulsed The Hertz wave imaging method detects the samples.The results show that the terahertz time-domain signal can be obtained after the terahertz wave penetrates the bonding structure of the multilayer heat-resistant composite material, and the defect images of different adhesive layers are obtained after the characteristic waveband data processing.It can clearly image the 0.15mm air layer and 0.15mm metal plate in the sizing layer between the heat-resistant composite material and the breathable composite material, and the imaging can distinguish the 0.15mm air layer in the lower rubber layer between the breathable composite material and the metal plate.The research results provide an effective method for the detection and evaluation of the bonding quality of multilayer heat-resistant composite materials.
Industrial pipeline is often used in petrochemical industry, which is a kind of common pressure special equipment in various chemical installations.Different from boilers and pressure vessels, industrial pipelines are very difficult to manage due to the large number of overhead laying and complex installation forms, and industrial pipelines are often in very bad working conditions, so the accident probability caused by corrosion leakage of industrial pipelines is higher than that of other pressure special equipment. There are many methods for the corrosion detection of industrial pipelines.Pulsed eddy current testing technology is one of the new non-destructive testing technology vigorously promoted in recent years.It has the advantage of realizing online detection without removing the insulation/cold protection layer.Through the actual testing cases, it is proved that the pulsed eddy current testing technology has a very good detection ability for industrial pipeline corrosion defects, which is worthy of further promotion.
The Phased Array Ultrasonic Testing（PAUT） and Digital Radiographic（DR） Testing were proposed to detect the Electro-Fusion Joints of polyethylene pipes with different welding defects, and analyzed the characteristic maps of different welding defects, then summarized the advantages and disadvantages of PAUT and DR in detecting electro-fusion welding defects of polyethylene pipeline.The test results showed that, the PAUT method had a high detection rate for process defects（cold and over welding）,slag inclusion, holes and incomplete fusion, especially to the process defects in different degrees, this method had a high detection sensitivity, but it was difficult to characterize holes, slag inclusion and incomplete fusion defects.DR method had a high defect detection rate for holes, slag inclusion, incomplete fusion and over welding defects, and the detection results were intuitive and reliable, but the detection rate for cold welding defects was low.
Aiming at the problem of effective identification of micro-defect on the surface and deep layers of the tab welding seam of aviation lithium battery, a magnetic eddy current detection method based on the combination of high-current and wide-area uniform eddy current field and high-sensitivity gradient differential coil is proposed.This paper systematically expounds the high-sensitivity detection mechanism of the gradient differential coil and its influencing factors.Based on the excitation coil wound by litz wire, a uniform eddy current excitation field is applied to the entire surface of the electrode plate, and the gradient differential coil array is used to pick up the induced eddy current signal.Accordingly, the tab welding seam micro-defect detection system is established.The research results show that the magnetic eddy current detection technology can be used to compare and analyze the difference between the eddy current field of the tab welding seam and the normal area, so as to accurately obtain the characteristic parameters such as the size and location of micro-defect in the tab welding seam, which could further improve the detection image reconstruction function.This method has great engineering value for ensuring the safe and stable operation of the aviation lithium batteries.
In order to study the performance of Q345R material under cyclic loading, fatigue crack propagation experiments were carried out at different frequencies.Acoustic emission signal characteristic parameters were extracted and comprehensively analyzed by comparing the damage process in the fatigue loading process.It is found that the relationship between the fatigue crack growth length and the number of cycles is different at different loading frequencies.At the same time, acoustic emission（AE） was used to monitor the characteristic parameters in the process of fatigue crack propagation and fracture, which provided a reference for the application of AE technology in the online detection of Q345R materials.
