Rayleigh wave has many unique propagation characteristics, such as being transmitted only close to the surface of the sample and propagating along the curved surface. It is especially suitable for detecting surface cracks and defects. The author takes the fuel plunger spring of a certain type of airplane with a diameter of 1.48mm cylindrical steel wire wound as an example to study the method and reliability of ultrasonic testing with Rayleigh wave.
Force Analysis of Cylindrical Compression Spring Since the helix angle of the coil spring is generally less than 9b, any cross section of the coil can be approximated as a plane on the axis of the spring. Under the action of the axial static load p, the force of any cross section of the spring coil can be simplified to a torque T and a tangential force pt, as shown. Pt=p, T=12pD2, spring deformation F=PD32n4GIpp.G is the spring material shear modulus, Ip is the polar moment of inertia, n is the number of spring working cycles, and for the circular section, the shear stress is S=k8D2Pd3p.
Where k is the section curvature coefficient and is related to the spring winding ratio. For the statically loaded spring, take k=1. From the stress distribution curve, the inner diameter of the coil spring is subjected to the largest shear stress, and the failure analysis result of the smallest outer diameter of the large diameter spring also proves that the fracture source of the compression spring generally occurs. The surface, and the probability of breaking at the end 1 to 3 turns is the largest. This is mainly due to the fact that the spring of the first to third turns is first loaded when the spring is subjected to an impact load, and the load cannot be quickly transmitted to the other coils. Therefore, the detection of surface defects on the inside of the spring is more critical. How to ensure that the detection method used has high sensitivity and reliability to the inner side of the spring is the focus of this paper. Acoustic wave incident direction, incident point and frequency In the production of compression coil spring, in order to make the spring stand upright, the contact with the support seat is stable, the deflection is reduced and the pressure is relatively uniform, the two ends of the spring are generally subjected to grinding processing. The machining plane provides the conditions for the surface wave probe to maintain good contact with the spring surface. According to the technical requirements, the flattened part of the cold ring compression spring support ring should not be less than 3/4, and the end face roughness should be kept appropriate. Therefore, when the surface wave is detected on the spring, the sound wave can be incident from the plane of the support ring, and the incident direction and the spring are wound. The direction is the same. When the acoustic axis of the spring is at an angle to the wire axis, it will advance along the surface of the wire to detect the entire surface. Based on the fatigue test results, the fuel plunger spring is determined to have a manual defect diameter of (0.2400.020) mm, a depth of (0.0340.003) mm, and a reference pressure of approximately 150 N. According to this test requirement, Libo is transducing and propagating on the surface or near surface of the medium (about several wavelength depths), and the information contained is more susceptible to influence (the higher the frequency, the more susceptible it is to surface conditions, and the more the attenuation inside the material is) <810>. In addition, the real defect is not as smooth as the standard defect, and it has a large reflection ability to the sound wave. Therefore, the incident sound wave frequency should be determined in combination with the actual detection effect.
The artificial surface defect wave of the artificial defect comparison sample needs to use the spring object as the comparison sample, and the artificial defect of a certain size and shape is made on the surface of the spring wire as required to adjust the detection sensitivity. According to the analysis of the force of the spring, the shear stress on the inner side of the coil spring is the largest and the outer side is the smallest. Therefore, the damage on the inside surface is more harmful, and the detection is more important. In order to test the ability of the ultrasonic Rayleigh wave to detect the inner and outer surface defects of the Fig.3 Geometryofspecimencontainingtwoinfects, we took two plunger spring specimens with no surface defects under the 4x magnifying glass in the same batch of spring workpieces. Each of the two types of processing (such as the most common pit defects in the spring and the most harmful lateral crack defects) is artificially simulated, the defect 1 is the inner surface defect, and the defect 2 is the outer surface defect. The experiment was carried out by direct contact method (40 oil is a coupling agent). The probe used was a single-pulse Rayleigh wave probe with a wafer size of 4 mm @ 7 mm and an acoustic wave incident angle of 62 b. The frequencies were 5.0 MHz and 7.5 MHz respectively. USIP The ultrasonic flaw detector is the main test. The height of the artificial defect echo on the outer surface of the standard sample is 40% of the full scale. The detection is performed multiple times from the two end faces of the spring, and the defect echo height is up to
It is indicated that adjusting the initial sensitivity with the outer surface defect sample may result in the inner surface defect being missed. The four springs were inspected with a 7.5 MHz probe and only two internal surface defects were found, one of which was not exceeded. In order to eliminate the contingency of the test results, the experiment was performed by the same technician using 4 technicians.
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