1 The composite structure composed of a variety of materials, to withstand high temperature, high speed, high pressure thermal ablation and erosion, the working environment is harsh, and therefore requires that each component has a high degree of reliability, nozzle metal shell and non-metallic bonding Interface, because the workpiece is not cleaned cleanly during bonding, the lining does not fit tightly with the housing, the gas inside the adhesive layer is not drained, etc., and it is easy to produce detackification, especially for large-area gap-type debonding, which is harmful to product reliability. Therefore, the non-destructive testing of bonding interface bonding quality is also a key process for product quality control in solid rocket motor production. Countries have invested a large amount of human and material resources to carry out research on the non-destructive testing technology of various components of solid rocket motors. Ultrasonic testing of metal materials has been widely used, and composite materials have the characteristics of high anisotropy, large acoustic attenuation, and complex structure. Ultrasonic inspection of composite materials and their components is a weak link, according to the Japan Aerospace Technology Institute. "Solid Rocket Engine Ultrasonic Testing" reported that they had successfully applied non-metallic coatings using ultrasonic multiple reflections. The steel shell adhesive surface was tested. After years of research, the ultrasonic longitudinal wave multiple reflection method was used to detect the bond quality between the nozzle metal shell and the non-metallic bonding interface. Now it has been successfully used in the product. Mass inspection. 2 Detection principle Ultrasound is an elastic vibration wave with a frequency higher than 20000Hz. The so-called longitudinal wave is the direction of propagation of the wave and the direction of movement of the particle, and the debonding of the bonding interface is the air gap type formed when the interface of different materials is not adhered. Defects, when the ultrasonic longitudinal wave passes perpendicularly through the metal and non-metal bonding surface, due to the different acoustic impedances of the two media in the product, the acoustic wave will be reflected and transmitted at the interface. The propagation path of the acoustic wave is shown in Figure 1. It is an incident wave; L is a reflected wave; t is a transmitted wave. Acoustic waves penetrate through all layers and interfaces of the product and pass through three types of media: metal, air, and non-metal. In these three media, the longitudinal wave sound velocities are 5900, 344, and 2200 m/s, respectively; when there is debonding at the interface of the acoustic impedance bond, the ultrasonic longitudinal wave is incident on the metal-air interface perpendicularly, and the acoustic pressure reflectance of the interface at this time. In the formula, P is the sound pressure of the incident wave; P is the acoustic impedance of the debonded interface and the reflection sound is the metallic medium; Z is the acoustic impedance of the air medium. Substituting the acoustic impedance data for calculation shows that, when R≈1, that is, there is a debonded solid rocket technology, the sound pressure reflectivity tends to 1, the transmittance tends to 0, and the sound wave is nearly 100% reflected here. However, when the bonding is good, the acoustic pressure reflectance of the interface is not 0, and the formula is as follows: where r is the sound pressure reflectance of the good bonding interface; P is the sound pressure of the sound reflection interface; Z is a non-metallic medium The acoustic impedance. It is calculated that the acoustic pressure of the reflected wave occupies 86% of the sound pressure of the incident wave, the sound pressure of the transmitted wave occupies 14%, and the acoustic wave has a part of transmission in addition to reflection. For a well-magnified ultrasonic flaw detector, the wave height on the screen of the instrument is proportional to the sound pressure, that is, the ratio of any two adjacent waves equals the ratio of the corresponding sound pressure. The decibel difference between the two is reflected by one pulse, and the debonding area The difference between the wave height and the good bonding area is 1dB. The multiple reflection method is used. When the ultrasonic wave is incident perpendicularly to the product, the sound pressure reflected from the first time is the sound pressure reflected from the second time and the sound pressure reflected from the nth time is returned. In the formula, P is the sound pressure reaching the surface of the metal layer; P is the sound pressure received by the probe after n reflections; R is the sound pressure reflection at the A interface is the sound pressure reflectance of the surface (bonding interface); T is the metal The attenuation coefficient of the part; t is the thickness of the metal part. For a given metal material, its thickness is certain, so T, t is constant, after selecting a fixed coupling agent, R is also a constant, the sound pressure after multiple reflection P is only related to R, ie Only with the bonding of the metal layer and the non-metal layer, then n de n = 10 good, ΔdB = 13dB, that is, the ultrasound longitudinal wave after 10 reflections, the debonding area and the good bonding area of ​​the reflected wave amplitude difference of 13dB Above, as reflected on the screen of the instrument, the debonding area has a higher amplitude and wave number than the good bonding area. According to this, the debonding area can be easily distinguished from the good bonding area and the bonding quality can be evaluated. 3 Comparison test block 3.1 Design and manufacturing Ultrasonic testing is to evaluate the quality of the tested piece by observing the position, amplitude and other characteristics of the reflected echo on the screen of the flaw detector. Taking into account the defects formed in the actual shape, acoustics The relationship is complex and difficult to quantify and analyze. Therefore, in the actual flaw detection, the detection sensitivity can only be adjusted by means of artificial defects of known specific shapes, and the defects can be evaluated by this scale to ensure the reproduction of the test results. The test block is used as a reference for comparison. It is a feature of ultrasonic flaw detection. In order to avoid the difference in acoustic properties between the test block and the product under test, the developed test block I (Fig. 2) has the same material type, thickness, curvature, and surface finish as the product under test and uses the same adhesive as the product under test. The metal adhesive surface is made of debonding wounds of different shapes and sizes. A in Figure 2 is a circular debonding (14mm oval). Contrast block No. II is a block containing natural defects cut from the tested product (Figure 3). Zhao Huirong: Ultrasonic testing of the bonding interface of the solid rocket motor nozzle 3.2 Detection of the test block 3.2.1 Adjustment of the scanning speed The type of the instrument used for the flaw detection is the CTS-22 type. The probe model should be adjusted according to the detection range before the inspection. The horizontal scale value of the time base scan line on the oscilloscope screen has a certain proportional relationship with the actual sound path. The thickness of the metal part being probed is 4mm. The standard depth test block produced by the SHANTOU Ultrasonic Instrument Research Institute is used to adjust the scanning speed, and the horizontal knob and the depth fine adjustment knob on the instrument panel are adjusted to expand the scanning range. The time base scanning line ratio is 1:2.5. Received multiple reflection echoes. 3.2.2 Test block test results and analysis The test block test results are shown in Figure 4. The waveform analysis of the test block test results is shown in Table 1. (a) Test block good adhesion area (b) A debonding area (circular) (c) B debonding area (oval) (d) C debonding area (irregular) From Fig. 4 and Table 1 It can be seen that: a) The reflected wavefronts are almost the same in height, because the ultrasonic beam does not begin to diffuse from the wave source, but there is a non-diffusion region near the wave source. In the non-diffusion region, the average sound pressure is basically unchanged. The sound field radiated by the wafer is shown in Figure 5; b) good adhesion zone, acoustic wave reflection, there are also non-metallic transmission wave, nozzle non-metallic insulation layer compared with metal steel, loose structure, organization Inhomogeneous, coarse crystal grains, its attenuation of acoustic energy is much more serious than steel, at 5MHz frequency, through calculation, the attenuation coefficient of steel is less than 0.002dB, non-metallic insulation layer reaches 6dB/mm, which makes good adhesion The transmitted waves entering the non-metallic parts are repeatedly absorbed and the energy attenuation is large. Within the horizontal scale of the instrument's oscilloscope screen, the envelope of the reflected wave is rapidly descending from the smooth arc; c) In the de-bonded area, the incident wave is 100% Reflected, reflected waves increase in wave level at the instrument's oscilloscope screen The scale 8 grid to the full screen wave, compared to a good bonding area, in the same horizontal scale of the oscilloscope screen, the amplitude of the wave increases, and with the increase of the debonding area, the more the wave, the higher the amplitude, the reflected wave packet The line slowly jagged. Solid rocket technology area flaw detector shows a good condition Bonded area multiple reflection wave in the oscilloscope screen horizontal scale "6" grid A debonding area multiple reflection wave in the oscilloscope screen horizontal scale "6" grid wave amplitude of 30% Above, in the “8†grid, the multi-reflected wave in the defoaming area of ​​the wave amplitude has a wave amplitude of 30% at the “8†grid of the horizontal scale of the oscilloscope, and the multiple amplitudes of the C wave in the de-bonding zone are shown in the “10†grid. Wave screen horizontal scale "10" grid amplitude 10% to 30% 3.3 test block method to determine the detection sensitivity of composite components is the use of test blocks for comparative detection to determine the detection sensitivity, according to the test results of the test block to test block A For detackifying circles, the probe is aligned to A-debonded, and the instrument attenuation and gain knobs are adjusted so that the multiple reflection waves from A debonding are up to 10% in the horizontal scale “8†grid of the instrument oscilloscope screen. In this case, the decibel value of the attenuator on the instrument panel is used as the detection sensitivity. After the sensitivity is adjusted, the decibel value is fixed. 4 Ultrasonic testing of the nozzle bonding interface 4.1 Detection process The metal part material being probed is 30CrMnSiA, the non-metallic part material is made of high silica/phenolic, the curvature of the investigated part is Υ 284mm, the thickness of the metal part is 4mm, the metal part and the non-metal insulation layer Between 944 adhesive, product acceptance requirements: debonding area shall not be greater than the total detection area detection sensitivity determined, you can test the nozzle metal and non-metallic bonding interface, with a 14mm circular detackification as a benchmark, if When the multiple reflection wave of a certain position is found to have a wave amplitude of more than 10% on the horizontal scale of the instrument's oscilloscope at 8 grids, the debonding is judged, and the debonding area is determined by the half-wave height method. The principle is that the incident sound pressure is removed More than ten percent of the viscous reflections are close to the spherical wave, which can be used in the simplified formula where P is the initial sound pressure; d is the wafer diameter; λ is the wavelength; s is the distance; A is the wafer area. If their reflections are regarded as a new sound source under the same conditions, the debonding area is equal to 100% of area A. When the half wave is equal to area A, the sound pressure is at the debonding center and the de-bonding edge to the center of the wafer. The difference is 6dB, the specific implementation method is: After finding out debonding, move the probe, make the reflection pulse amplitude on the fluorescent screen reach the highest, and then move the probe up and down and left and right, when the reflection amplitude drops to the original half, the probe centerline The location is the debonded area, the debonding is delineated with a 1 : 1 ratio clear paper, and the debonded area is calculated with a planimeter. Table 2 shows the inspection results of some batches of nozzle joint surface flaw detection. 4.2 Inspection results and analysis For the interface between the two metal and non-metallic nozzles, the ultrasonic longitudinal wave multiple reflection method described in this paper was used to test the internal debonding defects. After dissecting the nozzle, the debonding position and debonding area were also consistent with the test results. In later applications, after testing of nearly a hundred products, it has been proved that the method can more accurately find the following internal debonding defects of workpieces: a. gap-type large-area debonding. This type of detackification is mostly due to the fact that the workpiece is not cleaned cleanly, the lining is not tightly fitted to the housing, and the workpiece is deformed. At this time, the bonding strength is lower than the good bonding strength, which is reflected on the instrument oscilloscope screen. The amplitude is about 30% in the horizontal scale "10" grid. b. Detackification of voids. This kind of detackification is mostly due to the ultrasonic testing of the adhesive interface of the coated solid rocket motor nozzle, the failure of the gas inside the adhesive layer and the failure of the adhesive, etc. At this time, the adhesive strength is also lower than the good adhesive strength. Reflected on the instrument's oscilloscope screen, the multiple reflection amplitude is more than 10% in the horizontal scale “8†grid. 6 Concluding Remarks Using the ultrasonic multiple reflection method, the use of conventional instruments and equipment can accurately detect various debonding defects at the bonding interface. The actual inspection of the solid rocket motor nozzle bonding interface proves that this method is suitable for on-site inspection and position detection in the production line. Tungsten Carbide inserts and blades are widely used in industries such as metalworking, woodworking and general machining. These cutting tools have exceptional hardness, wear and heat resistance, making them ideal for a wide variety of cutting applications. Whether turning, milling, drilling or grooving, our tungsten carbide inserts and inserts deliver peak performance and extended tool life. 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