A bearingless rotor flexible beam full three-dimensional CT detection method

Abstract

The present application relates to the technical field of helicopter rotor composite structure detection, and particularly relates to a full three-dimensional CT detection method for bearingless rotor flexible beam. The method comprises the following steps: segmentally scanning the bearingless rotor flexible beam and constructing a three-dimensional model; processing to obtain the sectional view and three-dimensional stereogram of the flexible beam in three directions of front view, plan view and side view; identifying two density wave peaks, adjusting the display reference to the wave trough between the two wave peaks, adjusting the lowest density displayed to the bottom of the first wave peak, and adjusting the highest density displayed to the top of the second wave peak, so that four components, i.e. air, beam, cloth and resin, can be displayed, and the highest density displayed and the lowest density displayed are finely adjusted to make the three-dimensional stereogram complete and free of redundant information, and make the front view sectional view free of redundant information and clear in black and white; adjusting the sectional position to find the defect position of the air, beam, cloth and resin abnormalities, and measuring the size of the defects.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite material structure detection of helicopter rotor, in particular to a full three-dimensional CT detection method for flexible beam of bearingless rotor. BACKGROUND

[0002] As the fourth generation of advanced rotor technology, the bearingless rotor is one of the important development directions of helicopter rotor technology. The flexible beam, as the core component of the bearingless rotor, functions to replace the flap, lag and pitch hinges, realizes the flap, lag and pitch movements of the blades through its deformation, and connects the blades and the central part to transfer all centrifugal forces and most of the bending moments and shear forces on the blades. In order to obtain a high service life of the flexible beam, a three-section deformation design is adopted, each section bears different types of loads, such as a larger bending deformation at the root and a stronger torsional deformation capacity at the rear torsional section,

[0003] The flexible beam structure has a complex shape and is a typical thick-section composite key component. Its service life has been a bottleneck restricting the development of bearingless rotor technology at home and abroad. Due to the dramatic change in shape, the flexible beam has a serious problem of poor mold pressing process. Although a molding method of semi-mold pressing and re-bonding has been created through technical research to improve the product quality to some extent, the product quality is still unstable, the defect types are numerous and the defect positions are widely distributed. Therefore, a detection method with good adaptability and high reliability is needed to fully detect all internal defects of the flexible beam.

[0004] The existing detection technology often uses visual inspection, knocking, X-ray detection and other methods to non-destructively detect the composite material structure. However, only a vague defect range can be detected, and the specific three-dimensional morphology and position of the defect cannot be detected. Then, through fatigue test, the acceptance standard is formulated combined with the detected defect content. Due to the instability of the molding process, the flexible beam has many defects, and the morphology and position are random. If only the defect range is used as the acceptance standard of the flexible beam, the qualified rate will be very low, and a considerable part of the flexible beam containing acceptable defects will also be eliminated, causing great waste of resources. At present, there is no example of full three-dimensional CT detection applied to composite structure at home. SUMMARY

[0005] The present application relates to the technical field of composite material structure detection of helicopter rotor, in particular to a full three-dimensional CT detection method for flexible beam of bearingless rotor.

[0006] TECHNICAL SOLUTION

[0007] A full three-dimensional CT detection method for flexible beam of bearingless rotor, comprising:

[0008] Step 1: Fix the flexible beam, make the center of the flexible beam, the center of the detector and the position of the ray source on the same horizontal line, observe whether the flexible beam is in the imaging range of the detector, and the smaller the rotation radius of the flexible beam is, the better; if not, continue to adjust the placement position of the flexible beam until the requirements are met;

[0009] Step 2: Segmentally scan the bearingless rotor flexible beam and collect data, record the sampled voxel value, the number of sections and the sample range;

[0010] Step 3: According to the voxel value, the number of sections and the sample range, the sections are reconstructed into a three-dimensional model;

[0011] Step 4: Process the reconstructed model to obtain the sectional view and three-dimensional view of the flexible beam in the three directions of front view, top view and side view;

[0012] Step 5: Identify two density peaks, adjust the display reference to the trough between the two peaks, then adjust the lowest density of the display to the bottom of the first peak, and adjust the highest density of the display to the top of the second peak, so that four components can be displayed: air, beam, cloth and resin. At the same time, fine-tune the highest density and the lowest density of the display to make the three-dimensional view complete and without redundant information, and the front view sectional view clear and black and white.

[0013] Step 6: Adjust the section position to traverse the sectional view in the three directions of front view, top view and side view, find the defect position of air, beam, cloth and resin, and measure the size of the defect.

[0014] Further, step 2, specifically: the bearingless rotor flexible beam is divided into eight regions along the span, and each of the eight regions is scanned according to the parameters in the following table:

[0015] partition segment length voltage current scaling voxel 1 100 mm 250 kV 240 μA 750 99.49 μm 2 120 mm 160 kV 240 μA 600 79.59 μm 3 120 mm 160 kV 240 μA 550 72.95 μm 4 120 mm 160 kV 240 μA 550 72.95 μm 5 120 mm 160 kV 240 μA 550 72.95 μm 6 120 mm 160 kV 240 μA 550 72.95 μm 7 120 mm 160 kV 240 μA 600 79.59 μm 8 140 mm 200 kV 240 μA 650 86.22 μm .

[0016] Further, in step 6, according to the sectional view, in the case of other materials between the same materials, it is determined that there is a crack, which is a planar local separation, insufficient adhesion, delamination or cracking between adjacent layers of the same material.

[0017] Further, according to the sectional view, in the case of resin or air between two materials, it is determined that there is debonding, which is the failure of the adhesion between two different materials.

[0018] Further, according to the sectional view, in the case of air in the flexible beam region and the contour diameter ≥ 2mm, it is determined that there is a gas hole; the gas hole is some single isolated cavity and gap inside the material, and the maximum distance between two points on the contour on the sectional view is ≥ 2mm.

[0019] Further, according to the section view, in the case that there is air in the flexible beam area and the number of air existing positions is greater than or equal to 5, it is determined as dense micro-pores; the dense micro-pores are defects in the material in a diffuse form, the number of which is greater than or equal to 5, and generally the boundary is amorphous.

[0020] Further, according to the section view, in the case that there is an abnormal substance in the flexible beam area, which does not belong to air, a large beam, a pad cloth and resin, it is determined as an inclusion.

[0021] Further, according to the section view, in the case that there is a resin accumulation in the flexible beam area, it is determined as a glue accumulation, and the glue accumulation is a gray block on the large beam without fibers in it.

[0022] Further, according to the section view, in the case that there is a bending of the large beam in the flexible beam area, it is determined as a large beam wrinkle.

[0023] Beneficial effects:

[0024] The application provides a bearingless rotor flexible beam full three-dimensional CT detection method. By using the method, all defect morphologies and position information in the flexible beam can be accurately detected at a low cost of manpower and material resources, so that the fatigue test results can be combined to provide guiding basis for improvement of the flexible beam production process and establishment of acceptance criteria, and the acceptance qualified rate can be greatly improved, thereby creating more value. By using the nondestructive detection method, current industrial high-precision CT detection equipment can be used, and there is no special key technology, so that the method is strong in realizability. Meanwhile, the nondestructive detection method can be popularized to other composite material structural parts, and provides a kind of idea for fine design improvement and establishment of acceptance criteria. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Flexible beam detection segmentation schematic diagram;

[0026] Figure 2 Large beam wrinkle definition;

[0027] Figure 3 CT detection result section direction schematic diagram. DETAILED DESCRIPTION

[0028] Based on the structural characteristics of the composite material flexible beam, the application provides a bearingless rotor flexible beam full three-dimensional CT detection method. The method specifies the specific requirements, operation method and defect definition of the nondestructive detection method. The three-dimensional morphology and position of the flexible beam defects can be accurately detected at a low cost of manpower and material resources, so as to provide guiding basis for improvement of the flexible beam production process and establishment of acceptance criteria.

[0029] A bearingless rotor flexible beam full three-dimensional CT detection method adopts segmented cone beam CT scanning, and clear identification is performed at the junction between each two segments. The identification contains production sheet number, distance information between the junction and the root bush hole center. The specific implementation can be referred to Figure 1 . .

[0030] The equipment requirements are as follows:

[0031] 1. Ray source: considering the required ray energy, ray intensity, focus size, output stability, etc., X-ray is preferred, and a micro-focus ray tube with a voltage not less than 250KV is selected according to the process material, maximum thickness and detection accuracy.

[0032] 2. Detection plate: should meet the detection resolution requirement, pixel size ≤200μm, effective imaging area ≤40×40mm.

[0033] 3. Mechanical system: the effective stroke of the ray source detector is not less than 450mm.

[0034] The detection equipment setting parameters are shown in Table 1.

[0035] Table 1 Detection equipment setting parameters

[0036] partition segment length voltage current scaling voxel 1 100 mm 250 kV 240 μA 750 99.49 μm 2 120 mm 160 kV 240 μA 600 79.59 μm 3 120 mm 160 kV 240 μA 550 72.95 μm 4 120 mm 160 kV 240 μA 550 72.95 μm 5 120 mm 160 kV 240 μA 550 72.95 μm 6 120 mm 160 kV 240 μA 550 72.95 μm 7 120 mm 160 kV 240 μA 600 79.59 μm 8 140 mm 200 kV 240 μA 650 86.22 μm

[0037] The detection method is as follows:

[0038] 1. Check whether the personal radiation measuring instrument is working normally, and check whether the CT equipment mechanical system and the ray source are normally powered.

[0039] 2. Start the equipment, check whether the equipment vacuum state meets the requirements, and set the required voltage and current for scanning the flexible beam.

[0040] 3. Open the acquisition software, and complete bias correction, gain correction and bad point correction in turn.

[0041] 4. Fix the flexible beam, so that the center of the flexible beam, the center of the detector and the ray source beam position are on the same horizontal line, observe whether the flexible beam is within the imaging range of the detector, and the smaller the rotation radius of the flexible beam is, the better. If not, continue to adjust the flexible beam placement position until the requirements are met.

[0042] 5. Set according to the parameters in Table 1, start data acquisition, and record the sampled voxel value, section number and sample section range.

[0043] 6. According to the voxel value, section number and sample section range, reconstruct the section into a three-dimensional model.

[0044] 7. Process the reconstructed model to obtain the front view, top view, side view (i.e. section view) and three-dimensional perspective view of the flexible beam.

[0045] 8. Identify two density peaks, set display reference to the valley between the two peaks. Then set the lowest display density to the bottom of the first peak, and the highest display density to the top of the second peak. Thus, four components can be displayed: air, beam, veil, and resin, while the three-dimensional solid is complete and without extra information, and the main section is without extra information and black and white.

[0046] 9. Adjust the section position, find the defect position of air, beam, veil, and resin abnormality, and measure the size of the defect. The defects are defined as follows:

[0047] Crack: a planar local separation between adjacent layers of the same material, lack of adhesion, debonding, or cracking. It usually occurs inside, or at the edge close to the inside. In CT, it appears as other material between the same material.

[0048] Debonding: failure of the adhesive action between two different materials. In CT, it appears as resin or air between two materials.

[0049] Air hole: some single isolated cavities and voids inside the material, with a large volume, and the maximum distance between two points on the profile on the section is ≥2mm. In CT, it appears as air.

[0050] Dense micro air hole: the defect is in a diffuse form inside the material, with a number ≥5, and the boundary is generally amorphous. In CT, it appears as air.

[0051] Inclusion: contains irrelevant impurities, usually mixed in during the manufacturing process. In CT, it appears as an abnormal substance that does not belong to any material.

[0052] Glue accumulation: a gray block on the beam, without fiber in it. In CT, it appears as resin accumulation.

[0053] Beam wrinkle: as shown in Figure 2 , the beam wrinkle is the fiber not smooth, which can be divided into: shallow wrinkle, deep wrinkle. The height G > 0.1L is deep wrinkle, and the height G ≤ 0.1L is shallow wrinkle, and N is half of the total length of the wrinkle at this point. In CT, it appears as the bending of the beam.

[0054] The detection result of each section should be a three-dimensional solid, which can be cut horizontally, laterally, and sectionally according to Figure 3 . The horizontal section is parallel to the X-Y plane, the lateral section is parallel to the Y-Z plane, and the sectional section is parallel to the X-Z plane.

[0055] To obtain more accurate range of some defects, especially thickness, the entity can be rotated to make the cross section and side section parallel to the fiber direction of the position of interest. For defects near the surface, the entity can be rotated to make the cross section and side section parallel to the outer contour of the beam to obtain: the cross section is parallel to the upper and lower surfaces of the beam, and the side section is parallel to the side of the beam to detect the range of defects. Here, the thickness is defined as the distance H from the starting cross section / side section of the defect to the ending cross section / side section of the defect, and the smaller value of the two distances H is taken.

[0056] It is necessary to ensure that the detectable defect size is not greater than 0.2mm, the image is clear along the spanwise cross section, and different materials can be clearly distinguished.

[0057] The method of the present application uses cone beam CT segmented detection according to the structural characteristics of the flexible beam, and sets different detection parameters for regions of different thicknesses; the detection results are three-dimensionally reconstructed, and the defects are displayed in the form of cross sections, side sections and cross sections; all possible defect types of the flexible beam are defined; the direction of the section is defined according to the shape of the flexible beam to reduce measurement error; different structures and materials can be clearly distinguished by adjusting the display threshold; the three-dimensional morphology and position of the defects can be accurately obtained; the detectable defect size is not greater than 0.2mm, and the detection result image is clear; the influence of CT image edge diffusion on measurement accuracy can be overcome.

Claims

1. A bearingless rotor flexible beam full three-dimensional CT detection method, characterized in that, The method comprises the following steps: Step 1: Fix the flexible beam, so that the center of the flexible beam, the center of the detector and the position of the ray source are on the same horizontal line, and observe whether the flexible beam is within the imaging range of the detector, and the smaller the rotation radius of the flexible beam is, the better; if not, continue to adjust the placement position of the flexible beam until the requirements are met; Step 2: Segmentally scan the bearingless rotor flexible beam and collect data, and record the sampled voxel value, the number of sections and the sample section range; Step 3: According to the voxel value, the number of sections and the sample section range, the sections are reconstructed into a three-dimensional model; Step 4: Process the reconstructed model to obtain the section views and three-dimensional views of the flexible beam in the three directions of front view, top view and side view; Step 5: Identify two density wave peaks, adjust the display reference to the wave trough between the two wave peaks, then adjust the lowest density of the display to the bottom of the first wave peak, and adjust the highest density of the display to the top of the second wave peak, so that four components, air, beam, cloth and resin, can be displayed, and the highest density and the lowest density of the display are adjusted to make the three-dimensional view complete and without redundant information, and the front view section view is clear and black and white. Step 6: Adjust the section position to traverse the section views in the three directions of front view, top view and side view, find the defect positions of air, beam, cloth and resin, and measure the size of the defects.

2. The bearingless rotor flexible beam full three-dimensional CT detection method according to claim 1, characterized in that, In step 2, the bearingless rotor flexible beam is divided into eight regions along the span, and the eight regions are scanned according to the parameters in the following table: 。 3. The bearingless rotor flexible beam full three-dimensional CT detection method of claim 1, wherein, In step 6, according to the section view, when other materials appear between the same materials, it is determined that there is a crack, and the crack is a planar local separation, insufficient adhesion, delamination or cracking between adjacent layers of the same material.

4. The bearingless rotor flexible beam full three-dimensional CT detection method of claim 1, wherein, According to the section view, when resin or air appears between two materials, it is determined that there is debonding, and the debonding is the failure of the adhesion between the two different materials.

5. The bearingless rotor flexible beam full three-dimensional CT detection method of claim 1, wherein, According to the section view, when there is air in the flexible beam region and the profile diameter is greater than or equal to 2 mm, it is determined that there is a gas hole; the gas hole is a single isolated cavity and gap in the material, and the maximum distance between two points on the profile is greater than or equal to 2 mm.

6. The bearingless rotor flexible beam full three-dimensional CT detection method of claim 1, wherein, According to the section view, when there is air in the flexible beam region and the number of air positions is greater than or equal to 5, it is determined that there is dense micro-porosity; the dense micro-porosity is a defect in the material in a diffuse form, and the number is greater than or equal to 5, and the boundary is generally amorphous.

7. The bearingless rotor flexible beam full three-dimensional CT detection method of claim 1, wherein, According to the section view, when there is an abnormal substance in the flexible beam region which does not belong to air, beam, cloth and resin, it is determined that there is an inclusion.

8. The bearingless rotor flexible beam full three-dimensional CT detection method of claim 1, wherein, According to the section view, when there is resin accumulation in the flexible beam region, it is determined that there is glue accumulation; the glue accumulation is a gray block on the beam without fiber therein.

9. The bearingless rotor flexible beam full three-dimensional CT detection method of claim 1, wherein, According to the section view, when there is a bending of the beam in the flexible beam region, it is determined that there is a beam wrinkle.

Images