Bearingless rotor wing flexible beam full-three-dimensional CT (Computed Tomography) detection method

Abstract

The invention relates to the technical field of helicopter rotor composite material structure detection, in particular to a bearing-free rotor flexible beam full-three-dimensional CT detection method. Comprising the following steps: performing segmented scanning on the bearingless rotor wing flexible beam and constructing a three-dimensional model; processing to obtain section diagrams and three-dimensional diagrams of the flexible beam in three directions of a front view, a top view and a side view; the method comprises the following steps: identifying two density wave crests, adjusting a display reference to a wave trough between the two wave crests, adjusting the displayed lowest density to the bottom of a first wave crest, and adjusting the displayed highest density to the top of a second wave crest, so that four components, namely air, a girder, a cloth liner and resin, can be displayed; meanwhile, the displayed highest density and the displayed lowest density are finely adjusted, so that the three-dimensional stereogram is completely displayed and has no redundant information, and the main view section image has no redundant information and is clear in black and white; and adjusting the position of the tangent plane, finding out abnormal defect positions of air, a girder, a cloth liner and resin, and carrying out size measurement on defects.

Description

Technical Field

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

[0002] As the fourth generation of advanced rotor technology, the bearingless rotor is one of the important development directions of helicopter rotor technology. As the core component of the bearingless rotor, the flexible beam replaces the flapping, shimmying and pitch-changing hinges, and realizes the flapping, shimmying and pitch-changing movements of the blades through its own deformation. At the same time, it connects the blades and the centerpiece, transmitting all the centrifugal forces and most of the bending moments and shear forces on the blades. In order to obtain a long service life of the flexible beam, a three-stage deformation design is adopted, and each section bears a different type of load. For example, the root should have a larger bending deformation, and the rear torsion typical section should have a stronger torsional deformation ability.

[0003] The flexible beam structure has a complex appearance and is a typical thick-section composite material. Its lifespan has always been a bottleneck restricting the development of bearingless rotor technology at home and abroad. Due to the drastic changes in appearance, the flexible beam has a serious problem of poor molding processability. Although after technical research, a semi-mold molding and re-bonding molding method has been created, which can improve product quality to a certain extent, the product quality is still unstable, with many types of defects and extremely wide distribution of defect locations. Therefore, it is necessary to develop a set of detection methods with good adaptability and high reliability to fully detect all defects inside the flexible beam.

[0004] Existing detection technologies often perform non-destructive testing on composite structural parts through visual inspection, tapping, X-ray inspection, etc. 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 testing, acceptance criteria are formulated in combination with the detected defects. Affected by the instability of the forming process, flexible beams have many defects, and the morphology and position are highly random. If only the defect range is used as the acceptance criterion for flexible beams, the pass rate will become extremely low, and a considerable number of flexible beams with acceptable defects will also be eliminated, resulting in a huge waste of resources. At present, there is no example of the application of full three-dimensional CT detection on any composite structural parts in China. Summary of the invention

[0005] Purpose of the invention: To provide a full three-dimensional CT detection method for a bearingless rotor flexible beam.

[0006] Technical solution:

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

[0008] Step 1: Fix the flexible beam so that the center of the flexible beam, the center of the detector and the beam-emitting position of the ray source 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, the better. If not, continue to adjust the position of the flexible beam until the requirements are met.

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

[0010] Step 3: Reconstruct the slices into a three-dimensional model according to the voxel value, the number of slices and the range of the sample segment;

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

[0012] Step 5: Identify two density peaks, adjust the display reference to the valley between the two peaks, then adjust the lowest density displayed to the bottom of the first peak, and adjust the highest density displayed to the top of the second peak, so that four components can be displayed: air, beam, padding and resin, and at the same time fine-tune the highest density displayed and the lowest density displayed so that the three-dimensional stereogram is complete and has no redundant information, and the main view section has no redundant information and is clearly black and white;

[0013] Step 6: Adjust the section position and traverse the section views in the main view, top view, and side view to find the defect locations of air, beam, padding, and resin anomalies, and measure the size of the defects.

[0014] Further, step 2 is specifically: dividing the bearingless rotor flexible beam into eight regions along the span direction, and scanning the eight regions respectively according to the parameters in the following table:

[0015] Partition Segment length Voltage Current Zoom Voxel 1 100mm 250kV 240μA 750 99.49μm 2 120mm 160kV 240μA 600 79.59μm 3 120mm 160kV 240μA 550 72.95μm 4 120mm 160kV 240μA 550 72.95μm 5 120mm 160kV 240μA 550 72.95μm 6 120mm 160kV 240μA 550 72.95μm 7 120mm 160kV 240μA 600 79.59μm 8 140mm 200kV 240μA 650 86.22μm .

[0016] Furthermore, in step 6, according to the cross-sectional view, when other materials appear between the same materials, it is determined that cracks exist, and the cracks are local separation, insufficient adhesion, debonding or cracking between adjacent layers of the same material.

[0017] Furthermore, according to the cross-sectional view, when resin or air appears between two materials, it is determined that debonding exists, and debonding is the failure of the bonding effect between two different materials.

[0018] Furthermore, according to the cross-sectional view, when there is air in the flexible beam area and the contour diameter is ≥2mm, it is determined to be a pore; the pores are some single isolated holes and gaps inside the material with a large volume, and the maximum distance between two points on the contour on the cross-sectional view is ≥2mm.

[0019] Furthermore, according to the cross-sectional diagram, when there is air in the flexible beam area and the number of air locations is ≥5, it is determined to be dense micropores; dense micropores are defects that are diffuse in the material, the number is ≥5, and the boundaries are generally amorphous.

[0020] Further, according to the cross-sectional view, when there are abnormal substances other than air, beam, pad and resin in the flexible beam area, it is determined to be an inclusion.

[0021] Furthermore, according to the cross-sectional view, when there is resin accumulation in the flexible beam area, it is determined to be glue accumulation, which is a gray block on the beam without fibers in it.

[0022] Further, according to the cross-sectional view, when there is bending of the beam in the flexible beam region, it is determined to be beam wrinkling.

[0023] Beneficial effects:

[0024] The present invention provides a full three-dimensional CT detection method for a bearingless rotor flexible beam. By adopting this method, all defect morphologies and position information in the flexible beam can be accurately detected at the cost of less manpower and material resources, so that it can be combined with fatigue test results to provide a guiding basis for the improvement of the flexible beam production process and the formulation of acceptance specifications, which can greatly improve the acceptance rate and create more value. By adopting this non-destructive testing method, current industrial-grade high-precision CT detection equipment can be used, and there is no special key technology, so the method is highly feasible. At the same time, this non-destructive testing method can be extended to other composite material structural parts, providing a way of thinking for refined design improvement and the formulation of acceptance specifications. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of flexible beam detection segmentation;

[0026] Figure 2 Girder fold definition;

[0027] Figure 3 Schematic diagram of the section direction of CT detection results. DETAILED DESCRIPTION

[0028] Based on the structural characteristics of composite material flexible beams, this patent proposes a full three-dimensional CT detection method for bearingless rotor flexible beams. This method specifies the specific requirements, operation methods and defect definitions of non-destructive testing methods. With less manpower and material resources, the three-dimensional morphology and location of flexible beam defects can be accurately detected. It provides a guiding basis for the improvement of flexible beam production technology and the formulation of acceptance specifications.

[0029] A full 3D CT inspection method for bearingless rotor flexible beams uses segmented cone beam CT scanning to clearly mark the junction between each two segments. The mark includes the production piece number and the distance between the junction and the center of the root bushing hole. For specific implementation, please refer to Figure 1 way.

[0030] Equipment requirements are as follows:

[0031] 1. Radiation source: Consider the required radiation energy, radiation intensity, focal spot size, output stability, etc., give priority to X-rays, and select a micro-focus radiation tube with a voltage of not less than 250KV according to the process material, maximum thickness and detection accuracy.

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

[0033] 3. Mechanical system: The effective up and down travel of the radiation source detector shall not be less than 450mm.

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

[0035] Table 1 Testing equipment setting parameters

[0036] Partition Segment length Voltage Current Zoom Voxel 1 100mm 250kV 240μA 750 99.49μm 2 120mm 160kV 240μA 600 79.59μm 3 120mm 160kV 240μA 550 72.95μm 4 120mm 160kV 240μA 550 72.95μm 5 120mm 160kV 240μA 550 72.95μm 6 120mm 160kV 240μA 550 72.95μm 7 120mm 160kV 240μA 600 79.59μm 8 140mm 200kV 240μA 650 86.22μm

[0037] The detection method is as follows:

[0038] 1. Check whether the personal radiation meter is working properly and whether the mechanical system and radiation source of the CT equipment are powered normally.

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

[0040] 3. Open the acquisition software and complete the offset correction, gain correction, and bad pixel correction in sequence.

[0041] 4. Fix the flexible beam so that the center of the flexible beam, the center of the detector and the beam-emitting 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, the better. If not, continue to adjust the position of the flexible beam until the requirements are met.

[0042] 5. Set the parameters according to Table 1, start collecting data, and record the sampled voxel value, number of sections, and sample segment range.

[0043] 6. Reconstruct the slices into a three-dimensional model based on the voxel value, number of slices and sample range.

[0044] 7. The reconstructed model is processed to obtain the front view, top view, side view (i.e., cross-sectional view) and three-dimensional stereogram of the flexible beam.

[0045] 8. Identify the two density peaks and adjust the display reference to the valley between the two peaks. Then adjust the lowest density displayed to the bottom of the first peak and the highest density displayed to the top of the second peak. This will display the four components: air, beam, padding and resin, while making the three-dimensional image complete and free of redundant information, and making the main section image free of redundant information and clear in black and white.

[0046] 9. Adjust the section position, find the defect positions of air, beam, pad and resin abnormalities, and measure the size of the defects. The defect definitions are as follows:

[0047] Crack: Local separation, lack of adhesion, debonding or cracking between adjacent layers of the same material. Usually occurs inside or near the edge of the inside. In CT, it appears as other materials between the same materials.

[0048] Debonding: Failure of the bonding between two dissimilar materials. In CT, this is manifested as the presence of resin or air between the two materials.

[0049] Pores: Some isolated cavities and voids inside the material, which are relatively large in size and have a maximum distance of ≥2 mm between two points on the contour of the section. In CT scans, they appear as air.

[0050] Dense micropores: Defects are diffuse inside the material, with a number of ≥5, and generally amorphous boundaries. In CT, they appear as air.

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

[0052] Glue buildup: Gray patches on the beam with no fibers in them. In CT scans, this appears as resin buildup.

[0053] Beam folds: Figure 2 As shown in the figure, beam wrinkles, i.e., the fibers are not smooth, can be divided into: shallow wrinkles and deep wrinkles. Deep wrinkles are those with a height G>0.1L, shallow wrinkles are those with a height G≤0.1L, and N is half of the total length of the wrinkle. In CT, it appears as a bending of the beam.

[0054] The test result of each segment should be a three-dimensional entity, which can be Figure 3 Perform cross-section, side-section and sectioning. The cross-section plane is parallel to XY, the side-section plane is parallel to YZ, and the sectioning plane is parallel to XZ.

[0055] In order to obtain a more accurate range of certain defects, especially thickness, the entity can be rotated so that the cross section and side section are parallel to the fiber direction of the location of interest. For defects close to the surface, the entity can be rotated so that the cross section and side section are parallel to the outer contour on the beam to obtain: the cross section is close to parallel to the upper and lower surfaces of the beam, and the side section is close to parallel to the side of the beam, and the defect range is detected. The thickness is defined here as the distance H from the starting cross section / side section of the defect to the ending cross section / side section of the defect, taking the smaller value of the two distances H;.

[0056] It is necessary to ensure that the size of detectable defects is no larger than 0.2mm. The image along the span direction should be clear and different materials can be clearly distinguished. Clear textures can be seen on the beams and pads.

[0057] The method of the present invention uses cone beam CT segmented detection according to the structural characteristics of the flexible beam, and sets different detection parameters for areas of different thicknesses; reconstructs the detection results in three dimensions, and displays the defects in the form of cross sections, side sections, and sectional sections; defines all possible defect types of the flexible beam; defines the direction of the section by the shape of the flexible beam to reduce measurement errors; can clearly distinguish different structures and different materials by adjusting the display threshold; can accurately obtain the three-dimensional morphology and position of the defect; the detectable defect size is no more than 0.2 mm, and the detection result image is clear; and can overcome the influence of CT image edge diffusion on measurement accuracy.

Claims

1. A full three-dimensional CT detection method for a bearingless rotor flexible beam, characterized in that: include: Step 1: Fix the flexible beam so that the center of the flexible beam, the center of the detector and the beam-emitting position of the ray source 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, the better. If not, continue to adjust the position of the flexible beam until the requirements are met. Step 2: Scan the bearingless rotor flexible beam in sections and collect data, and record the sampled voxel value, number of sections, and sample segment range; Step 3: Reconstruct the slices into a three-dimensional model according to the voxel value, the number of slices and the range of the sample segment; Step 4: Process the reconstructed model to obtain the cross-sectional views and three-dimensional stereograms of the flexible beam in the front view, top view, and side view; Step 5: Identify two density peaks, adjust the display reference to the valley between the two peaks, then adjust the lowest density displayed to the bottom of the first peak, and adjust the highest density displayed to the top of the second peak, so that four components can be displayed: air, beam, padding and resin, and at the same time fine-tune the highest density displayed and the lowest density displayed so that the three-dimensional stereogram is complete and has no redundant information, and the main view section has no redundant information and is clearly black and white; Step 6: Adjust the section position and traverse the section views in the main view, top view, and side view to find the defect locations of air, beam, padding, and resin anomalies, and measure the size of the defects.

2. The full three-dimensional CT detection method for bearingless rotor flexible beam according to claim 1 is characterized in that: Step 2, specifically: divide the bearingless rotor flexible beam into eight regions along the span direction, and scan the eight regions respectively according to the parameters in the following table: 。 3. The full 3D CT detection method for bearingless rotor flexible beam according to claim 1 is characterized in that: In step 6, based on the cross-sectional view, when other materials appear between the same materials, it is determined that cracks exist, and the cracks are local separation, insufficient adhesion, debonding or cracking between adjacent layers of the same material.

4. The full 3D CT detection method for bearingless rotor flexible beam according to claim 1, characterized in that: According to the cross-sectional view, when resin or air appears between the two materials, it is determined that debonding exists, and debonding is the failure of the bonding between two different materials.

5. The full 3D CT detection method for bearingless rotor flexible beam according to claim 1, characterized in that: According to the cross-sectional diagram, if there is air in the flexible beam area and the contour diameter is ≥2mm, it is determined to be a pore; the pores are some single isolated holes and gaps inside the material with a large volume, and the maximum distance between two points on the contour on the cross-sectional surface is ≥2mm.

6. The full 3D CT detection method for bearingless rotor flexible beam according to claim 1, characterized in that: According to the cross-sectional diagram, when there is air in the flexible beam area and the number of air locations is ≥5, it is determined to be dense micropores; dense micropores are defects that are diffuse in the material, the number is ≥5, and the boundaries are generally amorphous.

7. The full 3D CT detection method for bearingless rotor flexible beam according to claim 1, characterized in that: Inclusions are determined when there are abnormal substances other than air, beam, padding, and resin in the flexible beam area based on the cross-sectional view.

8. The full 3D CT detection method for bearingless rotor flexible beam according to claim 1, characterized in that: According to the cross-sectional image, when there is resin accumulation in the flexible beam area, it is determined to be glue accumulation, which is a gray block on the beam without fibers in it.

9. The full 3D CT detection method for bearingless rotor flexible beam according to claim 1, characterized in that: In the case where there is bending of the beam in the flexible beam region according to the cross-sectional view, beam wrinkling is determined.

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