Method for calculating local porosity based on ct scans and method for characterizing local porosity of a structure as a whole

Abstract

This invention discloses a method for calculating local porosity based on CT scans and a method for characterizing the local porosity of a component as a whole. The calculation method includes the following steps: obtaining mesh data of the outer surface of the component and the inner surfaces of all holes; converting the mesh data of the inner surfaces of the holes into hole volume mesh data composed of multiple tetrahedral elements; obtaining the volume of a hole and the geometric center coordinates of the hole based on the hole volume mesh data of a hole; converting the mesh data of the outer surface of the component into component solid body mesh data composed of multiple tetrahedral elements; obtaining the equivalent region of a hole based on the volume of a hole and the corresponding geometric center coordinates; using the center point of each hole equivalent region as a reference, determining whether the mesh edge of each tetrahedral element in the component solid body mesh data within the range around the center point intersects with the local analysis region, and calculating the local solid volume; and calculating the local porosity of the current hole.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology for materials, and more specifically, to a method for three-dimensional quantitative characterization of internal pores in a component using computed tomography (CT) data, particularly a method for calculating the porosity of a local region of a pore based on CT scans, and a method for characterizing the local porosity of the entire component including the calculation method of the local porosity. Background Technology

[0002] Currently, to evaluate the local porosity of components based on CT data, the component is usually divided into several geometric bodies of equal volume, and the porosity inside each geometric body is calculated as the local porosity.

[0003] For example, patent CN119167450A uses CT scanning to obtain the microscopic features (including pores) in the electrode, and divides the microscopic geometric model into a target number of parts of the microscopic geometric model with the same volume; the non-uniformity index of the porous electrode is determined based on the overall porosity of the microscopic geometric model and the local porosity of the parts of the microscopic geometric model. Another example is patent CN118190347A, which uses a high-definition CCD camera to record the dissolution process of a two-dimensional porous medium. It exports the video of the dissolution process as an image sequence, divides each frame into several local units of equal size, extracts the morphology of the solid parts of these local units, and calculates the change in local porosity during the dissolution process using physical formulas to obtain the porosity distribution.

[0004] However, the above method for calculating the local porosity of components divided by equal volume / equal area has significant limitations: it cannot solve the problem of hole distribution when a hole appears in two different geometries, and it cannot be used to calculate the local porosity of the whole, so it cannot be practically applied in engineering.

[0005] The above background information is provided only to aid in understanding the inventive concept and technical solution of this invention. It does not necessarily belong to the prior art of this invention. In the absence of clear evidence that the above information was disclosed before the filing date of this invention, the above background information should not be used to evaluate the novelty and inventiveness of this invention. Summary of the Invention

[0006] In view of this, in order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for calculating the local porosity of components based on CT scans.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for calculating local porosity based on CT scans includes the following steps: The component is scanned using a CT scanning device to obtain grid data of the outer surface of the component and the inner surface of all its holes; For each individual hole's inner surface mesh data, finite element preprocessing software is used to convert it into hole volume mesh data composed of multiple tetrahedral elements; Based on the hole's volumetric mesh data, the volume of the hole and the coordinates of its geometric center are obtained. The mesh data of the outer surface of the component is converted into the mesh data of the component solid body composed of multiple tetrahedral elements; Each hole is processed sequentially. Based on the volume of a hole and the corresponding geometric center coordinates, the equivalent region of the hole is obtained, which serves as the local analysis region for that hole. Using the center point of the equivalent region of each hole as a reference, select the component solid mesh data within the surrounding area of ​​the center point, determine whether the mesh edge of each tetrahedral element in the component solid mesh data within the surrounding area of ​​the center point intersects with the local analysis region of the hole, calculate the sum of the volumes of tetrahedral elements in the component solid mesh data that intersect with the local analysis region of the hole, and obtain the local solid volume. The local porosity of the current hole is calculated based on the volume of the hole and the volume of the corresponding local solid.

[0008] According to some preferred embodiments of the present invention, the volume of the hole and / or the volume of the local solid is obtained by calculating and summing the volume using the formula for the volume of a tetrahedron.

[0009] According to some preferred embodiments of the present invention, the formula for calculating the volume of the tetrahedron is as follows: In the formula, a, b, and c are the three edges connected to any node in the tetrahedron.

[0010] According to some preferred embodiments of the invention, the geometric center coordinates of the hole are obtained by calculating the center coordinates of all tetrahedral elements by a volume-weighted average.

[0011] According to some preferred embodiments of the present invention, the formula for calculating the volume-weighted average is as follows: In the formula, M represents the x, y, and z coordinates, n represents the number of tetrahedrons that make up the hole, A, B, C, and D represent the four nodes of the tetrahedron, and i is an integer from 1 to n. For example, M Ai Let x, y, z be the x, y, z coordinates of node A in the i-th tetrahedron.

[0012] According to some preferred embodiments of the invention, the equivalent region of the hole is a spherical space with its geometric center coordinates as the center, defined according to the volume of the hole.

[0013] According to some preferred embodiments of the present invention, the equivalent region of the hole is a cubic space with volume equivalent to the hole, defined by the geometric center coordinates of the hole.

[0014] According to some preferred embodiments of the invention, the periphery of the center point is a spherical or cubic region formed by extending outward from the center point to a size greater than or equal to the minimum single-sided dimension of the component entity mesh.

[0015] According to some preferred embodiments of the present invention, whether the mesh edge of the tetrahedral element intersects with the local analysis region of the hole is determined by the following method: Calculate the maximum and minimum values ​​of the x, y, and z coordinates of the four nodes of each tetrahedral element in the component entity mesh data within the area surrounding the center point, and obtain the coordinate range of the x, y, and z of the component tetrahedral elements within the area surrounding the center point. Calculate the maximum and minimum values ​​of the x, y, and z coordinates of the local analysis region to obtain the coordinate range of the x, y, and z regions of the hole region; By comparing the x, y, and z coordinate intervals of the local analysis region and the tetrahedral elements of the component, if all x, y, and z coordinate intervals of the local analysis region intersect with the coordinate intervals of the tetrahedral elements of the component, it is considered that the tetrahedral element mesh of the component intersects with the local analysis region, and the holes intersect with the solid. That is, the intersection of the tetrahedral element mesh of the component and the local analysis region includes two cases: the tetrahedral element mesh intersecting with the local analysis region and the local analysis region enclosing the tetrahedral element mesh. Both of these cases must be included in the calculation of the local solid volume.

[0016] In some embodiments, the specific steps for calculating the local solid volume are as follows: taking the center point of the equivalent region of each hole as a reference, the component solid mesh data within the range of the center point are selected to form a mesh set Stemp. By determining whether the mesh edge of each tetrahedral element in Stemp intersects with the local analysis region, it is determined whether the overall mesh of the tetrahedral element contains the hole. Through this method, all component solid tetrahedral meshes (i.e., tetrahedral element meshes of components with intersection) in the local analysis region containing the hole are filtered out and stored in the Solid local set. The sum of the volumes of these tetrahedral elements is calculated to obtain the local solid volume Vsolid local.

[0017] In some embodiments, the method for determining whether the tetrahedral element mesh of the component entity intersects with the local analysis region is as follows: Calculate the maximum and minimum values ​​of the x, y, and z coordinates of the four nodes of each tetrahedral element in the component entity mesh data within the range of the center point: maxTx, maxTy, maxTz, minTx, minTy, minTz. This yields the coordinate intervals of the component tetrahedral elements within the range: Tx=[minTx, maxTx], Ty=[minTy, maxTy], Tz=[minTz, maxTz]. Calculate the maximum and minimum x, y, and z coordinates of the local analysis region: maxCx, maxCy, maxCz, minCx, minCy, minCz, to obtain the coordinate intervals of x, y, and z of the local analysis region of the hole: Cx=[minCx, maxCx], Cy=[minCy, maxCy], Cz=[minCz, maxCz]; By comparing the x, y, and z coordinate intervals of the component tetrahedral elements within the local analysis region and the area surrounding the center point, it is considered that the component's tetrahedral element mesh intersects (crosses or encloses) with the local analysis region when all x, y, and z coordinate intervals of the local analysis region intersect with the coordinate intervals of the component tetrahedral elements within the area surrounding the center point. When (n=x, y, z), the hole intersects with the solid.

[0018] According to some preferred embodiments of the invention, the local porosity of the current hole is the ratio of the volume of the hole to the volume of the local solid corresponding to the hole.

[0019] The present invention also provides a method for characterizing the overall local porosity of a component, including the method for calculating local porosity based on CT scans as described above.

[0020] According to some preferred embodiments of the present invention, the method for characterizing the local porosity of the entire component further includes repeating the above-described calculation method for local porosity based on CT scans for all pores within the component to obtain the local porosity of the entire component.

[0021] Due to the adoption of the above technical solutions, the advantages of this invention compared with the prior art are as follows: The local porosity calculation method based on CT scan of this invention performs separate calculations for each independent hole, and can assign a quantitative local porosity index to each local area, directly reflecting the density of the area surrounding the hole; by identifying areas with high local porosity, the weak links of the component can be accurately located, providing more scientific and accurate data support for the prediction of the service life and reliability assessment of the component. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the logic flow of the method for calculating local porosity based on CT scan in an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the conversion of surface mesh data (STL) of holes (tetrahedrons) into volume mesh data in an embodiment of the present invention; Figure 3 This is a schematic diagram of an equivalent sphere or equivalent cube defined according to the volume of the hole in an embodiment of the present invention; Figure 4 This is a schematic diagram showing a local analysis area containing holes and component solid meshes in an embodiment of the present invention; Figure 5 This is a visualization cloud map showing the local porosity distribution of the entire component in a specific embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0025] This invention can accurately calculate the porosity of a local region containing any hole inside a component, and it is easily implemented through a programmed method, thus enabling quantitative characterization of the overall local porosity distribution of the component. Specifically, such as... Figures 1 to 5 As shown, the method for calculating local porosity based on CT scan data according to the present invention includes the following steps: Step S1: Digital extraction and quantification of the geometric features of the hole.

[0026] 1.1 Data Acquisition The target component is scanned by an industrial CT scanner to obtain three-dimensional geometric data describing the outer surface of the component and the inner surfaces of all its holes. This data is a triangular mesh in STL format, which is called mesh data.

[0027] 1.2 Mesh Transformation and Feature Calculation of Porous Bodies like Figure 2As shown, for each individual hole's surface mesh data, finite element preprocessing software (such as Hyperworks, ANSA, etc.) is used to convert it into a volume mesh composed of multiple tetrahedral elements. All tetrahedral elements within the hole's volume mesh are traversed, and their volumes are calculated and summed using the tetrahedral volume calculation formula to obtain the total volume (Vpore) of the hole. Then, the geometric center coordinates (Cpore) of the hole are obtained by calculating the center coordinates of all tetrahedral elements using a volume-weighted average. Finally, the center coordinates and volume data of all holes are saved to a structured file.

[0028] The formula for calculating the volume of a tetrahedron is: In the formula, a, b, and c are the three edges connected to any node in the tetrahedron.

[0029] The formula for calculating the volume-weighted average is: In the formula, M represents the x, y, and z coordinates, n represents the number of tetrahedrons that make up the hole, A, B, C, and D represent the four nodes of the tetrahedron, and i is an integer from 1 to n. For example, M Ai Let x, y, z be the x, y, z coordinates of node A in the i-th tetrahedron.

[0030] Step S2: Define the local analysis region.

[0031] 2.1 Dynamic Construction of Local Analysis Region like Figure 3 As shown, each hole is processed sequentially, and a spherical space with its geometric center coordinates (Cpore) as the center and equivalent volume is defined according to its volume (Vpore); or, a cubic space with its geometric center coordinates (Cpore) as the geometric center and equivalent volume is defined as the "local analysis region" corresponding to the hole.

[0032] Step S3: Calculate the volume of the local solid.

[0033] 3.1 Component Solid Mesh Generation The STL mesh data of the outer surface of the component is converted into the component solid mesh data composed of multiple tetrahedral elements.

[0034] 3.2 Calculation of Local Solid Volume like Figure 4 As shown, taking the center point of the equivalent region (equivalent spherical space or cubic space) of each hole (i.e., the geometric center coordinates Cpore obtained in step 1.2) as the reference, the component solid mesh within the range around the center point is selected to form a mesh set Stemp. The range around the center point is a spherical or cubic region formed by extending outward from the center point with a size greater than or equal to the minimum single-sided size of the component solid mesh, such as 1-3 times the minimum single-sided size of the component solid mesh.

[0035] By determining whether each tetrahedral mesh edge within Stemp intersects with the local analysis region, it is determined whether the tetrahedral mesh contains the hole. Using this method, all tetrahedral cell meshes of component entities containing the region (i.e., tetrahedral cell meshes of components with intersections) are filtered out and stored in the Solid local set. The sum of the volumes of these cells is calculated to obtain the local entity volume Vsolid local, which contains the entire spatial volume of the local analysis region (including the volume of component entities other than the hole and the volume of the hole), i.e., the denominator for porosity calculation.

[0036] The method for determining whether the tetrahedral element mesh of the component entity within the mesh set Stemp intersects with the local analysis domain includes the following steps: 1) Calculate the maximum and minimum values ​​of the x, y, and z coordinates of the four nodes of the tetrahedral element of the component entity within the mesh set Stemp (i.e., the area around the center point), namely maxTx, maxTy, maxTz, minTx, minTy, and minTz, to obtain the coordinate intervals of the component tetrahedron: Tx = [minTx, maxTx], Ty = [minTy, maxTy], and Tz = [minTz, maxTz]. 2) Calculate the maximum and minimum values ​​of the x, y, and z coordinates of the local analysis region: maxCx, maxCy, maxCz, minCx, minCy, and minCz. This gives the coordinate intervals of the x, y, and z coordinates of the local analysis region of the hole: Cx = [minCx, maxCx], Cy = [minCy, maxCy], and Cz = [minCz, maxCz]. 3) Compare the x, y, and z coordinate intervals of the component tetrahedral elements within the local analysis region and the area surrounding the center point. If the x, y, and z coordinate intervals of the local analysis region all intersect with the coordinate intervals of the component tetrahedral elements within that region, then it is considered whether the component tetrahedral element mesh intersects with the local analysis region. When n=x, y, z, the hole intersects with the solid, including two cases: the intersection of tetrahedral cell mesh and local analysis region, and the local analysis region wrapping tetrahedral cell mesh. Both of these cases need to be included in the calculation of the local solid volume.

[0037] Step S4: Calculation of local porosity.

[0038] The local porosity of the current pore is calculated according to the formula Plocal = Vpore / Vsolid local, and the Plocal information is stored in the Solid local set.

[0039] At this point, the calculation of the local porosity for a single hole is complete.

[0040] Step S5: Characterization of the local porosity of the entire component.

[0041] Repeating steps S1 to S4 for all pores within the component yields the overall local porosity (the local porosity of a local region within the entire component), and also the overall average porosity. By visualizing the Solidlocal element set and its corresponding local porosity values ​​in three dimensions, a local porosity distribution map of the entire component is generated, as shown below. Figure 5 As shown.

[0042] Implementation Case: This example uses an aluminum alloy (AlSi10MnMg) support manufactured using high-pressure casting technology as a component to illustrate the method for calculating local porosity. The process is as follows: Figure 1 As shown.

[0043] Step S1: Digital extraction and quantification of the geometric features of the hole.

[0044] 1.1 Data Acquisition The component was scanned using an industrial CT scanner to obtain 3D data with a voxel resolution of 4μm. STL files of the outer surface and the inner surface with holes were exported using VGStudio MAX software. The following steps were performed on the STL file of a key hole, "Pore01".

[0045] 1.2 Mesh Transformation and Feature Calculation of Porous Bodies (Refer to...) Figure 2 ) Import the "Pore01.stl" file into the finite element preprocessing software to convert the triangular mesh on the hole surface into a volume mesh composed of 357 tetrahedral elements.

[0046] By traversing all tetrahedral elements within the mesh of the hole, calculating and summing the volumes using the tetrahedral volume formula, the total volume of the hole is obtained as VPore01 = 0.125 mm. 3 The geometric center coordinates of the hole are obtained by calculating the center coordinates of all tetrahedral elements using a volume-weighted average, which is CPore01 = (15.5, 42.1, 88.7). This information is saved to the file "Pore Features.csv".

[0047] Step S2: Define the local analysis region.

[0048] For the hole "Pore01", an equivalent cubic space is selected as the local analysis region corresponding to the hole. The calculated equivalent side length Leq = 0.5 mm. This region is a cube with a side length of 0.5 mm centered at the point (15.5, 42.1, 88.7). Figure 3 As shown.

[0049] Step S3: Calculate the volume of the local solid.

[0050] 3.1 Component Solid Mesh Generation Similarly, the STL file of the outer surface of the component is used to generate a solid mesh of the component composed of multiple tetrahedral elements in the finite element preprocessing software.

[0051] 3.2 Calculation of Local Solid Volume Following the aforementioned steps for determining whether the tetrahedral element mesh of the component entity within the perimeter of the center point intersects with the local analysis region and for calculating the local entity volume, within this cube-shaped region, all tetrahedral element meshes of the component entity that contain the local analysis region (and intersect with it) are selected, and their sum of volumes is calculated as Vsolidlocal = 0.613 mm. 3 .

[0052] Step S4: Calculation of local porosity.

[0053] Calculate the local porosity: Plocal=VPore01 / Vsolidlocal =0.125 / 0.613= 20.4%.

[0054] Step S5: Characterization of the local porosity of the entire component.

[0055] Repeat the above steps for all holes, and import the coordinates of all holes and their local porosity values ​​into post-processing software (such as the Python matplotlib module or finite element software such as Gmsh or Hyperworks) for 3D visualization. Figure 5 As shown, the "Pore01" area is highlighted in red due to its local porosity reaching 20.4%, clearly indicating that this is a high-risk area. The overall average porosity of the component is only 0.001%, meaning that this significant hidden danger would be overlooked if evaluated using traditional methods (which only calculate the overall average porosity of the component).

[0056] Compared with the prior art, the present invention has the following beneficial effects: 1. Achieved a leap from "macroscopic average" to "microscopic local": The method of this invention assigns a quantitative local porosity index to each local area inside the component, which directly reflects the density of the area surrounding the hole.

[0057] 2. Significantly improves the accuracy and guidance of defect evaluation: By identifying areas with high local porosity, the weak points of components can be accurately located, providing more scientific and accurate data support for component service life prediction and reliability assessment.

[0058] 3. It provides a strong basis for optimizing manufacturing processes: By analyzing the distribution pattern of local porosity, problems in the manufacturing process can be deduced and diagnosed, and clear guidance can be provided for optimizing process parameters.

[0059] 4. The method is highly versatile and easy to implement: This method is based on the standard STL data format and mature finite element preprocessing technology. The calculation process is clear and easy to automate through programming, making it highly valuable for engineering applications.

[0060] The above embodiments prepared by the method of the present invention are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for calculating local porosity based on CT scans, characterized in that, Includes the following steps: The component is scanned using a CT scanning device to obtain grid data of the outer surface of the component and the inner surface of all its holes; For each individual hole's inner surface mesh data, finite element preprocessing software is used to convert it into hole volume mesh data composed of multiple tetrahedral elements; Based on the hole's volumetric mesh data, the volume of the hole and the coordinates of its geometric center are obtained. The mesh data of the outer surface of the component is converted into the mesh data of the component solid body composed of multiple tetrahedral elements; Each hole is processed sequentially. Based on the volume of a hole and the corresponding geometric center coordinates, the equivalent region of the hole is obtained, which serves as the local analysis region for that hole. Using the center point of the equivalent region of each hole as a reference, select the component solid mesh data within the surrounding area of ​​the center point, determine whether the mesh edge of each tetrahedral element in the component solid mesh data within the surrounding area of ​​the center point intersects with the local analysis region of the hole, calculate the sum of the volumes of tetrahedral elements in the component solid mesh data that intersect with the local analysis region of the hole, and obtain the local solid volume. The local porosity of the current hole is calculated based on the volume of the hole and the volume of the corresponding local solid. Whether the mesh edge of the tetrahedral element intersects with the local analysis region of the hole is determined by the following method: Calculate the maximum and minimum values ​​of the x, y, and z coordinates of the four nodes of each tetrahedral element in the component entity mesh data within the area surrounding the center point, and obtain the coordinate range of the x, y, and z of the component tetrahedral elements within the area surrounding the center point. Calculate the maximum and minimum values ​​of the x, y, and z coordinates of the local analysis region to obtain the coordinate range of the x, y, and z regions of the hole region; By comparing the x, y, and z coordinate intervals of the local analysis region and the tetrahedral element of the component, it is considered that the tetrahedral element mesh of the component intersects with the local analysis region when the x, y, and z coordinate intervals of the local analysis region all intersect with the coordinate intervals of the tetrahedral element of the component. The local porosity of a hole is the ratio of the hole's volume to the volume of the corresponding local solid.

2. The calculation method according to claim 1, characterized in that, The volume of the hole and / or the volume of the local solid are obtained by calculating and summing the volume using the formula for the volume of a tetrahedron.

3. The calculation method according to claim 2, characterized in that, The formula for calculating the volume of the tetrahedron is: In the formula, a, b, and c are the three edges connected to any node in the tetrahedron.

4. The calculation method according to claim 1, characterized in that, The geometric center coordinates of the hole are obtained by calculating the center coordinates of all tetrahedral elements by a volume-weighted average.

5. The calculation method according to claim 4, characterized in that, The formula for calculating the volume-weighted average is as follows: In the formula, M represents the x, y, and z coordinates, n represents the number of tetrahedrons that make up the hole, A, B, C, and D represent the four nodes of the tetrahedron, and i represents an integer from 1 to n.

6. The calculation method according to claim 1, characterized in that, The equivalent region of the hole is defined as a spherical space with its geometric center coordinates as the center, and whose volume is equivalent to that of the hole.

7. The calculation method according to claim 1, characterized in that, The equivalent region of the hole is defined as a cubic space with its geometric center coordinates as its geometric center, based on the volume of the hole.

8. The calculation method according to claim 6 or 7, characterized in that, The area surrounding the center point is a spherical or cubic region formed by extending outward from the center point in a direction greater than or equal to the minimum single-sided dimension of the component's solid mesh.

9. A method for characterizing the local porosity of a component as a whole, characterized in that, The characterization method includes the method for calculating local porosity based on CT scans as described in any one of claims 1-8.

10. The characterization method according to claim 9, characterized in that, The characterization method further includes repeating the CT scan-based local porosity calculation method on all pores within the component to obtain the overall local porosity of the component.

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