Fracture toughness calculation method based on fracture morphology three-dimensional representation

Abstract

The invention relates to the technical field of titanium alloy material engineering, in particular to a fracture toughness calculation method based on fracture morphology three-dimensional characterization. According to the method, the three-dimensional expansion area of the crack is counted through a three-dimensional characterization means, the fracture toughness is calculated, the method for calculating the fracture toughness by counting the three-dimensional expansion area of the crack is innovatively provided, and a corresponding calculation formula is provided. According to a traditional method, a crack propagation path is counted through fracture section metallography, three-dimensional characteristics of crack propagation are ignored, the three-dimensional crack propagation path is represented and counted, and a corresponding calculation model is optimized. Compared with a traditional method, the method has the advantages that the model is closer to reality, the statistical method is more accurate and reliable, the error between the result and the reality is small, and the method can be applied to the engineering technical field of titanium alloy microstructure design, performance regulation and control and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy material engineering, and in particular to a fracture toughness calculation method based on three-dimensional characterization of fracture morphology. The method can be used in the technical fields of titanium alloy microstructure design and performance regulation. Background Art

[0002] Titanium alloys are widely used in aviation, aerospace, and shipbuilding due to their excellent specific strength, corrosion resistance, and high temperature resistance. As a structural material, the fracture toughness of titanium alloys is a key indicator for evaluating performance. By deeply analyzing the components of fracture toughness, establishing a formula to predict the fracture toughness of titanium alloys, and reversely speculating on methods to improve fracture toughness, it can guide the design and preparation of new titanium alloys.

[0003] The existing calculation method of titanium alloy fracture toughness based on crack propagation tortuosity is not very accurate. The fundamental reason is that crack propagation is a three-dimensional propagation process, and the existing method replaces the three-dimensional process by characterizing the two-dimensional crack propagation path on a certain cross section, which has a large error. Summary of the invention

[0004] The purpose of the present invention is to provide a fracture toughness calculation method based on three-dimensional characterization of fracture morphology, which method has higher accuracy.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A fracture toughness calculation method based on three-dimensional characterization of fracture morphology, the method comprising the following steps:

[0007] Step 1: Characterize the macroscopic morphology of the fracture surface of the fracture toughness sample and calculate the two-dimensional areas of the crack initiation zone, propagation zone and shear lip zone;

[0008] Step 2: Characterize the three-dimensional area of ​​the fracture in different regions and calculate the overall crack propagation tortuosity;

[0009] Step 3: Prepare smooth tensile and Young's modulus samples and measure the physical and mechanical properties;

[0010] Step 4: Calculate the intrinsic toughness and ultimate fracture toughness according to the formula.

[0011] In the fracture toughness calculation method based on three-dimensional characterization of fracture morphology, in step 1, the arc model is used to calculate the two-dimensional area S of the shear lip region:

[0012]

[0013] Where a is the semi-major axis of a single shear lip area (mm), b is the height of the shear lip area (mm), r is the radius of the fitting circle (mm), and S is the area of ​​a single shear lip area (mm). 2 ).

[0014] The fracture toughness calculation method based on three-dimensional characterization of fracture morphology, in the actual measurement process, assumes that the shape of the shear lip area is a partial arc of a complete ellipse, and the portion between the highest point of the shear lip area and the pre-crack is counted as the area statistical area; first, the highest point of the shear lip area on the two-dimensional fracture surface is confirmed, which is the vertex of the assumed arc, and the vertical distance from this point to the side of the fracture toughness sample is the height b of the shear lip area, and the vertical distance from this point to the pre-crack is the semi-major axis a of the shear lip area; then, the area S of the shear lip area is directly calculated by substituting it into the formula.

[0015] The fracture toughness calculation method based on three-dimensional characterization of fracture morphology is as follows: in the actual measurement process, the shear lip is divided into a crack initiation zone, an extension zone and a shear lip zone according to the test part; in some alloys, there is no obvious difference between the crack initiation zone and the extension zone, and they can be regarded as the same area; a white light interferometer or a laser confocal microscope is used to measure the three-dimensional morphology of each area, and each measurement area should be as large as possible, while ensuring that the area without data in each measurement result shall not exceed 10%; each area is sampled at least twice, and the average value is taken in the calculation.

[0016] In the fracture toughness calculation method based on three-dimensional characterization of fracture morphology, in step 2, the tortuosity calculation process of each region must comply with standard ISO 25178-2.

[0017] In the fracture toughness calculation method based on three-dimensional characterization of fracture morphology, in step 2, the overall extension tortuosity is calculated by weighting based on the size of the two-dimensional area.

[0018] In the fracture toughness calculation method based on three-dimensional characterization of fracture morphology, in step 3, the mechanical properties are measured by room temperature tensile testing in accordance with the national standard GB / T228.1-2021 "Metallic Materials Tensile Test Part 1: Room Temperature Test Method".

[0019] In the fracture toughness calculation method based on three-dimensional characterization of fracture morphology, in step 3, the physical properties of Young's modulus and Poisson's ratio are measured in accordance with the national standard GB / T22315-2008 "Test method for elastic modulus and Poisson's ratio of metallic materials".

[0020] The fracture toughness calculation method based on three-dimensional characterization of fracture morphology, during the sampling process, takes a Young's modulus sample parallel to the fracture surface at the same position close to the fracture surface, and performs physical property testing, at least two groups of parallel samples are taken and the average value of the measured properties is taken.

[0021] The fracture toughness calculation method based on three-dimensional characterization of fracture morphology, in step 4, calculates the fracture toughness according to the following formula

[0022]

[0023] Where k is 0.001, E is Young's modulus (MPa), v is Poisson's ratio, ε u is the elongation after fracture (%), σ y is the yield strength (MPa), σ UST is the tensile strength (MPa), S 3 A is the three-dimensional area of ​​the area statistics area, S 2 A is the two-dimensional area of ​​the area statistics area, and i is the area number.

[0024] The design idea of ​​the present invention is:

[0025] Compared with existing calculation methods, the present invention focuses on the three-dimensional crack expansion path, accurately characterizes the three-dimensional area of ​​the fracture surface through white light interferometer or laser confocal and other means, and calculates the overall three-dimensional expansion tortuosity. At the same time, the present invention establishes an intrinsic toughness calculation model based on the energy release rate, and establishes an external toughening calculation model based on the three-dimensional area characterization and three-dimensional expansion tortuosity. Compared with existing methods, the present invention predicts the fracture toughness values ​​of different materials with an error of less than 5%, and can calculate stable results for fracture toughness samples of different thicknesses. Therefore, the present invention has high accuracy and universality.

[0026] The advantages and beneficial effects of the present invention are:

[0027] The present invention uses three-dimensional characterization to count the three-dimensional crack extension area and calculate the fracture toughness. It innovatively proposes a method for calculating the fracture toughness by counting the three-dimensional crack extension area and proposes a corresponding calculation formula. The traditional method counts the crack extension path by metallographic analysis of the fracture section, ignoring the three-dimensional characteristics of crack extension. The present invention characterizes and counts the three-dimensional crack extension path and optimizes the corresponding calculation model. Compared with the traditional method, the model of the present invention is closer to reality, the statistical method is more accurate and reliable, and the result has a smaller error with the actual situation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of area statistics.

[0029] Figure 2 This is the fracture morphology in Example 1.

[0030] Figure 3 Characterization of the three-dimensional morphology of different regions in Example 1: (a) crack initiation zone (region I); (b) crack propagation zone (region II); (c) shear lip zone (region III).

[0031] Figure 4 Characterization of the three-dimensional morphology of different regions in Example 2: (a) crack initiation (extension) zone (region I); (b) shear lip zone (region II).

[0032] Figure 5 Characterization of the three-dimensional morphology of different regions in Example 3: crack initiation (extension) zone (region I); (b) shear lip zone (region II). DETAILED DESCRIPTION

[0033] like Figure 1 As shown in the figure, when calculating the two-dimensional area, only the part between the highest point of the shear lip area and the pre-crack is counted as the area statistical area. In actual measurement, we assume that the shape of the shear lip area is a partial arc of a complete ellipse, and confirm the highest point of the shear lip area on the two-dimensional fracture surface, which is the vertex of the assumed arc. Figure 2 As shown, place the shear lip in Figure 1 The test part is divided into crack initiation zone I, expansion zone II and shear lip zone III (in some alloys, there is no obvious difference between crack initiation zone I and expansion zone II, and they can be regarded as the same area). In the present invention, a high-precision instrument (such as white light surface topography interferometer) is used to characterize the three-dimensional area (S 3 A).

[0034] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0035] Embodiment 1:

[0036] The fracture toughness value K of a high-toughness titanium alloy was measured IC for The fracture toughness value is calculated using a 30 mm thick CT specimen:

[0037] The fracture morphology of the CT specimen was simply characterized by using a stereo microscope (or other similar methods), and the crack initiation zone I, crack extension zone II, shear lip zone III and instantaneous fracture zone IV were divided. The characterization results are shown in Figure 2 shown.

[0038] By determining the highest point of the shear lip area, the semi-major axis (half of the major axis) of the shear lip area was measured, a = 15 mm, b = 3 mm. r = 39 mm, S = 61.8 mm was calculated. 2 .

[0039] White light interferometry (or other similar methods) was used to characterize the three-dimensional area of ​​the crack initiation zone, crack propagation zone, and shear lip zone. The characterization results are shown in Figure 2. Figure 3 shown.

[0040] According to ISO 25178-2 standard, the three-dimensional area was counted and the three-dimensional tortuosity of each area was calculated. The tortuosity of the crack initiation zone in area I is 1.74, the tortuosity of the crack propagation zone in area II is 1.93, and the tortuosity of the shear lip zone in area III is 2.85.

[0041] The overall crack propagation tortuosity calculated based on the weighted two-dimensional area size is 1.974.

[0042] Take the fracture surface as the symmetry axis, take a tensile test specimen perpendicular to the fracture surface near the fracture toughness sample sampling position; take a Young's modulus specimen parallel to the fracture surface at the same position close to the fracture surface for mechanical and physical property testing. Take at least 2 sets of parallel samples for tensile and Young's modulus and take the average value of the measured properties.

[0043] According to the national standard GB / T228.1-2021 "Tensile test of metal materials Part 1: Room temperature test method", the average yield strength of the tensile samples was measured to be 979MPa, the average tensile strength was 1070MPa, and the average elongation after fracture was 16.2%.

[0044] According to the national standard GB / T22315-2008 "Test method for elastic modulus and Poisson's ratio of metallic materials", the average Young's modulus of the sample was measured to be 115020MPa, and the average Poisson's ratio was 0.329.

[0045] According to the fracture toughness calculation formula:

[0046]

[0047] Substitute the calculated fracture toughness into In this embodiment, the error between the fracture toughness calculated by the present invention and the actual fracture toughness is 1.1%, which proves that the calculation method and results of the present invention are accurate and reliable.

[0048] Embodiment 2:

[0049] Commonly used titanium alloy TC4, the fracture toughness value K IC for The fracture toughness value is calculated using a 30 mm thick CT specimen:

[0050] The fracture morphology of the CT specimen was simply characterized using a stereo microscope (or other similar methods), and was divided into crack extension zone I (there was no obvious difference in the initiation and extension zone), shear lip zone II and instantaneous fracture zone III.

[0051] By determining the highest point of the shear lip area, the semi-major axis of the shear lip area was measured to be a = 14 mm, b = 4 mm. r = 26.5 mm, S = 75.9 mm was calculated. 2 .

[0052] White light interferometry (or other similar methods) was used to characterize the three-dimensional area of ​​the crack initiation zone, crack propagation zone, and shear lip zone. The characterization results are shown in Figure 2. Figure 4 shown.

[0053] According to ISO 25178-2 standard, the three-dimensional area was counted and the three-dimensional tortuosity of each area was calculated. The tortuosity of the crack initiation (extension) zone in area I is 2.12, and the tortuosity of the shear lip zone in area II is 3.15.

[0054] The overall crack propagation tortuosity calculated based on the weighted two-dimensional area size is 2.31.

[0055] Take the fracture surface as the symmetry axis, take a tensile test specimen perpendicular to the fracture surface near the fracture toughness sample sampling position; take a Young's modulus specimen parallel to the fracture surface at the same position close to the fracture surface for mechanical and physical property testing. Take at least 2 sets of parallel samples for tensile and Young's modulus and take the average value of the measured properties.

[0056] According to the national standard GB / T228.1-2021 "Tensile test of metal materials Part 1: Room temperature test method", the average yield strength of the tensile samples was measured to be 843.5MPa, the average tensile strength was 914.5MPa, and the average elongation after fracture was 10.75%.

[0057] According to the national standard GB / T22315-2008 "Test method for elastic modulus and Poisson's ratio of metallic materials", the average Young's modulus of the Young's modulus samples was measured to be 110,000 MPa, and the average Poisson's ratio was 0.34.

[0058] According to the fracture toughness calculation formula:

[0059]

[0060] Substitute the calculated fracture toughness into In this embodiment, the error between the fracture toughness calculated by the present invention and the actual fracture toughness is 3.3%, which proves that the calculation method and results of the present invention are accurate and reliable.

[0061] Embodiment 3:

[0062] The fracture toughness value K of a high-toughness titanium alloy was measured IC for The fracture toughness value is calculated using a 30 mm thick CT specimen:

[0063] The fracture morphology of the CT specimen was simply characterized using a stereo microscope (or other similar methods), and was divided into crack extension zone I (there was no obvious difference in the initiation and extension zone), shear lip zone II and instantaneous fracture zone III.

[0064] By determining the highest point of the shear lip area, the semi-major axis of the shear lip area was measured to be a = 16mm, b = 7mm. The calculated r = 21.79mm, S = 154.9mm 2 .

[0065] White light interferometry (or other similar methods) was used to characterize the three-dimensional area of ​​the crack initiation zone, crack propagation zone, and shear lip zone. The characterization results are shown in Figure 2. Figure 5 shown.

[0066] According to ISO 25178-2 standard, the three-dimensional area was counted and the three-dimensional tortuosity of each area was calculated. The tortuosity of the crack initiation (extension) zone in area I is 2.05, and the tortuosity of the shear lip zone in area II is 3.11.

[0067] The overall crack propagation tortuosity calculated based on the weighted two-dimensional area size is 2.39.

[0068] Take the fracture surface as the symmetry axis, take a tensile test specimen perpendicular to the fracture surface near the fracture toughness sample sampling position; take a Young's modulus specimen parallel to the fracture surface at the same position close to the fracture surface for mechanical and physical property testing. Take at least 2 sets of parallel samples for tensile and Young's modulus and take the average value of the measured properties.

[0069] According to the national standard GB / T228.1-2021 "Tensile test of metal materials Part 1: Room temperature test method", the average yield strength of the tensile samples was measured to be 831.5MPa, the average tensile strength was 911MPa, and the average elongation after fracture was 16.75%.

[0070] According to the national standard GB / T22315-2008 "Test method for elastic modulus and Poisson's ratio of metallic materials", the average Young's modulus of the sample was measured to be 107000MPa, and the average Poisson's ratio was 0.31.

[0071] According to the fracture toughness calculation formula:

[0072]

[0073] Substitute the calculated fracture toughness into In this embodiment, the error between the fracture toughness calculated by the present invention and the actual fracture toughness is 1.6%, which proves that the calculation method and results of the present invention are accurate and reliable.

Claims

1. A fracture toughness calculation method based on three-dimensional characterization of fracture morphology, characterized in that: The method comprises the following steps: Step 1: Characterize the macroscopic morphology of the fracture surface of the fracture toughness sample and calculate the two-dimensional areas of the crack initiation zone, propagation zone and shear lip zone; Step 2: Characterize the three-dimensional area of ​​the fracture in different regions and calculate the overall crack propagation tortuosity; Step 3: Prepare smooth tensile and Young's modulus samples and measure the physical and mechanical properties; Step 4: Calculate the intrinsic toughness and ultimate fracture toughness according to the formula.

2. The fracture toughness calculation method based on three-dimensional characterization of fracture morphology according to claim 1 is characterized in that: In step 1, the arc model is used to calculate the two-dimensional area S of the shear lip area: Where a is the semi-major axis of a single shear lip area (mm), b is the height of the shear lip area (mm), r is the radius of the fitting circle (mm), and S is the area of ​​a single shear lip area (mm). 2 ).

3. The fracture toughness calculation method based on three-dimensional characterization of fracture morphology according to claim 2 is characterized in that: In the actual measurement process, it is assumed that the shape of the shear lip area is a partial arc of a complete ellipse, and the portion between the highest point of the shear lip area and the pre-crack is counted as the area statistical area; first, the highest point of the shear lip area on the two-dimensional fracture surface is confirmed. This point is the vertex of the assumed arc, and the vertical distance from this point to the side of the fracture toughness sample is the height b of the shear lip area, and the vertical distance from this point to the pre-crack is the semi-major axis a of the shear lip area; then, the area S of the shear lip area is directly calculated by substituting it into the formula.

4. The fracture toughness calculation method based on three-dimensional characterization of fracture morphology according to claim 2 is characterized in that: In the actual measurement process, the shear lip is divided into crack initiation zone, expansion zone and shear lip zone according to the test part; in some alloys, there is no obvious difference between the crack initiation zone and the expansion zone, and they can be regarded as the same area; a white light interferometer or a laser confocal microscope is used to measure the three-dimensional morphology of each area. The measurement area should be as large as possible each time, and at the same time, it should be ensured that the area with no data in each measurement result shall not exceed 10%; each area is sampled at least twice, and the average value is taken in the calculation.

5. The fracture toughness calculation method based on three-dimensional characterization of fracture morphology according to claim 1 is characterized in that: In step 2, the calculation process of the tortuosity of each area must follow the standard ISO 25178-2.

6. The fracture toughness calculation method based on three-dimensional characterization of fracture morphology according to claim 1 is characterized in that: In step 2, the overall extension tortuosity is calculated by weighting based on the size of the two-dimensional area.

7. The fracture toughness calculation method based on three-dimensional characterization of fracture morphology according to claim 1 is characterized in that: In step 3, the mechanical properties are measured by room temperature tensile test in accordance with the national standard GB / T228.1-2021 "Tensile test of metallic materials Part 1: Room temperature test method".

8. The fracture toughness calculation method based on three-dimensional characterization of fracture morphology according to claim 1 is characterized in that: In step 3, the physical properties of Young's modulus and Poisson's ratio should be determined according to the national standard GB / T22315-2008 "Test method for elastic modulus and Poisson's ratio of metallic materials".

9. The fracture toughness calculation method based on three-dimensional characterization of fracture morphology according to claim 8, characterized in that: During the sampling process, take a Young's modulus sample parallel to the fracture surface at the same position close to the fracture surface for physical property testing. Take at least 2 groups of parallel samples and take the average value of the measured properties.

10. The fracture toughness calculation method based on three-dimensional characterization of fracture morphology according to claim 1, characterized in that: In step 4, the fracture toughness is calculated according to the following formula Where k is 0.001, E is Young's modulus (MPa), v is Poisson's ratio, ε u is the elongation after fracture (%), σ y is the yield strength (MPa), σ UST is the tensile strength (MPa), S3A is the three-dimensional area of ​​the area statistics area, S2A is the two-dimensional area of ​​the area statistics area, and i is the area number.

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