Method for testing interlayer tensile strength of ceramic matrix composite material

Abstract

The invention discloses a method for testing interlayer tensile strength of a ceramic matrix composite material. Comprising the following steps: acquiring the geometric dimension of a sample, performing surface treatment on a test surface of the sample, marking a test section of the sample, acquiring the geometric dimension of a four-point bending clamp, determining a placement mode of the sample and a camera, and capturing a displacement field of the test surface of the sample by using the camera while performing a curved beam four-point bending test. Obtaining the load value and stroke of the first load drop, extracting the in-situ strain of the sample by using a camera, deducing a formula for calculating the interlayer radial and tangential modulus ratio of the sample, carrying out calculation, and calculating the interlayer tensile strength of the sample by using the existing formula. According to the method disclosed by the invention, the modulus ratio of the interlayer radial direction to the interlayer tangential direction is obtained by using in-situ strain, the problem that the interlayer radial modulus is difficult to accurately determine directly through the test is solved, and the accuracy of the interlayer tensile strength of the ceramic matrix composite material measured through the curved beam four-point bending test is improved.

Description

Technical Field

[0001] The invention relates to a method for testing the tensile strength between layers of a material, in particular to a method for testing the tensile strength between layers of a ceramic matrix composite material, and belongs to the technical field of aerospace. Background Art

[0002] In the aerospace field, ceramic matrix composites (CMCs) offer excellent properties, such as high-temperature resistance, lightweight, high strength-to-modulus ratio, good toughness, low thermal expansion, and insensitivity to cracks and notches. They are commonly used in hypersonic aircraft components and next-generation aircraft engines. When CMCs are subjected to shear and bending loads as L-shaped thin-walled structures, interlaminar delamination is the primary failure mode. These structures are often simplified into composite curved beams. Studying their interlaminar tensile strength (ILTS) is crucial for improving aircraft safety and reliability.

[0003] Currently, the characterization of ILTS in composite materials is gaining attention. Measurement methods are primarily targeted at polymer-based composites, but the ILTS calculation methods for ceramic-based and polymer-based materials can benefit from each other. Widely recognized measurement standards are ASTM D7291 and ASTM D6415. The former is a direct loading method, measuring ILTS using a plane tension test. However, due to difficulties in meeting laminate thickness requirements, ILTS values are unreliable and potentially conservative. The latter is an indirect loading method, measuring ILTS using a four-point bending test on a curved beam. While this testing method has advantages and is widely adopted, it requires prior knowledge of the ratio of the tangential to radial Young's modulus. The radial Young's modulus is difficult to measure directly experimentally, and using an approximate value can differ from the actual value. Therefore, existing methods for measuring ILTS in CMC curved beams have shortcomings, and new methods are needed to address these issues and meet the demands of CMC material performance research. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for testing the interlaminar tensile strength of ceramic matrix composite materials in order to solve at least one of the above technical problems.

[0005] The present invention achieves the above-mentioned object through the following technical solution: a method for testing the interlaminar tensile strength of a ceramic matrix composite material, the testing method comprising the following steps:

[0006] S1. Obtain the geometric dimensions of the specimen and perform surface treatment on the test surface of the specimen;

[0007] S2. Marking the test section of the sample;

[0008] S3. Obtain the geometric dimensions of the four-point bending fixture and determine the placement of the specimen and camera;

[0009] S4. Perform a four-point bending test on the specimen using a four-point bending fixture, and use a camera to capture the displacement field of the specimen test surface.

[0010] S5. Apply pressure to the four-point bending fixture using a testing machine to obtain the load value and stroke of the first load drop, and use a camera to extract the in-situ strain of the specimen;

[0011] S6. Derive the formula for calculating the ratio of the modulus between the radial and tangential directions of the interlayers of the specimen and perform the calculation;

[0012] S7. Calculate the interlaminar tensile strength of the specimen.

[0013] As a further solution of the present invention: in S1, the specimen is an "L"-shaped specimen in the shape of a curved beam, and the plane of the specimen is formed by two identical rectangles connected by a circular ring, and the circular ring is perpendicular to the plane;

[0014] The geometric dimensions of the specimen include the length of the plane rectangle of the "L"-shaped specimen, the width of the plane rectangle of the "L"-shaped specimen, the radius of the inner ring of the circular ring, the radius of the outer ring of the circular ring, and the width of the "L"-shaped specimen;

[0015] The test surface of the sample is the plane of the "L"-shaped test piece. The surface treatment of the test surface of the sample includes applying evenly distributed matte white paint on the test surface of the sample, and then spraying matte black paint on the matte white paint to form random spots.

[0016] As a further solution of the present invention: in S2, the test section is the connection of the "L"-shaped test piece;

[0017] The marking process includes marking arcs on the test section of the specimen close to the inner diameter side of the ring and close to the outer diameter side of the ring, respectively, and recording the radii of the two arcs.

[0018] As a further solution of the present invention: in S3, the geometric dimensions of the four-point bending fixture include an upper span, a lower span, and a pressure head diameter;

[0019] The specimen is placed symmetrically on the four-point bending fixture, the camera faces the test surface of the specimen, and the light sources are placed symmetrically on both sides of the camera.

[0020] As a further solution of the present invention: in S5, the in-situ strain of the sample includes the radial strain and the tangential strain at the midpoint of the two arcs at the marked position of the connection of the "L"-shaped specimen.

[0021] As a further solution of the present invention: in S6, based on the anisotropic plate theory, the stress component expression of the test section with cylindrical anisotropy is:

[0022]

[0023] in:

[0024]

[0025] Where: r and θ are the radial and tangential directions of the cylindrical coordinates, M represents the bending moment, r i and r o are the inner and outer diameters of the specimen, w is the width of the specimen, E r and E θ are Young's modulus in the interlayer radial and interlayer tangential directions, σ r and σ θ are the radial stress and tangential stress between layers, k, λ and g are parameters used for strength calculation.

[0026] As a further solution of the present invention: Since the test section with cylindrical anisotropy is also orthotropic, the strain component expression is:

[0027]

[0028] Where: ε r and ε θ are radial strain and tangential strain, ν r and ν θ is Poisson's ratio;

[0029] Due to orthotropy, the relationship between Young's modulus and Poisson's ratio is written as:

[0030]

[0031] Where: r i and r o are the inner and outer diameters of the specimen, E r and E θ is the Young's modulus in the interlayer radial and interlayer tangential directions.

[0032] As a further solution of the present invention, the ratio of the Young's modulus between the radial direction and the tangential direction between the layers is obtained by the following steps, specifically including:

[0033] The arc radius of the test section close to the inner diameter of the ring is recorded as r1 and the arc radius of the test section close to the outer diameter of the ring is recorded as r2. Substitute them into the strain component expression respectively, and combine them with the relationship between Young's modulus and Poisson's ratio to obtain:

[0034]

[0035] Where: (r1) and (r2) represent arcs with radii r1 and r2, respectively;

[0036] Combining the stress component expression with the relationship between Young's modulus and Poisson's ratio, the relationship between the interlayer radial and interlayer tangential Young's modulus ratio k and the strain component is obtained:

[0037]

[0038] Based on the above formula and using the extracted in-situ strain of the sample, the ratio k of the Young's modulus between the radial direction and the tangential direction of the interlayer is calculated.

[0039] As a further embodiment of the present invention: In S7, the interlaminar tensile strength of the sample is calculated using the formula for obtaining the interlaminar tensile strength of the sample in ASTM D6415, the standard test method for measuring the bending beam strength of fiber-reinforced beams, and the bending beam strength of the sample is:

[0040]

[0041] in:

[0042]

[0043] d x =(l b -l t ) / 2

[0044] Where: P and Δ are the load value and stroke of the first load drop, w and t are the width and thickness of the specimen, l b 、l t and D are the upper span, lower span and indenter diameter of the four-point bending fixture, φ i =45°, M represents bending moment, d x and d y are the horizontal and vertical distances between two adjacent top and bottom load bars, respectively, and φ represents the angle between the specimen legs and the horizontal plane.

[0045] As a further solution of the present invention: Based on the formula for obtaining the interlaminar tensile strength of a specimen in ASTM D6415, the standard test method for measuring the bending strength of fiber-reinforced beams, the interlaminar tensile strength of the specimen is:

[0046]

[0047] in:

[0048]

[0049] Where: r m is the radial position of the maximum interlaminar (radial) tensile stress.

[0050] The beneficial effects of the present invention are as follows: the testing method adopted by the present invention uses digital image correlation technology to capture the surface displacement field of the sample, obtains and utilizes the in-situ strain of the sample to obtain the interlayer radial modulus and interlayer tangential modulus ratio, solves the problem that it is difficult to accurately determine the interlayer radial modulus directly through experiments, and improves the accuracy of the interlayer tensile strength of the ceramic matrix composite material measured by the curved beam four-point bending test. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a flow chart of the present invention;

[0052] Figure 2 A schematic structural diagram of a sample according to a specific embodiment of the present invention;

[0053] Figure 3 A schematic diagram of a marking area of a sample according to a specific embodiment of the present invention;

[0054] Figure 4 Schematic diagram of the structure of a four-point bending fixture according to a specific embodiment of the present invention;

[0055] Figure 5 A schematic diagram of the placement of a sample and a camera according to a specific embodiment of the present invention;

[0056] Figure 6 This is a load-displacement response image of a sample during the loading process recorded by a testing machine according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0058] Example 1, as Figure 1 As shown, a method for testing the interlaminar tensile strength of a ceramic matrix composite material comprises the following steps:

[0059] S1. Obtain the geometric dimensions of the specimen and perform surface treatment on the test surface of the specimen.

[0060] The specimen is an "L"-shaped specimen. The shape of the specimen is a curved beam. The plane of the specimen is formed by two identical rectangles connected by a 90° circular ring. At the same time, the 90° circular ring is perpendicular to the plane and has a certain width.

[0061] The geometric dimensions of the specimen include: the length of the right-angled side of the "L"-shaped specimen (the length of the plane rectangle), the thickness of the right-angled side of the "L"-shaped specimen (the width of the plane rectangle), the radius of the inner ring of the ring, the radius of the outer ring of the ring and the width of the "L"-shaped specimen (the width of the specimen);

[0062] The test surface of the sample is the plane of the "L"-shaped test piece. The surface treatment of the test surface of the sample includes applying evenly distributed matte white paint (white primer) on the test surface of the sample, and then spraying matte black paint on the matte white paint to form random spots.

[0063] S2. Mark the test section of the sample.

[0064] The test section refers to the connection of the "L" shaped specimen;

[0065] The marking process includes marking an arc with a length of one quarter of a circle on the test section of the specimen close to the inner diameter side of the ring and close to the outer diameter side of the ring, respectively, and recording the radius of the two arcs.

[0066] S3. Obtain the geometric dimensions of the four-point bending fixture and determine the placement of the specimen and camera.

[0067] The geometric dimensions of the four-point bending fixture include the upper span, lower span, and indenter diameter;

[0068] The specimen is placed symmetrically on the four-point bending fixture, the camera faces the test surface of the specimen, and the light sources are placed symmetrically on both sides of the camera.

[0069] S4. A four-point bending test of the curved beam is performed on the specimen based on a four-point bending fixture, and the displacement field of the specimen surface (test surface) is captured using digital image correlation technology (camera).

[0070] S5. Apply pressure to the four-point bending fixture through the testing machine to obtain the load value and stroke of the first load drop, and use digital image correlation technology (camera) to extract the in-situ strain of the specimen.

[0071] The in-situ strain of the specimen includes the radial strain and tangential strain at the midpoint of the two arcs at the connection mark position of the “L”-shaped specimen.

[0072] S6. Derive the formula for calculating the ratio of the modulus between the radial and tangential directions of the specimen, and perform the calculation.

[0073] The new formula for calculating the ratio of the modulus between the radial and tangential directions of the interlayer of the sample is derived as follows:

[0074] Based on the anisotropic plate theory, the stress component expressions of the test section with cylindrical anisotropy are:

[0075]

[0076] in:

[0077]

[0078] Where: r and θ are the radial and tangential directions of the cylindrical coordinates, M represents the bending moment, r i and r o are the inner and outer diameters of the specimen, w is the width of the specimen, E r and E θ are Young's modulus in the interlayer radial and interlayer tangential directions, σ rand σ θ are the radial stress and tangential stress between layers, k, λ and g are parameters used for strength calculation.

[0079] Since the test section with cylindrical anisotropy is also orthotropic, the strain component expression is:

[0080]

[0081] Where: ε r and ε θ are radial strain and tangential strain, ν r and ν θ is Poisson's ratio;

[0082] Due to orthotropy, the relationship between Young's modulus and Poisson's ratio is written as:

[0083]

[0084] Where: r i and r o are the inner and outer diameters of the specimen, E r and E θ is the Young's modulus in the interlayer radial and interlayer tangential directions.

[0085] The ratio of the Young's modulus between the interlayer radial direction and the interlayer tangential direction is obtained by the following steps, specifically including:

[0086] The arc radius of the test section close to the inner diameter of the ring is recorded as r1 and the arc radius of the test section close to the outer diameter of the ring is recorded as r2. Substitute them into the strain component expression respectively, and combine them with the relationship between Young's modulus and Poisson's ratio to obtain:

[0087]

[0088] Where: (r1) and (r2) represent arcs with radii r1 and r2, respectively;

[0089] Combining the stress component expression with the relationship between Young's modulus and Poisson's ratio, the relationship between the interlayer radial and interlayer tangential Young's modulus ratio k and the strain component is obtained:

[0090]

[0091] Based on the above formula and using the extracted in-situ strain of the sample, the ratio k of the Young's modulus between the radial direction and the tangential direction of the interlayer is calculated.

[0092] S7. Use the existing formula to calculate the interlaminar tensile strength of the specimen.

[0093] The interlaminar tensile strength of the specimen is calculated using the formula for obtaining the interlaminar tensile strength of the specimen in ASTM D6415, the standard test method for measuring the bending beam strength of fiber-reinforced beams. The bending beam strength of the specimen is:

[0094]

[0095] in:

[0096]

[0097] d x =(l b -l t ) / 2

[0098] Where: P and Δ are the load value and stroke of the first load drop, w and t are the width and thickness of the specimen, l b 、l t and D are the upper span, lower span and indenter diameter of the four-point bending fixture, φ i =45°, M represents bending moment, d x and d y are the horizontal and vertical distances between two adjacent top and bottom load bars, respectively, and φ represents the angle between the specimen legs and the horizontal plane.

[0099] Based on the formula for calculating the interlaminar tensile strength of the specimen in ASTM D6415, the standard test method for measuring the bending strength of fiber-reinforced beams, the interlaminar tensile strength of the specimen is:

[0100]

[0101] in:

[0102]

[0103] Where: r m is the radial position of the maximum interlaminar (radial) tensile stress.

[0104] Example 2: This example provides a method for testing the interlaminar tensile strength of a ceramic matrix composite material. The testing method comprises the following steps:

[0105] First: obtain the geometric dimensions of the specimen and perform surface treatment on the test surface of the specimen.

[0106] 1) A batch of ceramic matrix composites were selected as specimens (as shown in Table 1). The specimens were L-shaped specimens. The shape of the specimens was a curved beam. The plane of the specimen was formed by connecting two identical rectangles through a 90° circular ring. The 90° circular ring was perpendicular to the plane and had a certain width.

[0107] 2) If Figure 2、 Figure 3 As shown in Table 1, the geometric dimensions of the sample include the length of the right-angle side of the plane rectangle of the sample L (the length of the rectangle), the thickness of the right-angle side of the plane rectangle of the sample t (the width of the rectangle), the radius r of the inner diameter of the 90° ring, and the inner diameter of the 90° ring. i 、The outer diameter r of the 90° ring o (Radius of the outer ring of the 90° circle = width of the rectangle t + radius of the inner diameter of the 90° circle r i ) and the width w of the specimen;

[0108] 3) The surface treatment of the test surface of the sample includes: applying evenly distributed matte white paint on the test surface of the sample to form a white primer, and spraying matte black paint on the white primer to form random spots.

[0109] Table 1 shows the geometric dimensions of the specimens

[0110] Sample number Right angle leg length L / mm <![CDATA[Inner diameter r i / mm]]> Thickness t / mm Width w / mm Sample 1 60 2.5 5.14 25.16 Sample 2 60 2.5 5.12 25.20 Sample 3 60 2.5 5.15 25.19 average value 60 2.5 5.14 25.18

[0111] Second: mark the test section of the sample.

[0112] 1) The test section of the specimen is the connection of the "L"-shaped specimen, that is, the 90° circular area;

[0113] 2) The marking process includes marking an arc of one-quarter the length of a circle on the test section of the specimen close to the inner diameter side of the 90° ring and close to the outer diameter side of the 90° ring, and recording the radius of the arc on the inner diameter side of the 90° ring as r1 and the radius of the arc on the outer diameter side of the 90° ring as r2.

[0114] Third: Obtain the geometric dimensions of the four-point bending fixture and determine the placement of the specimen and camera.

[0115] 1) If Figure 4 As shown in Table 2, the geometric dimensions of the four-point bending fixture include the upper span l t , lower span l b and the pressure head diameter D;

[0116] 2) If Figure 5 As shown, the specimen is placed symmetrically on a four-point bending fixture, the camera faces the test surface of the specimen, and light sources are placed symmetrically on both sides of the camera.

[0117] Table 2 shows the geometric dimensions of the four-point bending fixture.

[0118] Structure Name <![CDATA[Upper span l t / mm]]> <![CDATA[Lower span l b / mm]]> Indenter diameter D / mm Four-point bending fixture 30 60 4

[0119] Fourth: Perform a four-point bending test on a curved beam based on a four-point bending fixture, and use a camera to capture the displacement field of the specimen test surface.

[0120] Fifth: Figure 4As shown in Table 3, the four-point bending fixture was pressurized by the testing machine to obtain the load value P and stroke Δ of the first load drop, and the in-situ strain of the specimen was extracted using a camera.

[0121] Table 3 Key parameters of the testing machine

[0122] Sample number First descent load P / N Stroke Δ / mm Sample 1 952.2 1.973 Sample 2 966.7 2.141 Sample 3 900.1 1.965 average value 2.026 3.46

[0123] Sixth: Based on the new formula k for calculating the modulus ratio k between the interlayer radial direction and the interlayer tangential direction of the sample derived in step S6 of the first embodiment, calculation is performed, as shown in Table 4.

[0124] Seventh: Based on step S7 in Example 1, the interlaminar tensile strength ILTS of the sample is calculated, as shown in Table 4.

[0125] Table 4 Calculation results of modulus ratio and interlaminar tensile strength of samples

[0126]

[0127] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0128] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for testing the interlaminar tensile strength of a ceramic matrix composite material, characterized in that: The test method comprises the following steps: S1. Obtain the geometric dimensions of the specimen and perform surface treatment on the test surface of the specimen; S2. Marking the test section of the sample; S3. Obtain the geometric dimensions of the four-point bending fixture and determine the placement of the specimen and camera; S4. Perform a four-point bending test on the specimen using a four-point bending fixture, and use a camera to capture the displacement field of the specimen test surface. S5. Apply pressure to the four-point bending fixture using a testing machine to obtain the load value and stroke of the first load drop, and use a camera to extract the in-situ strain of the specimen; S6. Derive the formula for calculating the ratio of the modulus between the radial and tangential directions of the interlayers of the specimen and perform the calculation; S7. Calculate the interlaminar tensile strength of the specimen.

2. The testing method according to claim 1, wherein: In S1, the specimen is an L-shaped specimen in the shape of a curved beam, and the plane of the specimen is formed by two identical rectangles connected by a circular ring, and the circular ring is perpendicular to the plane; The geometric dimensions of the specimen include: the length of the plane rectangle of the "L"-shaped specimen, the width of the plane rectangle of the "L"-shaped specimen, the radius of the inner ring of the circular ring, the radius of the outer ring of the circular ring, and the width of the "L"-shaped specimen; The test surface of the sample is the plane of the "L"-shaped test piece. The surface treatment of the test surface of the sample includes applying evenly distributed matte white paint on the test surface of the sample, and then spraying matte black paint on the matte white paint to form random spots.

3. The testing method according to claim 2, wherein: In S2, the test section is the connection of the "L"-shaped test piece; The marking process includes marking arcs on the test section of the specimen close to the inner diameter side of the ring and close to the outer diameter side of the ring, respectively, and recording the radii of the two arcs.

4. The testing method according to claim 1, wherein: In S3, the geometric dimensions of the four-point bending fixture include an upper span, a lower span, and a pressure head diameter; The sample is symmetrically placed on a four-point bending fixture, the camera faces the test surface of the sample, and light sources are symmetrically placed on both sides of the camera.

5. The testing method according to claim 3, wherein: In S5, the in-situ strain of the specimen includes the radial strain and tangential strain at the midpoint of the two arcs at the marked position of the connection of the "L"-shaped specimen.

6. The testing method according to claim 1, wherein: In S6, based on the anisotropic plate theory, the stress component expression of the test section with cylindrical anisotropy is: in: Where: r and θ are the radial and tangential directions of the cylindrical coordinates, M represents the bending moment, r i and r o are the inner and outer diameters of the specimen, w is the width of the specimen, E r and E θ are Young's modulus in the interlayer radial and interlayer tangential directions, σ r and σ θ are the radial stress and tangential stress between layers, k, λ and g are parameters used for strength calculation.

7. The testing method according to claim 6, wherein: Since the test section with cylindrical anisotropy is also orthotropic, the strain component expression is: Where: ε r and ε θ are radial strain and tangential strain, ν r and ν θ is Poisson's ratio; Due to orthotropy, the relationship between Young's modulus and Poisson's ratio is written as: Where: r i and r o are the inner and outer diameters of the specimen, E r and E θ is the Young's modulus in the interlayer radial and interlayer tangential directions.

8. The testing method according to claim 7, wherein: The ratio of the Young's modulus between the interlayer radial direction and the interlayer tangential direction is obtained by the following steps, specifically including: The arc radius of the test section close to the inner diameter of the ring is recorded as r1 and the arc radius of the test section close to the outer diameter of the ring is recorded as r2. Substitute them into the strain component expression respectively, and combine them with the relationship between Young's modulus and Poisson's ratio to obtain: Where: (r1) and (r2) represent arcs with radii r1 and r2, respectively; Combining the stress component expression with the relationship between Young's modulus and Poisson's ratio, the relationship between the interlayer radial and interlayer tangential Young's modulus ratio k and the strain component is obtained: Based on the above formula and using the extracted in-situ strain of the sample, the ratio k of the Young's modulus between the radial direction and the tangential direction of the interlayer is calculated.

9. The testing method according to claim 1, wherein: In S7, the interlaminar tensile strength of the sample is calculated using the formula for obtaining the interlaminar tensile strength of the sample in ASTM D6415, the standard test method for measuring the bending beam strength of fiber-reinforced beams. The bending beam strength of the sample is: in: Where: P and Δ are the load value and stroke of the first load drop, w and t are the width and thickness of the specimen, l b 、l t and D are the upper span, lower span and indenter diameter of the four-point bending fixture, φ i =45°, M represents bending moment, d x and d y are the horizontal and vertical distances between two adjacent top and bottom load bars, respectively, and φ represents the angle between the specimen legs and the horizontal plane.

10. The testing method according to claim 9, wherein: Based on the formula for calculating the interlaminar tensile strength of the specimen in ASTM D6415, the standard test method for measuring the bending strength of fiber-reinforced beams, the interlaminar tensile strength of the specimen is: in: Where: r m is the radial position of the maximum interlaminar tensile stress.

Images