A method for evaluating the fracture toughness of ceramics without prenotching
By introducing blunt notches into ceramics and combining them with bending tests, the fracture toughness of ceramics can be calculated, solving the problems of poor operability and high equipment requirements in existing technologies, and achieving efficient and accurate assessment of ceramic fracture toughness.
Patent Information
- Application Number
- CN202211343827.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-10-31
- Publication Date
- 2026-01-23
- Estimated Expiration
- 2042-10-31
AI Technical Summary
Existing methods for assessing the fracture toughness of ceramics are difficult to operate, require sophisticated equipment, and are difficult to prepare sharp notches, which limits the accuracy of the tests.
A method that does not require pre-fabricated sharp notches is adopted. By introducing blunt notches into the ceramic, and combining the three-point or four-point bending method to test the original strength and apparent toughness, the fracture toughness of the ceramic is calculated using formulas.
It simplifies the ceramic fracture toughness assessment process, improves operability and accuracy, reduces equipment requirements, has small errors, and is suitable for the research and development and selection of brittle materials.
Smart Images
Figure CN115655920B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to a ceramic fracture toughness evaluation method without pre-preparing a sharp notch, and belongs to the technical field of fracture mechanics performance evaluation. BACKGROUND
[0002] Fracture toughness is an important mechanical property index of ceramics, and its accurate evaluation is crucial for the selection of structural materials and safe application. In the past few decades, although a number of fracture toughness test standards have been introduced at home and abroad, such as GB / T 23806-2009, GB / T 37900-2019, ISO 23146-2012, ASTM E1820-13, ASTM C1421-10 and ASTM E399, there are still many problems in actual operation. The indentation method recommended in GB / T 37900-2019 is limited in test accuracy due to the difficulty in accurately measuring the crack size, the difficulty in evaluating the influence of residual stress, and the difficulty in unifying the calculation formula. The single-edge precracked beam (SEPB) method recommended in GB / T 23806-2009 standard can theoretically obtain the true fracture toughness of ceramics, but the prerequisite is to introduce a uniform true crack with a required depth in the hard and brittle ceramic sample. The practice shows that the propagation of the straight-through crack pre-prepared in the sample is not easy to control, often leading to the crack size exceeding the tolerance range of the standard, and the preparation of a suitable crack needs to rely on experience and has a low success rate, and the number of invalid samples is often more than one order of magnitude higher than the number of effective samples.
[0003] Compared with the above, the single-edge notched beam (SENB) method recommended by ASTM E399 is more operable, but the notch blunting effect often leads to a serious overestimation of the fracture toughness value. The single-edge V-notch beam (SEVNB) method proposed in ISO 23146-2012 and ASTM E1820-13 uses a sharp V-notch instead of a true crack to accurately measure the fracture toughness, but the preparation of the V-notch is still very difficult, and it needs to rely on a blade and fine abrasive to obtain the V-notch through repeated grinding. Even so, the sharpness of the notch cannot be guaranteed to meet the test requirements. In theory, the radius of the V-notch tip in the ceramic sample should be below 10 mu m, and for some fine ceramics, it may even be below 1 mu m. In recent years, the exploration of laser methods has expanded the ideas for the preparation of sharp V-notch, but laser inevitably causes remelting and recrystallization, and introduces residual stress, so the accuracy of the test results needs to be discussed, and the laser processing equipment has high dependence on precision lasers. SUMMARY
[0004] The application aims to provide a ceramic fracture toughness evaluation method without pre-preparing a sharp notch, and solves the defects of poor operability and high equipment requirements in the prior art.
[0005] To achieve the above objectives, the present invention employs the following technical solution:
[0006] This invention provides a method for evaluating the fracture toughness of ceramics without the need for pre-fabricated sharp notches, comprising:
[0007] Test the original strength of the ceramic;
[0008] A blunt notch was introduced into the ceramic, and the tip radius of the blunt notch was tested. The apparent toughness of the ceramic containing the blunt notch was then tested.
[0009] The fracture toughness of ceramics is calculated based on the original strength, tip radius, and apparent toughness.
[0010] Furthermore, the original strength is measured by the three-point bending method or the four-point bending method.
[0011] Furthermore, when testing the original strength using the three-point bending method or the four-point bending method, the loading rate is 0.5 to 1 mm / min.
[0012] Furthermore, the method for introducing the blunt cut includes wire cutting and internal circle cutting, the depth of the blunt cut is 0.35-0.7 times the thickness of the ceramic, and the tip radius of the blunt cut is 100μm-1.5mm.
[0013] Furthermore, the depth of the blunt incision is obtained by observation using an optical microscope or a scanning electron microscope.
[0014] Furthermore, the apparent toughness is obtained by the following method:
[0015] The depth of the blunt notch was tested using the single-sided notch beam method. The failure load of ceramics with blunt notches was tested using the three-point bending method or the four-point bending method. The loading rate during the test was 0.01 to 0.1 mm / min. The apparent toughness was calculated based on the depth and failure load.
[0016] Furthermore, based on the original strength, tip radius, and apparent toughness, the fracture toughness of the ceramic is calculated using the following formula:
[0017]
[0018] Among them, K Ic It is fracture toughness, K c σ is the apparent toughness, σ0 is the original strength, and ρ is the tip radius.
[0019] Compared with the prior art, the beneficial effects achieved by the present invention are:
[0020] This invention provides a method for evaluating the fracture toughness of ceramics without the need for pre-fabricated sharp notches. By introducing a conventionally readily available blunt notch into the ceramic, its apparent toughness is tested, and the true fracture toughness of the ceramic is calculated by combining the original strength of the ceramic and the tip radius of the blunt notch. This method is highly operable and simple, effectively evaluating the fracture toughness of ceramics by eliminating the cumbersome and low-success-rate pre-fabrication process of sharp V-shaped notches or through cracks. It can provide technical support for toughness assessment in the research and development and selection of brittle materials. The process of preparing the blunt notch and testing the apparent toughness and tip radius has low equipment requirements. Attached Figure Description
[0021] Figure 1 This is a flowchart of a method for evaluating the fracture toughness of ceramics without the need for pre-fabricated sharp notches, provided by an embodiment of the present invention;
[0022] Figure 2 This is a schematic diagram of the blunt cut of ZrB2-SiC ceramic provided in an embodiment of the present invention. Detailed Implementation
[0023] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.
[0024] Example 1
[0025] like Figure 1 As shown, the present invention provides a method for evaluating the fracture toughness of ceramics without the need for pre-fabricated sharp notches, comprising the following steps:
[0026] S1. Test the original strength of the ceramic.
[0027] Ten ZrB2-SiC ceramic specimens with dimensions of 4mm×2mm×22mm (thickness×width×length) were tested using the three-point bending method. The average original strength (σ0) was measured to be 740MPa. The loading rate during the test was 0.5mm / min, and the span was 40mm.
[0028] S2. Introduce blunt notches into ceramics, test the tip radius of the blunt notches, and test the apparent toughness of ceramics containing blunt notches.
[0029] A blunt notch was introduced into a ZrB2-SiC ceramic sample with dimensions of 4 mm × 2 mm × 22 mm (thickness × width × length) using wire cutting. Scanning electron microscopy revealed that the depth (a) of the blunt notch was 1.884 mm, and the tip radius (ρ) was approximately 1 mm. Figure 2 As shown;
[0030] The calculated relative cut depth (α = a / W) is 0.471, which is between 0.35 and 0.7. The tip radius of the blunt cut is also between 100μm and 1.5mm, which meets the cut requirements and can be used for subsequent testing.
[0031] Using the single-sided notched beam (SENB) method, the bending failure load of the ceramic specimen with the blunt notch was tested using the three-point bending method. The downward rate of the indenter was 0.05 mm / min. After obtaining the maximum failure load, the values of the notch depth and specimen size were substituted into the following formula for calculating fracture toughness:
[0032]
[0033]
[0034] Among them, P max =51N, S0 = 16mm, B = 2mm, W = 4mm, a = 1.884mm, α = 0.471, β = 0.529, Y = 2.492, the apparent toughness (K) of the ZrB2-SiC ceramic sample with blunt notch was calculated. c The value is 10.3 MPa·m 1 / 2 .
[0035] S3. The fracture toughness of the ceramic is calculated based on the original strength, tip radius, and apparent toughness.
[0036] Using the original strength (σ0 = 740 MPa), blunt notch tip radius (ρ = 1 mm), and apparent toughness (K) c =10.3 MPa·m 1 / 2 The following formula is used for calculation:
[0037]
[0038] The fracture toughness (K) of ZrB2-SiC ceramics was obtained. Ic The value is 2.56 MPa·m 1 / 2 .
[0039] The fracture toughness value of ZrB2-SiC ceramic evaluated using this method is 2.56 MPa·m. 1 / 2 Compared with the previous measurement value after preparing a sharp incision using the SEVNB method (2.86 MPa·m) 1 / 2A comparison with the literature [Wang A, Hu P, Zhang X, et al. Accurate measurement of fracture toughness in structural ceramics[J]. Journal of the European Ceramic Society, 2017, 37(13):4207-4212.] shows that the error is only 10%. Clearly, by eliminating the cumbersome and low-success-rate pre-fabrication process of sharp V-shaped cuts or through-cracks, the method proposed in this invention can still effectively evaluate the fracture toughness of ZrB2-SiC ceramics.
[0040] Example 2
[0041] Six yttrium-stabilized zirconia (3Y-TZP) ceramic specimens with dimensions of 4mm×2mm×22mm (thickness×width×length) were tested using the three-point bending method. The average original strength (σ0) was measured to be 770MPa. The loading rate during the test was 0.5mm / min and the span was 40mm.
[0042] Using an internal circle cutter, blunt notches were introduced into 3Y-TZP ceramic samples with dimensions of 4mm×2mm×22mm (thickness×width×length). Blunt notches with different sharpnesses were prepared in two samples. The depth (a) of the blunt notches was approximately 2mm and the tip radius (ρ) was approximately 100μm and 250μm, respectively, as observed by scanning electron microscopy.
[0043] The calculated relative cut depth (α = a / W) is 0.5, which is between 0.35 and 0.7. The tip radius of the blunt cut is also between 100 μm and 1.5 mm, which meets the cut requirements and can be used for subsequent testing.
[0044] Using the single-sided notched beam (SENB) method, the bending failure load of the ceramic specimen with the blunt notch was tested using the three-point bending method. The downward rate of the indenter was 0.05 mm / min. After obtaining the maximum failure load, the values of the notch depth and specimen size were substituted into the following formula for calculating fracture toughness:
[0045]
[0046]
[0047] Where S0 is 16mm, B is 2mm, W is 4mm, a is 2mm, α = 0.5, β = 0.5, Y = 2.633, P max The apparent toughness (K) of the 3Y-TZP ceramic specimens with blunt notches was calculated based on 36N and 46N respectively.c The values were 7.7 MPa·m 1 / 2 and 9.8 MPa·m 1 / 2 ;
[0048] Using the original strength (σ0 = 770 MPa), blunt notch tip radius (ρ = 100 μm and 250 μm) and apparent toughness (K) c It is 7.7 MPa·m 1 / 2 and 9.8 MPa·m 1 / 2 The following formula is used for calculation:
[0049]
[0050] The fracture toughness (K) of 3Y-TZP ceramic was obtained. Ic The value is 4.34 MPa·m 1 / 2 and 4.45 MPa·m 1 / 2 .
[0051] The average fracture toughness of 3Y-TZP ceramics evaluated using this method was 4.4 MPa·m. 1 / 2 Compared with the previous measurement value after preparing a sharp incision using the SEVNB method (4.05 MPa·m) 1 / 2 A comparison with the literature [Wang A, Hu P, Zhang X, et al. Accurate measurement of fracture toughness in structural ceramics[J]. Journal of the European Ceramic Society, 2017, 37(13): 4207-4212.] shows that the error is only 9%. Clearly, by eliminating the cumbersome and low-success-rate pre-fabrication process of sharp V-shaped cuts or through-cracks, the method proposed in this invention can still effectively evaluate the fracture toughness of 3Y-TZP ceramics.
[0052] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for evaluating the fracture toughness of ceramics without the need for pre-fabricated sharp notches, characterized in that, include: Test the original strength of the ceramic; A blunt notch was introduced into the ceramic, and the tip radius of the blunt notch was tested. The apparent toughness of the ceramic containing the blunt notch was then tested. The fracture toughness of ceramics is calculated using the following formula based on the original strength, tip radius, and apparent toughness: ； in, It is fracture toughness. It is apparent toughness. It is the original strength. It is the tip radius.
2. The method for evaluating the fracture toughness of ceramics without the need for pre-fabricated sharp notches according to claim 1, characterized in that, The original strength was measured by the three-point bending method or the four-point bending method.
3. The method for evaluating the fracture toughness of ceramics without the need for pre-fabricated sharp notches according to claim 2, characterized in that, When testing the original strength using the three-point bending method or the four-point bending method, the loading rate is 0.5~1mm / min.
4. The method for evaluating the fracture toughness of ceramics without the need for pre-fabricated sharp notches according to claim 1, characterized in that, The method for introducing the blunt cut includes wire cutting and internal circle cutting. The depth of the blunt cut is 0.35-0.7 times the thickness of the ceramic, and the tip radius of the blunt cut is 100μm-1.5mm.
5. The method for evaluating the fracture toughness of ceramics without the need for pre-fabricated sharp notches according to claim 4, characterized in that, The depth of the blunt incision was observed using an optical microscope or a scanning electron microscope.
6. The method for evaluating the fracture toughness of ceramics without the need for pre-fabricated sharp notches according to claim 1, characterized in that, The apparent toughness was obtained by the following method: The depth of the blunt notch was tested using the single-sided notch beam method. The failure load of ceramics with blunt notches was tested using the three-point bending method or the four-point bending method. The loading rate during the test was 0.01~0.1 mm / min. The apparent toughness was calculated based on the depth and failure load.