CN113740159A - In-situ test method for micro-fracture toughness of ceramic matrix composite - Google Patents
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Abstract
The invention relates to an in-situ test method for micro fracture toughness of a ceramic matrix composite, which comprises the following steps: processing the ceramic matrix composite to be tested to obtain a sample for in-situ testing; processing a cylindrical microcolumn on the surface of a sample, and measuring the actual radius of the cylindrical microcolumn; performing splitting test on the cylindrical microcolumn, and recording corresponding critical load; performing splitting simulation on the cylindrical microcolumn by using a finite element method, and calculating a correction factor based on a simulated critical stress intensity factor used for the splitting simulation, the radius of the simulated cylindrical microcolumn and a critical load obtained by the simulation; and calculating a corresponding critical stress intensity factor based on the actual radius of the cylindrical microcolumn, the correction factor and the corresponding critical load. The invention can realize the high-efficiency and accurate determination of the fracture toughness of the micro-components in the ceramic matrix composite.
Description
Technical Field
The invention relates to the technical field of material mechanical property testing, in particular to an in-situ testing method for micro fracture toughness of a ceramic matrix composite.
Background
The fiber reinforced ceramic matrix composite (also called ceramic matrix composite) has excellent high-temperature oxidation resistance and thermal mechanical property, and is widely applied to key thermal protection parts such as hypersonic aircraft tips and wing leading edges.
Due to the intrinsic brittleness characteristics of the ceramic matrix and the reinforcing fibers in the composite material, the ceramic matrix composite material risks brittle failure in the process of bearing aerodynamic or thermomechanical load, thereby affecting the service life and reliability of the ceramic matrix composite material. Fracture toughness is a key mechanical parameter for evaluating the toughness and brittleness of the composite material, and the value represents the capability of the material for resisting crack propagation.The critical stress intensity factor (K) is generally usedIC) As a measure of fracture toughness. Due to the complex microstructure characteristics of ceramic matrix composites, the fracture toughness is mainly affected by the microstructure of the ceramic matrix, the reinforcing fibers, and the ceramic-matrix interface. In the ceramic matrix composite material, a high-density fiber braid is often contained in the ceramic matrix, the diameter of a single fiber is generally less than or equal to 15 mu m, and the small-scale characteristic makes the traditional fracture toughness testing method unable to meet the in-situ quantitative testing requirements of the ceramic matrix composite material microconstituent (such as ceramic matrix and reinforced fiber).
At present, the mainstream technology for quantitatively obtaining the fracture toughness of the ceramic matrix composite material from local micro-areas is indentation technology and micro-beam bending technology. The key of the indentation technology is to successfully induce cracks to generate and expand on the surface of a sample, a larger plastic deformation area or a crack expansion area is inevitably introduced, and for anisotropic materials, the lengths of the induced cracks in different directions are often greatly different due to the difference of oriented microstructures of different materials, so the indentation technology is not suitable for testing the fracture toughness of the anisotropic materials. The difficulty of the micro-beam bending technology is mainly in the processing of micro-cantilever beams and prefabricated microcracks, samples are easy to damage in the processing process, and the influence may be brought to the crack transmission process, so that the fracture toughness test result is influenced.
Disclosure of Invention
The invention aims to provide an in-situ test method for the microcosmic fracture toughness of a ceramic matrix and reinforcing fibers based on a micro-column splitting technology to efficiently and accurately measure the microcosmic component fracture toughness in a ceramic matrix composite.
In order to achieve the above object, the present invention provides an in-situ test method for micro fracture toughness of ceramic matrix composite material, comprising:
processing the ceramic matrix composite to be tested to obtain a sample for in-situ testing;
processing a cylindrical microcolumn on the surface of a sample, and measuring the actual radius of the cylindrical microcolumn;
performing splitting test on the cylindrical microcolumn, and recording corresponding critical load;
performing splitting simulation on the cylindrical microcolumn by using a finite element method, and calculating a correction factor based on a simulated critical stress intensity factor used for the splitting simulation, the radius of the simulated cylindrical microcolumn and a critical load obtained by the simulation;
and calculating a corresponding critical stress intensity factor based on the actual radius of the cylindrical microcolumn, the correction factor and the corresponding critical load.
Optionally, the processing the ceramic matrix composite material to be tested to obtain the sample for in-situ testing includes:
determining the fiber bundle direction of the ceramic matrix composite material to be tested;
cutting the ceramic matrix composite material in a direction perpendicular to the fiber bundle to determine a surface for in-situ testing, and cutting the cut block sample into square samples;
grinding and polishing the surface of the sample for in-situ test; the surface of the sample for in-situ testing is parallel to the bottom surface of the sample, and the sample contains a ceramic matrix enrichment area and a fiber cross section enrichment area.
Optionally, the processing of the cylindrical microcolumn on the surface of the sample includes:
locating a ceramic matrix enrichment zone and a fiber cross-section enrichment zone on a surface for in situ testing;
and processing a plurality of cylindrical microcolumns at the ceramic matrix in the ceramic matrix enrichment region and at the fiber cross section in the fiber cross section enrichment region respectively.
Optionally, the performing the splitting test on the cylindrical microcolumn and recording the corresponding critical load includes:
fixing the sample in a nano mechanical testing system, and enabling the surface for in-situ testing to be vertical to the assembly direction of a pressure head of the nano mechanical testing system;
assembling a diamond conical pressure head for splitting test;
the assembled pressure head is used as a scanning probe to accurately position the center of a tested cylindrical microcolumn in situ;
applying an axial load to the tested cylindrical micro-column, and recording load and displacement data in real time until the tested cylindrical micro-column is split and damaged;
the critical load to cleave the cylindrical microcolumn being tested was recorded.
Optionally, the correction factor γ is calculated based on a simulated critical stress intensity factor used for the cleavage simulation, a simulated cylindrical microcolumn radius, and a simulated critical load, and the following formula is adopted:
wherein R is0Represents the radius of the simulated cylindrical microcolumn, KIC_InputDenotes the simulated critical stress intensity factor, P'InstabilityRepresenting the simulated critical load.
Optionally, the performing the splitting simulation of the cylindrical microcolumn by using a finite element method includes:
establishing a corresponding model in finite element software according to the size and the material of the tested cylindrical microcolumn and the pressure head; wherein, the pressure head is set as a perfect rigid material, and the cylindrical microcolumn is set as an elastic-perfect plastic body;
selecting an 1/3 model of the cylindrical microcolumn along the circumferential direction by using a symmetric boundary condition, arranging a cohesion unit on a longitudinal cutting and bisecting surface of the 1/3 model of the cylindrical microcolumn, and presetting a simulation critical stress intensity factor;
applying a displacement boundary condition to an 1/3 model of the cylindrical microcolumn, and loading a pressure head at the axis of a 1/3 model of the cylindrical microcolumn to simulate the splitting process of the cylindrical microcolumn;
load and displacement data at the pressure head are calculated through a finite element method, and critical load when the displacement suddenly drops is recorded as critical load obtained through simulation.
Optionally, the size of the cylindrical microcolumn, theCalculating the corresponding critical stress intensity factor K according to the correction factor and the corresponding critical loadICThe following formula is adopted:
wherein R represents the actual radius of the cylindrical microcolumn, γ represents a correction factor, PInstabilityRepresenting the corresponding critical load.
Optionally, the diameter of the cylindrical microcolumn ranges from 3 to 5 μm.
Optionally, the aspect ratio of the cylindrical microcolumn is 1: 1.
Optionally, when the cylindrical microcolumn is processed on the surface of the sample, a focused ion beam technology is adopted.
The technical scheme of the invention has the following advantages: the invention provides an in-situ test method for micro fracture toughness of a ceramic matrix composite, which is realized based on cylindrical micro-fracture test and fracture simulation, is suitable for a plurality of fiber reinforced ceramic matrix composites, can obtain the micro fracture toughness of reinforced fibers and ceramic matrixes in situ, has small sample processing difficulty and short time consumption, does not need to prefabricate microcracks, can limit crack expansion areas, avoids damage possibly caused by a complex processing process, and is more accurate and efficient compared with the traditional indentation technology and micro-beam bending technology.
Drawings
FIG. 1 is a schematic illustration showing the steps of an in situ test method for micro fracture toughness of a ceramic matrix composite according to an embodiment of the present invention;
FIG. 2 shows a polished surface metallographic micrograph of a sample made of a typical SiCf/SiC composite;
FIG. 3(a) shows a SEM image of a sample made of a typical SiCf/SiC composite material after processing a cylindrical microcolumn;
FIG. 3(b) is an enlarged view of the boxed area within FIG. 3 (a);
FIG. 4(a) shows load-displacement curves obtained from a cylindrical micropillar cleavage test of a typical SiC base component at different composite sintering temperatures;
FIG. 4(b) shows load-displacement curves obtained from cylindrical micro-column splitting tests of a typical SiC fiber component at different composite sintering temperatures;
FIG. 5(a) shows an 1/3 model for a cylindrical micropillar and a diamond cone indenter model;
fig. 5(b) is a plan view of fig. 5 (a).
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
As mentioned above, the key of the indentation fracture toughness test is to successfully induce crack generation and propagation on the surface of a sample, and generally, a higher indentation load or a smaller taper pressure head is adopted to carry out the test, so that a larger plastic deformation area or a crack propagation area is inevitably introduced, for a second phase material with a smaller size, such as a ceramic fiber (the diameter is less than or equal to 15 μm), when the indentation fracture toughness test is adopted, it is difficult to completely limit the indentation deformation and the crack growth area inside the fiber, and if the crack penetrates or deflects at the interface between the fiber and a matrix, the failure of the test result is caused. In addition, one key parameter for calculating the fracture toughness by adopting the indentation technology is the crack length, and for the anisotropic material, the induced crack lengths in different directions are often greatly different due to the difference of the oriented microstructures of different materials, so the indentation technology is not suitable for the fracture toughness test of the anisotropic material. In addition, when the indentation technology is used for calculating the fracture toughness, the crack length of each test needs to be artificially counted, certain subjectivity exists, and the method is low in test precision and large in error.
The micro-beam bending technology can limit the test volume to micron level, and for the ceramic matrix composite material, the micro-beam bending technology can test the fracture toughness of the ceramic matrix and can be applied to the fiber and the fiber/matrix interface with smaller size. However, the difficulty of the micro-beam bending technology is mainly in the processing of the micro-cantilever beam and the prefabricated micro-cracks, the current mainstream processing technology is a focused ion beam technology, the processing process is complex, and generally 2 to 3 hours are consumed to process one micro-cantilever beam. In addition, sample damage is easily caused in the focused ion beam processing process, particularly at the prefabricated micro-crack tip of the micro-cantilever, and the most important point for the technology in the world at present is ion implantation at the crack tip, which may affect the crack transmission process, thereby affecting the fracture toughness test result. In addition, the micro-beam bending test process needs to depend on an advanced nano mechanical positioning device and a force/load distinguishing device so as to realize the accurate loading of the micro-cantilever beam bending load, and the test process is complex. These technical problems limit the application of the micro-beam bending technique to a wider range.
In view of the above, the invention provides an in-situ testing method for the micro fracture toughness of ceramic matrix and reinforcing fiber based on micro-column splitting technology, which aims to integrate the advantages of indentation technology and micro-beam bending technology, thereby realizing the high-efficiency and accurate determination of the fracture toughness of the micro-component in the ceramic matrix composite.
As shown in fig. 1, an in-situ testing method for micro fracture toughness of a ceramic matrix composite according to an embodiment of the present invention includes:
and step 100, processing the ceramic matrix composite to be tested to obtain a sample for in-situ testing.
The test specimen for in situ testing has a surface for in situ testing for testing.
And 102, machining a cylindrical microcolumn on the surface of the sample, and measuring the actual radius of the cylindrical microcolumn.
The method comprises the following steps of processing a cylindrical micro-column on the surface of a sample, namely processing a corresponding micro-column on the surface for in-situ test, wherein the micro-column is cylindrical in shape, the length-diameter ratio is preferably 1:1, and the deviation is preferably not more than 5 percent; if the cylindrical microcolumn is too short (the length-diameter ratio is too small), the cylindrical microcolumn is difficult to split in the splitting test process, and the test is also influenced. This step preferably allows processing of multiple microcolumns for repeated testing.
Furthermore, in order to ensure the accuracy of subsequent splitting test and reduce the test difficulty, the diameter range of the cylindrical micro-column is preferably 3-5 μm. If the diameter is too small, the positioning difficulty of the pressure head in subsequent tests can be increased; if the diameter is too large, large plastic deformation may be introduced in subsequent tests, so that the splitting test difficulty is increased. For most ceramic fibers, the diameter range is generally 5-15 μm, and the cylindrical microcolumns processed by the method of the present invention can be completely limited to the axial fiber region. In order to ensure the reliability of the calculated result of the fracture toughness, the radius R of each cylindrical microcolumn needs to be accurately measured. After the processing is finished, a high-resolution scanning electron microscope can be used for high-resolution imaging, and the radius R of each cylindrical microcolumn is measured and recorded.
And 104, applying axial load to the cylindrical micro-columns, performing splitting test, and recording corresponding critical load when each cylindrical micro-column is split.
The axial load is applied to the cylindrical micro-column to perform the splitting test, and the splitting test can be realized by a high-resolution nano mechanical test system (such as Hysitron TI950, NanoTestvantage and the like) in the prior art.
And 106, performing splitting simulation on the cylindrical microcolumn by using a finite element method, and calculating a correction factor based on a simulated critical stress intensity factor used by the splitting simulation, the simulated cylindrical microcolumn radius and the simulated critical load.
The correction factor is used for calibrating the influence of the pressure head and the external dimension of the cylindrical micro-column on the calculation result of the fracture toughness. In order to obtain the correction factor gamma, finite element simulation is respectively carried out on the micro-column splitting of different materials, different pressure head shapes and different micro-column sizes. The simulated cylindrical microcolumn radius should be as close as possible to the actual radius of the cylindrical microcolumn.
According to the ceramic matrix composite microcosmic fracture toughness in-situ test method (the method is abbreviated as the invention), the axial load is applied to the cylindrical microcolumn through the pressure head, and cracks are induced to generate and expand; different from the indentation technology, in the method, the crack propagation path is strictly restricted by the pressure head and the appearance of the cylindrical microcolumn, the maximum crack length is approximately equal to the radius of the cylindrical microcolumn, and the unique advantage enables quantitative test of the microscopic fracture toughness of the material without prefabricating microcracks when the cylindrical microcolumn is processed; compared with the micro-beam bending technology, the method has the advantages that the sample processing difficulty is lower, the influence of ion implantation on the crack tip expansion behavior and the fracture toughness test result is effectively avoided, and the test result is more reliable and accurate.
In some embodiments, to obtain a more suitable test sample, for step 100, further comprising:
step 100-1, determining the fiber bundle direction of the ceramic matrix composite material to be tested.
And step 100-2, cutting the ceramic matrix composite material in a direction perpendicular to the fiber bundle to determine the surface for in-situ testing, and further cutting the block sample obtained by cutting the ceramic matrix composite material into a square sample.
Cutting perpendicular to the direction of the fiber bundle advantageously allows the surface for in situ testing to contain more fiber cross-section. The length, width and height of the square sample are preferably not more than 1cm, so that the square sample can be processed and tested. The block sample obtained by cutting the ceramic matrix composite material can utilize the prior art such as a wire/disc cutting machine and the like.
Step 100-3, grinding and polishing the surface of the sample for in-situ test to finally obtain the sample for in-situ test; the surface of the sample for in-situ testing is parallel to the bottom surface of the sample and contains a ceramic matrix enrichment region and a fiber cross-section enrichment region.
In order to avoid stress damage to the fibers and interfaces during sanding, the minimum paste particle size used is preferably no more than 1 μm. After polishing, the surface finish for in situ testing can be examined by optical microscopy, the surface needs to be smooth and free of scratches, and contains a clear and distinguishable ceramic matrix enrichment region and a fiber cross-sectional enrichment region. Fig. 2 shows a surface metallographic micrograph of a typical SiCf/SiC composite sample after polishing, where the SiC matrix-rich region marked in fig. 2 is a ceramic matrix-rich region, and the SiC fiber-rich region marked in fig. 2 is a fiber cross-section-rich region.
By adopting the technical scheme, the sample which is easy to quantitatively test and used for the in-situ test of the microscopic fracture toughness of the ceramic matrix and the reinforced fiber can be obtained, and the accuracy and the reliability of the test can be improved.
In some embodiments, for the step 102 of machining a cylindrical microcolumn on the surface of the sample, further comprising:
102-1, locating the ceramic matrix enrichment region and the fiber cross-sectional enrichment region on the surface of the sample for in-situ testing.
Furthermore, the step can utilize a scanning electron microscope/focused ion beam testing system to carry out secondary electron scanning imaging on the surface morphology of the polished ceramic matrix composite sample so as to position the ceramic matrix enrichment region and the ceramic fiber enrichment region.
102-2, respectively processing a plurality of cylindrical microcolumns at the ceramic matrix in the ceramic matrix enrichment region and the fiber cross section in the fiber cross section enrichment region. Further, it is preferable that the number of microcolumn processing in each of the ceramic matrix-rich region and the ceramic fiber-rich region is not less than 5.
In this embodiment, the cylindrical microcolumns are processed at the ceramic matrix and the reinforcing fiber respectively, and can be used for testing the micro fracture toughness of the ceramic matrix and the reinforcing fiber respectively. Correspondingly, step 104 includes performing a splitting test on the ceramic matrix and the cylindrical microcolumns processed at the fiber positions respectively to obtain corresponding critical loads; step 106, performing splitting simulation on the ceramic matrix and the cylindrical microcolumns at the fiber positions respectively by using a finite element method so as to calculate correction factors corresponding to the ceramic matrix and the cylindrical microcolumns at the fiber positions respectively; step 108 includes calculating critical stress intensity factors corresponding to the ceramic matrix and the fibers, respectively. And a plurality of cylindrical microcolumns are processed at the ceramic matrix and the fiber respectively, so that repeated testing is facilitated, the result is verified, and the reliability of the testing is further ensured.
Further, in step 102, when the cylindrical microcolumn is processed on the surface of the sample, the cylindrical microcolumn is processed on the surface of the sample by using the focused ion beam technique.
In some embodiments, the focused ion beam technology process is preferably: firstly, tilting the surface of a sample for in-situ test in a double-beam test system to a direction vertical to an ion beam, and then bombarding the surface of the sample at fixed points in the order of increasing the accelerating current (21nA → 80pA) under the ion accelerating voltage of 30kV and removing materials, wherein the bombarding region is the periphery of the processed cylindrical micro-column region. In the processing process, a scanning electron microscope is adopted to detect the change of the geometric dimension of the cylindrical microcolumn in real time until the dimension of the cylindrical microcolumn reaches a set value, and the processing is stopped. FIG. 3(a) shows a SEM image of a sample made of a typical SiCf/SiC composite material after processing a cylindrical microcolumn; FIG. 3(b) is an enlarged view of the boxed area within FIG. 3 (a); the cylindrical microcolumn in FIG. 3(b) had a diameter of 5.048 μm and a length of 4.994 μm.
In some embodiments, step 104 further comprises:
and 104-1, fixing the sample in the nano mechanical testing system, and enabling the surface of the sample for in-situ testing to be vertical to the assembling direction of a pressure head of the testing device. Preferably, in order to reduce the flexibility of the nano mechanical testing system, 502 strong glue or silver paste can be selected to fix the sample.
And 104-2, assembling the diamond conical pressure head for the splitting test, namely taking the diamond conical pressure head as the pressure head of the splitting test. Preferably, for the micro-column cleaving test, the types of indenters commonly used are mainly two types, the Boss indenter and the cubic cone indenter.
And step 104-3, using the assembled pressure head (namely the diamond conical pressure head assembled in the step 104-2) as a scanning probe to accurately position the center of the tested cylindrical microcolumn in situ. The invention uses the scanning probe module of the nanometer mechanics testing system to realize the high-precision positioning of the pressure head, uses the diamond conical pressure head as the probe to continuously scan the area of the micro-column to be tested, forms the micro-area shape cloud picture through the height difference of the scanning area, and can carry out the in-situ precise positioning on the circle center of the micro-column to be tested based on the shape cloud picture.
And step 104-4, applying an axial load to the tested cylindrical micro-column by using a nano mechanical testing system, and recording load and displacement data in real time until the tested cylindrical micro-column is cracked. After the pressure head and the micro-column to be tested are accurately positioned, an axial load is applied to the cylindrical micro-column to be tested by utilizing a loading device of a nano mechanical testing system, the loading mode is preferably a load or displacement control mode, in order to accurately capture crack expansion signals, the loading speed does not exceed 5nm/s, load and displacement data are recorded in real time in the loading process, once the load or displacement is obviously mutated, the micro-column is proved to be cracked and damaged, and the test is stopped. FIGS. 4(a) and 4(b) show graphs of (cleaving) load (in mN) - (indenter) displacement (in μm) obtained by a cylindrical micro-column cleaving test of two types of components of a typical SiC matrix and SiC fiber at different sintering temperatures of the composite material.
104-5, recording the critical load P for causing the tested cylindrical microcolumn to generate the splitting damageInstability。
By adopting the technical scheme, the critical load of the tested cylindrical micro-column which is subjected to splitting damage can be accurately and efficiently obtained so as to carry out subsequent calculation.
Since the load-displacement curve data obtained by the cleaving test in step 104 is related to the dimensions of the indenter and the microcolumn, and the fracture toughness is an intrinsic parameter of the material and should be independent of the test conditions. In order to calibrate the influence of the pressure head and the overall dimension of the microcolumn on the fracture toughness calculation result, a finite element method is utilized to carry out microcolumn fracture simulation, and a correction factor is obtained for subsequent fracture toughness calculation.
In some embodiments, the correction factor γ is calculated in step 106 using the following equation:
wherein R is0Denotes the radius of the simulated cylindrical microcolumn used for the cleavage simulation, preferably the same as the actual radius of the cylindrical microcolumn to be tested, KIC_InputDenotes the simulated critical stress intensity factor, P ', for cleavage simulation'InstabilityRepresenting the simulated critical load.
Further, in step 106, performing a cylindrical microcolumn splitting simulation by using a finite element method, which may specifically include:
106-1, establishing a corresponding model in finite element software (such as commercial Abaqus finite element software) according to the size and the material of the tested cylindrical microcolumn and the pressure head; wherein the pressure head is made of perfect rigid material, and the cylindrical microcolumn is made of elastic-perfect plastic body. The elastic modulus and yield strength of the indenter and the cylindrical microcolumn can be obtained by nanoindentation experiments in the prior art.
106-2, in the finite element software, selecting an 1/3 model of the cylindrical microcolumn along the circumferential direction by using a symmetric boundary condition, arranging a cohesive force unit on a longitudinal cutting plane of the 1/3 model of the cylindrical microcolumn (namely, a central plane of the 1/3 model for cutting the cylindrical microcolumn along the axial direction), and presetting a simulation critical stress intensity factor. To reduce the amount of model computation, only the model size of 1/3 is set using symmetric boundary conditions, and the geometry of the model is shown in fig. 5(a) and 5 (b).
106-3, in the finite element software, applying a displacement boundary condition to the 1/3 model of the cylindrical microcolumn, loading a pressure head at the axis of the 1/3 model of the cylindrical microcolumn, and simulating the splitting process of the cylindrical microcolumn.
106-4, calculating the load and displacement number of the pressure head in the finite element software by a finite element methodAccording to the method, the critical load at the time of sudden drop of displacement is recorded as the critical load P obtained by simulationInstabilityThe physical meaning is the critical stress for breaking the micro-column, and the corresponding critical crack length is the radius of the simulated cylindrical micro-column used for splitting simulation.
It should be noted that, due to the difference in mechanical properties between the ceramic matrix and the reinforcing fiber, correction factors for the splitting of the microcolumns are still different, and in order to make the test result accurate and reliable, finite element simulation should be performed on the ceramic matrix microcolumns and the fiber microcolumns respectively to obtain the respective correction factors.
In some embodiments, the corresponding critical stress intensity factor K is calculated in step 108ICThe following formula is adopted:
wherein R represents the actual radius of the cylindrical microcolumn being tested, γ represents the corresponding correction factor of the cylindrical microcolumn being tested, and PInstabilityRepresenting the respective critical loads of the cylindrical microcolumn being tested.
In conclusion, the invention provides an in-situ test method for the micro fracture toughness of a ceramic matrix composite, which is based on a cylindrical micro-column splitting test, ensures that cracks are generated and expanded from the center, the crack expansion path is strictly restricted, the maximum crack length is approximately equal to the radius of the cylindrical micro-column, the diameter of the cylindrical micro-column required to be processed by the splitting test is only 3-5 μm and is smaller than the diameter of the conventional common ceramic fiber, and the technical method is suitable for most ceramic fiber reinforced ceramic matrix composites and obtains the micro fracture toughness of the ceramic fiber and the ceramic matrix in situ; in addition, the cylindrical microcolumn in the method is low in processing difficulty and short in time consumption, and the micro-cracks do not need to be prefabricated, so that damage to the tips of the cracks in the complex processing process is avoided.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. The in-situ test method for the microscopic fracture toughness of the ceramic matrix composite is characterized by comprising the following steps of:
processing the ceramic matrix composite to be tested to obtain a sample for in-situ testing;
processing a cylindrical microcolumn on the surface of a sample, and measuring the actual radius of the cylindrical microcolumn;
performing splitting test on the cylindrical microcolumn, and recording corresponding critical load;
performing splitting simulation on the cylindrical microcolumn by using a finite element method, and calculating a correction factor based on a simulated critical stress intensity factor used for the splitting simulation, the radius of the simulated cylindrical microcolumn and a critical load obtained by the simulation;
and calculating a corresponding critical stress intensity factor based on the actual radius of the cylindrical microcolumn, the correction factor and the corresponding critical load.
2. The in-situ test method for micro fracture toughness of ceramic matrix composite material according to claim 1, characterized in that:
the ceramic matrix composite to be tested is processed to obtain a sample for in-situ testing, and the method comprises the following steps:
determining the fiber bundle direction of the ceramic matrix composite material to be tested;
cutting the ceramic matrix composite material in a direction perpendicular to the fiber bundle to determine a surface for in-situ testing, and cutting the cut block sample into square samples;
grinding and polishing the surface of the sample for in-situ test; the surface of the sample for in-situ testing is parallel to the bottom surface of the sample, and the sample contains a ceramic matrix enrichment area and a fiber cross section enrichment area.
3. The in-situ test method for micro fracture toughness of ceramic matrix composite material according to claim 2, characterized in that:
the method for processing the cylindrical microcolumn on the surface of the sample comprises the following steps:
locating a ceramic matrix enrichment zone and a fiber cross-section enrichment zone on a surface for in situ testing;
and processing a plurality of cylindrical microcolumns at the ceramic matrix in the ceramic matrix enrichment region and at the fiber cross section in the fiber cross section enrichment region respectively.
4. The in-situ test method for micro fracture toughness of ceramic matrix composite material according to claim 2, characterized in that:
the splitting test is carried out on the cylindrical micro-column, and the corresponding critical load is recorded, and the method comprises the following steps:
fixing the sample in a nano mechanical testing system, and enabling the surface for in-situ testing to be vertical to the assembly direction of a pressure head of the nano mechanical testing system;
assembling a diamond conical pressure head for splitting test;
the assembled pressure head is used as a scanning probe to accurately position the center of a tested cylindrical microcolumn in situ;
applying an axial load to the tested cylindrical micro-column, and recording load and displacement data in real time until the tested cylindrical micro-column is split and damaged;
the critical load to cleave the cylindrical microcolumn being tested was recorded.
5. The in-situ test method for micro fracture toughness of ceramic matrix composite material according to claim 1, characterized in that:
calculating a correction factor gamma based on a simulated critical stress intensity factor used by the splitting simulation, the simulated cylindrical microcolumn radius and the simulated critical load, and adopting the following formula:
wherein R is0Represents the radius of the simulated cylindrical microcolumn, KIC_InputDenotes the simulated critical stress intensity factor, P'InstabilityRepresenting the simulated critical load.
6. The in-situ test method for micro fracture toughness of ceramic matrix composite material according to claim 5, characterized in that:
the method for simulating the splitting of the cylindrical microcolumn by using the finite element method comprises the following steps:
establishing a corresponding model in finite element software according to the size and the material of the tested cylindrical microcolumn and the pressure head; wherein, the pressure head is set as a perfect rigid material, and the cylindrical microcolumn is set as an elastic-perfect plastic body;
selecting an 1/3 model of the cylindrical microcolumn along the circumferential direction by using a symmetric boundary condition, arranging a cohesion unit on a longitudinal cutting and bisecting surface of the 1/3 model of the cylindrical microcolumn, and presetting a simulation critical stress intensity factor;
applying a displacement boundary condition to an 1/3 model of the cylindrical microcolumn, and loading a pressure head at the axis of a 1/3 model of the cylindrical microcolumn to simulate the splitting process of the cylindrical microcolumn;
load and displacement data at the pressure head are calculated through a finite element method, and critical load when the displacement suddenly drops is recorded as critical load obtained through simulation.
7. The in-situ test method for micro fracture toughness of ceramic matrix composite material according to claim 1, characterized in that:
calculating corresponding critical stress intensity factor K based on the dimension of the cylindrical microcolumn, the correction factor and the corresponding critical loadICThe following formula is adopted:
wherein R represents the actual radius of the cylindrical microcolumn, γ represents a correction factor, PInstabilityRepresenting the corresponding critical load.
8. The in-situ test method for micro fracture toughness of ceramic matrix composite material according to claim 1, characterized in that:
the diameter range of the cylindrical microcolumn is 3-5 mu m.
9. The in-situ test method for micro fracture toughness of ceramic matrix composite material according to claim 1, characterized in that:
the length-diameter ratio of the cylindrical microcolumn is 1: 1.
10. The in-situ test method for micro fracture toughness of ceramic matrix composite material according to claim 1, characterized in that:
when the cylindrical microcolumn is processed on the surface of the sample, a focused ion beam technology is adopted.
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