CN113776970A - Method for testing fracture toughness of brittle material - Google Patents
Method for testing fracture toughness of brittle material Download PDFInfo
- Publication number
- CN113776970A CN113776970A CN202111042878.8A CN202111042878A CN113776970A CN 113776970 A CN113776970 A CN 113776970A CN 202111042878 A CN202111042878 A CN 202111042878A CN 113776970 A CN113776970 A CN 113776970A
- Authority
- CN
- China
- Prior art keywords
- fracture toughness
- indentation
- acoustic emission
- length
- crack
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/40—Investigating hardness or rebound hardness
- G01N3/42—Investigating hardness or rebound hardness by performing impressions under a steady load by indentors, e.g. sphere, pyramid
- G01N3/44—Investigating hardness or rebound hardness by performing impressions under a steady load by indentors, e.g. sphere, pyramid the indentors being put under a minor load and a subsequent major load, i.e. Rockwell system
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
- G01N3/06—Special adaptations of indicating or recording means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0001—Type of application of the stress
- G01N2203/0003—Steady
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0019—Compressive
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/006—Crack, flaws, fracture or rupture
- G01N2203/0067—Fracture or rupture
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0076—Hardness, compressibility or resistance to crushing
- G01N2203/0078—Hardness, compressibility or resistance to crushing using indentation
- G01N2203/008—Residual indentation measurement
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/025—Geometry of the test
- G01N2203/0258—Non axial, i.e. the forces not being applied along an axis of symmetry of the specimen
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/0658—Indicating or recording means; Sensing means using acoustic or ultrasonic detectors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0676—Force, weight, load, energy, speed or acceleration
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
The invention provides a method for testing fracture toughness of a brittle material, which is realized by combining an acoustic emission detection technology and an instrumented indentation technology to dynamically detect the crack propagation state in real time. The crack propagation is effectively controlled by utilizing the load controllability of an instrumented indentation technology, an acoustic emission detection system collects damage acoustic signals of the material in real time, indirect measurement of fracture toughness is provided by establishing the relation between the size of the surface crack and acoustic emission signal parameters, and a new method is provided for representing the fracture toughness of the coating. Relevant experimental data are perfected based on the method, the fracture toughness of the brittle coating can be rapidly and reliably obtained, and the method has important significance for evaluating the mechanical property of the coating.
Description
Technical Field
The invention belongs to the technical field of material performance characterization, and particularly relates to a method for testing fracture toughness of a brittle material, in particular to a method for evaluating the fracture toughness of the brittle material based on an acoustic emission detection technology.
Background
With the continuous development of surface protection technology of materials, the application of high-performance ceramic coatings to the manufacture of key parts of large-scale engineering equipment is more and more extensive. Under a complex and severe service environment, the ceramic coating is easy to generate unpredictable cracking failure behaviors, and reliable representation and failure degree evaluation of the mechanical property of the ceramic coating are key problems which need to be urgently solved for ensuring stable and reliable work of the ceramic coating.
The spalling failure of the coating is caused by the initiation and the propagation of cracks, and the fracture toughness is often used for evaluating the capability of the coating for resisting the unstable propagation or the fracture of the cracks and is an important mechanical parameter for evaluating the damage of materials. In the existing fracture toughness evaluation method, the indentation test method is simple and quick to operate, has no strict requirements on the shape and the size of a sample, can conveniently and effectively obtain the mechanical property of the coating, and is widely applied to the aspect of testing the mechanical property of the coating. Chinese patent (CN102393341A) discloses an integrated device for testing the fracture toughness of brittle materials by indentation method, which calculates the fracture toughness of materials in the indentation fracture process based on the measured length of indentation cracks according to the indentation fracture mechanics model. However, most brittle coating materials are difficult to distinguish in indentation morphology sometimes under high indentation load, most cracks are in irregular forms, and the crack length measurement is not accurate enough under the influence of image resolution, so that certain error exists in the calculation precision of fracture toughness; meanwhile, the measurement of the crack length needs more energy and is more tedious, and the method is difficult to be quickly and effectively applied to the evaluation of the material performance.
In summary, fracture toughness is used as an important index for evaluating mechanical properties of coating materials, fracture toughness can be effectively and quantitatively calculated by adopting an indentation technology and establishing a relationship between surface crack length and indentation load, although the method is feasible in principle, because accurate measurement of crack length of a brittle coating is complicated, and evaluation of fracture toughness by the indentation technology lacks a simpler and more reliable method, a more superior test method needs to be developed to solve the key technical problem.
Disclosure of Invention
The invention aims to provide a method for testing the fracture toughness of a brittle material, and the proposed quantitative fracture toughness evaluation method is realized by combining an acoustic emission detection technology and an instrumented indentation technology to dynamically detect the crack propagation state in real time. The crack propagation is effectively controlled by utilizing the load controllability of an instrumented indentation technology, an acoustic emission detection system collects damage acoustic signals of the material in real time, indirect measurement of fracture toughness is provided by establishing the relation between the size of the surface crack and acoustic emission signal parameters, and a new method is provided for representing the fracture toughness of the coating. Relevant experimental data are perfected based on the method, the fracture toughness of the brittle coating can be rapidly and reliably obtained, and the method has important significance for evaluating the mechanical property of the coating.
The invention specifically adopts the following technical scheme:
a method of testing the fracture toughness of a brittle material, comprising the steps of:
step S1: preparing experimental materials, including parallelism treatment and polishing treatment of the upper surface and the lower surface of a sample;
step S2: building an experiment platform and setting acoustic emission signal acquisition parameters; the experimental platform at least comprises: the device comprises an indentation generating device and an acoustic emission signal acquisition system;
step S3: carrying out an indentation test, carrying out real-time detection by adopting the acoustic emission acquisition system, and acquiring the appearance of an indentation after the test is finished;
step S4: measuring the length of the half diagonal line of the indentation and the size of the surface crack, and calculating the fracture toughness based on the size of the crack;
step S5: selecting an accumulative acoustic emission characteristic parameter for replacing the surface crack size;
step S6: constructing a fracture toughness evaluation equation based on the characteristic parameters of the cumulative acoustic emission signals;
step S7: and based on the fracture toughness evaluation equation, acquiring the characteristic parameters of the cumulative acoustic emission signals of the material to be detected according to the steps S1-S3, and calculating to obtain the fracture toughness.
Further, step S1 specifically includes: processing a test sample into a cuboid sample with the specification and the size suitable for a clamp on an experiment platform; grinding the upper and lower bottom surfaces of the sample by using metallographic abrasive paper to ensure that the upper and lower surfaces are parallel; and polishing the surface to be measured of the sample by using a metallographic polishing machine until no scratch is observed on the surface under an optical microscope.
Further, in step S2, the experimental platform is provided with: the device comprises instrumented indentation equipment, a two-dimensional precision adjusting platform, an acoustic emission signal acquisition system, a piezoelectric sensor and a preamplifier; the piezoelectric sensor is fixed on the experiment platform through the coupling of a conductive adhesive tape and vacuum silicone grease, comprises a resonant sensor and a broadband sensor, and ensures that the sensor is well coupled with a sample through performance test;
the preferred type of indenter employs a knoop indenter;
the acoustic emission signal acquisition parameters comprise preamplifier gain, signal sampling frequency, sampling length, acoustic emission amplitude threshold value, cut-off frequency of low-pass and high-pass filters, and system timing parameters determined according to experimental material types, and comprise: peak definition time PDT, impact definition time HDT and impact lockout time HLT.
Measuring the size of the surface crack in the step S4, and accurately measuring the length of the crack by adopting a fractal theory;
further, the concrete implementation process of calculating the fracture toughness based on the crack size in step S4 is as follows:
collecting indentation appearances under different indentation loads, measuring the length of an indentation diagonal line and the total length of a crack, taking logarithms for the indentation load, the diagonal line half-length and the surface crack length, performing linear fitting on the data points by using a least square method, enabling the indentation crack and the indentation half-diagonal size parameters to intersect at one point, substituting the corresponding parameters into a calculation formula (1) of the fracture toughness of the coating as a critical point of the surface cracking of the coating, and calculating to obtain the fracture toughness Kc of the coating:
wherein, KcFor fracture toughness, P is indentation load, d/2 is diagonal half length, laSurface crack length.
Further, the cumulative acoustic emission characteristic parameters in step S5 include cumulative ringing count, cumulative energy, and duration; wherein the selection of the cumulative acoustic emission characteristic parameter in place of the surface crack size is determined based on a linear correlation of the different types of cumulative acoustic emission signal characteristic parameters plotted against the total length of the surface crack.
The specific process of selecting the acoustic emission signal characteristic parameters in the step S5 is as follows, different types of accumulated acoustic emission signal characteristic parameters and the total length of the surface crack are plotted, a least square method is used for carrying out linear fitting on the parameters, and an acoustic emission characteristic parameter X suitable for replacing the size of the surface crack is selected according to the linear correlation; further, the specific implementation process of step S6 is as follows:
according to the accumulated acoustic signal characteristic parameters which are acquired in the step S3 and used for replacing the surface crack size, and the indentation diagonal size obtained in the step S4, a relation graph of indentation load and accumulated acoustic emission factor is made, the slope of a straight line is obtained by linearly fitting the acoustic emission energy factor and the indentation load, and then the fracture toughness measured in the step S4 based on the surface crack size is combined, and an acoustic signal constant related to the material is deduced according to a general formula (2) of the fracture toughness, so that the fracture toughness evaluation equation based on the accumulated acoustic emission signal characteristic parameters is constructed:
wherein k isAEIs the acoustic signal constant associated with the material, d is the length of the diagonal of the indentation, and the cumulative acoustic emission factor is recorded as
Further, in step S7, the precondition for obtaining the fracture toughness is calculated as: carrying out an indentation test, and carrying out real-time detection by adopting the acoustic emission acquisition system; collecting the appearance of the indentation, and measuring the length of the semi-diagonal line of the indentation; and extracting the characteristic parameters of the cumulative acoustic emission signals in the indentation damage process.
That is, when the fracture toughness evaluation equation based on the accumulated acoustic signal energy is established, the fracture toughness evaluation of the same material can be easily completed. The method comprises the following specific steps:
1. providing an experimental material;
2. building an experiment platform and setting acoustic emission signal acquisition parameters;
3. carrying out indentation test and combining with an acoustic emission acquisition system for real-time detection;
4. collecting the shape of the indentation, and measuring the length of the semi-diagonal line of the indentation
5. And calculating fracture toughness based on the characteristic parameters of the cumulative acoustic emission signals.
The specific test theory and process of the invention are as follows,
according to the indentation morphology of most brittle materials, the observed crack types are mainly divided into surface radial cracks (Palmqvist crack) and radial median cracks (Half-penny crack), and the surface radial cracks generally appear under low load. The present invention is based on the numerical model of surface radial cracks proposed by Shetty et al, which is based on the load P and the surface crack size laDetermination of the fracture toughness of the coating:
ponton et al relate the coating fracture toughness to the indentation crack pattern, propose a general equation based on the Palmqvist and radial-median crack model, and the present invention replaces the average radial crack size l by findingaThe characteristic parameter X, giving a modified general equation,
wherein k isAEIs a constant associated with the material and d is the indentation diagonal length.
Acoustic emission is a phenomenon in which transient elastic mechanical waves are generated inside a material due to the rapid release of energy. The acoustic signal energy reflects the relative energy and intensity of the acoustic emission event, and can effectively characterize the damage degree of the coating. When the indentation load is small, the generated acoustic emission energy is also small, the compressive stress is increased along with the increase of the indentation load, the damaged area of the coating is large, and the released acoustic emission energy is also large. By researching the quantitative relation between the acoustic emission energy and the total length of the surface crack, an effective way is provided for simplifying the calculation process of the fracture toughness.
Compared with the prior art, the invention and the preferred scheme thereof have the following beneficial effects: the traditional fracture toughness evaluation formula is obtained based on the surface crack size, and the accurate measurement of the crack size is usually complicated. On the basis of the theory that the acoustic emission signal characteristic parameters are feasible to replace the surface crack sizes, the method constructs a fracture toughness evaluation equation based on the accumulated acoustic emission signal characteristic parameters to provide indirect measurement of the fracture toughness of the coating. In the subsequent evaluation, the crack size does not need to be measured, and the fracture toughness can be quickly and effectively calculated by extracting the accumulated acoustic emission characteristic parameters, so that the complicated crack size measurement is omitted.
Drawings
The invention is described in further detail below with reference to the following figures and detailed description:
FIG. 1 is a schematic flow chart of the test analysis method of the present invention.
FIG. 2 is a graph showing the relationship between indentation load, indentation diagonal length, and crack size in example 1 of the present invention.
FIG. 3 is a graph of the cumulative acoustic emission energy versus the total crack length in example 1 of the present invention.
FIG. 4 is a graph of the cumulative acoustic emission energy factor versus indentation load for example 1 of the present invention.
FIG. 5 is a graph of the cumulative acoustic emission energy factor versus indentation load for example 2 of the present invention.
FIG. 6 is a graph showing the relationship between indentation load, indentation diagonal length, and crack size in example 2 of the present invention.
Detailed Description
In order to make the features and advantages of this patent more comprehensible, 2 embodiments accompanied with figures are described in detail below:
it should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
Example 1
Taking an indentation test of the plasma sprayed 8YSZ thermal barrier coating as an example, the fracture toughness evaluation equation of the 8YSZ ceramic coating based on the characteristic parameters of the cumulative acoustic emission signal is obtained by adopting the following steps:
s1, providing experimental materials: the thermal barrier coating of the embodiment is prepared by adopting an atmospheric plasma spraying method, the substrate is made of Inconel718 high-temperature alloy, the bonding layer is NiCoCrAlY, the ceramic layer is 8YSZ, and the thicknesses of the bonding layer and the ceramic layer are respectively 100 micrometers and 300 micrometers. The test sample is processed into a cuboid sample with the specification and dimension of 15mm in length, 10mm in width and 4mm in thickness. And the upper and lower bottom surfaces of the sample are ground by metallographic abrasive paper, so that the upper and lower surfaces are parallel. Wherein, the surface with the sample is further polished on a metallographic polisher until no scratch is observed on the surface under an optical microscope.
S2, building an experiment platform and setting acoustic emission signal acquisition parameters: fixing the sample on a clamp of a two-dimensional precision platform, adjusting the pressing-in position of the sample, coupling and fixing the piezoelectric sensor on the experiment platform through a conductive adhesive tape and vacuum silicone grease, and connecting the sensor, a preamplifier, an acoustic emission detection system and a computer. Before experimental test, the working performance of the sensor needs to be tested to ensure good coupling with the sample. The specific test parameters for acoustic emission signal acquisition in this embodiment are set such that the gain of the preamplifier is 40dB, the signal sampling frequency f is 5MHz, the sampling length l is 2048 bytes, the acoustic emission amplitude threshold is set to 38dB, and the cutoff frequencies of the low-pass filter and the high-pass filter are set to 0.1kHz and 1MHz, respectively; the system timing parameters, Peak Definition Time (PDT)50 μ s, impact definition time (HDT)200 μ s and impact latch-up time (HLT)300 μ s, were set according to the experimental material type.
S3, carrying out an indentation test, combining with a real-time detection of an acoustic emission acquisition system, and finally acquiring the appearance of the indentation: and controlling the application of indentation load by adopting displacement, setting the displacement loading speed to be 0.1mm/min, changing the peak indentation load P, and sequentially carrying out tests under the indentation loads of 10N, 50N, 100N, 200N, 300N and 500N. In order to ensure good reproducibility of failure evolution in the loading process, the test is repeated for 5 times under each load, and the impression morphology under different loads is collected. During the experiment, the loading of the mechanical testing machine load and the recording of the acoustic signal are carried out synchronously.
S4, measuring the length of the half diagonal line of the indentation and the size of the surface crack, and calculating the fracture toughness Kc based on the size of the crack: measuring the length of the diagonal line of the indentation of the collected indentation morphology and recording the length as d; accurately calculating the total length of the crack by utilizing a fractal theory, averaging the results of 5 times of tests under the same load, and recording as la. For indentation load P, diagonal half length d/2 and surface crack length laThe logarithm was taken and a linear fit was made to these experimental points using the least squares method, as shown in figure 2.
The indentation crack and the indentation half diagonal size parameter are intersected at one point, so that the point is the critical point of the coating surface cracking, and the corresponding parameter (P, d, l) is compared with the pointa) Substituting the obtained product into a calculation formula of the fracture toughness of the coating to calculate the fracture toughness Kc of the coating to be 2.96Mpa m1/2。
S5, selecting the accumulative acoustic emission characteristic parameters replacing the surface crack size: the extracted acoustic emission signal characteristic parameters mainly comprise ringing count, energy and duration, different types of cumulative acoustic emission signal characteristic parameters and the total length of the surface crack are plotted, and least square is usedThe method carries out linear fitting on the surface crack, and selects the size l suitable for replacing the surface crack according to the linear correlationaThe acoustic emission characteristic parameter X;
FIG. 3 is a graph of the cumulative acoustic emission energy of the coating surface versus the total crack length in this example. The linear correlation r was 0.91186, the highest of the three acoustic signal characteristic parameters, and therefore the fracture toughness was calculated using the acoustic emission energy instead of the total crack length.
S6, constructing a fracture toughness evaluation equation based on the characteristic parameters of the cumulative acoustic emission signals: and (4) according to the cumulative acoustic signal energy E measured by the 5 groups of different indentation loads, combining the indentation diagonal dimension d obtained in the step S4 to make the indentation load (P) and the cumulative acoustic emission factor (recorded as
) FIG. 4 shows a graph of the relationship of (A). The slope of the straight line is obtained by linear fitting of the acoustic emission energy factor and the indentation load
Is 3.76X 10-9The linear correlation reaches 0.97197. Fracture toughness K obtained by combining S4cAccording to the general formula of fracture toughness, the acoustic signal constant k related to the material can be calculatedAEIs 9.0X 10-9. Thus, the fracture toughness evaluation equation based on the accumulated acoustic signal energy for an 8YSZ ceramic coating is expressed as:
example 2
When the fracture toughness evaluation equation based on the accumulated acoustic signal energy is established, the fracture toughness evaluation of the same material can be completed very easily. In this example 2, the fracture toughness evaluation equation of example 1 is used to test the fracture toughness of the same material in the cross-sectional direction, and the steps of the specific example are as follows:
s1, providing experimental materials: the test material of this example 2 was an 8YSZ ceramic coating prepared by an atmospheric plasma spray process. The test specimen is processed into a sample with the specification and dimension of 15mm in length, 10mm in width and 4mm in thickness. The cross section of the sample was further polished until no visible scratches were observed under an optical microscope.
S2, building an experiment platform and setting acoustic emission signal acquisition parameters: fixing the sample on a clamp of a two-dimensional precision platform, adjusting the pressing-in position of the sample, coupling and fixing the piezoelectric sensor on the experiment platform through a conductive adhesive tape and vacuum silicone grease, and connecting the sensor, a preamplifier, an acoustic emission detection system and a computer. The specific test parameter setting for acoustic emission signal acquisition in this example is the same as that in example 1.
S3, carrying out an indentation test, and detecting in real time by combining an acoustic emission acquisition system; finally, collecting the impression appearance, and measuring the length of the half diagonal line of the impression: and controlling the application of indentation load by adopting displacement, setting the displacement loading speed to be 0.1mm/min, changing the peak indentation load P, and sequentially carrying out tests under indentation loads of 10N, 50N and 100N. To ensure good reproducibility of the evolution of the failure during loading, the test was repeated 5 times at each load. And (5) collecting the impression morphology under different loads, and measuring the length of the diagonal line of the impression, and recording the length as d.
S4, calculating fracture toughness based on the characteristic parameters of the cumulative acoustic emission signals: based on the fracture toughness evaluation equation based on the accumulated acoustic signal energy of the 8YSZ ceramic coating obtained in example 1, the calculated fracture toughness of the coating cross section is 1.37Mpa m1/2The results were compared with the fracture toughness value Kic of 1.48MPa m measured by indentation method1/2Closely, it is further demonstrated that it is feasible to calculate the coating fracture toughness using acoustic emission energy instead of the total surface crack length.
The present invention is not limited to the above preferred embodiments, and all other various methods for testing the fracture toughness of brittle materials can be obtained by anyone who can use the present invention, and all equivalent changes and modifications made according to the claims of the present invention shall be covered by the present invention.
Claims (7)
1. A method of testing the fracture toughness of a brittle material, comprising the steps of:
step S1: preparing experimental materials, including parallelism treatment and polishing treatment of the upper surface and the lower surface of a sample;
step S2: building an experiment platform and setting acoustic emission signal acquisition parameters; the experimental platform at least comprises: the device comprises an indentation generating device and an acoustic emission signal acquisition system;
step S3: carrying out an indentation test, carrying out real-time detection by adopting the acoustic emission acquisition system, and acquiring the appearance of an indentation after the test is finished;
step S4: measuring the length of the half diagonal line of the indentation and the size of the surface crack, and calculating the fracture toughness based on the size of the crack;
step S5: selecting an accumulative acoustic emission characteristic parameter for replacing the surface crack size;
step S6: constructing a fracture toughness evaluation equation based on the characteristic parameters of the cumulative acoustic emission signals;
step S7: and based on the fracture toughness evaluation equation, acquiring the characteristic parameters of the cumulative acoustic emission signals of the material to be detected according to the steps S1-S3, and calculating to obtain the fracture toughness.
2. The method of testing the fracture toughness of a brittle material as claimed in claim 1, characterized in that: step S1 specifically includes: processing a test sample into a cuboid sample with the specification and the size suitable for a clamp on an experiment platform; grinding the upper and lower bottom surfaces of the sample by using metallographic abrasive paper to ensure that the upper and lower surfaces are parallel; and polishing the surface to be measured of the sample by using a metallographic polishing machine until no scratch is observed on the surface under an optical microscope.
3. The method of testing the fracture toughness of a brittle material as claimed in claim 1, characterized in that: in step S2, the experimental platform is provided with: the device comprises instrumented indentation equipment, a two-dimensional precision adjusting platform, an acoustic emission signal acquisition system, a piezoelectric sensor and a preamplifier; the piezoelectric sensor is fixed on the experiment platform through the coupling of a conductive adhesive tape and vacuum silicone grease, comprises a resonant sensor and a broadband sensor, and ensures that the sensor is well coupled with a sample through performance test; the acoustic emission signal acquisition parameters comprise preamplifier gain, signal sampling frequency, sampling length, acoustic emission amplitude threshold value, cut-off frequency of low-pass and high-pass filters, and system timing parameters determined according to experimental material types, and comprise: peak definition time PDT, impact definition time HDT and impact lockout time HLT.
4. The method of testing the fracture toughness of a brittle material as claimed in claim 1, characterized in that: the concrete implementation process of calculating the fracture toughness based on the crack size in step S4 is as follows:
collecting indentation appearances under different indentation loads, measuring the length of an indentation diagonal line and the total length of a crack, taking logarithms for the indentation load, the diagonal line half-length and the surface crack length, performing linear fitting on the data points by using a least square method, enabling the indentation crack and the indentation half-diagonal size parameters to intersect at one point, substituting the corresponding parameters into a calculation formula (1) of the fracture toughness of the coating as a critical point of the surface cracking of the coating, and calculating to obtain the fracture toughness Kc of the coating:
wherein, KcFor fracture toughness, P is indentation load, d/2 is diagonal half length, laSurface crack length.
5. The method of testing the fracture toughness of a brittle material as claimed in claim 1, characterized in that: the cumulative acoustic emission characteristic parameters in step S5 include cumulative ringing count, cumulative energy, and duration; wherein the selection of the cumulative acoustic emission characteristic parameter in place of the surface crack size is determined based on a linear correlation of the different types of cumulative acoustic emission signal characteristic parameters plotted against the total length of the surface crack.
6. The method of testing the fracture toughness of a brittle material as claimed in claim 1, characterized in that: the specific implementation process of step S6 is as follows:
according to the accumulated acoustic signal characteristic parameters which are acquired in the step S3 and used for replacing the surface crack size, and the indentation diagonal size obtained in the step S4, a relation graph of indentation load and accumulated acoustic emission factor is made, the slope of a straight line is obtained by linearly fitting the acoustic emission energy factor and the indentation load, and then the fracture toughness measured in the step S4 based on the surface crack size is combined, and an acoustic signal constant related to the material is deduced according to a general formula (2) of the fracture toughness, so that the fracture toughness evaluation equation based on the accumulated acoustic emission signal characteristic parameters is constructed:
wherein k isAEIs the acoustic signal constant associated with the material, d is the length of the diagonal of the indentation, and the cumulative acoustic emission factor is recorded as
7. The method of testing the fracture toughness of a brittle material as claimed in claim 1, characterized in that: in step S7, the precondition for obtaining the fracture toughness is calculated as: carrying out an indentation test, and carrying out real-time detection by adopting the acoustic emission acquisition system; collecting the appearance of the indentation, and measuring the length of the semi-diagonal line of the indentation; and extracting the characteristic parameters of the cumulative acoustic emission signals in the indentation damage process.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111042878.8A CN113776970A (en) | 2021-09-07 | 2021-09-07 | Method for testing fracture toughness of brittle material |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111042878.8A CN113776970A (en) | 2021-09-07 | 2021-09-07 | Method for testing fracture toughness of brittle material |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN113776970A true CN113776970A (en) | 2021-12-10 |
Family
ID=78841387
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202111042878.8A Pending CN113776970A (en) | 2021-09-07 | 2021-09-07 | Method for testing fracture toughness of brittle material |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN113776970A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115356223A (en) * | 2022-10-20 | 2022-11-18 | 中国矿业大学(北京) | Device and method for measuring shale brittleness index continuous section based on high-temperature and high-pressure scratches |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102305746A (en) * | 2011-08-04 | 2012-01-04 | 西南石油大学 | Method and device for simulating multi-rush fracture toughness of well drilling working condition |
| CN104044069A (en) * | 2014-07-03 | 2014-09-17 | 上海理工大学 | Optical workpiece subsurface damage depth prediction method based on acoustic emission signal |
| CN105628610A (en) * | 2016-04-05 | 2016-06-01 | 大连理工大学 | Integration equipment and detection method for evaluating coating bonding strength based on interface fracture toughness |
| CN109406280A (en) * | 2018-12-05 | 2019-03-01 | 航天科工防御技术研究试验中心 | A kind of quantitative detecting method of coating material impression fracture toughness |
-
2021
- 2021-09-07 CN CN202111042878.8A patent/CN113776970A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102305746A (en) * | 2011-08-04 | 2012-01-04 | 西南石油大学 | Method and device for simulating multi-rush fracture toughness of well drilling working condition |
| CN104044069A (en) * | 2014-07-03 | 2014-09-17 | 上海理工大学 | Optical workpiece subsurface damage depth prediction method based on acoustic emission signal |
| CN105628610A (en) * | 2016-04-05 | 2016-06-01 | 大连理工大学 | Integration equipment and detection method for evaluating coating bonding strength based on interface fracture toughness |
| CN109406280A (en) * | 2018-12-05 | 2019-03-01 | 航天科工防御技术研究试验中心 | A kind of quantitative detecting method of coating material impression fracture toughness |
Non-Patent Citations (2)
| Title |
|---|
| CAICAI LI等: "《Damage evolution and failure mechanism of thermal barrier coatings under Vickers indentation by using acoustic emission technique》", 《PROGRESS IN NATURAL SCIENCE: MATERIALS INTERNATIONAL》 * |
| 张群梅: "《声发射法表征热障涂层的断裂韧性与损伤演化》", 《中国学位论文全文数据库》 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115356223A (en) * | 2022-10-20 | 2022-11-18 | 中国矿业大学(北京) | Device and method for measuring shale brittleness index continuous section based on high-temperature and high-pressure scratches |
| CN115356223B (en) * | 2022-10-20 | 2022-12-20 | 中国矿业大学(北京) | Device and method for measuring shale brittleness index continuous section based on high-temperature and high-pressure scratches |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Song et al. | Measurement of surface wave transmission coefficient across surface-breaking cracks and notches in concrete | |
| CN105628610B (en) | Integrated equipment and detection method based on interfacial fracture toughness evaluation anchoring strength of coating | |
| Lavrov | Kaiser effect observation in brittle rock cyclically loaded with different loading rates | |
| Valdes et al. | Delamination detection in composite laminates from variations of their modal characteristics | |
| Quek et al. | Practical issues in the detection of damage in beams using wavelets | |
| Zhou et al. | In-situ crack propagation monitoring in mortar embedded with cement-based piezoelectric ceramic sensors | |
| CN107831085B (en) | Method for testing hardness of metal material at different pressing depths | |
| Castellini et al. | Non-invasive measurements of damage of frescoes paintings and icon by laser scanning vibrometer: experimental results on artificial samples and real works of art | |
| CN113776970A (en) | Method for testing fracture toughness of brittle material | |
| CN109239138A (en) | A kind of detection method in concrete structural surface new life crack | |
| CN107741368B (en) | Test system for three-dimensional structure internal crack propagation test | |
| JP3523806B2 (en) | Defect inspection method in concrete structure | |
| Li et al. | P-wave arrival determination and AE characterization of concrete | |
| JP6061767B2 (en) | Method and apparatus for exploring delamination inside concrete | |
| CN112858474A (en) | Ultrasonic testing method and system for stress of ceramic rock plate | |
| Lu et al. | Frequency characteristic analysis on acoustic emission of mortar using cement-based piezoelectric sensors | |
| Zubova et al. | Experimental study of the damage accumulation in composite materials and ceramic coatings by using of acoustic emission technique | |
| CN115078086A (en) | Method for measuring bonding force between metal matrix and oxide film by using SEM (scanning electron microscope) in-situ tensile instrument | |
| Dyjak et al. | Acoustic emission analysis of nanoindentation-induced fracture events | |
| Prosser | Waveform analysis of AE in composites | |
| CN111487128A (en) | Device and method for describing compression shear damage of concrete-surrounding rock bonding surface | |
| Schmidt et al. | A Portable Microwave Scanning Technique for Nondestructive Testing of Multi layered Dielectric Materials | |
| Václavek et al. | Effect of Machining on Mechanical Properties of Borosilicate Glasses | |
| Santhanam | Ultrasonic characterization of damage in concrete | |
| Lu et al. | Crack detection using embedded cement-based piezoelectric sensor |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| RJ01 | Rejection of invention patent application after publication | ||
| RJ01 | Rejection of invention patent application after publication |
Application publication date: 20211210 |