CN113188890A - Method for measuring material surface residual stress by using nano indentation technology - Google Patents
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Abstract
The invention relates to the technical field of residual stress testing, in particular to a method for measuring the residual stress of a material surface by utilizing a nano indentation technology, which comprises the following specific steps: carrying out nano indentation test on the material to be measured to obtain a load-displacement relation curve of the material to be measured; carrying out differential operation on the load-displacement relation curve of the material to be measured; and obtaining a differential curve of load-displacement and a slope value of the differential curve according to the obtained differential operation result, and obtaining the surface residual stress state of the material to be measured after comparing according to the obtained slope values. The method has the advantages that the method is simple, the residual stress condition of the surface of the tested sample can be directly obtained, and a stress-free sample is not needed to be used as a standard sample. Therefore, the surface residual stress of some special materials such as metallic beryllium can be measured.
Description
Technical Field
The invention relates to the technical field of residual stress testing, in particular to a method for measuring the residual stress of a material surface by using a nanoindentation technology.
Background
At present, residual stress is critical to the performance of materials and the service life of components, and has been widely concerned and studied. Residual stress is a static stress in a material and is in equilibrium with the surrounding environment. It is an internal stress generated by local non-uniform elastic or plastic deformation caused by the variation of loaded force, temperature field or chemical behavior during production, processing, connection and heat treatment. The existence of the residual stress can not only influence the technological level of the material in the processing process, but also can give hidden dangers to the performance and the service life of the subsequent component in the service process. Furthermore, residual stress is widely present in various aspects of engineering applications, and thus, processing and measuring of residual stress of materials becomes particularly important.
There are various methods for measuring the residual stress of materials, and the methods are roughly divided into two types: destructive testing (including drilling, layer-by-layer stripping, profiling, etc.) and non-destructive testing (X-ray diffraction, synchrotron radiation, neutron diffraction, nanoindentation, etc.). However, for some special materials such as metallic beryllium, destructive detection and X-ray diffraction methods are not suitable, while synchrotron radiation and neutron diffraction methods are too expensive, so that the nanoindentation method is also called a depth-sensitive compression technique, and is a relatively new material surface residual stress detection technique which is of great interest to scientists in various countries. Class 2 basic models (Suresh and Lee) have been developed to measure the residual stress of a material surface by nanoindentation. However, the common feature of both methods is that a stress-free standard sample is required, and then the residual stress on the surface of the material is qualitatively and quantitatively obtained by comparing and calculating the load-displacement curve of the measured sample with the load-displacement curve of the standard sample. But sometimes it is difficult to obtain a stress-free standard for certain particular materials, and the complexity of the measurement itself is increased.
Disclosure of Invention
The invention discloses a method for measuring residual stress on a material surface by using a nanoindentation technology, which aims to solve any of the above technical problems and other potential problems in the prior art.
In order to solve the problems, the technical scheme of the invention is as follows: a method for measuring the residual stress on the surface of a material by nano indentation specifically comprises the following steps:
s1) carrying out nano indentation test on a sample to be detected to obtain a relation curve of load and indentation depth (displacement) and a nano hardness value;
s2) differentiating the load and displacement relation curve obtained in S1),
s3) obtaining a differential curve of load-displacement and a slope value of the curve according to the differential operation result obtained in S2) and obtaining the surface residual stress of the measured material.
Further, the S1) specifically includes the following steps:
s1.1) carrying out surface treatment on a material to be measured and cleaning the material by using acetone,
s1.2) placing the processed sample into a nano-indenter, setting the loading indentation depth, measuring,
s1.3) obtaining a load-displacement curve and a material nanometer hardness value H.
Further, the value of the pressing-in depth in the S1.2) is more than 5 times of the depth of the residual stress to be measured.
Further, in the method for obtaining the material nanometer hardness value H in S1.3), the calculation formula is as follows:
H＝F/A，(1)
in the formula, a is an indentation projection area (which can be calculated or directly measured according to an indentation depth and an indenter shape), and F is a loaded force, namely a load.
Further, the specific steps of S3) are:
s3.1) obtaining a differential calculation result according to S2), drawing a differential curve of load-displacement, and obtaining slope values K of the front section and the rear section of the curveIAnd KII，
S3.2) obtaining a slope value K from S3.1)IAnd KIIAnd substituting the judgment condition to confirm the residual stress on the surface of the measured material.
Further, the judgment condition is:
when curve slope value KI＝KIIWhen the material is in a stress-free state, the surface of the material is basically in a stress-free state;
when K isI>KIIThe residual stress state of the surface of the material is expressed as compressive stress;
when K isI<KIIIt indicates that the residual stress state of the material surface is tensile stress.
The method has the advantages that due to the adoption of the technical scheme, the method is simple in measurement method, and the residual stress condition of the surface of the measured sample can be directly obtained. No stress-free samples were required as standards. Therefore, the surface residual stress of some special materials such as metallic beryllium can be measured.
Description of the drawings:
FIG. 1 is a flow chart of a method for measuring residual stress on a material surface by using a nanoindentation technique according to the present invention.
FIG. 2 is a schematic diagram of a method for measuring the residual stress on the surface of a material by using the nanoindentation technique according to the present invention.
Detailed Description
The technical solution of the present invention is further described in detail with reference to the accompanying drawings and embodiments.
As shown in fig. 1, the method for measuring the residual stress on the surface of the material by nano indentation specifically comprises the following steps:
s1) carrying out nano indentation test on the material to be measured to obtain a load-displacement relation curve of the material to be measured;
s2) carrying out differential operation on the load-displacement relation curve of the material to be measured obtained in S1);
s3) obtaining a differential curve of load-displacement and a slope value of the differential curve according to the differential operation result obtained in S2), and obtaining the surface residual stress state of the measured material according to the measured material after the obtained slope value is compared.
The S1) specifically includes the following steps:
s1.1) pretreating a material to be measured,
s1.2) loading the processed material to be measured into a testing device, setting the loading press-in depth to complete the test,
s1.3) obtaining a load-displacement curve according to the test result, and obtaining the average nano hardness value H of the material to be tested after calculation.
The pretreatment in S1.1) is specifically to clean the surface of the material to be measured by using an acetone solution.
And S1.2) the value of the pressing depth is more than 5 times of the predicted thickness.
The testing device in S1.2) is a nanoindenter.
And in S1.3), the nano hardness value H of the material to be measured is obtained through the following formula (1), and the calculation formula is as follows:
H＝F/A，(1)
in the formula, a is an indentation projection area, and F is a loaded force, i.e., a load.
The S3) comprises the following specific steps:
s3.1) obtaining a differential calculation result according to the S2), drawing a differential curve of load-displacement, and obtaining a slope value K of the differential curveIAnd KII，
S3.2) obtaining a slope value K from S3.1)IAnd KIIAnd substituting the residual stress into a judgment condition for judgment to finally obtain the state of the residual stress of the surface of the material to be measured.
The judgment conditions are as follows:
when curve slope value KI＝KIIWhen the stress is detected, the surface of the material to be measured is in an unstressed state;
when K isI>KIIWhen the stress is measured, the residual stress state of the material to be measured is the compressive stress;
when K isI<KIIThe residual stress state of the material to be measured is indicated as tensile stress.
The material to be measured is metal or nonmetal.
Example 1
1) The surface of a hexagonal close-packed pure metal titanium (Ti) sample (containing a rolling state and a rolling annealing state) is simply treated and cleaned by acetone.
2) The sample was loaded into the nanoindenter, closed, and the indentation depth was set at 2000 nm.
3) A plurality of points were randomly impressed and average hardness and load-displacement curves were obtained.
4) And carrying out differential operation on the obtained load-displacement curve and drawing a dF/dh-h curve.
5) According to the drawn dF/dh-h curve and KIAnd KIIAnd qualitatively and quantitatively obtaining the residual stress on the surface of the titanium material.
Surface residual stress test results of pure titanium under different states
Example 2
1) A sample of a metallic beryllium (Be) component was subjected to a simple surface treatment and cleaned with acetone.
2) The sample was loaded into the nanoindenter, closed, and the indentation depth was set to 1000 nm.
3) A plurality of points were randomly impressed and average hardness and load-displacement curves were obtained.
4) And carrying out differential operation on the obtained load-displacement curve and drawing a dF/dh-h curve.
5) According to the drawn dF/dh-h curve and KIAnd KIIAnd qualitatively and quantitatively obtaining the residual stress of the surface of the beryllium member.
Surface residual stress test result of pure beryllium in original state
The method for measuring the residual stress on the surface of the material by using the nanoindentation technology provided by the embodiment of the application is described in detail above. The above description of the embodiments is only for the purpose of helping to understand the method of the present application and its core ideas; meanwhile, for a person skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present application.
As used in the specification and claims, certain terms are used to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This specification and claims do not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. "substantially" means within an acceptable error range, and a person skilled in the art can solve the technical problem within a certain error range to substantially achieve the technical effect. The description which follows is a preferred embodiment of the present application, but is made for the purpose of illustrating the general principles of the application and not for the purpose of limiting the scope of the application. The protection scope of the present application shall be subject to the definitions of the appended claims.
It is also noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a good or system that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such good or system. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a commodity or system that includes the element.
It should be understood that the term "and/or" as used herein is merely one type of association that describes an associated object, meaning that three relationships may exist, e.g., a and/or B may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.
The foregoing description shows and describes several preferred embodiments of the present application, but as aforementioned, it is to be understood that the application is not limited to the forms disclosed herein, but is not to be construed as excluding other embodiments and is capable of use in various other combinations, modifications, and environments and is capable of changes within the scope of the application as described herein, commensurate with the above teachings, or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the application, which is to be protected by the claims appended hereto.
Claims (9)
1. A method for measuring the residual stress on the surface of a material by nano indentation is characterized by comprising the following steps:
s1) carrying out nano indentation test on the material to be measured to obtain a load-displacement relation curve of the material to be measured;
s2) carrying out differential operation on the load-displacement relation curve of the material to be measured obtained in S1);
s3) obtaining a differential curve of load-displacement and a slope value of the differential curve according to the differential operation result obtained in S2), and obtaining the surface residual stress state of the measured material after comparing according to the obtained slope values.
2. The method according to claim 1, wherein S1) specifically comprises the steps of:
s1.1) pretreating a material to be measured,
s1.2) loading the processed material to be measured into a testing device, setting the loading press-in depth to complete the test,
s1.3) obtaining a load-displacement curve according to the test result, and obtaining the average nano hardness value H of the material to be tested after calculation.
3. The method according to claim 2, characterized in that the pretreatment in S1.1) is in particular to clean the surface of the material to be measured with an acetone solution.
4. The method according to claim 2, wherein the depth of the press-in S1.2) is greater than 5 times the predicted thickness.
5. The method according to claim 2, characterized in that the testing device in S1.2) is a nanoindenter.
6. The method according to claim 2, wherein the nano-hardness value H of the material to be measured is obtained in S1.3) by the following formula (1), and the calculation formula is as follows:
H＝F/A，(1)
in the formula, a is an indentation projection area, and F is a loaded force, i.e., a load.
7. The method as claimed in claim 1, wherein the specific steps of S3) are:
s3.1) obtaining a differential calculation result according to the S2), drawing a differential curve of load-displacement, and obtaining a slope value K of the differential curveIAnd KII，
S3.2) obtaining a slope value K from S3.1)IAnd KIIAnd substituting the residual stress into a judgment condition for judgment to finally obtain the state of the residual stress of the surface of the material to be measured.
8. The method according to claim 7, wherein the determination condition is:
when curve slope value KI＝KIIWhen the stress is detected, the surface of the material to be measured is in an unstressed state;
when K isI>KIIWhen the stress is measured, the residual stress state of the material to be measured is the compressive stress;
when K isI<KIIThe residual stress state of the material to be measured is indicated as tensile stress.
9. The method of claim 7, wherein the material to be measured is a metal or a non-metal.
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