KR20220128904A - Evaluation system of directionality of material yield strength using spherical indentation and surface displacement analysis - Google Patents

Abstract

According to embodiments of the present invention, it is possible to evaluate a direction ratio of yield strength for a material having directionality of mechanical properties, and it is convenient and quick to evaluate with a small number of indentation tests. The present invention includes a press-fitting device; a camera device; and a processing device.

Description

Yield strength direction evaluation system of materials using indentation test and surface displacement analysis

The present embodiments relate to a system for evaluating the directionality of yield strength of a material using an indentation test and surface displacement analysis, and more particularly, to an evaluation system capable of evaluating the directionality ratio of yield strength from the directionality of a material surface by an indentation test. .

In order to evaluate the soundness of structural materials, various information such as operating environment, working stress, bonding properties, and mechanical properties are essential. In the case of operating environment and operating stress, it is possible to approximate it from design information, and in the case of defect characteristics, it is possible to measure it in an industrial field using acoustic emission test and ultrasonic test method. On the other hand, the intrinsic mechanical properties of materials cannot be measured in the field by conventional standardized destructive evaluation methods. In addition, since standards related to material testing such as ASTM (American Society for Testing Material) and ISO (International Organization for Standardization) stipulate specific shapes and sizes, there are limitations in application to ultra-fine structures or structures having complex shapes. exist. Therefore, in order to diagnose the level of soundness of structures during operation or to evaluate the quality of complex and diversified cutting-edge industrial products, an evaluation method that can overcome the limitations of existing test methods is required.

Continuous indentation testing (IIT), developed from the existing hardness measurement method, can basically measure hardness and modulus, as well as tensile properties, residual stress, and fracture toughness through elastic and plastic analysis of load and displacement curves. It is a test method that can measure advanced physical properties such as In addition, it is possible to measure the mechanical properties at various scales from micro to nano scale by adjusting the size or load and displacement range of the indenter. As such, experimental/analytic studies have been actively carried out by many researchers due to the characteristics and advantages of the continuous indentation test method. In particular, since yield strength among various mechanical properties is the most basic information for predicting material failure as the stress at which permanent deformation of the material, that is, plastic deformation, begins, yield strength can be calculated using the continuous indentation test method and load and displacement curves. Many studies are being conducted to predict.

Existing studies established a model that can correlate indentation parameters and yield strength through experimental or analytical methods, and the accuracy of the proposed model was verified for materials with various work-hardening behaviors. However, most of the existing models did not consider the directionality information because the mechanical properties for each direction were derived for the same isotropic material.

Structural materials in general industry are manufactured by a plastic deformation process in a specific direction, such as cold or hot rolling. As shown in FIG. 1, as the reduction rate increases, the grain is elongated. ), which causes the directionality of mechanical properties. In addition, 3D printing materials, which have been actively studied recently, are also produced through material printing in a specific direction per production unit as shown in FIG. Similarly, different directions appear in the mechanical properties depending on the printing direction.

It is generally known that these products show the directionality of mechanical properties despite residual stress relaxation and homogenization of crystal properties by heat treatment after processing. Therefore, a new study that can accurately evaluate the mechanical properties of materials showing directionality is needed.

H. Lee, J. Haeng Lee, G. M. Pharr, A numerical approach to spherical indentation techniques for material property evaluation, Journal of the Mechanics and Physics of Solids 53(9) (2005) 2037-2069

The present embodiments relate to an evaluation system that can evaluate the direction ratio of the yield strength from the directionality of the material surface by the indentation test as devised in the background described above.

According to the present embodiments, an indentation device for performing an indentation test on the surface of a material, a camera device for detecting image information by photographing the surface of the material before and after the indentation test is performed, and a surface of a material by an indentation test from image information A system for evaluating the directionality of yield strength of a material using an indentation test and surface displacement analysis, including a processing device that derives the displacement data, which is the displacement of , and derives the directionality of the material's yield strength from the displacement data.

According to the present embodiments, the direction ratio of the yield strength can be evaluated for a material having the directionality of the mechanical properties, and the evaluation is possible even with a small number of indentation tests, which is convenient and quick.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the directionality of the mechanical property of the material produced by cold rolling.
2 is a diagram showing the directionality of the mechanical properties of a material produced by 3D printing.
3 is a diagram showing the configuration of an evaluation system according to the present embodiments.
4 is a view showing an example of deriving the displacement of the material surface by the indentation test.
5 is a diagram showing the difference in the displacement of the material surface by the indentation test in an isotropic material and an anisotropic material.
6 is a view showing the directionality of surface displacement detected by performing an indentation test on a cold-rolled material.
7 is a graph showing the displacement of the material surface by the indentation test derived by varying the yield strength in the x-axis direction and the direction of the yield strength.
8 is a view showing the relationship between the directionality of the displacement of the material surface and the directionality of the yield strength by the indentation test.
9 is a view showing the direction of displacement of the surface of the material by the indentation test of the cold-rolled material derived by varying the reduction ratio.
10 is a view showing a comparison of the directionality of the yield strength according to the tensile test and the directionality of the yield strength derived by the evaluation system according to the present Examples.

Hereinafter, some embodiments of the present disclosure will be described in detail with reference to exemplary drawings. In adding reference numerals to components of each drawing, the same components may have the same reference numerals as much as possible even though they are indicated in different drawings. In addition, in describing the present embodiments, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present technical idea, the detailed description may be omitted. When "includes", "having", "consisting of", etc. mentioned in this specification are used, other parts may be added unless "only" is used. When a component is expressed in a singular, it may include a case in which the plural is included unless otherwise explicitly stated.

In addition, in describing the components of the present disclosure, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only for distinguishing the elements from other elements, and the essence, order, order, or number of the elements are not limited by the terms.

In the description of the positional relationship of components, when two or more components are described as being "connected", "combined" or "connected", two or more components are directly "connected", "coupled" or "connected" ", but it will be understood that two or more components and other components may be further "interposed" and "connected," "coupled," or "connected." Here, other components may be included in one or more of two or more components that are “connected”, “coupled” or “connected” to each other.

In the description of the temporal flow relation related to the components, the operation method or the manufacturing method, for example, the temporal precedence relationship such as "after", "after", "after", "before", etc. Alternatively, when a flow precedence relationship is described, it may include a case where it is not continuous unless "immediately" or "directly" is used.

On the other hand, when numerical values or corresponding information (eg, level, etc.) for a component are mentioned, even if there is no explicit description separately, the numerical value or the corresponding information is based on various factors (eg, process factors, internal or external shock, It may be interpreted as including an error range that may be caused by noise, etc.).

1 is a view showing the directionality of mechanical properties of a material produced by cold rolling, FIG. 2 is a view showing the directionality of mechanical properties of a material produced by 3D printing, and FIG. 3 is an evaluation system according to the present embodiments A diagram showing the configuration, Fig. 4 is a diagram showing an example of deriving the displacement of the material surface by the indentation test, Fig. 5 is a diagram showing the difference in the displacement of the material surface by the indentation test in an isotropic material and an anisotropic material, Fig. 6 is a view showing the directionality of the detected surface displacement after performing an indentation test on the cold-rolled material, and FIG. 7 is a diagram showing the displacement of the material surface by the indentation test derived by varying the yield strength and the direction of the yield strength in the x-axis direction 8 is a graph showing the relationship between the directionality of the displacement of the material surface by the indentation test and the directionality of the yield strength. 10 is a view showing a comparison of the directionality of the yield strength according to the tensile test and the directionality of the yield strength derived by the evaluation system according to the present Examples.

The yield strength direction evaluation system 300 of the material using the indentation test and the surface displacement analysis according to the present embodiments is the indentation device 310 for performing the indentation test on the surface of the material, before and after the indentation test is performed. A camera device 320 that detects image information by photographing a surface, a processing device that derives displacement data that is displacement of the material surface by indentation test from image information, and derives the directionality of the yield strength of the material from the derived displacement data (330).

Referring to FIG. 3 , the yield strength direction evaluation system 300 of the material using the indentation test and surface displacement analysis according to the present embodiments includes the indentation device 310 , the camera device 320 and the processing device 330 . include

The press-in device 310 press-inserts the indenter into the surface of the material. Vickers, knoop, berkovich, spherical, conical indenters, etc. may be used as the indenter. However, in the present embodiments, for a material having the directionality of mechanical properties, Since the system is intended to evaluate the directionality, it is preferable to use an axisymmetric indenter. That is, when an indentation test is performed on a material having mechanical properties directionality using a non-axially symmetric indenter such as Vickers, Knoop, or Bulkovich, it is difficult to obtain accurate data because different indentation results are generated depending on the direction of the indenter. of the indentation test should be performed. However, when an indentation test is performed on a material having the directionality of mechanical properties using an axisymmetric indenter, the same indentation result is generated regardless of the direction of the indenter, so accurate data can be obtained even with a single indentation test. From this, the directionality of the mechanical properties of the material can be evaluated. Hereinafter, the descriptions of the present examples relate to the results of performing the indentation test using the circular indenter, but the present Examples are not limited to performing the indentation test using the circular indenter.

In the case of evaluating the mechanical properties of a material using an indentation test as in the present examples, for example, a more practical evaluation result can be obtained because the mechanical properties can be evaluated directly in the field, such as a structure installed in an industrial site, and operation There is an advantage in that the mechanical properties can be evaluated even for a target having a medium or complex shape.

The camera device 320 detects image information by photographing the surface of the material before and after the indentation test, and transmits the detected image information to the processing device 330 .

The processing device 330 is a computer, for example, from the image information detected by the camera device 320 to derive displacement data that is the displacement of the material surface by the indentation test, and from the derived displacement data, the directionality of the yield strength of the material to derive

By performing an indentation test on a material, plastic deformation by the indentation test occurs in the material, and the displacement data is the displacement of the material surface before and after the indentation test.

The processing device 330 may use, for example, digital image correlation (DIC) to analyze the image information detected by the camera device 320 and derive displacement data therefrom.

The processing device 330 may analyze image information using a strain gage, electronic speckle pattern interferometry (ESPI), etc., but when using a strain gage, one Displacement values can only be derived and the ESPI technique is expensive and cumbersome to use, such as having a laser device. However, when using the DIC technique, displacement analysis can be easily performed on the area around the press-in position.

That is, as shown in FIG. 4 , the processing device 330 may derive the displacement data by analyzing the image information by the DIC technique and comparing the material surface before and after the indentation test.

The displacement data derived by the processing device 330 is the displacement of the material surface in the surface direction. In the past, there have been attempts to evaluate the directionality of mechanical properties of materials from the displacement of the protruding material surface by the indentation test, that is, the z-direction displacement. There was a problem. However, the evaluation system 300 according to the present embodiments detects the displacement of the material surface in the surface direction by using the DIC technique and evaluates the directionality therefrom, so that the directionality can be evaluated more simply and conveniently.

) 및 y방향으로의 변위(

)의 비(

)로서 나타낼 수 있으며, 마찬가지로 항복강도의 방향성 역시 x방향으로의 항복강도(

) 및 y방향으로의 항복강도(

)의 비(

)로서 나타낼 수 있다.On the other hand, when evaluating the directionality of the displacement of the material surface, the direction in which the magnitude of the displacement is greatest may be set as the x-direction, and thus the magnitude of the displacement may be the smallest in the y-direction perpendicular thereto. It goes without saying that the x-direction and the y-direction can be set in a manner different from the above. The processing device 330 may detect displacement data from the image information detected by the camera device 320 and set the x-direction and the y-direction from the magnitude of the displacement, and the displacement from the displacement in the x-direction and the y-direction. direction can be derived. Therefore, after setting the x-direction and the y-direction according to a predetermined criterion in the displacement data, the direction of the displacement of the material surface is

) and displacement in the y direction (

) of the ratio (

), and similarly, the directionality of the yield strength is also the yield strength in the x direction (

) and the yield strength in the y direction (

) of the ratio (

) can be expressed as

5 shows the displacement in the x-direction and the displacement in the y-direction for each indentation test performed on an isotropic material having no directionality of mechanical properties and an anisotropic material having a directionality of mechanical properties, respectively. As shown, it can be seen that the displacement in the x-direction and the y-direction of the isotropic material is almost the same, whereas the change in the x-direction and the displacement in the y-direction of the anisotropic material are different from each other.

Referring to FIG. 6 , when an indentation test is performed on a cold-rolled material, it can be seen that the direction of displacement of the material surface by the indentation test depends on the rolling direction. That is, when the indentation test is performed on the cold-rolled material, it can be confirmed that the displacement of the surface in the rolling direction is larger than the displacement in the transverse direction to the rolling direction. As such, the mechanical properties of the material may change due to various causes, such as being processed by other processes other than cold rolling, and thus may have directionality. According to the present embodiments, the directionality of the yield strength of such materials can be evaluated. it can be

) 및 항복강도의 방향성(

)이 서로 다르게 설정된 재료들을 준비하고 상기 준비된 재료들에 대하여 압입시험을 수행하여 변위데이터(

)를 도출한 결과를 도시한다. x방향 항복강도(

)는 265, 350, 450, 550, 650 MPa 중 어느 하나로, 항복강도의 방향성(m)은 1.0, 1.2, 1.4, 1.6 중 어느 하나로 설정되었다. 즉, y방향 항복강도(

)가 x방향 항복강도(

)보다 크게 설정되었으며, 따라서 x방향으로의 변위의 크기가 y방향으로의 변위의 크기보다 크게 검출되었다.7 shows the yield strength in the x direction (

) and the directionality of yield strength (

) is set differently from each other, and the displacement data (

), the result obtained is shown. Yield strength in the x direction (

) was set to any one of 265, 350, 450, 550, and 650 MPa, and the directionality (m) of the yield strength was set to any one of 1.0, 1.2, 1.4, and 1.6. That is, the yield strength in the y direction (

) is the yield strength in the x direction (

), and therefore the magnitude of the displacement in the x-direction was detected to be larger than the magnitude of the displacement in the y-direction.

)과 항복강도의 방향성(

) 간의 상관관계를 나타내며, 이는 다음 수학식 1과 같이 표현되었다.Fig. 8 shows the direction of displacement of the material surface derived from the result of Fig. 7 (

) and the directionality of yield strength (

), which is expressed as Equation 1 below.

In other words, by using Equation 1, it is possible to derive the directionality of the yield strength of the material from the displacement data detected by performing an indentation test on the material.

9 shows the results of performing an indentation test on materials cold-rolled with different reduction ratios and deriving displacement data. The reduction ratios were set to 0, 10, and 20%, and the derived material surface displacement directions for each were 1.09, 0.79, and 0.64.

)으로부터 수학식 1을 이용하여 도출된 항복강도의 방향성(

)을 비교하여 나타낸다. 도시된 바와 같이, 인장시험에 의한 결과와 본 실시예들에 의한 평가 시스템(300)에 의한 결과가 거의 동일함을 확인할 수 있다.10 shows the directionality of the yield strength derived by performing a tensile test on the materials used in FIG. 9 and the directionality of the material surface displacement by the indentation test (

), the directionality of the yield strength derived using Equation 1 (

) are compared. As shown, it can be seen that the results of the tensile test and the results of the evaluation system 300 according to the present embodiments are almost the same.

Therefore, according to the present embodiments, the directionality of the yield strength can be evaluated for a material having the directionality of the mechanical properties more conveniently and simply by using the indentation test.

The above description is merely illustrative of the technical spirit of the present disclosure, and various modifications and variations will be possible without departing from the essential characteristics of the present disclosure by those skilled in the art to which the present disclosure pertains. In addition, the present embodiments are not intended to limit the technical spirit of the present disclosure, but to explain, and thus the scope of the present technical spirit is not limited by these embodiments. The protection scope of the present disclosure should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present disclosure.

300: Yield strength direction evaluation system of materials using indentation test and surface displacement analysis
310: press-in device 320: camera device
330: processing unit

Claims (5)

an indentation device for performing an indentation test on the surface of the material;
a camera device for detecting image information by photographing the surface of the material before and after the indentation test is performed;
a processing device for deriving displacement data that is displacement of the material surface by an indentation test from the image information, and deriving a directionality of yield strength of the material from the displacement data;
A system for evaluating the directionality of yield strength of materials using indentation tests and surface displacement analysis, including. The method of claim 1,
The indenter of the indentation device is a spherical indenter (spherical indenter), the yield strength direction evaluation system of the material using the indentation test and surface displacement analysis. The method of claim 1,
The treatment device is a system for evaluating the directionality of yield strength of a material using an indentation test and surface displacement analysis, characterized in that it analyzes the displacement of the material surface using a digital image correlation (DIC) technique. The method of claim 1,
The processing apparatus derives the directionality of the displacement of the material surface from the displacement data, and the yield strength directionality of the material using an indentation test and surface displacement analysis, characterized in that deriving the directionality of the yield strength from the directionality of the displacement evaluation system. 5. The method of claim 4,
The processing device, the yield strength direction evaluation system of the material using the indentation test and surface displacement analysis, characterized in that deriving the directionality of the yield strength by the following equation.

Here, a is the directionality of the displacement of the material surface and m is the directionality of the yield strength.

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