KR101328475B1 - Method for estimating interface bonding properties in layered materials using digital image analysis - Google Patents

Abstract

The present invention relates to a method for evaluating bonding properties of a multi-layered metal plate using a digital image interpretation technique and, more particularly, to a method for evaluating interface bonding properties in a tension test which is a method for evaluating mechanical properties of a general metal specimen and is simpler than the conventional methods for evaluating interface bonding properties. In addition, through digital image analysis, the existence of interface bonding can be determined by analyzing the distance between layers, a local deformation rate, etc. The analysis on a bonding property can become easy through the relationship with a transformation rate-stress curve, which is a general property of a material and is obtained from a tension test. A method for analyzing interface bonding properties prepared by the present invention comprises the following steps of: (a) realizing a random pattern on a side of a specimen; (b) obtaining an image of the side of the specimen through an in-situ or an ex-situ test simultaneously with a tension test; (c) observing interface properties through digital image interpretation.

Description

Method for Evaluation of Interfacial Bonding Characteristics of Layered Composites Using Digital Image Analysis {METHOD FOR ESTIMATING INTERFACE BONDING PROPERTIES IN LAYERED MATERIALS USING DIGITAL IMAGE ANALYSIS}

The present invention relates to a method for evaluating interfacial bonding properties of layered composite materials. More specifically, the present invention relates to an interfacial joint by measuring the local vertical strain on both sides of a bonded interface by taking pictures of the specimen laminated surfaces during tensile tests of various layered composite materials. A method of quantitatively analyzing state and bond strength.

Layered composite materials, such as clad metal, in which different metals are bonded together, are composite materials formed by laminating heterogeneous materials through methods such as rolling or bonding. Since the layered composite material can take advantage of each of the different materials, it is possible to realize physical properties that are difficult to realize by a single material alone, and thus, demands are increasing in all industries such as automobiles, airplanes, and constructions.

However, the biggest problem in using a layered composite material is that when the bonding strength at the interface of the dissimilar materials is not sufficient, the bonded materials are separated from each other during use, which is a major factor that lowers the reliability of the layered composite material. It is becoming.

Accordingly, it is necessary to measure in advance whether the layered composite material has the bonding strength required for the intended use.

As a method of measuring the bonding strength of the layered composite material, a peel test, a 4-point bending test, a lap shear test, etc. are used. Specimen fabrication and testing methods are applied differently from material to material, making it difficult to obtain reproducible data. Therefore, the bonding strength measured by the above method is not useful when processing a laminated board.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and is simpler than the conventional methods for evaluating the interfacial bonding properties of a conventional layered composite material by evaluating the bonding properties of a multi-layered metal sheet using a digital image analysis technique. In addition, it is a problem to be solved to provide a method for evaluating interfacial bonding properties of a layered composite material that can provide reliable data.

As a means for solving the above problems, the present invention, (a) forming a predetermined pattern on the side of the layered structure revealed in the tensile specimen made of a layered composite material; (b) obtaining a time-series image of the side surface while performing a tensile test using the tensile test piece; And (c) deriving the interfacial bonding properties of the layered composite material by analyzing the image.

In addition, in the method according to the invention, the pattern of step (a) may be formed differently depending on the size of the tensile specimen and the image magnification obtained.

In addition, in the method according to the present invention, in the step (a), the formation of the pattern may include a method using a spray, a method of etching a surface, a method of depositing a micro grid, a method of scratching through mechanical polishing, and the like. This can be used.

In addition, in the method according to the present invention, in the step (b), the time series image may be obtained by an in-situ or an ex-situ method.

In addition, in the method according to the present invention, in the step (b), the method of obtaining an image of the specimen may vary depending on the size and shape of the pattern.

Further, in the method according to the present invention, in step (c), it is possible to determine whether the interface is separated and the time of separation through the change of the predetermined distance with the change of the distance between the layers of the layered composite material between the interfaces. . In this case, the distance between the layers of the layered composite material may use the distance between two points located inward from the center of each layer by the interface between the layers.

In the method according to the present invention, the interfacial bond strength of the layered composite material can be obtained through the strain-stress data of the layered composite material obtained in the step (b) and the separation point obtained in the step (c). have.

In addition, in the method according to the present invention, it is possible to analyze the local strain through the image analysis obtained in step (c) and to analyze the interfacial bonding properties of the layered composite material.

According to the method for evaluating the interfacial bond strength of the layered composite material according to the present invention, it is possible to determine whether the interface is bonded during the tensile test, to accurately know the time point of the interfacial separation, thereby obtaining accurate data.

In addition, since the interfacial bond strength can be measured through a general tensile test, it is simpler than the conventional peel test.

In addition, since the interfacial bond strength is measured based on the tensile test, the strain-stress relationship can be seen through the tensile test of the laminated composite material, and the interfacial bond characteristics can be observed. Easy to do

Figure 1a is a side photograph of the tensile specimen of the layered composite material showing a structure consisting of CuNiZn-CuCr-CuNiZn.
FIG. 1B shows an example in which a digital image analysis is performed by applying an arbitrary pattern on the tensile specimen side.
2 is a schematic diagram of selecting two points of each layer in order to measure the distance between layers when performing digital image analysis.
3 is a result of analyzing the strain by measuring the strain-stress curve obtained in the tensile test and the distance between each layer as shown in FIG.
FIG. 4 is a result of analyzing a digital image corresponding to a specific position as shown in FIG. 3.

Hereinafter, a method for evaluating a layered composite material interface property according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. Accordingly, it is obvious that those skilled in the art can variously change the present invention without departing from the technical idea of the present invention.

Digital image analysis techniques have recently been widely used as a measurement method for visual analysis to measure the displacement and strain of an object surface in various fields such as machinery, materials, electronics and automobiles. The basic principle is to obtain the local displacement and strain from the change in position between the undeformed image and the post-deformation image. This method creates a set of square pixels with regular or arbitrary intensity patterns in the initial image, finds the set of pixels with the most similar pattern in the deformed image, and determines the change in position.

In contrast to the conventional method for evaluating the interfacial bonding properties of layered composites, the present inventors have found that the interfacial bonding of layered composites in a reliable and simple manner when applying a tensile test and a digital image analysis technique using tensile specimens made of layered composites. It was confirmed that interface bonding characteristics such as strength can be obtained, and the present invention has been attained.

The method of evaluating the bonding interface properties of a layered composite material according to the present invention is largely a step of forming a predetermined pattern on the side surface (part where the layered structure is revealed) of the tensile test specimen (first step), and the tensile deformation during the tensile test. Obtaining a time-series digital image of the side of the specimen (second step), and analyzing the obtained digital image (step 3).

In the first step, as shown in FIG. 1, a predetermined pattern is formed on the side surface of the tensile test specimen made of the layered metal composite material, that is, the layered structure is exposed. The pattern is formed by spraying a white or black paint onto the side of the tensile test specimen to form a random pattern, or etching by dipping or spraying the side surface of the tensile test specimen to form a predetermined pattern. For example, a deposition method for forming a micro-grid through a known deposition process, and a mechanical polishing method for forming a pattern such as a scratch through mechanical polishing may be used.

At this time, the pattern forming method may be used by selecting an appropriate method from the above-described pattern forming method or other pattern forming method in accordance with the size of the tensile specimen used or the magnification of the image to be analyzed.

The second step is to secure a time-series image of the pattern formed on the side of the tensile specimen while performing the tensile test. Image acquisition may be performed using both an in-situ or ex-situ method. In this case, it is preferable that an image is a digital image and a continuous image is obtained in time series at the same magnification. Specifically, the image may be acquired using a digital camera, a high speed camera, a camcorder, an optical microscope, a scanning electron microscope, an atomic force microscope, or the like.

In the third step, the digital image analysis using the image obtained in the second step. In this step, the positional change caused by the deformation of the tensile test piece by regular or irregular patterns formed on the side of the tensile test piece in the first step is measured, and the interfacial bonding properties of the layered composite material are analyzed.

The interfacial bond strength of the layered composite material can be measured by changing the distance between the layers constituting the layered composite material.

Specifically, in the analysis method using the change of distance between layers, as shown in FIG. 2, the distance change is selected by selecting two arbitrary points inside the center line (dashed line on the drawing) of each layer with the boundary between layers. It is preferable to observe.

In general materials, as the specimen is stretched in the stress direction through a tensile test, the thickness of the specimen decreases. In the case of the layered composite material, if the interface of each layer constituting the tensile specimen is bonded, the specimen is reduced in thickness as if it is a single specimen, and the distance between two selected points as shown in FIG. 2 is always reduced. . However, if the interface of each layer of the specimen is not bonded, the thickness of each layer will be reduced separately, and the distance between two points selected as described above will be increased. Therefore, by measuring the change in distance between the two points selected inward from the center of each layer it is possible to accurately determine whether the interface between the layer and the interface between the layers and the time point of the interface separation.

Digital image analysis also reveals the local deformation of the material. In addition, since the deformation amount of the portion increases when the interface of each layer is separated, the interface characteristics can be analyzed through this.

[Example]

A plate-like tensile specimen was prepared by processing a layered metal composite material consisting of three layers of CuNiZn-CuCr-CuNiZn. The prepared tensile test piece has a layered structure as shown in FIG. 1A, and a white paint was sprayed using a sprayer to form a pattern of a random shape on the side of the tensile test piece.

Subsequently, the prepared tensile test piece was mounted in a tensile tester, and a tensile test was performed at a strain rate of 0.001 s ⁻¹ . At this time, the two sides of the tensile tester formed a pattern by using two cameras in real time. Got an image.

The images thus obtained were analyzed using ARAMIS software. From the analyzed results, first, a strain-stress curve of three layers of CuNiZn-CuCr-CuNiZn was obtained.

And, as shown in Figure 2, in order to measure the distance between each layer constituting the layered composite material, two points were selected over the interlayer interface. The two points were selected to be located inward from the center of each layer (dotted line on the drawing) toward the interface. In this way, a total of four points were selected. As shown in FIG. 2, the distance between the first floor and the second floor was T1, and the distance between the second floor and the third floor was T2.

In addition, by analyzing the time-series images obtained during the tensile test, the change (strain) of T1 and T2 during the tension was measured, and the stress-strain data of the layered composite material was obtained from the tensile test results.

Two data thus obtained, the stress-strain data of the layered composite material and the change of T1 and T2 obtained through image analysis were plotted on one graph to obtain FIG. 3.

As shown in FIG. 3, the strain of T1 showed a negative number, which means that the distance between two points continued to decrease, which means that the interface was continuously bonded. By comparison, T2 decreased and then increased again, meaning that it retained some degree of interfacial junction and then separated at a particular moment. That is, the time of debonding of the layered composite material can be accurately confirmed from the data of T2, and the stress at this time can be said to be the bonding strength of the layered composite material.

4 illustrates a digital image analysis result corresponding to each time point indicated by a number in the strain-stress curve of FIG. 3.

In contrast to the time point (Fig. 3) on which the interface of the layered composite material is separated through the analysis of FIG. 3 and the corresponding point 3 in FIG. 4, it is difficult to visually check whether the interface is separated in FIG. The strain of the part where the interface is separated increases and after some separation, the gap between layers can be observed. That is, according to the method according to the embodiment of the present invention, it is possible to measure the exact time of separation between layers, which is difficult to visually discriminate, thereby obtaining a reliable bonding strength of the layered composite material.

On the other hand, in accordance with the results of FIG. 3, it can be seen from ⑤ and ⑥ in FIG. 4 that the interface between the first layer and the second layer does not occur until the tensile specimen is broken.

That is, according to the evaluation method of the layered composite material according to the present invention, not only the interface characteristics, especially the interface strength of the layered composite material can be measured very accurately, but also the state of each interface can be accurately evaluated.

Claims (9)

(a) forming a predetermined pattern on the side surface of the layered structure in the tensile specimen made of the layered composite material;
(b) obtaining a time-series image of the side surface during the tensile test using the tensile specimen; And
(c) analyzing the image to derive interfacial bonding properties of the layered composite material;
In the step (c), the interface bonding property of the layered composite material is determined by the change of the distance between the layers of the layered composite material with the interface therebetween to determine whether the interface is separated and the time of separation. Assessment Methods. The method of claim 1,
The method of step (a) is the evaluation method of the interfacial bonding characteristics of the layered composite material, characterized in that formed according to the size of the tensile specimen and the image magnification obtained. The method of claim 1,
In the step (a), the formation of the pattern, the method of using a spray, the method of etching the surface, the method of depositing a micro grid or the method of scratching through mechanical polishing is used. Evaluation method of interface bonding property. The method of claim 1,
In the step (b), wherein the time-series image is obtained by the in-situ (ex-situ) or ex-situ (ex-situ) method of the evaluation of the interface bonding characteristics of the layered composite material. The method of claim 1,
In the step (b), the method of obtaining the image of the specimen is an evaluation method of the interfacial bonding characteristics of the layered composite material, characterized in that it depends on the size and shape of the pattern. delete The method of claim 1,
The interface between the layered composite material characterized in that the bond strength of the layered composite material is obtained through the strain-stress data of the layered composite material obtained in the tensile test of step (b) and the separation point obtained in the step (c). Method of Evaluation of Bonding Properties. The method of claim 1,
A method of evaluating interfacial bonding properties of a layered composite material, characterized in that the analysis of the local strain through the image analysis obtained in step (c) and thereby analyzing the interfacial bonding properties of the layered composite material. The method of evaluating interfacial bonding characteristics of a layered composite material according to claim 1, wherein the distance between the layers of the layered composite material is a distance between two points located inward from the center of each layer with respect to the interface between the layers.

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