A method for approximating the elastic-plastic parameters of metals based on the Knoop indentation method

Abstract

The present invention is a method for approximately obtaining the elastic-plastic parameters of metals based on the indentation method of the Nuno indenter. The method extracts the curve fitting parameters by obtaining the load-displacement curve of the indentation process. For each load-displacement point on the loading section curve, the corresponding energy-to-work ratio curve with the indentation depth, i.e., the work-to-depth curve, is obtained through numerical processing and calculation. Three independent indentation characteristic parameters, i.e., the slope of the unloading section of the load-displacement curve, the slope of the work-to-depth curve, and the maximum work-to-work ratio, are extracted, thereby approximately obtaining the elastic-plastic parameters. Due to the unique shape of the Nuno indenter, the indentation depth of this method is shallow, the measurement accuracy is high, and the material measurement is non-destructive. It can effectively solve the technical problem of the difficulty in obtaining the elastic-plastic parameters of metal materials such as small-sized components, thin shells and coatings in the prior art.

Description

Technical Field

[0001] The invention belongs to the technical field of material elastic-plastic parameter measurement, and in particular relates to a method for approximately obtaining metal elastic-plastic parameters based on a Knoop indentation method. Background Art

[0002] For metal materials that can undergo tensile tests, it is easy to obtain their elastic-plastic parameters. However, the elastic-plastic mechanical properties measurement requirements of small-sized and service structural materials are difficult to meet through tensile tests, and it is also difficult to directly obtain the elastic-plastic parameters in the existing technology. The indentation method has the advantages of easy implementation, minimal damage, and the ability to measure local mechanical properties. It also provides a solution for obtaining the elastic-plastic parameters of materials under non-tensile test conditions. Known studies have shown that most indentation methods directly use load-displacement curves to extract limited independent parameters, thereby determining the correlation with the material mechanical properties parameters, such as the classic elastic modulus indentation test method. But the problem is that if the three elastic-plastic parameters (E, σ y , n), at least three independent equations are required, and the independent characteristic parameters that can be extracted from a single load-displacement curve are obviously not enough.

[0003] The indentation method has also derived multiple branches due to the different types of indenters. Commonly used indenters include spherical indenters, conical indenters, and pyramidal indenters. Among them, spherical and conical indenters are highly symmetrical rotational structures, which can be simplified for analysis. In addition, they have been developed for a long time, and the related indentation test technology is relatively mature. The pyramidal indenter refers to a type of indenter with similar geometric shapes, such as Vickers indenter, Berkovich indenter, and Knoop indenter, which are mostly used for instrument indentation and high-precision hardness testing. For example, Chinese patent ZL201911315968.2 discloses a method for approximating the elastic-plastic parameters of metals based on the Vickers indentation method. This method defines a third parameter from the morphology and uses the ratio of the maximum pressure value to the square of the maximum indentation depth in the load-displacement curve, the ratio of plastic work to total work, and the indentation size parameter to solve this problem. However, this method is bound to have measurement errors when measuring the indentation size. The mechanical properties of the tested materials are different, and the indentation morphologies obtained are also diverse. Dimensionless processing is also required to achieve specific indentation size parameter extraction, which makes the test method more complicated. In this method, due to the high symmetry of the Vickers indenter and the four identical edges, the cross-sectional area S of the material above the initial plane after being compressed, extracted based on the indentation morphology, is unique and can be applied. However, the Knoop indenter is a diamond pyramid indenter with a rhombus bottom surface. The angles between the two top edges are 172.5° and 130° respectively. It is also called an asymmetric indenter. If the independent characteristic parameter S is to be used in the Knoop indenter penetration test, two different S values ​​will be obtained. Due to the special shape of the Knoop indenter, the two S values ​​will differ greatly. At the same time, it will be affected by the pile-up and sink-in phenomena of the material being tested, making it difficult to implement.

[0004] Compared with spherical, conical indenters and Vickers indenters, the Nuno indenter has the advantages of higher measurement accuracy, shallower indentation depth, better non-destructive measurement, etc. due to its unique geometric shape. It has great application value in the measurement of mechanical properties of some small-sized, thin-shell and coated materials. The shape of the Nuno indenter determines its unique advantages, but it also increases its theoretical analysis and application difficulties. With the improvement of the manufacturing process level of modern materials, its geometric dimensions are getting smaller and smaller, and its shape is becoming more and more complex, and traditional testing methods are difficult to effectively meet the mechanical testing requirements of these small-sized materials. Therefore, the present invention proposes a Nuno indenter indentation test technology, which lays the foundation for the development of a Nuno indenter material mechanical property testing instrument. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for approximating the elastic-plastic parameters of metals based on the Knoop indentation method, which is suitable for small-sized, thin-shell and coated components. The method is a two-line three-parameter method. The main research object of the present invention is the load-displacement curve and the corresponding work-to-depth curve. From these two curves, three independent indentation characteristic parameters are extracted, including the slope of the unloading section of the load-displacement curve, the slope of the work-to-depth curve and the maximum work-to-maximum, so as to approximate the elastic-plastic parameters.

[0006] In order to achieve the above technical objectives, the present invention provides a method for approximating the elastic-plastic parameters of metals based on the Knoop indentation method, the method comprising the following contents:

[0007] Finite element simulation analysis was performed on the Knob indentation test to simulate the indentation process of the Knob indenter and obtain various known elastic-plastic parameters (E, σ y , n) of the metal material load displacement curve, obtain the corresponding energy work ratio with the indentation depth curve, that is, the work ratio depth curve, and extract the unloading slope K of the load displacement curve unloading section, the work ratio slope A of the work ratio depth curve and the maximum work ratio (W e / W t ) max These three independent indentation characteristic parameters can be used to approximately obtain the elastic-plastic parameters;

[0008] The energy-to-work ratio is W e / W t , that is, the elastic work W when the pressing depth is h e and total power W t The ratio of E is the Young's elastic modulus of the material; σ y is the yield strength in the material stress-strain curve; n is the hardening exponent in the material stress-strain curve.

[0009] The process of obtaining the work ratio depth curve is:

[0010] Fitting loading section, the relationship between the loading section load P and displacement h satisfies P=Ch 2 , C is the loading curvature;

[0011] Fitting unloading section, unloading section load P u and displacement h conforms to P u =Kh+b, K is the unloading slope, b is the fitting parameter;

[0012] The loading curvature C and unloading slope K are obtained by fitting the overall load-displacement curve. For each load-displacement point on the loading section, the values ​​of loading curvature C and unloading slope K are fixed to obtain the approximate loading section curve and unloading section curve information of each load-displacement point, and the work ratio W under different penetration depths h is obtained. e / W t, get W e / W t With h / h max The changing trend of the power ratio is the power ratio depth curve, and the characteristic quantities are extracted: the power ratio slope A, the maximum power ratio (W e / W t ) max ;

[0013] Among them, h / h max is the relative penetration depth, a dimensionless parameter; A is the power ratio slope. The second half of the power ratio depth curve is linear, and its slope value is A; (W e / W t ) max For the maximum power ratio, when h / h max =1, the work ratio W e / W t Get the maximum value.

[0014] The process of approximating the elastic-plastic parameters is as follows: the three indentation characteristic parameters K, A and (W e / W t ) max The corresponding elastic-plastic parameters (E, σ y , n) association, the association formula is as follows:

[0015] K(E,σ y , n)=105.000104×E+3.11292×σ y -2932.894441×n+1731.183749 (1)

[0016]

[0017]

[0018] in, is the yield strain, a dimensionless parameter;

[0019] During the measurement, an indenter based on a Nuno indenter is used to obtain the load displacement curve and work ratio depth curve of the material under test through the indentation method, and obtain the K, A and (W e / W t ) max Finally, the K, A and We / W corresponding to the material being tested t ) max Substituting the values ​​of into the correlation equations (1), (2), and (3), we obtain three ternary equations, which are then solved to obtain the elastic-plastic parameters (E, σ y , n).

[0020] The known elastic-plastic parameters (E, σy , n) in metal materials, the selection range of E is 70-210GPa; σ y The selection range of is 50-400MPa; the selection range of n is 0.1-0.5.

[0021] The total work W when the penetration depth is h t By integrating the loading part of the load-displacement curve, we get:

[0022]

[0023] Here P is the load during loading, and C is the loading curvature;

[0024] The elastic work W released by unloading when the pressing depth is h e By integrating the unloading part of the load displacement curve, we get:

[0025]

[0026] Here P u is the load during unloading, K is the unloading slope, h r is the residual indentation depth after unloading, and b is the fitting parameter.

[0027] For the load displacement curve obtained, the indenter is pressed to the maximum depth h max After unloading, the pressing depth is h = h max , relative penetration depth h / h max =1, the ratio of elastic work to total work is the maximum work ratio (W e / W t ) max .

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The method of the present invention extracts independent indentation characteristic parameters K, A and W from the load displacement curve and the work ratio depth curve. e / W t ) max , and successfully combined the three with the material elastic-plastic parameters (E, σ y , n) are associated to obtain the correlation formula, which realizes the method of approximately obtaining the elastic-plastic parameters of the material, solves the technical problem that it is difficult to obtain the elastic-plastic parameters of metal materials in the existing technology for small-sized components, thin shells, coatings, finished parts, and service parts, and has a good pressing effect on the above-mentioned components, making the test method simpler and can minimize the influence of measurement errors.

[0030] The present invention creatively associates the independent characteristic parameters obtained during the Knoop indentation test with the elastic-plastic parameters of the material being tested, thereby achieving an approximate prediction of the compressed material. The elastic-plastic parameters can be directly obtained from the Knoop indentation test through numerical analysis, which is of great significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the Nu-type pressure head pressing in;

[0032] Figure 2 It is a typical load displacement curve of the indentation method;

[0033] Figure 3 Load-displacement scatter plot obtained for the indentation method;

[0034] Figure 4 Work-to-depth curve obtained by indentation method. DETAILED DESCRIPTION

[0035] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0036] The present invention provides a method for approximately obtaining metal elastic-plastic parameters based on the Knob indentation method. The schematic diagram of the Knob indentation is as follows: Figure 1 As shown, the method is implemented specifically by the following steps:

[0037] a) Perform finite element simulation analysis on the Knob indentation test to simulate the Knob indentation process. After the solution is completed, various known elastic-plastic parameters (E, σ y , n) load-displacement curve of metal materials.

[0038] in,

[0039] E is Young's elastic modulus of the material;

[0040] σ y is the yield strength in the material stress-strain curve;

[0041] n is the hardening exponent in the material stress-strain curve;

[0042] Select known elastic-plastic parameters (E, σ y , n) metal material, the selection range of E is 70-210GPa; σ y The selection range of is 50-400MPa; the selection range of n is 0.1-0.5. In the present invention, a large number of known materials within this range are used to perform orthogonal calculations to determine the subsequent correlation equation.

[0043] Figure 2The figure below is a schematic diagram of the load-displacement curve of a certain material, including the loading section and the unloading section. Figure 2 The curvature of the part after the middle unloading section increases significantly because the anti-yield phenomenon occurs in the late stage of unloading, which has nothing to do with the elastic mechanical properties and elastic release work of the compressive material. The unloading section mainly focuses on the unloading slope K and elastic work W related to the elastic modulus of the compressive material. e , and the anti-yield phenomenon belongs to the plastic strain of the material, so the unloading curve is linearized, and the slope of the first section that satisfies the linear relationship is taken as the overall slope. It is considered that the entire unloading curve is linear, and the integral lower limit h when calculating the elastic work is r This is the x-intercept of the unloading line.

[0044] The relationship between the loading section load P and displacement h satisfies P = Ch 2 , C is the loading curvature; unloading section load P u and displacement h conforms to P u =Kh+b, K is the unloading slope, and b is the fitting parameter.

[0045] b) Integrate the loading and unloading sections of the load-displacement curve to obtain the total work W t and elastic work W e , calculate the energy-to-work ratio W e / W t ;

[0046] W t is the total work, which is the work done during the loading process when the indenter is pressed into a depth of h, including elastic work and plastic work;

[0047] W e is the elastic work. When the indenter is unloaded from the indentation depth h, the material elastically recovers and in turn does work on the indenter, i.e., the elastic work W e release;

[0048] The total work W when the pressing depth is h t By integrating the loading part of the load-displacement curve, we get:

[0049]

[0050] Here P is the load during loading, and C is the loading curvature;

[0051] The elastic work W released by unloading when the pressing depth is h e By integrating the unloading part of the load-displacement curve, we get:

[0052]

[0053] Here P u is the load during unloading, K is the unloading slope, h ris the residual indentation depth after unloading, and b is the fitting parameter.

[0054] For the load displacement curve obtained, the indenter is pressed to the maximum depth h max After unloading, the pressing depth is h = h max , relative penetration depth h / h max =1, the ratio of elastic work to total work is the maximum work ratio (W e / W t ) max .

[0055] The loading curvature C and unloading slope K are obtained by fitting the overall load-displacement curve. For each load-displacement point on the loading section, the values ​​of loading curvature C and unloading slope K are fixed to obtain the approximate loading and unloading section curve information of each load-displacement point. According to the above formula for obtaining the work ratio, the work ratio W at different penetration depths h is obtained. e / W t , get W e / W t With h / h max The changing trend of , that is, the power ratio depth curve, such as Figure 4 As shown, the characteristic quantities are extracted: power ratio slope A, power ratio maximum value (W e / W t ) max .

[0056] in,

[0057] h / h max is the relative indentation depth, a dimensionless parameter;

[0058] A is the power ratio slope. The second half of the power ratio depth curve is linear, and its slope value is A.

[0059] (W e / W t ) max For the maximum power ratio, when h / h max =1, the work ratio W e / W t Get the maximum value;

[0060] For the load displacement curve obtained by the indentation test, the curve characteristic parameters such as loading curvature C and unloading slope K are fitted. The loading section curve satisfies the above quadratic equation and has a high degree of fit, while the unloading section is linearly processed, and the slope of the previous linear section is taken as the overall slope. It is considered that the entire unloading curve is linear, and the integral lower limit h when calculating the elastic work is rIt is the x-axis intercept of this unloading straight line, the fixed loading curvature C and the unloading slope K. With the fixed loading curvature C and the unloading slope K, the approximate loading and unloading segment curve information of each load-displacement point on the load-displacement curve is obtained to realize the work ratio calculation under different penetration depths.

[0061] c) For the three elastic-plastic parameters (E, σ y , n) respectively perform single variable analysis and orthogonal calculation, obtain multiple sets of simulation data through simulation tests of various materials, and extract the three indentation characteristic parameters K, A and W corresponding to each material e / W t ) max With the help of SPSS and Matlab fitting tools, the indentation characteristic parameters K, A and (W e / W t ) max Each parameter in the equation is the same as the corresponding elastic-plastic parameter (E, σ y , n) association, the association formula is as follows:

[0062] K(E,σ y , n)=105.000104×E+3.11292×σ y -2932.894441×n+1731.183749 (1)

[0063]

[0064]

[0065] in, is the yield strain, a dimensionless parameter;

[0066] d) During the measurement, an indenter based on a Nuno indenter is used to obtain the load displacement curve and work-to-depth curve of the material under test by the indentation method, and then obtain K, A and (W e / W t ) max Finally, the K, A and (W e / W t ) max Substitute the values ​​of into the correlation equations (1), (2), and (3) in step d to obtain three ternary equations, which are then solved to obtain the elastic-plastic parameters (E, σ y , n).

[0067] In the step d), the elastic-plastic parameters (E, σ y , n), the applicable range of E is 70-210GPa; σ yThe applicable range is 50-400MPa; the applicable range of n is 0.1-0.5.

[0068] The present invention uses a Nuno-type indenter to perform an indentation test, obtains the load-displacement data during indentation, and then performs further numerical processing and calculation on the obtained load-displacement curve to obtain the relationship between the energy-to-work ratio and the indentation depth, that is, the work-to-depth curve, from which more independent parameters can be extracted and combined with the load-displacement curve to achieve the solution of elastic-plastic parameters. The indentation test based on the energy method of the present invention uses the ratio of elastic release work to total work W e / W t As the research object, this parameter has the advantages of good stability, easy acquisition, no influence of material pile-up and sink-in, and simplified analysis, etc., to explore the changing trend of work ratio under different indentation depths. When establishing the correlation formula, it is necessary to conduct indentation tests on a variety of materials with different mechanical properties within the range, and the load-displacement data of each material must be further numerically processed and calculated. At the same time, it is necessary to ensure that there are enough and continuous data at different depths to obtain the changing trend of work ratio.

[0069] The present invention obtains the work ratio for each load-displacement point on the loading section of the load-displacement curve of different tested materials, and makes approximate simplification processing on the loading section and unloading section curves of each load-displacement point. In the process of simulating the indentation of the Nunotype indenter, the vertical downward displacement of the indenter is constantly changing, and the total force applied to the pressure plate corresponding to each step of displacement also changes. To obtain relevant data information, it is necessary to record and extract the indentation displacement and load value in real time, generate a load-displacement result file, and make a load-displacement scatter plot of the indentation test, such as Figure 3 As shown, the horizontal axis represents the indentation displacement (i.e., indentation depth), and the vertical axis represents the load. The points on the load-displacement scatter plot represent the corresponding load values ​​that need to be applied to the indenter when the indenter is pressed down to a certain depth during the indentation process. The load-displacement curve is the curve obtained after the load-displacement scatter plot is fitted. If the work ratio at different indentation depths is required, the general practice is to change the maximum indentation depth to the target indentation depth, integrate the obtained overall load-displacement curve, and calculate the work ratio value. However, this inevitably requires multiple indentation tests, and there are many materials to be tested. It will be more difficult to explore the changing trend of the work ratio, and the workload is huge. Therefore, after determining a maximum indentation depth, the present invention conducts a simulated indentation test on a material to be tested to obtain load-displacement scatter data. After fitting, the overall curve characteristic parameters such as loading curvature C and unloading slope K are obtained, and then the work ratio is obtained for each load displacement point thereon, that is, each different indentation depth. As shown in Figure 3 As shown in the figure, the load and displacement at point i and point j are known. i and hj When the loading curve is only the part before point i and point j, the change of the indentation depth will not affect the overall form of the obtained load-displacement curve. The load and displacement of the loading part still meet the requirements of P = Ch 2 The relationship between P and C i h 2 and P = C j h 2 The loading curvature C of this part of the curve is i and C j The loading curvature C of the fitted overall curve is fixed, and the indentation depth is approximately h. i and h j The loading curve at this time is expressed as P = Ch 2 , h takes h i and h j , C is fixed and known. According to the above total work integral formula, the total work under the current penetration depth can be obtained. Since the same material is only pressed to different depths, the slope of the unloading section should be kept consistent, that is, the pressure head is from the penetration depth h i and h j When unloading, the slope of the unloading curve is K i and K j It should be the same as the unloading slope K of the overall curve. Similarly, the elastic work at the current indentation depth is obtained through the unloading segment expression, and then the work ratio at the current indentation depth is obtained. Because only one indentation test was actually carried out, the loading and unloading segment curves at points i and j are virtual and approximate, and are not actually obtained from h. i and h j The randomly selected points i and j are used to represent all the load displacement points for the convenience of expression and have no practical significance. After obtaining the approximate loading and unloading curves at all the load displacement points, the corresponding work ratio value is obtained according to the above work ratio calculation method, that is, the change trend of the work ratio of a material with the indentation depth is obtained. Figure 4 In order to make the parameters dimensionless, the relative penetration depth h / h is introduced. max As the horizontal coordinate of the work-to-depth curve, the corresponding penetration depth of each load displacement point is known, and the maximum penetration depth is also determined. The relative penetration depth h / h max Then, repeat the above steps for other tested materials with different mechanical properties to establish a one-to-one correspondence between the mechanical properties of the tested materials and the work-to-depth curve.

[0070] Example

[0071] This embodiment uses the above-mentioned correlation equations (1)-(3) to obtain the metal elastic-plastic parameters:

[0072] 1. The load-displacement curve of the component to be tested is obtained by performing an indentation experiment using an indenter based on a Nuno indenter. After extracting the fitting parameters of the load-displacement curve, the corresponding work-to-depth curve is obtained for each load-displacement point on the loading section through numerical processing and calculation.

[0073] 2. Extract independent indentation characteristic parameters: unloading slope K, work ratio slope A and maximum work ratio (W e / W t ) max .

[0074] 3. Substitute the three indentation characteristic parameter values ​​of the material to be tested into the correlation equations (1), (2), and (3) respectively. After solving, the three elastic-plastic parameters (E, σ y , n), to realize the prediction of material mechanical properties.

[0075] K(E,σ y , n)=105.000104×E+3.11292×σ y -2932.894441×n+1731.183749 (1)

[0076]

[0077]

[0078] Example verification: The three known elastic-plastic parameters (E, σ y , n) materials are proved by the above method: through finite element simulation, eight commonly used engineering materials such as 1Cr18Ni9, T225NG alloy, 304 stainless steel, 1Cr18Ni9Ti, 316L, A105, A508, and T2 copper are selected as the test objects, and the Nuo-type indenter pressing process is simulated. After the solution is completed, the unloading slope K, the power ratio slope A, and the maximum power ratio (W) are extracted. e / W t ) max , and then continue to substitute the correlation equations (1)-(3) to solve the equations to obtain the three solved parameters, which are compared as follows:

[0079]

[0080]

[0081] From the above table, it can be seen that the predicted results are close to the actual input parameters, and the error meets the requirements.

[0082] In this embodiment, when the indenter is pressed to the maximum indentation depth h maxFor all the load-displacement points obtained before, their loading curvature C and unloading slope K are fixed as the fitting values ​​of the loading segment and unloading segment of the overall load-displacement curve to obtain the approximate loading and unloading segment curve information of each load-displacement point. Then, the Matlab program is used for multiple integrations, and finally a curve diagram of the change of work ratio with the indentation depth is sorted out, and independent characteristic parameters are extracted for association with elastic-plastic parameters. Finally, the correlation formula is used to predict the mechanical properties of the compressed material.

[0083] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended to include all changes within the meaning and scope of the equivalent elements of the claims. Any figure mark in the claims should not be regarded as limiting the claims involved. In addition, it should be understood that although this specification is described in accordance with the implementation mode, not each implementation mode contains only one independent technical solution. This narrative mode of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0084] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for approximating the elastic-plastic parameters of metals based on the Knoop indentation method, the method comprising the following contents: Finite element simulation analysis was performed on the Knob indentation test to simulate the Knob indentation process and obtain various known elastic-plastic parameters (E, σ y , n), obtain the corresponding energy-to-work ratio curve with the indentation depth, that is, the work-to-depth curve, and extract the unloading slope K of the unloading section of the load-displacement curve, the work-to-depth curve work-to-work ratio slope A and the maximum work-to-work ratio (W e / W t ) max These three independent indentation characteristic parameters can be used to approximately obtain the elastic-plastic parameters; The energy-to-work ratio is W e / W t , that is, the elastic work W when the pressing depth is h e and total power W t The ratio of E is the Young's elastic modulus of the material; σ y is the yield strength in the material stress-strain curve; n is the hardening exponent in the material stress-strain curve; The process of obtaining the work ratio depth curve is: Fitting loading section, the relationship between the loading section load P and displacement h satisfies P=Ch 2 , C is the loading curvature; Fitting unloading section, unloading section load P u and displacement h conforms to P u =Kh+b, K is the unloading slope, b is the fitting parameter; The loading curvature C and unloading slope K are obtained by fitting the overall load-displacement curve. For each load-displacement point on the loading section, the values ​​of loading curvature C and unloading slope K are fixed to obtain the approximate loading section curve and unloading section curve information of each load-displacement point, and the work ratio W under different penetration depths h is obtained. e / W t , get W e / W t With h / h max The changing trend of the power ratio is the power ratio depth curve, and the characteristic quantities are extracted: the power ratio slope A, the maximum power ratio (W e / W t ) max ; Among them, h / h max is the relative penetration depth, a dimensionless parameter; A is the power ratio slope. The second half of the power ratio depth curve is linear, and its slope value is A; (W e / W t ) max For the maximum power ratio, when h / h max =1, the work ratio W e / W t Get the maximum value.

2. The method for approximating the elastic-plastic parameters of metals based on the Knoop indentation method according to claim 1, It is characterized in that The process of approximating the elastic-plastic parameters is as follows: the three indentation characteristic parameters K, A and (W e / W t ) max The corresponding elastic-plastic parameters (E, σ y , n) association, the association formula is as follows: K(E, σ y ,n)=105.000104×E+3.11292×p y -2932.894441×n+1731.183749 (1) in, is the yield strain, a dimensionless parameter; During the measurement, an indenter based on a Nuno indenter is used to obtain the load displacement curve and work ratio depth curve of the material under test through the indentation method, and obtain the K, A and (W e / W t ) max Finally, the K, A and (W e / W t ) max Substituting the values ​​of into the correlation equations (1), (2), and (3), we obtain three ternary equations, which are then solved to obtain the elastic-plastic parameters (E, σ y , n).

3. The method for approximating the elastic-plastic parameters of metals based on the Knoop indentation method according to claim 1, It is characterized in that The known elastic-plastic parameters (E, σ y , n) in metal materials, the selection range of E is 70-210GPa; σ y The selection range of is 50-400MPa; the selection range of n is 0.1-0.

5.

4. The method for approximating the elastic-plastic parameters of metals based on the Knoop indentation method according to claim 1, It is characterized in that The total work W when the pressing depth is h t By integrating the loading part of the load-displacement curve, we get: Here P is the load during loading, and C is the loading curvature; The elastic work W released by unloading when the pressing depth is h e By integrating the unloading part of the load-displacement curve, we get: Here P u is the load during unloading, K is the unloading slope, h r is the residual indentation depth after unloading, b is the fitting parameter; For the load displacement curve obtained, the indenter is pressed to the maximum depth h max After unloading, the pressing depth is h = h max , relative penetration depth h / h max =1, the ratio of elastic work to total work is the maximum work ratio (W e / W t ) max .

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