Alloy fracture toughness analysis method and system based on nanoindentation technology

Abstract

The invention belongs to the technical field of metal material science, and particularly relates to an alloy fracture toughness analysis method and system based on a nanoindentation technology, and the method comprises the following steps: S1, carrying out nanoindentation continuous rigidity test on an alloy sample by adopting a Berkovich indenter to obtain an indentation load-indentation depth curve; performing a tensile property test on the alloy sample to obtain the elongation at break and the intrinsic elastic modulus of the material; s2, linear fitting parameters are determined according to the logarithmic linear relation between the effective elastic modulus and the indentation depth; s3, calculating a critical effective elastic modulus according to a continuous damage mechanics theory; S4, calculating the critical indentation energy of the unit contact area of the target alloy through a P-h curve; and S5, calculating a fracture toughness index according to continuum mechanics and a Griffith fracture theory. The method solves the problems of low efficiency and macro-micro data disjunction of a traditional method, and provides a systematic solution for fracture toughness analysis of plastic materials including but not limited to plastic metals such as zinc alloy, aluminum alloy, magnesium alloy and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal material science and technology, and particularly relates to an alloy fracture toughness analysis method and system based on nanoindentation technology. BACKGROUND

[0002] Plastic metal materials play a key role in engineering structures, precision manufacturing and functional devices, and are widely used in many fields such as aerospace, automobiles, electronics, biomedical, etc. The fracture toughness of a material is a core index for measuring its ability to resist crack initiation and propagation, and directly affects the service safety of components under complex stress conditions. However, the traditional fracture toughness evaluation method (such as compact tension test and three-point bending test) mainly faces brittle materials, and has great limitations in applicability to plastic metals. Because for typical plastic materials, significant plastic deformation occurs rather than brittle fracture under stress, the traditional fracture toughness analysis method needs to pre-prepare a crack and evaluate the toughness by crack propagation, but the high plasticity of plastic alloys makes it difficult to form a stable crack in the test, and plastic deformation can mask the true fracture behavior, resulting in data deviation. For example, in the three-point bending test, a sharp crack needs to be pre-prepared in the sample to simulate the actual fracture behavior. For example, a typical plastic alloy, zinc alloy, is prone to plastic passivation during crack pre-preparation due to its high plasticity, and the crack tip is difficult to maintain sharpness, and even the pre-prepared crack may be completely closed due to plastic flow. And the zinc alloy undergoes large-scale plastic deformation during loading, and the crack propagation is accompanied by significant necking and energy dissipation, resulting in unstable crack propagation path and poor repeatability.

[0003] In addition, conventional test methods often require large samples and complex loading systems, making it difficult to meet the needs of local mechanical property evaluation of small size, special-shaped structure or gradient material region. Nanoindentation technology, as a high-resolution micro / nano-scale mechanical property testing method, can obtain high-resolution load-displacement curve response information of materials, and has been widely used in hardness, elastic modulus and other performance characterization of bulk materials such as metals, ceramics and polymers, as well as low-dimensional materials such as thin films and fibers. However, existing researches mainly focus on brittle materials or specific systems (such as ceramics and carbon fibers), and there are obvious deficiencies in the fracture toughness analysis of high plasticity alloy materials. Therefore, the present application provides an alloy fracture toughness analysis method and system based on nanoindentation technology. SUMMARY

[0004] The purpose of the present application is to provide an alloy fracture toughness analysis method based on nanoindentation technology, which solves the problem of low efficiency and disconnection between macro and micro data of traditional methods, and provides a systematic solution for the fracture toughness analysis of plastic materials, especially alloy materials, and realizes the accurate evaluation of the fracture behavior of plastic metal materials in micro-scale regions.

[0005] The technical solutions adopted by the present application are as follows:

[0006] An alloy fracture toughness analysis method based on nanoindentation technology, comprising the following steps:

[0007] S1: using a Berkovich indenter to perform nanoindentation continuous stiffness testing on an alloy sample, obtaining an indentation load-indentation depth curve; performing tensile property testing on the alloy sample to obtain the fracture elongation δ and the intrinsic elastic modulus E of the material, with a loading rate of 10 -3 mm / min;

[0008] In the S1, the nanoindentation testing equipment testing parameters are: indentation load range 100-500 mN, loading rate 5 mN / s, no load holding stage, the nanoindentation testing equipment loading interval is 100 mN, each load point is repeated 4 times to obtain the mean value data.

[0009] S2: according to the logarithmic linear relationship between the effective elastic modulus E * and the indentation depth h p , determine:

[0010] ln(E * )=m·ln(h p )+c

[0011] Wherein, m and c are the linear fitting parameters through 4 loading data points;

[0012] The S2 comprises the following steps:

[0013] S21: calculate the effective elastic modulus E * by the unloading curve segment of the P-h curve;

[0014] S22: obtain multiple sets of E * and h p data, and fit the straight line in S2.

[0015] S3: according to the continuous damage mechanics theory, introduce the damage variable D to calculate the critical effective elastic modulus

[0016]

[0017] Wherein, E is the intrinsic elastic modulus of the material before being damaged;

[0018] The S3 comprises the following steps:

[0019] S31: the straight line obtained by fitting S2 is used to calculate the critical damage elastic modulus to obtain the corresponding According to the continuous damage mechanics theory, introduce the damage variable D;

[0020] S32: Calculate the critical damage variable D based on the basic concept of continuous damage mechanics * :

[0021]

[0022] where δ is the elongation at break obtained from the tensile test in S1, and D is obtained * , and then calculated by S32

[0023] S4: Calculate the critical indentation energy per unit contact area γ of the target alloy by P-h curve * :

[0024]

[0025] where P is the applied indentation load, A p is the indentation tip projection area due to plastic deformation, both of which are functions of h p , is the critical indentation depth corresponding to the fracture initiation point, and γ is the crack initiation energy per unit area;

[0026] S4 includes the following steps:

[0027] S41: For the target alloy, the critical indentation energy per unit contact area γ * is calculated by the indentation load-depth curve, and the expression is as follows:

[0028]

[0029] where P is the applied indentation load, A p is the indentation tip projection area due to plastic deformation, both of which are functions of h p , is the critical indentation depth corresponding to the fracture initiation point;

[0030] S42: P(h p ) can be obtained by quadratic polynomial fitting between indentation load and plastic indentation depth h p ;

[0031] S43: For Berkovich indenter, the relationship between indentation projection area and indentation depth is

[0032] S5: According to the continuum mechanics and Griffith fracture theory, the fracture toughness index is calculated by the following formula:

[0033]

[0034] wherein K

[0035] An alloy fracture toughness analysis system based on nanoindentation technology, the alloy fracture toughness analysis system is used for executing the alloy fracture toughness analysis method in any one of claims 1-5, the alloy fracture toughness analysis system comprises:

[0036] A nanoindentation testing unit and a tensile testing unit: the nanoindentation testing unit and the tensile testing unit are configured with a Berkovich indenter and a load control system, and are used for executing S1, obtaining a plurality of P-h curves and a fracture elongation rate by performing a continuous stiffness test on a target alloy;

[0037] A linear fitting unit: used for executing S2, for calculating a linear fitting parameter m, c of an effective elastic modulus and an indentation depth of a target alloy according to experimental data obtained by the nanoindentation testing unit and the tensile testing unit;

[0038] A critical damage elastic modulus calculation unit: used for executing S3, for calculating a critical damage elastic modulus of a target alloy according to the experimental data;

[0039] A critical indentation energy per unit contact area calculation unit: used for executing S4, for calculating a critical indentation energy of a target alloy according to the experimental data;

[0040] A fracture toughness calculation unit: used for executing S5, for generating a fracture toughness index of the target alloy by the critical indentation energy and the critical damage elastic modulus, wherein the fracture toughness index algorithm is:

[0041]

[0042] wherein K IC is a fracture toughness index of the target alloy, E is an intrinsic elastic modulus of the target alloy, and γ is an energy required for generating a crack per unit area of the target alloy.

[0043] The technical effects obtained by the present application are:

[0044] Firstly, the present application obtains material mechanical response data based on continuous stiffness nanoindentation testing, and combines an improved fracture toughness calculation model, is suitable for plastic alloy materials that do not generate cracks during indentation, overcomes the limitation that traditional methods can only be used for brittle materials, and provides a feasible path for fracture toughness evaluation of alloy plastic materials.

[0045] Secondly, the present application obtains the hardness, elastic modulus and plastic energy consumption of the material by using force-depth curve data inversion, and introduces K IC The evaluation target alloy fracture toughness has good applicability and universality.

[0046] Finally, the present application, without preparing crack sample or carrying out complex macroscopic fracture experiment, has simple experimental process and high efficiency, is especially suitable for mechanical property analysis of microscale or thin-walled complex structural member, and has important theoretical significance and practical application value for new material development, quality control and micro-region mechanics research of plastic alloy. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a flow chart of the alloy fracture toughness analysis method based on nanoindentation technology of the present application;

[0048] Figure 2 is a specific flow chart of S2 in the alloy fracture toughness analysis method based on nanoindentation technology of the present application;

[0049] Figure 3 is a specific flow chart of S3 in the alloy fracture toughness analysis method based on nanoindentation technology of the present application;

[0050] Figure 4 is a specific flow chart of S4 in the alloy fracture toughness analysis method based on nanoindentation technology of the present application;

[0051] Figure 5 is five P-h curve graphs obtained by nanoindentation test in the alloy fracture toughness analysis method based on nanoindentation technology of the present application. DETAILED DESCRIPTION

[0052] In order to make the purpose and advantages of the present application more clear and explicit, the present application is specifically described below in combination with examples. It should be understood that the following text is only used to describe one or several specific embodiments of the present application, and does not strictly limit the specific protection scope of the present application.

[0053] Example 1:

[0054] As shown in Figures 1-4 , an alloy fracture toughness analysis method based on nanoindentation technology comprises the following steps:

[0055] S1: Berkovich indenter is used to perform nanoindentation continuous stiffness test on a zinc alloy sample to obtain an indentation load-indentation depth curve (P-h curve); tensile property test is performed on the zinc alloy sample to obtain a fracture elongation δ and an intrinsic elastic modulus E of the material, and the loading rate is 10 -3 mm / min;

[0056] In S1, the nanoindentation testing equipment is Agilent G200 nanoindenter, and the testing parameters of the nanoindentation testing equipment are as follows: indentation load range 100-500 mN, loading rate 5 mN / s, no load holding stage, nanoindentation testing equipment loading interval is 100 mN, each load point is tested twice to obtain mean value data, and a total of 5 load points are tested.

[0057] Figure 5 Five P-h curves obtained by nanoindentation testing can obtain relevant subsequent required data as shown in Table 1:

[0058] Table 1 Load-displacement data example

[0059]

[0060] S2: According to the logarithmic linear relationship between the effective elastic modulus E * and the indentation depth h p , the following is determined:

[0061] ln(E * )=m·ln(h p )+c

[0062] Wherein, m and c are linear fitting parameters through 4 loading data points;

[0063] In actual use, the following steps are included in S2: S21, since the target zinc alloy has no particularly obvious position that can be identified as the occurrence of fracture in the loading process, the critical indentation depth h cannot be directly measured, but after taking the logarithm of h p and the effective elastic modulus E * of the target zinc alloy, lnh p and lnE * exist an approximate linear relationship, and through 5 times of loading, 5 points are obtained for linear fitting:

[0064] ln(E * )=m·ln(h p )+c

[0065] Wherein, m and c are parameters of the straight line fitted by 5 points obtained by 5 different loading times;

[0066] The effective elastic modulus E * of the target zinc alloy is calculated, and the unloading curve of the P-h curve is analyzed to obtain:

[0067] lnP=lnB+k·ln(h-h r )

[0068] Wherein, B and k are fitting parameters, and h ris the residual depth after unloading, which is obtained from the unloading stage of P-h curve;

[0069] By calculating the equivalent elastic modulus, E * :

[0070]

[0071] where, v and v B are the Poisson's ratios of the material and the indenter, respectively, 0.29 and 0.07, and E B is the Young's modulus of the indenter, 1141 Gpa;

[0072] The original equivalent elastic modulus evaluation method is obtained by the instrument, as follows:

[0073]

[0074] where, β is a value of 1.05, which is a correction factor related to the shape of the indenter, S is the elastic contact stiffness, and A m is the projected contact area;

[0075] The elastic contact stiffness S is given by the unloading curve slope at the maximum indentation depth h m :

[0076]

[0077] The projected contact area is expressed as follows:

[0078]

[0079] where, h c is the contact depth, and θ is the angle between the indenter surface and the sample surface plane, the indenter θ is 19.7°;

[0080] The contact depth h c is expressed as:

[0081]

[0082] where ω is a geometric factor related to the shape of the indenter, and the indenter ω is 0.75.

[0083] S3: According to the continuous damage mechanics theory, the damage variable D is introduced to calculate the critical effective elastic modulus

[0084]

[0085] where E is the intrinsic elastic modulus of the material before being damaged.

[0086] Table 2 Related data fitted by S2 calculation

[0087]

[0088] The obtained parameters are: m = 0.1098, c = 3.7526

[0089] S3 comprises the following steps:

[0090] S31: In actual use, the straight line obtained by fitting S2 is used to calculate the critical damage elastic modulus The corresponding

[0091]

[0092] S32: According to the continuous damage mechanics theory, the damage variable D is introduced:

[0093]

[0094] S33: Based on the basic concept of continuous damage mechanics, the critical damage variable D is calculated * :

[0095]

[0096] Where δ is the elongation at break obtained from the tensile test in S1, and D is obtained * Then the relationship between the damage variable D and is used to calculate Where E is 100 GPa.

[0097] S4: The critical indentation energy per unit contact area γ of the target zinc alloy is calculated by the P-h curve * :

[0098]

[0099] Where P is the applied indentation load, A p is the indentation tip projection area due to plastic deformation, both of which are functions of h p , is the critical indentation depth corresponding to the crack initiation point, and γ is the crack generation energy per unit area;

[0100]

[0101] S4 comprises the following steps:

[0102] S41: For the target zinc alloy which is a plastic material, the critical indentation energy per unit contact area γ * is calculated by the indentation load-depth curve, and the expression is as follows:

[0103]

[0104] where P is the applied indentation load, A p is the projected area of the indentation tip due to plastic deformation, both in h p are functions of h is the critical indentation depth corresponding to the initiation of fracture;

[0105] S42: The expression P(h p ) can be obtained by quadratic polynomial fitting between the indentation load and the plastic indentation depth h p -5 p 2 -0.172·h p +191.6;

[0106] S43: For the Berkovich indenter, the relationship between the indentation projected area and the indentation depth is

[0107] According to the S4 step, the critical indentation energy per unit contact area γ * = 8.01445 (kJ / m 2 )

[0108] S5: According to the continuum mechanics and Griffith fracture theory, the fracture toughness index K IC is calculated by the following formula:

[0109]

[0110] where K IC is the fracture toughness index of the target zinc alloy.

[0111] Specifically, the calculated critical damage elastic modulus S2 is fitted to obtain a straight line After that, γ * is calculated, and finally the fracture toughness unit is:

[0112]

[0113] The fracture toughness index of the target zinc alloy is output, and the specific value is about 40.036 MPam 1 / 2

[0114] Example two:

[0115] An alloy fracture toughness analysis system based on nanoindentation technology, the x fracture toughness analysis system comprises:

[0116] The nanoindentation testing unit and the tensile testing unit are configured with a Berkovich indenter and a load control system, and are used to perform S1, to obtain a plurality of P-h curves and a fracture elongation rate by performing continuous stiffness testing on the target zinc alloy;

[0117] The linear fitting unit is used to perform S2, to calculate the effective elastic modulus of the target zinc alloy and the linear fitting parameters m and c of the indentation depth according to the experimental data obtained by the nanoindentation testing unit and the tensile testing unit;

[0118] The critical damage elastic modulus calculation unit is used to perform S3, to calculate the critical damage elastic modulus of the target zinc alloy according to the experimental data;

[0119] The critical indentation energy per unit contact area calculation unit is used to perform S4, to calculate the critical indentation energy of the target alloy according to the experimental data;

[0120] The fracture toughness calculation unit is used to perform S5, to generate a fracture toughness index of the target zinc alloy according to the critical indentation energy and the critical damage elastic modulus, and the fracture toughness index algorithm is:

[0121]

[0122] Wherein, K IC is the fracture toughness index of the target zinc alloy, E is the intrinsic elastic modulus of the target zinc alloy, and γ is the energy required to generate a crack per unit area of the target zinc alloy.

[0123] Compared with the prior art, the present application has the following advantages:

[0124] Firstly, the present application obtains material mechanical response data based on continuous stiffness nanoindentation testing, and combines an improved fracture toughness calculation model, is suitable for plastic zinc alloy materials that do not generate cracks during indentation, overcomes the limitation that traditional methods can only be used for brittle materials, and provides a feasible path for fracture toughness evaluation of zinc alloy plastic materials.

[0125] Secondly, the present application uses force-depth curve data inversion to obtain material hardness, elastic modulus and plastic energy consumption parameters, and introduces K IC to evaluate the fracture toughness of the target zinc alloy, has good applicability and universality.

[0126] Finally, the present application does not need to prepare a crack sample or perform a complex macroscopic fracture experiment, the experimental process is simple and efficient, is especially suitable for mechanical property analysis of micro-scale or thin-walled complex structural parts, and has important theoretical significance and practical application value for plastic alloy new material development, quality control and micro-region mechanical research.

[0127] The alloy fracture toughness analysis method and system based on the nanoindentation technology in the application are also suitable for biodegradable magnesium-based alloys, high corrosion-resistant plated aluminum-zinc-magnesium alloys and hot-processed zinc-based alloys such as Zn-Cu-Zr alloys.

[0128] The above only describes the preferred embodiments of the present application, and it should be noted that, for those skilled in the art, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application. The structures, devices and operation methods not specifically described and explained in the present application are implemented according to the conventional means in the art, unless otherwise specified and limited.

Claims

1. A method for analyzing alloy fracture toughness based on nanoindentation technology, characterized by: The following steps are involved: S1: Nanoindentation continuous stiffness test of alloy samples was performed using Berkovich indenter to obtain indentation load-indentation depth curve; tensile property test of alloy samples was performed to obtain elongation at break δ and intrinsic elastic modulus E of the material. The loading rate was 10 -3 mm / min; S2: According to the effective elastic modulus E * and indentation depth h p The log-linear relationship is determined by: ln(E * )=m·ln(h p )+c Where m and c are the linear fitting parameters through 5 loading data points; S3: According to the theory of continuum damage mechanics, the damage variable D is introduced to calculate the critical effective elastic modulus Where E is the intrinsic elastic modulus of the material before damage; S4: Calculate the critical indentation energy per unit contact area of ​​the target alloy using the Ph curve * : Where P is the applied indentation load, A p is the projected area of ​​the indentation tip due to plastic deformation, both are h p function, is the critical indentation depth corresponding to the fracture initiation point, γ is the crack initiation energy per unit area; S5: According to continuum mechanics and Griffith fracture theory, the fracture toughness index is calculated by the following formula: where K IC is an indicator of the fracture toughness of the target alloy.

2. The alloy fracture toughness analysis method based on nanoindentation technology according to claim 1, characterized in that: In S1, the test parameters of the nanoindentation test equipment are: indentation load range 100-500mN, loading rate 5mN / s, no load holding stage, the loading interval of the nanoindentation test equipment is 100mN, and each load point is tested twice to obtain the average data.

3. The alloy fracture toughness analysis method based on nanoindentation technology according to claim 1, characterized in that: The S2 comprises the following steps: S21: Calculate the effective elastic modulus E through the unloading curve segment of the Ph curve * ; S22: Get multiple groups of E * and h p Data, fit the straight line in S2.

4. The alloy fracture toughness analysis method based on nanoindentation technology according to claim 1, characterized in that: The S3 comprises the following steps: S31: The straight line obtained by fitting S2 is calculated by calculating the critical damage elastic modulus Get the corresponding According to the theory of continuum damage mechanics, the damage variable D is introduced; S32: Calculate the critical damage variable D based on the basic concepts of continuum damage mechanics * : where δ is the elongation at break obtained from the tensile test in S1, giving D * Then calculate it through S32 5. The alloy fracture toughness analysis method based on nanoindentation technology according to claim 1, characterized in that: The S4 comprises the following steps: S41: For the target alloy, a plastic material, the critical indentation energy per unit contact area is γ * It is calculated through the indentation load-depth curve, and the expression is as follows: Where P is the applied indentation load, A p is the projected area of ​​the indentation tip due to plastic deformation, both are h p function, is the critical indentation depth corresponding to the fracture initiation point; S42: Through indentation load and plastic indentation depth h p The quadratic polynomial fitting between P(h p ); S43: For the Berkovich indenter, the relationship between the indentation projected area and the indentation depth is:

6. An alloy fracture toughness analysis system based on nanoindentation technology, characterized by: The alloy fracture toughness analysis system is used to perform the alloy fracture toughness analysis method according to any one of claims 1 to 5, and the alloy fracture toughness analysis system comprises: Nanoindentation test unit and tensile test unit: The nanoindentation test unit and tensile test unit are equipped with a Berkovich indenter and a load control system, which are used to perform S1, continuously test the stiffness of the target alloy to obtain multiple sets of Ph curves and elongation at break; A linear fitting unit: used to execute S2, used to calculate linear fitting parameters m and c of the effective elastic modulus and indentation depth of the target alloy based on the experimental data obtained by the nanoindentation test unit and the tensile test unit; A critical damage elastic modulus calculation unit: configured to execute S3, configured to calculate the critical damage elastic modulus of the target alloy according to the experimental data; A critical indentation energy calculation unit per unit contact area: used to execute S4, used to calculate the critical indentation energy of the target alloy according to the experimental data; A fracture toughness calculation unit is used to execute S5, and is used to generate a fracture toughness index of the target alloy using the critical indentation energy and the critical damage elastic modulus, wherein the fracture toughness index algorithm is: Among them, K IC is the fracture toughness index of the target alloy, E is the intrinsic elastic modulus of the target alloy, and γ is the energy required to generate a crack per unit area of ​​the target alloy.

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