A method for predicting mechanical properties of heterogeneous structural materials based on mixture rule and elastic strain energy density

Abstract

The present invention relates to the technical field of mechanical property prediction for heterogeneous structural materials, and in particular to a method for predicting the mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density. The method utilizes the parameters of soft and hard pure materials and the hardness variation of the heterogeneous transition zone to characterize spatial material parameters that vary with position, and introduces elastic strain energy density to determine the strain magnitude when damage occurs, thereby ensuring interaction between materials and improving the accuracy of strength and plasticity prediction. The method can better predict the mechanical properties under various heterogeneous zone ratios, greatly reducing experimental costs, achieving the purpose of obtaining the mechanical properties under various heterogeneous zone ratios without or with minimal preparation of heterogeneous structural parts, and providing a new approach for the subsequent design and development of heterogeneous structural materials.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical property prediction of heterogeneous structural materials, and in particular to a mechanical property prediction method of heterogeneous structural materials based on mixture rule and elastic strain energy density. Background Art

[0002] Heterogeneous structural materials are materials composed of heterogeneous regions with significantly different mechanical or physical properties. Due to the interaction between the heterogeneous regions, such materials can maintain high plasticity while having high yield strength, thereby improving the overall mechanical properties of the material and providing new directions for the research and development of high-strength and high-toughness materials and the repair of expensive engine parts after damage. However, current research on the tensile properties of materials is mainly obtained through experiments. Unlike homogeneous materials, the distribution ratio of heterogeneous regions in heterogeneous materials is closely related to the final mechanical properties. After determining the preparation process, the distribution ratio of heterogeneous regions needs to be adjusted, which will greatly increase the experimental cost. However, current simulations of heterogeneous structural materials mainly focus on improving thermodynamic equations and predicting the segregation of phases and elements during the solidification process, while simulation and prediction work on macroscopic mechanical properties is very scarce.

[0003] The determination of material parameters is closely related to the final mechanical properties of the material. However, due to the existence of heterogeneous regions, the material performance parameters of heterogeneous structural materials are not uniform in space, so there are difficulties in simulating the mechanical properties of heterogeneous structural materials. At present, the mainstream methods for determining composite material parameters include: The rule of mixtures, The Mori-Tanaka model, Self-consistent model and other models, among which the rule of mixtures is the most widely used. However, these models ignore the interaction between different materials and only obtain the final performance of the material through simple superposition, which makes the calculated results differ greatly from the actual mechanical properties, especially in terms of plasticity. During the stretching process, brittle tearing occurs due to the different ductility of the heterogeneous regions, and this method ignores the interaction between heterogeneous materials, resulting in large errors.

[0004] In summary, a prediction method is needed that can predict the stress-strain curve of the material to obtain complete mechanical properties. Through this method, a simple preparation of a heterogeneous region ratio structure sample can be achieved to obtain the mechanical properties of various heterogeneous ratios under the same process, thereby reducing the cost in the development process of heterogeneous structural materials and providing directional guidance for optimizing the heterogeneous region ratio. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings, the present invention aims to provide a technical solution that can solve the above-mentioned problems.

[0006] A method for predicting the mechanical properties of heterogeneous structural materials based on mixture rule and elastic strain energy density comprises the following steps:

[0007] Step 1: Prepare soft and hard pure materials separately and use metal 3D printing technology to prepare "hard-soft-hard" heterogeneous structure materials;

[0008] Step 2: Processing the material prepared in step 1 into a bone rod-shaped tensile part using wire cutting technology;

[0009] Step 3: Grinding and polishing the bone rod-shaped tensile part prepared in step 2;

[0010] Step 4: Perform microhardness measurement on the heterogeneous structure tensile component after polishing in step 3 to obtain the “position-hardness” relationship;

[0011] Step 5: Use Matlab to fit the "position-hardness" relationship obtained in step 4 to obtain the "position-material function ratio" relationship;

[0012] Step 6: Perform a tensile test on each tensile part polished in step 3;

[0013] Step 7: Process the tensile curves of the soft material and the hard material obtained in step 6 to obtain the "stress-strain-position" relationship of the heterostructure material;

[0014] Step 8: Create a bone rod tensile model in ABAQUS and import the stress-strain relationships of the soft and hard materials obtained in step 6 and the materials in step 7. Set the tensile direction and boundary conditions, and execute the operation.

[0015] Step 9: Determine the strain when the heterogeneous material is damaged and obtain the stress-strain curve.

[0016] As a further solution of the present invention: in step 2, the material prepared in step 1 is processed into a bone rod type tensile part and then heat treated.

[0017] As a further solution of the present invention: the heat treatment process is to keep the temperature at 980℃ for 2 hours, then air cool, keep the temperature at 720℃ for 8 hours, cool to 620℃ for two hours, keep the temperature at 620℃ for 8 hours, and then air cool.

[0018] As a further solution of the present invention: in step 3, mechanical grinding is performed successively with 320-mesh and 2500-mesh sandpapers, and then polishing is performed with polishing liquids with particle sizes of 3 μm, 1 μm, and 0.02 μm.

[0019] As a further solution of the present invention: In step 4, the hardness of the heterogeneous structure is measured using a hardness tester at a pressure of 200 g per 100 μm.

[0020] As a further solution of the present invention: the conversion relationship of "position-material function ratio" in step 5 is:

[0021] Z n×1 =[z 11 z 21 …z n1 ] T

[0022]

[0023] Among them, Z n1 is the n×1 hardness point position matrix, W n1 Z n1 The functional proportion of a single material at the hardness point. HV is the hardness value measured in step 4. HV1 and HV2 are the hardness values ​​of pure soft and hard materials, respectively.

[0024] As a further solution of the present invention: in step 7, the tensile curve of the pure material is processed and the strain is evenly discretized into m points to form a strain matrix ε m×1 , the stress relationships corresponding to the m strain points at the n hardness points are superimposed according to the “position-material function ratio” relationship obtained in step 5 to form the stress matrix σ m×n , the parameter distribution relationship of heterogeneous structure materials is obtained as follows:

[0025] ε m×1 =[ε 11 ε 21 …ε m1 ] T

[0026]

[0027]

[0028] Among them, P (m×n)×3 It is the "stress-strain-position" relationship of heterogeneous structural materials.

[0029] As a further solution of the present invention: Step 9 specifically further includes the following steps:

[0030] Step 9.1: Extract the relationship between the elastic strain energy density and strain of the hard material in step 8 and determine the maximum elastic strain energy density Q that the hard material can withstand. max ;

[0031] Step 9.2: Extract the relationship between elastic strain energy and strain of the heterostructure material in step 8, and determine the strain when the hard region of the heterostructure material reaches the maximum elastic strain energy density;

[0032] Step 9.3: Set damage to the heterogeneous material tensile model and set the strain energy density Q at ε strain ε ≥Q max When damage occurs, the operation is performed again to obtain the stress-strain curve of the heterogeneous structure material.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a method for predicting the mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density. The method uses the parameters of soft and hard pure materials and the hardness changes in the heterogeneous transition zone to characterize the spatial material parameters that change with position, and introduces elastic strain energy density to determine the strain size when damage occurs, ensure the interaction between materials, and improve the accuracy of strength and plasticity prediction. Through this method, the mechanical properties under various heterogeneous zone ratios can be well predicted, which greatly reduces the experimental cost and achieves the purpose of obtaining the mechanical properties under various heterogeneous zone ratios without preparing or with less preparation of heterogeneous structural parts, providing a new idea for the subsequent design and development of heterogeneous structural materials.

[0034] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 It is a schematic diagram of the structure of the bone rod tensile component.

[0037] Figure 2 This is the relationship diagram between the clamping end position and hardness of heterogeneous structural parts.

[0038] Figure 3 It is a spatial material parameter diagram.

[0039] Figure 4 is the true stress-true strain curve.

[0040] Figure 5 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0041] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0042] See also Figures 1 to 5 In an embodiment of the present invention, a method for predicting the mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density includes the following steps:

[0043] Step 1: Prepare soft and hard pure materials respectively, and use metal 3D printing technology to prepare "hard-soft-hard" heterogeneous structure materials. The preparation of the heterogeneous structure material is prepared to verify the accuracy of the method. In this case, the soft material is the purchased commercial Inconel625 hot-rolled material steel plate; the hard material is the Inconel718 pure material prepared by using a powder feeding laser metal 3D printing system with a power of 970W, a scanning speed of 480mm / min, and an overlap rate of 60%. The material size is 50mm long and 10mm wide; the "hard-soft-hard" heterogeneous structure material is the prepared "718-625-718" heterogeneous structure material. The specific operation is to successively clad the Inconel718 material on the front and back of the purchased Inconel625 steel plate. The printing parameters are the same as those of Inconel718, and the dimensions of the Inconel718 cladding on both sides are 10mm high, 60mm long, and 10mm wide.

[0044] Step 2: Using wire cutting technology, the material prepared in step 1 is processed into a bone rod type tensile part and heat treated; the size of the cut bone rod is as follows: Figure 1 As shown in the figure, the Inconel 625 area of ​​the heterogeneous structure is 4.21mm, and the Inconel 718 areas on both sides are 800μm and 500μm, respectively. The heat treatment process is to hold at 980°C for 2 hours, then air cool, then hold at 720°C for 8 hours, cool to 620°C over 2 hours, hold at 620°C for 8 hours, and then air cool.

[0045] Step 3: Grind and polish the bone rod-shaped tensile component prepared in step 2; mechanically grind it with 320-mesh and 2500-mesh sandpapers, and then polish it with polishing liquids with particle sizes of 3 μm, 1 μm, and 0.02 μm.

[0046] Step 4: Perform microhardness measurement on the heterogeneous structure tensile member after polishing in step 3 to obtain the "position-hardness" relationship; use a hardness tester to measure the hardness of the heterogeneous structure member at a pressure of 200g per 100μm. The measurement results are as follows: Figure 2 shown.

[0047] Step 5: Use Matlab to fit the position-hardness relationship obtained in step 4 to obtain the "position-material function ratio" relationship. The conversion relationship is:

[0048] Z n×1 =[z 11 z 21 …z n1 ] T

[0049]

[0050] Among them, Z n1 is the n×1 hardness point position matrix, W n1 Z n1 The functional proportion of a single material at the hardness point, HV is the hardness value measured in step 4, HV1 and HV2 are the hardness values ​​of pure soft and hard materials respectively; because the hardness relationship is symmetrically distributed, half of the hardness points are imported into Matlab for function fitting, and the functional relationship between position and Inconel718 material functional proportion can be obtained

[0051] Step 6: Perform a tensile test on each tensile part after polishing in step 3; perform a tensile test on each tensile part using a Shimadzu in-situ tensile system.

[0052] Step 7: Process the tensile curves of the soft material and the hard material obtained in step 6, and discretize the strain uniformly into m points to form the strain matrix ε m×1 , the stress relationships corresponding to the m strain points at the n hardness points are superimposed according to the “position-material function ratio” relationship obtained in step 5 to form the stress matrix σ m×n , the parameter distribution relationship of heterogeneous structure materials is obtained as follows:

[0053] ε m×1 =[ε 11 ε 21 …ε m1 ] T

[0054]

[0055]

[0056] Among them, P (m×n)×3The "stress-strain-position" relationship of heterogeneous structural materials; the tensile curves of the obtained Inconel718 and Inconel625 materials are fitted using Matlab, and points are taken at every 0.001 strain. Since the Inconel718 material has poor elongation, there is no data support when the elongation exceeds 10%. At this time, it is assumed that it has not necked. With the help of the function fitted by Matlab, the plastic part is extended and points are taken according to the above method. The obtained data point set is superimposed on Inconel718 and Inconel625 at different positions to obtain the required spatial material parameters, such as Figure 3 shown.

[0057] The obtained spatial material parameters are further processed to obtain field variable material parameters suitable for ABAQUS-VUSDFLD; the obtained spatial material parameters are processed into the plastic stress and strain parameters required by ABAQUS, and user-defined field variables are added. The field variables correspond to the material position information Z n×1 , in order to realize the function that material parameters change with the change of position.

[0058] Step 8: Create a bone rod tensile model in ABAQUS and import the stress-strain relationship of the soft and hard materials obtained in step 6, set the tensile direction and boundary conditions, and execute the operation; the size of the established bone rod tensile model is as follows: Figure 1 As shown in the figure, the imported soft and hard materials are the tensile data of Inconel625 and Inconel718 respectively. The tensile direction is the x direction. The left clamping end is set as the fixed end, and the displacement is applied to the right clamping end. The mesh division of the transition zone between the clamping end and the arc adopts the default mesh, and the mesh size in the z direction of the parallel segment is set to 0.1.

[0059] Further establish the bone rod tensile model in ABAQUS and import the materials in step 7, set the tensile direction and boundary conditions, and execute the operation; the size of the established bone rod tensile model is as follows Figure 1 As shown in the figure, the applied boundary conditions, displacement control, mesh division, etc. are also consistent with the modeling of Inconel625 and Inconel718 materials. For the output of elastic strain energy in the field output, the center position mesh of one side of the Inconel718 area with an area of ​​800 μm is selected.

[0060] Step 9: Extract the relationship between the elastic strain energy density and strain of the hard material in step 8 and determine the maximum elastic strain energy density Q that the hard material can withstand max ;

[0061] Further, extracting the relationship between elastic strain energy and strain of the heterogeneous structure material in step 8, and determining the strain when the hard region of the heterogeneous structure material reaches the maximum elastic strain energy density;

[0062] Furthermore, damage is set for the tensile model of heterogeneous structure materials, and the strain energy density Q at ε strain is set ε ≥Q max When damage occurs, the operation is performed again to obtain the stress-strain curve of the heterogeneous structure material.

[0063] The mechanical properties of the heterogeneous structure tensile parts predicted by the present invention are as follows: Figure 4 In order to verify the accuracy of the prediction method of the present invention, tensile tests were also carried out on heterogeneous structural tensile parts of corresponding sizes, and their mechanical properties are shown in Figure 4 As shown, by comparison, it can be seen that the method of the invention has high accuracy in predicting the mechanical properties of heterogeneous structural materials.

[0064] Table 1 shows the mechanical properties of the experimental

[0065] Inconel625 Inconel718 Heterostructured materials Maximum true stress / MPa 1224.787 1444.623 1086.247 Maximum elongation 38.821 11.507 19.373

[0066] Table 2 shows the mechanical properties calculated by simulation.

[0067] Traditional methods This method Maximum true stress / MPa 1276.63 1059.309 Maximum elongation 32.37 21.163

[0068] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A method for predicting the mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density, characterized in that: The steps include: Step 1: Prepare soft and hard pure materials separately and use metal 3D printing technology to prepare "hard-soft-hard" heterogeneous structure materials; Step 2: Processing the material prepared in step 1 into a bone rod-shaped tensile part using wire cutting technology; Step 3: Grinding and polishing the bone rod-shaped tensile part prepared in step 2; Step 4: Perform microhardness measurement on the heterogeneous structure tensile component after polishing in step 3 to obtain the "position-hardness" relationship; Step 5: Use Matlab to fit the "position-hardness" relationship obtained in step 4 to obtain the "position-material function ratio" relationship; Step 6: Perform a tensile test on each tensile part polished in step 3; Step 7: Process the tensile curves of the soft material and the hard material obtained in step 6 to obtain the "stress-strain-position" relationship of the heterogeneous structure material; Step 8: Create a bone rod tensile model in ABAQUS and import the stress-strain relationships of the soft and hard materials obtained in step 6 and the materials in step 7. Set the tensile direction and boundary conditions, and execute the operation. Step 9: Determine the strain when the heterogeneous material is damaged and obtain the stress-strain curve.

2. The method for predicting mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density according to claim 1, characterized in that: In step 2, the material prepared in step 1 is processed into a bone rod type tensile part and then heat treated.

3. The method for predicting mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density according to claim 2, characterized in that: The heat treatment process is to keep it at 980℃ for 2 hours, then air cool it, keep it at 720℃ for 8 hours, cool it down to 620℃ in two hours, keep it at 620℃ for 8 hours, and then air cool it.

4. The method for predicting mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density according to claim 1, characterized in that: In step 3, mechanical grinding is performed with 320-mesh and 2500-mesh sandpapers, and then polishing is performed with polishing liquids with particle sizes of 3 μm, 1 μm, and 0.02 μm.

5. The method for predicting mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density according to claim 1, characterized in that: In step 4, the hardness of the heterogeneous structure is measured using a hardness tester at a pressure of 200 g per 100 μm.

6. The method for predicting mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density according to claim 1, characterized in that: The conversion relationship of "Position-Material Function Ratio" in step 5 is: WITH n×1 =[z 11 With 21 …With n1 ] T Among them, Z n1 is the n×1 hardness point position matrix, W n1 Z n1 The functional proportion of a single material at the hardness point. HV is the hardness value measured in step 4. HV1 and HV2 are the hardness values ​​of pure soft and hard materials, respectively.

7. The method for predicting mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density according to claim 1, characterized in that: In step 7, the tensile curve of the pure material is processed and the strain is evenly discretized into m points to form the strain matrix ε m×1 , the stress relationships corresponding to the m strain points at the n hardness points are superimposed according to the "position-material function ratio" relationship obtained in step 5 to form the stress matrix σ m×n , the parameter distribution relationship of heterogeneous structure materials is obtained as follows: e m×1 =[e 11 e 21 ...he m1 ] T Among them, P (m×n)×3 It is the "stress-strain-position" relationship of heterogeneous structural materials.

8. The method for predicting mechanical properties of heterogeneous structural materials based on the mixture rule and elastic strain energy density according to claim 1, characterized in that: Step 9 specifically includes the following steps: Step 9.1: Extract the relationship between the elastic strain energy density and strain of the hard material in step 8 and determine the maximum elastic strain energy density Q that the hard material can withstand. max ; Step 9.2: Extract the relationship between elastic strain energy and strain of the heterostructure material in step 8, and determine the strain when the hard region of the heterostructure material reaches the maximum elastic strain energy density; Step 9.3: Set damage to the heterogeneous material tensile model and set the strain energy density Q at ε strain ε ≥Q max When damage occurs, the operation is performed again to obtain the stress-strain curve of the heterogeneous structure material.

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