A mechanical structure impact strength analysis method

Abstract

The application discloses a mechanical structure impact strength analysis method, which comprises the following steps in sequence: 3D model simplification, material property setting, mesh division before finite element analysis, mesh quality evaluation, boundary condition setting, constraint and connection analysis, impact response spectrum load application, modal simulation analysis on a three-dimensional digital model, modal parameter evaluation, impact response spectrum analysis, result post-processing and the like; compared with the prior art, the analysis method can greatly simplify the calculation amount, save the calculation time and the hardware cost.

Description

Technical Field

[0001] This invention belongs to the field of mechanical system dynamics technology, and relates to mechanical vibration technology, specifically a method for analyzing the impact strength of mechanical structures. Summary of the Invention

[0003] Mechanical impact is one of the causes of mechanical structure failure. In product design, the impact resistance of mechanical structures is a key indicator for evaluating product performance. Currently, the most common method for evaluating a product's impact resistance is to conduct impact vibration tests. However, this method has the drawback of not performing impact resistance analysis and verification during the product design phase. This often results in insufficient impact resistance, necessitating redesign, or over-design to ensure impact resistance, leading to excessively large product dimensions and weight.

[0004] Impact strength analysis is a mechanical analysis performed on a mechanical structure. Its purpose is to verify whether the structural mechanical properties in the mechanical design meet the requirements. If they do, it determines whether there is over-design and how much room for weight reduction and optimization exists. If not, further optimization is performed based on the simulation results of weak points. The significance lies in addressing the mechanical performance issues of the structure during the design phase, thereby shortening the development cycle and reducing human and material costs.

[0005] In the product design phase, using computer simulation analysis technology to verify impact strength is an effective solution to improve the impact resistance performance of products and optimize product design. CN106777490B discloses a method for calculating the impact resistance of stern shaft sealing devices based on the large mass method of the substrate, but its application scope is too small due to its environmental background and implementation conditions. CN113742955A discloses a method for optimizing the impact resistance performance of ship relays based on impact spectrum and finite element calculation, but it also lacks significant application value due to its calculation method. Summary of the Invention

[0006] This invention provides a method for analyzing the impact strength of mechanical structures, which can quickly and effectively evaluate the impact resistance of product mechanical structures, and has wide applicability.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for analyzing the impact strength of mechanical structures, mainly including the following steps:

[0008] Step S1, 3D model simplification: The three-dimensional digital model of the mechanical structure is simplified by removing components or structural features that have little impact on the stress, resulting in a simplified model including but not limited to a single component, a single component of a multi-body structure, or an assembly of multiple components.

[0009] Step S2, Material property settings: Set the material properties including the elastic modulus, density, Poisson's ratio, damping, and yield strength;

[0010] Step S3, Mesh generation before finite element analysis: Divide the 3D digital model into a finite number of element bodies, and perform mesh generation on the element bodies to obtain the 3D model after mesh generation. The type of element body is tetrahedron, hexahedron, or triangular prism.

[0011] Step S4: Evaluate whether the mesh quality meets the calculation requirements. If it does not meet the requirements, return to step S3 to re-mesh. If it meets the requirements, proceed to the next step.

[0012] Step S5, Boundary Condition Setting: Set boundary conditions for the mechanical structure, including displacement boundary conditions, stress boundary conditions, and contact parameters. Setting displacement boundary and stress boundary conditions is the preprocessing work for finite element analysis.

[0013] Step S6, Impact Response Spectrum Load Application: Apply impact loads to the three-dimensional digital model in one or more directions according to the analysis requirements;

[0014] Let the differential equation of the mechanical structure for impact vibration be: In the formula, ξ is the structural damping ratio, which ranges from 0.01 to 0.1, δ(t) is the unit amplitude impact load, and A is the amplitude of the impact load;

[0015] According to the Fourier transform formula of impact load The impact load is converted into a finite number of harmonic components to facilitate the calculation of the impact response. m harmonic components are extracted from the formula to approximate the original unit amplitude impact load, with the error controlled within 5%, resulting in the differential equation for impact vibration. Formula for calculating the steady-state response of one component of an impact load Take the natural frequency ω respectively n For ω1, ω2, ω3, ..., ω k For each natural frequency of the structure, the responses of each harmonic component of the impact load are x1, x2, x3, ..., x... m Its maximum frequency response is:

[0016] y1 = max{x1,x2,x3,…,x m}

[0017] y2=max{x1,x2,x3,…,x m}

[0018] y3=max{x1,x2,x3,…,x m}

[0019] …

[0020] y k=max{x1,x2,x3,…,x m};

[0021] Based on the correspondence between the natural frequencies of each order and the maximum acceleration response of each harmonic component of the impact load after data processing, the converted impact response spectrum is obtained.

[0022] Step S7: Perform modal simulation analysis on the three-dimensional digital model to obtain modal parameters including mode shapes, natural frequencies, and modal participation coefficients;

[0023] Step S8: Evaluate whether the modal parameters, including the range of natural frequencies and modal participation coefficients, meet the requirements for calculation accuracy. If they do not meet the requirements, return to step S7 to adjust the modal analysis parameters and recalculate. If they meet the requirements, proceed to the next step.

[0024] Step S9: Depending on the requirements, single-point response spectrum or multi-point response spectrum can be used, and modal merging method and load scaling factor can be set to perform impact response spectrum analysis.

[0025] Step S10: Process the analysis results to obtain the stress distribution cloud map, displacement cloud map, and stress curve along the specified path direction of the mechanical structure;

[0026] Step S11: Extract the stress values ​​at stress concentration points;

[0027] Step S12: Determine whether each stress value is a stress singularity. If a stress singularity exists, return to step S3, readjust the mesh generation method, mesh parameters, etc., and re-mesh.

[0028] Step S13: Compare the obtained stress value with the material's ultimate strength and output the analysis results.

[0029] In the mechanical structure impact strength analysis method described above, in step S1, the components of the simplified model of the assembly of multiple parts are connected by linear contact; the multiple parts of the simplified model of the single part of the multi-body are connected by a common node; preferably, the common node wall coupling method is used as the connection between the multiple parts.

[0030] In the mechanical structure impact strength analysis method described above, in step S3 of the mesh generation, the number of mesh layers in the wall thickness direction of plate structures is not less than 3.

[0031] In the mechanical structure impact strength analysis method, in step S4 of the mesh quality assessment, the aspect ratio of the mesh is not greater than 5, the mesh warpage is not greater than 15°, and the mesh skew angle is not greater than 60°.

[0032] The method for analyzing the impact strength of a mechanical structure, wherein step S5 includes:

[0033] Step S5a, Constraint and Connection Analysis: Analyze the connection relationship between the mechanical structure and the external environment to transform it into mechanical boundary conditions that can be used for analysis and calculation;

[0034] Step S5b: Extract boundary conditions to select equivalent physical connection types or constraints, which are used to equivalently replace the constraints and connections in step S5a.

[0035] The method for analyzing the impact strength of a mechanical structure, wherein step S6 includes:

[0036] Step S6a: Select the time-domain waveform of the impact load according to the requirements or characteristics of the impact load. The impact load type includes, but is not limited to, half-sine impact load, sawtooth waveform impact load, trapezoidal wave impact load, and their approximate waveforms, or a waveform composed of the linear superposition of these waveforms.

[0037] Step S6b: Set impact load parameters, including impact load duration and impact acceleration amplitude;

[0038] Step S6c converts the time-domain impact load into the impact response spectrum of the frequency-domain load.

[0039] The relationship between the natural frequencies of each order and the maximum acceleration response of each harmonic component of the impact load in step S6 of the mechanical structure impact strength analysis method is shown in the table below:

[0040] Natural frequency <![CDATA[ω1]]> <![CDATA[ω2]]> <![CDATA[ω3]]> … <![CDATA[ω k ]]> Acceleration response value <![CDATA[y1]]> <![CDATA[y2]]> <![CDATA[y3]]> … y .

[0041] In the aforementioned method for analyzing the impact strength of mechanical structures, the modal participation coefficients in the six degrees of freedom (X, Y, Z, RX, RY, RZ) of step S8 are not less than 0.85, and the set natural frequency range is not less than 12 orders.

[0042] In the aforementioned method for analyzing the impact strength of mechanical structures, the stress concentration factor at the stress concentration location in step S11 is not less than 1.5, i.e., σ0 / σ m ≥1.5, where σ0 is the stress value at the stress concentration point, σ m This represents the average stress value.

[0043] In the aforementioned method for analyzing the impact strength of mechanical structures, the determination criterion for stress singularities in step S12 must satisfy at least one of the following two determination criteria:

[0044] 1) The stress concentration factor is greater than 10, i.e., σ / σ m ≥10;

[0045] 2) The stress distribution along any path passing through the stress concentration point, where the stress concentration point is the stress maximum, and the stress curves on both sides of the stress concentration point along the selected path are concave curves.

[0046] Compared with the prior art, the beneficial effects of the present invention are:

[0047] 1. This invention can quickly calculate the stress of a mechanical structure under impact load, so as to evaluate the impact resistance of the mechanical structure. Compared with the prior art, it can greatly simplify the calculation and save calculation time and hardware costs.

[0048] 2. The present invention can also select different waveforms according to different load requirements, and can define the impact duration and impact acceleration amplitude, which has universal applicability.

[0049] 3. This invention provides a method for identifying stress singularities under mechanical impact loads, which can effectively eliminate the influence of stress singularities on the analysis results. Attached Figure Description

[0050] Figure 1 This is a flowchart of the steps of the method of the present invention;

[0051] Figure 2 The half-sine impact load applied to the three-dimensional digital model of this invention;

[0052] Figure 3 The equivalent frequency domain load of the half-sine impact load applied by the three-dimensional digital model of this invention;

[0053] Figure 4 The serrated impact load applied by the three-dimensional digital model of this invention;

[0054] Figure 5 The equivalent frequency domain load of the sawtooth impact load applied by the three-dimensional digital model of this invention;

[0055] Figure 6 The trapezoidal impact load applied to the three-dimensional digital model of this invention;

[0056] Figure 7 The equivalent frequency domain load of the trapezoidal impact load applied by the three-dimensional digital model of this invention;

[0057] Figure 8 An example of stress singularity applied to the three-dimensional digital model of this invention. Detailed Implementation

[0058] To further illustrate the purpose and technical solution of the present invention, a more detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments.

[0059] This invention discloses a method for analyzing the impact strength of mechanical structures, combined with Figure 1 Follow these steps.

[0060] Step S1, 3D Model Simplification: The 3D digital model of the mechanical structure is simplified by removing components or structural features that have little impact on the stress. The resulting simplified model includes, but is not limited to, a single component, a single component of multiple bodies, and an assembly of multiple components. In the simplified model of an assembly of multiple components, the components are connected by linear contact; in the simplified model of a single component of multiple bodies, the multiple bodies are connected by a common node. Preferably, a common node wall coupling method is used for the connection between multiple bodies.

[0061] Step S2, setting material properties: including the material's elastic modulus, density, Poisson's ratio, damping, yield strength, etc.

[0062] Step S3, Mesh Generation Before Finite Element Analysis: The 3D digital model is divided into a finite number of element bodies. Mesh generation is then performed on these element bodies to obtain the meshed 3D model. The element body types are tetrahedrons, hexahedrons, or triangular prisms. For plate-type structures, the number of mesh layers in the wall thickness direction should be no less than 3.

[0063] Step S4: Evaluate whether the mesh quality meets the calculation requirements. If not, return to step S3 to re-mesh; if it meets the requirements, proceed to the next step. In the mesh quality evaluation, the aspect ratio of the mesh should not exceed 5, the mesh warpage should not exceed 15°, and the mesh skew angle should not exceed 60°.

[0064] Step S5, Boundary Condition Setting: Set boundary conditions for the mechanical structure, including displacement boundary conditions, stress boundary conditions, and contact parameters; setting displacement boundary and stress boundary conditions is the preprocessing work for finite element analysis.

[0065] Step S5a, Constraint and Connection Analysis: Analyze the connection relationship between the mechanical structure and the external environment to transform it into mechanical boundary conditions that can be used for analysis and calculation.

[0066] Step S5b extracts boundary conditions, which is mainly used to select reasonable physical connections or constraints to equivalently replace the constraints and connections in step S5a.

[0067] Step S6, Applying impact response spectrum load: Apply impact loads to the three-dimensional digital model in one or more directions according to the analysis requirements.

[0068] Let the differential equation of the mechanical structure for impact vibration be: In the formula, ξ is the structural damping ratio, which ranges from 0.01 to 0.1, δ(t) is the unit amplitude impact load, and A is the amplitude of the impact load;

[0069] According to the Fourier transform formula of impact load The impact load is converted into a finite number of harmonic components to facilitate the calculation of the impact response. m harmonic components are extracted from the formula to approximate the original unit amplitude impact load, with the error controlled within 5%, resulting in the differential equation for impact vibration. Formula for calculating the steady-state response of one component of an impact load Take the natural frequency ω respectively n For ω1, ω2, ω3, ..., ω k For each natural frequency of the structure, the responses of each harmonic component of the impact load are x1, x2, x3, ..., x... m Its maximum frequency response is:

[0070] y1=max{x1,x2,x3,…,x m}

[0071] y2=max{x1,x2,x3,…,x m}

[0072] y3=max{x1,x2,x3,…,x m}

[0073] …

[0074] y k =max{x1, x2, x3, ..., x m};

[0075] The correspondence between each natural frequency and the maximum acceleration response of each harmonic component of the impact load is shown in the table below:

[0076] Natural frequency <![CDATA[ω1]]> <![CDATA[ω2]]> <![CDATA[ω3]]> … <![CDATA[ω k ]]> Acceleration response value <![CDATA[y1]]> <![CDATA[y2]]> <![CDATA[y3]]> … y .

[0077] Based on the correspondence between the natural frequencies of each order and the maximum acceleration response of each harmonic component of the impact load obtained after data processing, the converted impact response spectrum is obtained.

[0078] This step involves applying the impact response spectrum load, which can be applied in one or more directions depending on the analysis requirements.

[0079] Step S6a: Select the time-domain waveform of the impact load according to the requirements or characteristics of the impact load. The impact load type includes, but is not limited to, half-sine impact load, sawtooth waveform impact load, trapezoidal wave impact load, and their approximate waveforms, or a waveform composed of the linear superposition of these waveforms.

[0080] Please refer to Figures 2-7As shown in the example, a half-sine impact load, a sawtooth impact load, or a trapezoidal impact load can be selected as the external load for impact loudness calculation.

[0081] Step S6b involves setting impact load parameters, including the impact load duration and the magnitude of the impact acceleration. The impact load parameter settings include the impact load duration and the magnitude of the impact acceleration. Please refer to... Figure 2 When a half-sine impact load is selected, the impact load can be defined by defining the impact load duration t0 and the impact acceleration amplitude A; when a sawtooth impact load is selected, the impact load can be defined by defining the impact load duration t0, the impact peak time t1, and the impact acceleration amplitude A; when a trapezoidal impact load is selected, the impact load can be defined by defining the impact duration t0, the impact peak occurrence time t1, the impact peak end time t2, and the impact acceleration amplitude A.

[0082] Step S6c converts the time-domain impact load into the frequency-domain impact response spectrum. For an example, please refer to... Figure 3 , Figure 5 and Figure 7 When the half-sine impact load t0 = 11 ms and the impact acceleration A = 10g, the obtained impact response spectrum is as follows: Figure 3 As shown; when the sawtooth impact load t0 = 11 ms, t1 = 10 ms, and A = 10g, the obtained impact response spectrum is as follows: Figure 5 As shown; when the trapezoidal impact load t0 = 11 ms, t1 = 1 ms, t2 = 10 ms, and A = 10g, the obtained impact response spectrum is as follows: Figure 5 As shown.

[0083] Step S7: Perform modal simulation analysis on the three-dimensional digital model to obtain modal parameters, mainly including mode shapes, natural frequencies, and modal participation coefficients.

[0084] Step S8: Evaluate whether the modal parameters meet the calculation accuracy requirements. This mainly includes evaluating parameters such as the range of natural frequencies and modal participation coefficients. If the requirements are not met, return to step S7 to adjust the modal analysis parameters and recalculate. If the requirements are met, proceed to the next step. Specifically, the modal participation coefficients in the six degrees of freedom (X, Y, Z, RX, RY, RZ) should not be less than 0.85, and the set natural frequency range should not be less than 12 orders.

[0085] Step S9, Impact Response Spectrum Analysis: Depending on the requirements, single-point or multi-point response spectra can be used. Modal merging methods and load scaling factors are set to perform impact response spectrum analysis.

[0086] Step S10, Post-processing of results: Obtain the stress distribution cloud map, displacement cloud map, and stress curve along the specified path direction of the analyzed mechanical structure.

[0087] Step S11: Extract the stress values ​​at stress concentration points, where the stress concentration factor at the stress concentration points is not less than 1.5, i.e., σ0 / σ m ≥1.5, where σ0 is the stress value at the stress concentration point, σ m This represents the average stress value.

[0088] Step S12: Determine whether each stress value is a stress singularity point. If a stress singularity exists, return to step S3, readjust the mesh generation method, mesh parameters, etc., and re-mesh. The determination of a stress singularity point must satisfy at least one of the following two conditions:

[0089] 1) The stress concentration factor is greater than 10, i.e., v0 / σ m ≥10;

[0090] 2) The stress distribution along any path passing through the stress concentration point, where the stress concentration point is the stress maximum, and the stress curves on both sides of the stress concentration point along the selected path are concave curves.

[0091] Step S13: Compare the obtained stress value with the material's ultimate strength and output the analysis results.

[0092] As an example, please refer to Figure 8 , Figure 8 The graph shows the stress distribution curves along a path that passes through a stress singularity point. In the graph, x0 represents the location of the stress singularity point on the path, and σ0 represents the stress value at the stress singularity point. The average stress value σ near this point is then calculated. m It can be calculated using the following formula:

[0093]

[0094] When σ0 / σ m If the value is ≥10, then the point is determined to be a stress singularity point.

[0095] In addition, from Figure 8 It can be seen that when x≤x0, the curve is a concave curve; when x≥x0, the curve is still a concave curve, thus determining that the point is a stress singularity point.

[0096] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0097] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to the steps or embodiments of the invention without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for analyzing the impact strength of mechanical structures, characterized in that: Includes the following steps Step S1: Simplify the three-dimensional digital model of the mechanical structure by removing components or structural features that have little impact on the stress, and obtain a simplified model of a single component, a multi-body single component, or an assembly of multiple components. Step S2: Set the material properties, including elastic modulus, density, Poisson's ratio, damping, and yield strength. Step S3: Divide the three-dimensional digital model into a finite number of unit cells, and mesh the unit cells. The type of unit cell is tetrahedron, hexahedron, or triangular prism. Step S4: Evaluate whether the mesh quality meets the calculation requirements. If it does not meet the requirements, return to step S3 to re-mesh. If it meets the requirements, proceed to the next step. Step S5: Set boundary conditions for the mechanical structure, including displacement boundary conditions, stress boundary conditions, and contact parameters. Step S6: Apply impact loads to the three-dimensional digital model in one or more directions; Let the differential equation of the mechanical structure for impact vibration be: In the formula, ξ is the structural damping ratio, which ranges from 0.01 to 0.1, δ(t) is the unit amplitude impact load, and A is the amplitude of the impact load; According to the Fourier transform formula of impact load The impact load is converted into a finite number of harmonic components. Then, m harmonic components are extracted from the formula to approximate the original unit amplitude impact load, with the error controlled within 5%, resulting in the differential equation for impact vibration. The formula for calculating the steady-state response of one component of the impact load is: Take the natural frequency ω respectively n For ω1, ω2, ω3, ..., ω k For each natural frequency of the structure, the responses of each harmonic component of the impact load are x1, x2, x3, ..., x... m Its maximum frequency response is: y1=max{x1,x2,x3,…,x m } y2=max{x1,x2,x3,…,x m } y3=max{x1,x2,x3,…,x m } … y k =max{x1,x2,x3,…,x m }; Based on the correspondence between the natural frequencies of each order and the maximum acceleration response of each harmonic component of the impact load after data processing, the converted impact response spectrum is obtained. Step S7: Perform modal simulation analysis on the three-dimensional digital model to obtain modal parameters including mode shapes, natural frequencies, and modal participation coefficients; Step S8: Evaluate whether the modal parameters meet the requirements for calculation accuracy. If they do not meet the requirements, return to step S7 to adjust the modal analysis parameters and recalculate. If they meet the requirements, proceed to the next step. Step S9: Use single-point or multi-point response spectra, set the modal merging method and load scaling factor to perform impact response spectrum analysis; Step S10: Process the analysis results to obtain the stress distribution cloud map, displacement cloud map, and stress curve along the specified path direction of the mechanical structure; Step S11: Extract the stress values ​​at stress concentration points; Step S12: Determine whether each stress value is a stress singularity. If a stress singularity exists, return to step S3, readjust the mesh generation method and mesh parameters, and re-mesh. Step S13: Compare the obtained stress value with the material's ultimate strength and output the analysis results.

2. The method for analyzing the impact strength of a mechanical structure according to claim 1, characterized in that, In step S1, the simplified model of the assembly of multiple components uses linear contact connections between the components; the simplified model of the single component of a multi-body assembly uses a common node connection between the multiple bodies.

3. The method for analyzing the impact strength of a mechanical structure according to claim 2, characterized in that, In the mesh generation of step S3, the number of mesh layers in the wall thickness direction of the plate structure shall not be less than 3.

4. The method for analyzing the impact strength of a mechanical structure according to claim 3, characterized in that, In the mesh quality assessment of step S4, the aspect ratio of the mesh is not greater than 5, the mesh warpage is not greater than 15°, and the mesh skew angle is not greater than 60°.

5. The method for analyzing the impact strength of a mechanical structure according to claim 4, characterized in that, Step S5 includes: Step S5a: Analyze the connection relationship between the mechanical structure and the external environment to transform it into mechanical boundary conditions that can be used for analysis and calculation; Step S5b: Extract boundary conditions to select equivalent physical connection types or constraints, which are used to equivalently replace the constraints and connections in step S5a.

6. The method for analyzing the impact strength of a mechanical structure according to claim 5, characterized in that, Step S6 includes: Step S6a: Select a half-sine impact load, a sawtooth waveform impact load, a trapezoidal wave impact load, and their approximate waveforms, or a waveform composed of the linear superposition of these waveforms. Step S6b: Set impact load parameters, including impact load duration and impact acceleration amplitude; Step S6c: Convert the time-domain impact load into the impact response spectrum of the frequency-domain load.

7. The method for analyzing the impact strength of a mechanical structure according to claim 6, characterized in that, The correspondence between the natural frequencies of each order in step S6 and the maximum acceleration response of each harmonic component of the impact load is shown in the table below: 。 8. The method for analyzing the impact strength of a mechanical structure according to claim 7, characterized in that, In step S8, the modal participation coefficients in the six degrees of freedom (X, Y, Z, RX, RY, RZ) are all no less than 0.

85.

9. The method for analyzing the impact strength of a mechanical structure according to claim 8, characterized in that, The stress concentration factor at the stress concentration location in step S11 is not less than 1.

5.

10. The method for analyzing the impact strength of a mechanical structure according to claim 9, characterized in that, The determination condition for stress singularities in step S12 satisfies one of the following two conditions: 1) Stress concentration factor greater than 10; 2) The stress distribution along any path passing through the stress concentration point, where the stress concentration point is the stress maximum, and the stress curves on both sides of the stress concentration point along the selected path are concave curves.

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