Finite element simulation method for multiple impact tests of materials

Abstract

The invention relates to the technical field of material mechanics, in particular to a finite element simulation method for multiple impact tests of a material, which comprises the following steps: acquiring mechanical parameters of a test material, establishing initial models of incident bar and transmission bar material test pieces of a Hopkinson pressure bar test, defining keywords according to the determined parameters, and establishing a finite element model of the incident bar and transmission bar material test pieces of the Hopkinson pressure bar test. A stress curve is input on the end face of an incident bar, a stress initialization file dynin of a material test piece is output by adding a keyword * INRFACESPRINGBACKLSDYNA, a test piece PART grid in a k file is deleted, input of multiple impact stress waves is completed by modifying the stress wave input curve for the second time and adding the keyword * INCLUDE, post-processing of a calculation result is completed, and the impact stress waves are obtained. In this way, the numerical simulation process of multiple impact loads of the Hopkinson test is achieved, the authenticity of simulation is ensured, and important reference is provided for impact performance research of materials.

Description

Technical Field

[0001] The present invention relates to the technical field of material mechanics, and in particular to a finite element simulation method for multiple impact tests of materials. Background Art

[0002] Because materials are often subjected to impact loads during use, testing and analysis of their impact mechanical properties are particularly important in the study of material mechanics. However, in many projects, materials are subjected to multiple impact loads, such as slopes and buildings subjected to multiple blasting during open-pit mining, cars driving on uneven roads, and aircraft taking off and landing. Therefore, the response characteristics of materials under a single impact load are difficult to fully reveal the damage, fracture, and failure of materials in engineering applications. In these studies, the Hopkinson compression bar test device has been widely used. For example, Pan Bo studied the dynamic response characteristics of phyllite under cyclic impact loads, and Gao Hua studied the compressive mechanical properties of foamed aluminum under multiple impact conditions.

[0003] However, research on material performance under multiple impact loading conditions primarily relies on a combination of theoretical analysis and laboratory testing. While the Hopkinson bar apparatus is often used for multiple and cyclic impact loading, numerical simulation methods are mostly applied to single-impact test conditions, with limited research on multiple-impact loading conditions. Therefore, a stress initialization method is employed to provide a finite element simulation method for multiple-impact material testing. Summary of the Invention

[0004] The present invention provides a finite element simulation method for multiple impact tests of materials, which is used to study the mechanical properties of materials under multiple impact conditions. It achieves the numerical simulation process of multiple impact loads in the Hopkinson test, ensures the authenticity of the simulation, and provides an important reference for the research on the impact performance of materials.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A finite element simulation method for multiple impact tests of materials comprises the following steps:

[0007] Step 1: Obtain the mechanical parameters of the test material, including the incident rod, transmitted rod, and material specimen, and select keyword parameters to describe the mechanical behavior of the material;

[0008] Step 2: Create a model based on the dimensions of the material specimen, incident rod, and transmission rod, and perform meshing.

[0009] Step 3: Add the parameters and keywords determined in step 1 to the model and mesh in LS-DYNA software;

[0010] Step 4: Set various parameters of numerical simulation in LS-DYNA software, including boundary conditions, contact conditions, constraints, output parameters and PART type;

[0011] Step 5: Use the *SET_SEGMENT keyword to add units to form a unit set;

[0012] Step 6: Add the keyword *DEFINE_CURVE for defining the time-stress curve and define the stress input curve of the incident rod end face;

[0013] Step 7: Add the *LOAD_SEGMENT_SET keyword to apply the time-stress curve defined by the keyword *DEFINE_CURVE to the element. Select the set defined in step 5 in the SSID option and select the stress input curve defined in step 6 in the LCID.

[0014] Step 8: Add the *SET_PART_LIST keyword to represent the PART set, and select the PART where the material specimen is located in the PID option;

[0015] Step 9: Add the keyword *INTERFACE_SPRINGBACK_LSDYNA for outputting the dynain file, and select the material specimen set set in step 8 in the PSID option;

[0016] Step 10: Output the k file, solve the operation, output the dynain file, and complete the stress initialization;

[0017] Step 11: Modify the k file output in step 10 and delete all the grids in the PART where the specimen is located;

[0018] Step 12: Modify the keyword *DEFINE_CURVE in step 6 to define the next stress wave input curve;

[0019] Step 13: Add the keyword *INCLUDE for reading the dyain file;

[0020] Step 14: Determine whether the number of impacts meets the test requirements. If not, return to step 10. If yes, proceed to step 15.

[0021] Step 15: Output the k file, solve the operation, and perform post-processing.

[0022] Furthermore, the incident rod is located at the front end of the material specimen and is a stress wave input rod of the Hopkinson compression bar test device.

[0023] Furthermore, the transmission rod is located at the rear end of the material specimen and is a stress wave transmission rod of a Hopkinson pressure bar test device.

[0024] Furthermore, the material specimen is cylindrical.

[0025] Furthermore, the keyword selection method in step 5 is all units on the end surface of the incident rod.

[0026] Furthermore, the field dynain file location\dynain is added after the keyword in step 13.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention realizes data transmission of multi-stage impact simulation through the stress initialization file of the LS-DYNA method, without repeated modeling, which significantly improves the calculation efficiency. Compared with the traditional method, the present method only needs to modify the stress input curve and update the initial stress field, which greatly shortens the simulation time and achieves the numerical simulation process of multiple impact loads of the Hopkinson test, ensuring the authenticity of the simulation and providing an important reference for the impact performance research of materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of modeling the incident rod, test piece, and transmission rod of the Hopkinson device described in the present invention.

[0030] Figure 2 It is a flow chart of the method of the present invention.

[0031] In the figure: 1. Incident rod; 2. Transmitted rod; 3. Material specimen; 4. End face of incident rod; 5. Stress curve input position. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0033] The present invention provides a finite element simulation method for a multiple impact test of a material. The method obtains mechanical parameters of a test material, establishes an initial model of an incident rod 1, a transmission rod 2, and a material specimen 3 of a Hopkinson pressure bar test, defines keywords based on the determined parameters, and the keywords are core control instructions in LS-DYNA explicit dynamics analysis, which are used to define parameters, material properties, boundary conditions, loads, and solution control of the simulation model. Each keyword begins with *. A stress curve is input on the incident rod end face 4. By adding the keyword *INTERFACE_SPRINGBACK_LSDYNA, a stress initialization file dynain of the material specimen 3 is output. The specimen PART mesh in the k file is deleted. The input of multiple impact stress waves is completed by secondary modification of the stress wave input curve and adding the keyword *INCLUDE. The calculation results are then processed after completion.

[0034] The specific steps include:

[0035] Step 1: Obtain the mechanical parameters of the test material, including the incident rod 1, the transmitted rod 2, and the material specimen 3, and select keyword parameters to describe the mechanical behavior of the material;

[0036] Step 2: Create a model based on the dimensions of the material specimen 3, the incident rod 1, and the transmission rod 2, and perform meshing.

[0037] Step 3: Add the parameters and keywords determined in step 1 to the model and mesh in LS-DYNA software;

[0038] Step 4: Set various parameters of numerical simulation in LS-DYNA software, including boundary conditions, contact conditions, constraints, output parameters and PART type;

[0039] Step 5: Use the *SET_SEGMENT keyword to add elements to form an element set. Select all elements on the end face of incident rod 1 in the SID option.

[0040] Step 6: Add the keyword *DEFINE_CURVE for defining the time-stress curve and define the stress input curve of the incident rod end face 4;

[0041] Step 7: Add the *LOAD_SEGMENT_SET keyword to apply the time-stress curve defined by the keyword *DEFINE_CURVE to the element. Select the set defined in step 5 in the SSID option and select the stress input curve defined in step 6 in the LCID.

[0042] Step 8: Add the *SET_PART_LIST keyword to represent the PART set, and select the PART where the material specimen 3 is located in the PID option;

[0043] Step 9: Add the keyword *INTERFACE_SPRINGBACK_LSDYNA for outputting the dynain file, and select the material specimen 3set set in step 8 in the PSID option;

[0044] Step 10: Output the k file, solve the operation, output the dynain file, and complete the stress initialization; the k file is the standardized input file of the LS-DYNA solver

[0045] Step 11: Modify the k file output in step 10 and delete all the grids in the PART where the specimen is located;

[0046] Step 12: Modify the keyword *DEFINE_CURVE in step 6 to define the next stress wave input curve;

[0047] Step 13: Add the keyword *INCLUDE for reading the dynain file, and add the field dynain file location\dynain after the keyword;

[0048] Step 14: Determine whether the number of impacts meets the test requirements. If not, return to step 10. If yes, proceed to step 15.

[0049] Step 15: Output the k file, solve the operation, and perform post-processing.

[0050] The incident rod 1 is located at the front end of the material specimen 3 and is the stress wave input rod of the Hopkinson compression bar test device;

[0051] The transmission rod 2 is located at the rear end of the material specimen 3 and is a stress wave transmission rod of the Hopkinson compression bar test device;

[0052] The material specimen 3 is determined according to the research objectives and is generally cylindrical;

[0053] The mechanical parameters are determined according to the research objectives and the selected material keywords;

[0054] The keyword *SET_SEGMENT is a built-in keyword in LS-DYNA software, indicating a set of units;

[0055] The keyword *DEFINE_CURVE is a built-in keyword in LS-DYNA software and is used to define the time-stress curve;

[0056] The keyword *LOAD_SEGMENT_SET is a built-in keyword in LS-DYNA software, which is used to apply the time-stress curve defined by the keyword *DEFINE_CURVE to the element;

[0057] The keyword *SET_PART_LIST is a built-in keyword in LS-DYNA software, representing the set of PART;

[0058] The keyword *INTERFACE_SPRINGBACK_LSDYNA is a built-in keyword in LS-DYNA software and is used to output dynain files;

[0059] The k file is a file format used for LS-DYNA software calculation;

[0060] The keyword *INCLUDE is a built-in keyword of LS-DYNA software and is used to read dyain files.

[0061] In steps 6 and 7, the stress input curve is applied to the end of the incident rod 1.

[0062] The PART is a basic geometric unit of the simulation model. By defining the keyword *PART, each PART is associated with a unique PID.

[0063] The SET is a set of nodes, units or components defined by keywords such as *SET_NODE and *SET_PART in LS-DYNA, and is used for batch operations.

[0064] The DYNAIN file is an intermediate file in binary / text format generated by LS-DYNA and is output through the *INTERFACE or *DATABASE_DYNAIN keyword.

[0065] The PSID is a set identifier defined in LS-DYNA by the keyword *SET_PART, keyword *SET_NODE or keyword *SET_ELEMENT.

[0066] The LCID is the load segment identifier defined in LS-DYNA by keywords such as *DEFINE_CURVE or *LOAD_SEGMENT

[0067] The following examples are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the scope of protection of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0068] Example:

[0069] like Figure 2 The present invention provides a finite element simulation method for multiple impact tests of materials, comprising the following steps:

[0070] 1) Obtain the mechanical parameters of the test material; 2) Build the model and divide the mesh; 3) Set parameters and add keywords; 4) Add the *INTERFACE_SPRINGBACK_LSDYNA keyword; 5) Output the k file, calculate the dynain file, and complete the stress initialization; 6) Modify the k file and delete the PART mesh where the specimen is located; 7) Define the next stress wave input curve; 8) Add the *INCLUDE keyword; 9) Determine whether the number of impacts meets the test requirements; 10) Output the k file, solve the calculation, and perform post-processing.

[0071] like Figure 1 The figure shows the modeling schematic diagram of the incident rod 1, material specimen 3, and transmission rod 2 of the Hopkinson device; 1 is the incident rod of the Hopkinson device, 2 is the transmission rod of the Hopkinson device, 3 is the material specimen, 4 is the end face of the incident rod, and 5 is the stress curve input position.

[0072] In this example, the incident rod 1 of the model is 3050 mm long, the transmission rod 2 is 1825 mm long, with a diameter of 12.7 mm, an elastic modulus of 200 GPa, and a wave speed of 4970 m / s. The *MAT_ELASTIC_TITLE keyword is used to define the rod material, and the contact mode is *CONTACT_AUTOMATIC_SINGLE_SURFACE. The Lagrangian algorithm is used, the test material is rock, and the material model *MAT_CSCM_TITLE is used. The material parameters including density, shear modulus and other parameters are set. The length and diameter of the specimen are both 12.7 mm. Add the *SET_SEGMENT keyword, add *DEFINE_CURVE, *LOAD_SEGMENT_SET, *SET_PART_LIST and set the relevant parameters. Add the *INTERFACE_SPRINGBACK_LSDYNA keyword and select Figure 1 Output the k file and solve the calculation to get the dynain file; modify the k file and Figure 1 Delete the mesh in PART where material specimen 3 is located, define the *DEFINE_CURVE keyword again, add the *INCLUDE keyword, C:\Users\Administrator\Desktop\11\dynain, and since the test requires only two impact tests, output the k file, solve the operation, and perform post-processing.

Claims

1. A finite element simulation method for multiple impact tests of materials, characterized in that: The steps include: Step 1: Obtain the mechanical parameters of the test material, including the incident rod, transmitted rod, and material specimen, and select keyword parameters to describe the mechanical behavior of the material; Step 2: Create a model based on the dimensions of the material specimen, incident rod, and transmission rod, and perform meshing. Step 3: Add the parameters and keywords determined in step 1 to the model and mesh in LS-DYNA software; Step 4: Set various parameters of numerical simulation in LS-DYNA software, including boundary conditions, contact conditions, constraints, output parameters and PART type; Step 5: Use the *SET_SEGMENT keyword to add units to form a unit set; Step 6: Add the keyword *DEFINE_CURVE for defining the time-stress curve and define the stress input curve of the incident rod end face; Step 7: Add the *LOAD_SEGMENT_SET keyword to apply the time-stress curve defined by the keyword *DEFINE_CURVE to the element. Select the set defined in step 5 in the SSID option and select the stress input curve defined in step 6 in the LCID. Step 8: Add the *SET_PART_LIST keyword to represent the PART set, and select the PART where the material specimen is located in the PID option; Step 9: Add the keyword *INTERFACE_SPRINGBACK_LSDYNA for outputting the dynain file, and select the material specimen set set in step 8 in the PSID option; Step 10: Output the k file, solve the operation, output the dynain file, and complete the stress initialization; Step 11: Modify the k file output in step 10 and delete all the grids in the PART where the specimen is located; Step 12: Modify the keyword *DEFINE_CURVE in step 6 to define the next stress wave input curve; Step 13: Add the keyword *INCLUDE for reading the dyain file; Step 14: Determine whether the number of impacts meets the test requirements. If not, return to step 10. If yes, proceed to step 15. Step 15: Output the k file, solve the operation, and perform post-processing.

2. The finite element simulation method for multiple impact tests of materials according to claim 1, characterized in that: The incident rod is located at the front end of the material specimen and is the stress wave input rod of the Hopkinson compression bar test device.

3. The finite element simulation method for multiple impact tests of materials according to claim 2, characterized in that: The transmission rod is located at the rear end of the material specimen and is a stress wave transmission rod of the Hopkinson pressure bar test device.

4. The finite element simulation method for multiple impact tests of materials according to claim 1, characterized in that: The material test piece is cylindrical.

5. The finite element simulation method for multiple impact tests of materials according to claim 1, characterized in that: The keyword selection method in step 5 is all the units on the end surface of the incident rod.

6. The finite element simulation method for multiple impact tests of materials according to claim 1, characterized in that: In step 13, add the field dynain file location\dynain after the keyword.

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