Finite element model of plough body curved surface and its breaking process and construction method thereof

Abstract

The application belongs to the technical field of computer model, disclose a kind of plow body surface and its finite element model of fracture process and its construction method, including using finite element grid to plowshare modeling, hard layer on plow body surface is described by shell element, while internal soft layer is described by solid element;Soil and gravel are described by discrete element, soil modeling and gravel modeling are carried out;Contact force is calculated by the interaction between soil discrete element and plow body finite element, and the wear amount is calculated by contact force combined with general Archard wear model;The destruction of plow body soft layer and hard layer is described by inherent aggregation model.The application proposes a kind of finite element model for describing the wear of plowshare in plowing process from wear to fracture failure according to the characteristics of plow body surface wear and fracture in plowing process, which has practical significance for the development of simulation technology and agricultural implement manufacturing industry in China.

Description

Technical Field

[0001] This invention belongs to the field of computer modeling technology, and particularly relates to a finite element model of a plow body surface and its fracture process, and a method for constructing such a model. Background Technology

[0002] Insufficient wear resistance of key agricultural machinery components is one of the problems plaguing my country's agricultural machinery manufacturing industry. The plowshare is a commonly used component in agricultural implements. The plow body is mostly made of 65Mn steel, and to improve its service life, special processes are used during manufacturing to form a thin, hardened layer on its surface. During operation, the plow body comes into direct contact with soil and gravel, and the surface, especially the plow tip, wears down quickly. This significant wear reduces the thickness of the hardened layer on the plow body surface, leading to breakage or tearing of the plow tip during tillage, which is a major form of plowshare failure.

[0003] The soil in Northwest my country contains a high amount of sand; the higher the sand content, the more severe the wear on the plowshare. Currently, research on plowshare wear between the plow and soil primarily employs experimental methods. While experimentation is undoubtedly the most effective method for studying plowshare wear performance, it requires significant manpower, resources, financial investment, and time. With the continuous improvement of simulation analysis software, using simulation analysis to study plowshare wear and fracture not only saves time and effort but also eliminates the interference of accidental factors during experimental research, representing a modern design development direction.

[0004] Based on the above analysis, the existing technologies have the following problems and shortcomings: Current methods for testing the wear between the plowshare and soil require significant manpower, material resources, financial resources, and time. Numerical calculation methods can save considerable manpower, material resources, financial resources, and time; however, due to the limitations of simulation methods, no method has been found that can accurately calculate the wear amount at each location of the plow body during plowing. To better study the wear of the plowshare during plowing, this paper proposes a finite element model of the plow body surface and its fracture process, along with its construction method. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a finite element model of the plow body surface and its fracture process, as well as a method for constructing it. As is well known, a finite element model mainly includes modules such as element selection, material constitutive model selection, constraint and load setting, contact setting, and connections between elements or components. The finite element modeling method for the plow model is detailed below:

[0006] This invention is implemented as follows: a method for constructing a finite element model of a plowshare surface and its fracture process includes:

[0007] Step 1: Model the plowshare using a finite element method (FEM) mesh. The hard layer on the surface of the plowshare is described by shell elements, while the soft layer inside is described by solid elements (since the hard layer is very thin, it is best suited for shell elements, while the soft layer is the main material inside the plowshare, and is best suited for solid elements).

[0008] Step two: Use Discrete Element Method (DEM) to describe the soil and gravel, and perform soil and gravel modeling (since gravel is a loose material, it is very suitable for DEM description; since the soil is destroyed during plowing, that is, the soil transforms from a continuous to a discontinuous material, it is also suitable for DEM description).

[0009] Step 3: The contact force is calculated through the interaction between the soil discrete element and the plow body finite element. The wear amount is then calculated using the contact force combined with the general Archard wear model (this is the first time the Archard wear model has been used to calculate plowshare wear, enabling the calculation of wear amount for each part of the plowshare).

[0010] Step four: Use the intrinsic polymerization model to describe the failure of the soft and hard layers of the plowshare (the intrinsic polymerization model is suitable for describing interlayer failure of materials).

[0011] Furthermore, the shell unit and the solid unit in step one are bound together using a tied algorithm to achieve continuity of the medium.

[0012] Furthermore, in step two, soil modeling uses a connectivity DEM to describe the bonding between soil particles, the transformation from a connectivity DEM to a contact DEM to describe soil failure, and a contact DEM to describe the interaction between soil particles after tillage failure.

[0013] Furthermore, in the sand and gravel modeling in step two, the sand and gravel are described using connected discrete elements, and they do not fail during the calculation process; the discrete elements between the sand and gravel and the soil are connected discrete elements at the beginning of the calculation, and are transformed into contact discrete elements after the failure condition is reached.

[0014] Furthermore, step three involves calculating the contact force through the interaction between the soil discrete element and the plow body finite element, and then calculating the wear amount using the contact force combined with the general Archard wear model. Specifically, this includes:

[0015] (1) Calculate the contact pressure between the discrete element and the finite element contact surface according to the discrete element / finite element coupling algorithm;

[0016] (2) The amount of slippage of the discrete element on the finite element contact surface is calculated by tangential velocity and time step, and then the amount of wear is calculated;

[0017] (3) Distribute the wear amount to each node of the finite element according to the shape function of the element.

[0018] Furthermore, the calculation model for wear in step (2) is as follows:

[0019]

[0020] In the formula, W represents the wear amount, P represents the contact pressure between the discrete element and the finite element contact surface, and S represents the wear amount. L Let k be the slip of the discrete element on the finite element contact surface. cc Where is the wear coefficient, and H is the hardness of the contact area.

[0021] Furthermore, in step (3), if the contact midpoint is O and its natural coordinates are (ζ, η), then the wear amount is distributed to each node of the finite element according to the following formula:

[0022]

[0023] Furthermore, to reduce computational load, the finite element model of the plow body surface and its fracture process follows the following principles:

[0024] (1) Due to the large difference in material properties between the plow body and the soil, the plow body deforms less during the plowing process. It is assumed that within a certain plowing distance, surface wear will not cause a significant change in the deformation of the plow body.

[0025] (2) For every 1.0m of plow body tilled, the wear amount remains constant, and the total wear amount can be accumulated;

[0026] (3) The stone undergoes minimal deformation during its interaction with the plowshare and does not fail.

[0027] Another objective of this invention is to provide a finite element model of the plow body surface and its fracture process, wherein the finite element model of the plow body surface and its fracture process includes plowshare modeling, soil and gravel modeling, wear algorithm and fracture algorithm.

[0028] Based on the above technical solutions and the technical problems solved, please analyze the advantages and positive effects of the technical solution to be protected by this invention from the following aspects:

[0029] First, addressing the technical problems existing in the prior art and the difficulty of solving them, this paper closely analyzes, in conjunction with the technical solution to be protected by this invention and the results and data obtained during the research and development process, how the technical solution of this invention solves the technical problems, and the inventive technical effects brought about by solving these problems. The specific description is as follows:

[0030] Due to limitations in simulation methods, no precise calculations of wear at every location on the plow body during plowing were found, and no research has been conducted on the wear calculation throughout the entire lifecycle of the plowshare from its initial use to its scrapping. To better study plowshare wear during plowing, this invention proposes a finite element model describing the plowshare's plowing process from wear to fracture failure, based on the characteristics of wear and fracture on the plowshare's curved surfaces during plowing. This model, combined with subsequent simulation studies, can clarify the failure mechanism of the plowshare during plowing, thereby guiding plowshare design and having practical significance for the development of simulation technology and agricultural machinery manufacturing in my country.

[0031] Second, considering the technical solution as a whole or from a product perspective, the technical effects and advantages of the technical solution to be protected by this invention are specifically described as follows:

[0032] The advantages of this invention are: 1. Using this invention, the wear of each part of the plowshare during plowing can be accurately calculated; 2. This invention considers the independent modeling of the surface hard layer and the internal soft layer after heat treatment or tempering of the plowshare. This modeling method theoretically has higher calculation accuracy and is currently the first of its kind; 3. This solution can realize the wear calculation of the plowshare throughout its entire life cycle from being put into use to being scrapped.

[0033] Third, as supplementary evidence of the inventive step of the claims of this invention, it is also reflected in the following important aspects:

[0034] (1) The expected benefits and commercial value of the technical solution of this invention after transformation are as follows: At present, my country's agricultural machinery relies heavily on imports. As the most commonly used agricultural machinery, the plowshare is used in enormous quantities. However, there is very little research on its failure mechanism. This invention can be used for numerical research on failures such as wear and breakage during plowing. The research results can guide the production of plowshares with a longer life cycle, which has great economic potential. At the same time, the use of simulation research can save a lot of manpower, material resources, financial resources and time consumed by experimental research, which has good economic benefits.

[0035] (2) The technical solution of this invention fills a technical gap in the industry both domestically and internationally:

[0036] This invention fills the gap in the lack of numerical research on the failure of plowshares during plowing, both domestically and internationally, and can also enrich the research on the failure mechanism of plowshares.

[0037] (3) The technical solution of the present invention solves a technical problem that people have long wanted to solve but have never been able to solve successfully:

[0038] This invention enables researchers to more accurately calculate the wear and tear of plowshares throughout their entire lifecycle, from commissioning to scrapping, a process that has long been anticipated. Attached Figure Description

[0039] Figure 1 This is a flowchart illustrating the method for constructing a finite element model of the plow body surface and its fracture process, as provided in an embodiment of the present invention.

[0040] Figure 2 This is a three-dimensional structural diagram of the plow body provided in an embodiment of the present invention;

[0041] Figure 3 This is the discrete element model of soil pavement provided in the embodiments of the present invention;

[0042] Figure 4 This is a simulation model diagram of plow body wear provided in an embodiment of the present invention;

[0043] Figure 5 This is a schematic diagram of plow body wear provided in an embodiment of the present invention;

[0044] Figure 6 This is a schematic diagram of wear amount node allocation provided in an embodiment of the present invention;

[0045] Figure 7 This is a simulation model diagram of plow body fracture provided in an embodiment of the present invention;

[0046] Figure 8 This is a schematic diagram of the plow body mesh update provided in an embodiment of the present invention; (a) before wear; (b) after wear; (c) mesh update. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] I. Explanatory and Illustrative Embodiments. To enable those skilled in the art to fully understand how the present invention is specifically implemented, this section provides an explanatory and illustrative description of the embodiments described in the claims.

[0049] like Figure 1 As shown, the method for constructing a finite element model of the plow body surface and its fracture process provided in this embodiment of the invention includes:

[0050] S101 uses a finite element mesh to model the plowshare. The hard layer on the surface of the plowshare is described by shell elements, while the soft layer inside is described by solid elements.

[0051] S102 uses discrete element method to describe soil and gravel, and performs soil and gravel modeling.

[0052] S103, the contact force is calculated by the interaction between the soil discrete element and the plow body finite element, and the wear amount is calculated by combining the contact force with the general Archard wear model;

[0053] S104 uses an inherent polymerization model to describe the failure of the soft and hard layers of the plowshare.

[0054] The finite element model of the plow body surface and its fracture process provided in this invention includes three aspects: plowshare modeling, soil and gravel modeling, wear algorithm, and fracture algorithm. The specific technical solution is as follows:

[0055] A 3D model of the plow body was created using 3D modeling software, as shown in the attached image. Figure 2 As shown, the 3D model is imported into HyperMesh. The surface hard layer 1 is discretized using shell elements, and the matrix soft layer 2 is discretized using solid elements. The surface hard layer 1 and the surface soft layer 2 are bound together using the Tied algorithm.

[0056] Assuming that the deformation of the lateral section at a distance of 0.4m from the plow centerline is very small, and the deformation of the bottom section at a depth of 0.5m is also very small, therefore, in the calculation, as shown in the attached... Figure 3 As shown, the boundary is set at the green section and a fixed constraint is applied. To further reduce the computational load, in the plow body wear model, the effective calculation road surface size is selected as 1.0m × 0.8m × 0.5m (Note: Due to the large calculation errors of the initial and final road surface, the actual calculation road surface size is selected as 1.2m × 0.8m × 0.5m, and the initial 0.1m and final 0.1m are removed, resulting in an effective calculation road surface size of 1.0m × 0.8m × 0.5m). In the plow body fracture model, the effective calculation road surface size is selected as 0.5m × 0.8m × 0.5m.

[0057] A simulation diagram of plow body wear is attached. Figure 4 As shown. At the initial moment of calculation, all discrete elements are connected. As the plow body comes into contact with the road surface, some connected discrete elements meet the failure condition and transform from connected to contact elements. The contact discrete elements come into contact with the finite element plow body, and wear occurs during the contact process. The wear amount is calculated based on the wear model.

[0058] As attached Figure 5 As shown, soil particles 10, pear network 11, and scratches 12 are depicted. The center point of scratch 12 is O, and its length is S. L If the contact pressure between the discrete element and the finite element interface is P, calculate the slippage S of the discrete element on the finite element interface using the tangential velocity and time step. L The wear amount W is calculated using the general Archard wear model.

[0059]

[0060] In the formula, k cc is the wear coefficient; H is the hardness of the contact area. (See attached diagram) Figure 6 As shown, if the contact midpoint is O and the natural coordinates are (ζ,η), the calculated wear amount is distributed to each node of the unit according to equation (2) (i is the number of nodes).

[0061]

[0062] A simulation diagram of plow body fracture under the interaction of plow body, soil, and stones is attached. Figure 7 As shown, there are unit interface 13, aggregate unit 14, stone model 15, and soil model 16. During cultivation, the plow tip comes into contact with the stones. The stones are described using connected discrete elements and do not fail during the calculation. The discrete elements between the stones and the soil are initially connected discrete elements, but are transformed into contact discrete elements after the failure condition is met (assuming that the failure criteria between soil and stones are consistent with the failure criteria between soil and soil). If the plow body breaks during the calculation, the plowshare fails.

[0063] Before simulating the fracture of the plow body, the finite element model of the plow body needs to be processed as follows:

[0064] (1) Since the failure of the plow body is described by the aggregate model, aggregate elements need to be inserted between the hard shell elements and the soft solid elements of the plow body at the beginning of the simulation.

[0065] (2) In the plow body fracture model, the plow body has undergone long-term wear. Therefore, at the beginning of the calculation, it is necessary to translate the mesh nodes of the hard layer of the plow body and correct the thickness of the shell elements, as shown in the attached figure. Figure 8 As shown. Hard layer (shell element) 17, shell mid-surface 18, Tied connection 19, soft layer (solid element) 20, outer surface (before wear) 21, outer surface (after wear) 22, outer surface (after mesh update).

[0066] II. Application Examples. To demonstrate the inventiveness and technical value of the technical solution of this invention, this section provides application examples of the technical solution of the claims on specific products or related technologies.

[0067] This invention employs a modeling approach that minimizes computation without compromising accuracy; therefore, the computational scheme involved in this invention can be implemented on general-performance computers. It is worth noting that currently, no readily available finite element program can meet the computational requirements of the model; the inventor's developed explicit finite element analysis software (DYNA-WD, 2021SR1280709) for composite material failure simulation is required for calculation. DYNA-WD software is an independently developed finite element analysis software, programmed in Fortran, and includes modules for model reading, data initialization, model calculation, and data output, possessing the basic functions of finite element calculation. The computer device provided by this invention includes a memory and a processor. The memory stores a computer program, which, when executed by the processor, causes the processor to perform the steps of constructing the finite element model of the plowshare surface and its fracture process.

[0068] This invention allows for modeling using 3D modeling software such as UG and Solidworks. The 3D model is then imported into Hypermesh software for finite element modeling. After completion, a .k file readable by LS-DYNA is exported. The self-developed software DYNA-WD can also read the .k file, enabling simulation calculations within DYNA-WD. The invention provides a computer-readable storage medium storing a computer program. When executed by a processor, this computer program causes the processor to perform the steps of a method for constructing a finite element model of the plowshare surface and its fracture process.

[0069] The present invention provides an information data processing terminal, which is used to implement the steps of the method for constructing a finite element model of the plow body surface and its fracture process.

[0070] During the calculation process, DYNA-WD can generate a D3plot file, which can be read by LS-PrePost.

[0071] III. Evidence of the Relevant Effects of the Embodiments. The embodiments of the present invention have achieved some positive effects during research and development or use, and indeed possess significant advantages compared to existing technologies. The following description, in conjunction with data, charts, and other materials from the experimental process, illustrates these advantages.

[0072] 1. Use 3D modeling software such as UG or Solidworks to draw a 3D model of the plow body, and then import the 3D model into Hypermesh. Use a shell element to discretize the surface hard layer, and use solid elements to discretize the matrix soft layer. Use the Tied algorithm to bind the hard layer and the soft layer together.

[0073] 2. Establish as shown in the appendix Figure 3As shown, bottom surface fixed constraint 4 and side surface fixed constraint 3 are applied. To further reduce the computational load, in the plow body wear model, the effective calculation road surface size is selected as 1.0m × 0.8m × 0.5m. In the plow body fracture model, the effective calculation road surface size is selected as 0.5m × 0.8m × 0.5m.

[0074] 3. Use as shown in the attached document. Figure 4 The simulation model of plow body wear shown calculates the wear of the plow body during the plowing process. It includes: surface layer (hard layer, shell element) 5, matrix (soft layer, hexahedral element) 6, discrete element / finite element coupling and contact wear 7, discrete element (after failure, contact type) 8, discrete element (before failure, connected type) 9; at the initial moment of calculation, all discrete elements are connected type. As the plow body comes into contact with the road surface, some connected discrete elements meet the failure conditions and transform from connected type to contact type. The contact type discrete elements contact the plow body finite element, and wear occurs during the contact process. The wear amount is calculated based on the wear model.

[0075] 4. The unit volume wear amount calculated in step 3 is allocated to each node of the unit according to formulas (1) and (2), and is defined as the node wear amount.

[0076] 5. As per the appendix Figure 7 The simulation model shown simulates the fracture process of the plowshare when it comes into contact with a large stone during plowing, based on the interaction between the plowshare, soil, and stone. The stone is described using a connected discrete element method (EMI) and does not fail during the calculation. The discrete element method between the stone and the soil is initially a connected discrete element method, but transforms into a contact discrete element method after the failure condition is met. If the plowshare fractures during the calculation, the plowshare fails.

[0077] 6. If the plowshare does not break after calculation in step 5, then proceed as per attached... Figure 8 The mesh nodes of the hard layer of the plowshare are translated and the shell element thickness is corrected. The model is updated, and this process is repeated 3, 4, and 5 until the plowshare breaks.

[0078] It should be noted that embodiments of the present invention can be implemented in hardware, software, or a combination of both. The hardware portion can be implemented using dedicated logic; the software portion can be stored in memory and executed by a suitable instruction execution system, such as a microprocessor or dedicated-design hardware. Those skilled in the art will understand that the above-described devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuitry such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field-programmable gate arrays, programmable logic devices, etc., or by software executed by various types of processors, or by a combination of the above-described hardware circuitry and software, such as firmware.

[0079] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for constructing a finite element model of a plowshare surface and its fracture process, characterized in that, The method for constructing the finite element model of the plow body surface and its fracture process includes: Step 1: Model the plowshare using a finite element (FEM) mesh. The hard layer on the surface of the plowshare is described by shell elements, while the soft layer inside is described by solid elements. Step 2: Use Discrete Element Method (DEM) to describe the soil and gravel, and perform soil and gravel modeling. Step 3: Calculate the contact force through the interaction between the soil discrete element and the plow body finite element, and calculate the wear amount by combining the contact force with the general Archard wear model; Step four: The inherent polymerization model is used to describe the failure of the soft and hard layers of the plowshare; In step one, the shell unit and the solid unit are bound together using a tied algorithm to achieve continuity of the medium; The soil modeling in step two uses a connectivity DEM to describe the bonding between soil particles, the transformation from connectivity DEM to contact DEM to describe soil failure, and the contact DEM to describe the interaction between soil particles after tillage failure. In the sand and gravel modeling in step two, the sand and gravel are described using connected discrete elements, and they do not fail during the calculation process; the discrete elements between the sand and gravel and the soil are connected discrete elements at the beginning of the calculation, and are transformed into contact discrete elements after the failure condition is reached.

2. The method for constructing a finite element model of the plow body surface and its fracture process as described in claim 1, characterized in that, Step three involves calculating the contact force through the interaction between the soil discrete element and the plow body finite element, and then calculating the wear amount using the contact force combined with the general Archard wear model. Specifically, this includes: (1) Calculate the contact pressure between the discrete element and the finite element contact surface according to the discrete element / finite element coupling algorithm; (2) The amount of slippage of the discrete element on the finite element contact surface is calculated by tangential velocity and time step, and then the amount of wear is calculated; (3) Distribute the wear amount to each node of the finite element according to the shape function of the element; The calculation model for wear in step (2) is as follows: ； In the formula, W is the wear amount, P is the contact pressure between the discrete element and the finite element contact surface, SL is the slippage of the discrete element on the finite element contact surface, kcc is the wear coefficient, and H is the hardness of the contact area. In step (3), if the contact midpoint is O and the natural coordinates are (ζ, η), then the wear amount is distributed to each node of the finite element according to the following formula: ， i represents the number of nodes.

3. The method for constructing a finite element model of the plow body surface and its fracture process as described in claim 1, characterized in that, To reduce computational load, the finite element model of the plow body surface and its fracture process follows the following principles: (1) Due to the large difference in material properties between the plow body and the soil, the plow body deforms less during the plowing process. It is assumed that within a certain plowing distance, surface wear will not cause a significant change in the deformation of the plow body. (2) For every 1.0m of plow body tilled, the wear amount remains constant, and the total wear amount can be accumulated; (3) The stone undergoes minimal deformation during its interaction with the plowshare and does not fail.

4. A finite element model of a plowshare surface and its fracture process, characterized in that, The finite element model is constructed using the finite element model construction method of the plow body surface and its fracture process as described in any one of claims 1 to 3. The finite element model of the plow body surface and its fracture process includes plowshare modeling, soil and gravel modeling, wear algorithm and fracture algorithm.

5. A computer device, characterized in that, The computer device includes a memory and a processor. The memory stores a computer program, which, when executed by the processor, causes the processor to perform the steps of the method for constructing a finite element model of the plowshare surface and its fracture process as described in any one of claims 1 to 3.

6. A computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the method for constructing a finite element model of a plowshare surface and its fracture process as described in any one of claims 1 to 3.

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