CN112685940A - Finite element modeling method for simulating bolt collision fracture failure - Google Patents
Finite element modeling method for simulating bolt collision fracture failure Download PDFInfo
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Abstract
The invention provides a finite element modeling method for simulating bolt collision fracture failure, which comprises the following steps: the beam unit is used for establishing a bolt central unit, the bolt shell unit is arranged, material parameters are given to the bolt shell unit, the bolt central unit corresponds to the nodes of the bolt shell unit one by one, and rigid connection is arranged between the corresponding nodes. And establishing a nut model, dividing the outer surface of the nut model into nut shell units, and giving material parameters and nut quality to the nut shell units. And rigid connection is established between corresponding nodes of the bolt shell unit and the nut shell unit. A bolt housing element and a nut housing element are added in contact with the external component. A preload is placed on each beam element generated in the bolt modeling step. And giving material parameters to the beam unit, and adding corresponding failure force and failure moment limit values to the material parameters. The model established by the modeling method is used for simulating collision response, the simulation result is more accurate, the number of real vehicle collisions is reduced, and the development cost is saved.
Description
Technical Field
The invention relates to the field of automobiles, in particular to a finite element modeling method for simulating bolt collision fracture failure.
Background
The bolt connection is used as an important connection mode of automobile parts, and the loading condition and whether the bolt is broken or not at a key part in a whole automobile collision simulation model have very important influence on a simulation result. If the local loading and deformation states of the bolts can be accurately simulated in the whole vehicle collision simulation model, and whether the key connection positions are broken or failed can be predicted, the whole vehicle simulation precision can be greatly improved, and the development cost can be reduced.
In current practice, four methods are generally used.
The first method is to make the units of the parts needing bolt connection near the bolt holes into RIGID BODIES, and the RIGID BODIES are rigidly bound by a DYNA keyword CONSTRATINED _ RIGID _ BODIES keyword.
And in the second method, nodes around bolt hole holes of parts needing to be bolted are directly and rigidly connected through a one-dimensional rigid body unit rigidbody.
The former two methods are simple and effective in modeling and are widely applied in the whole vehicle simulation. However, the influence of the bolt body is neglected during modeling by the two methods, the bolt connection is approximate to rigid connection, the preloading of the bolt body and the loading condition of the bolt body in the collision process cannot be reflected, and the bolt fracture failure risk in a key area cannot be predicted.
And thirdly, establishing the bolt body through a three-dimensional solid unit and connecting the bolt body with surrounding parts needing to be connected through contact. Generally, the size of solid units in a finished automobile model is required to be not less than 3.5mm, and the solid units are distributed at least more than 3 layers, so that the method is only suitable for large bolts at least more than M14, the general type is not strong, and the 3.5mm units are too large compared with the bolts, and the precision is difficult to guarantee.
And coupling nodes around bolt hole holes of a fourth part A to be connected into a one-dimensional rigid body unit rigidbody a, coupling nodes around bolt hole holes of a fourth part B to be connected into another one-dimensional rigid body unit rigidbody B, and finally connecting the rigidbody a and the rigidbody B through a one-dimensional deformable beam unit. The method is characterized in that the contact relation between a nut, a bolt head and a part to be connected is approximate to rigid body constraint, and a one-dimensional beam unit is used for simulating a screw rod. The method cannot simulate the contact relation between the bolt structure and surrounding parts, and only can simulate and monitor the loading condition of the screw rod at the position through the beam.
The four methods have considerable limitations, and the bolt loading condition cannot be accurately simulated under the condition of meeting the precision requirement.
Disclosure of Invention
The invention aims to provide a finite element modeling method for simulating bolt collision fracture failure, which accurately simulates the preloading and loading conditions of a bolt in a whole vehicle simulation environment, improves the simulation precision of local stress and deformation of the bolt, and can predict the fracture failure of the bolt. The model established by the modeling method is used for simulating collision response, the simulation result is more accurate, the reliability of the whole vehicle collision simulation prediction can be improved, the number of times of real vehicle collision is reduced, and the development cost is saved.
The invention provides a finite element modeling method for simulating bolt collision fracture failure, which comprises the following steps:
modeling a bolt model: arranging points, establishing a bolt central unit by using a beam unit, arranging a bolt shell unit on the periphery of the bolt central unit, and giving material parameters to the bolt shell unit; the bolt center unit corresponds to the nodes of the bolt shell unit one by one, and rigid connection is arranged between the corresponding nodes of the bolt shell unit and the bolt center unit.
Modeling a nut model: establishing a nut model, and dividing the outer surface of the nut model into nut shell units; and, give the nut shell unit the material parameter, give the nut quality to the centroid of nut model.
Connecting the bolt model and the nut model: and rigid connection is established between corresponding nodes of the bolt shell unit and the nut shell unit.
An external contact setting step: the bolt housing unit and the nut housing unit are added to the contact with the external part so that the bolt housing unit and the nut housing unit are in contact with the external part mold.
Bolt preloading adding step: a preload is placed on each beam element generated in the bolt modeling step.
Bolt failure criterion setting step: and giving material parameters to the beam unit in the bolt modeling step, adding corresponding failure force and failure moment limit values to the material parameters, and when the load of the bolt exceeds the limit values, the beam unit of the bolt fails.
By adopting the scheme, the bolt appearance is considered through a reasonable modeling method, bolt contact is accurately simulated, preloading of the bolt is considered, and failure setting is carried out on the bolt. The model established by the modeling method is used for simulating collision response, can accurately simulate the real loading condition of the bolt in the collision environment of the whole vehicle, and can accurately simulate fracture failure after exceeding the allowable range. The invention improves the simulation precision of bolt connection, is beneficial to improving the reliability of the collision simulation of the whole vehicle, and can reduce the times of development and test, shorten the development period and reduce the development cost.
According to another specific embodiment of the invention, in the bolt modeling step, points are distributed at two circle centers of a bolt head plane and a screw head plane respectively, at least one beam unit is used for connecting the two circle centers and establishing a bolt central unit, a layer of bolt shell unit is arranged on the outer surface of the bolt central unit, and each node of the bolt shell unit is connected with the corresponding node of the bolt central unit by a rigid unit; wherein the bolt center unit is defined as a threaded portion and an unthreaded portion according to the cross-sectional diameters, respectively; and the section diameter of the thread part is the diameter at the thread bottom, and the section diameter of the thread-free part is the real diameter of the screw.
By adopting the scheme, the center of the bolt, particularly the thread part of the center of the bolt is the position where the fracture failure is most likely to occur. The section of the beam unit is divided into two sections according to the threaded part and the unthreaded part, so that the simulation precision can be improved.
According to another specific embodiment of the invention, the finite element modeling method for simulating the bolt collision fracture failure is disclosed in the embodiment of the invention, in the bolt preloading adding step, the friction coefficient between the bolt and the external component is determined according to the actual material properties of the bolt and the external component, and the mounting moment calculated according to the friction coefficient is converted into the axial force to be applied to each beam unit of the bolt central unit.
According to another specific embodiment of the invention, the embodiment of the invention discloses a finite element modeling method for simulating bolt collision fracture failure, in the bolt preloading adding step, after axial force is applied to each beam unit of a bolt center unit, a forward motion is started to be released in actual calculation working conditions, and preloading is stably applied to a bolt model.
According to another specific embodiment of the invention, the embodiment of the invention discloses a finite element modeling method for simulating bolt collision fracture failure, in the connecting step of the bolt model and the nut model, a node at the upper part of the bolt model, which exceeds the upper surface of the nut model, and a node at the uppermost surface of the nut model are connected through a rigid unit so as to rigidly connect the bolt model and the nut model.
According to another embodiment of the present invention, a finite element modeling method for simulating a bolt collision fracture failure is disclosed in which in the step of connecting a bolt model to a nut model, a nut shell element on an upper surface of the nut model is made into a first rigid body element, a bolt shell element on an upper portion of the bolt model exceeding the nut portion is made into a second rigid body element, and the first rigid body element and the second rigid body element are rigidly connected to rigidly connect the bolt model to the nut model.
According to another specific embodiment of the invention, the finite element modeling method for simulating the bolt collision fracture failure is disclosed in the embodiment of the invention, the cell sizes of the beam cell, the bolt shell cell, the nut shell cell and the rigid cell all satisfy the condition that: the three-dimensional solid unit characteristic degree is not less than 3.5mm, the two-dimensional shell unit characteristic length is not less than 3mm, and the one-dimensional unit characteristic length is not less than 2 mm.
According to another specific embodiment of the present invention, the embodiment of the present invention discloses a finite element modeling method for simulating a bolt collision fracture failure, wherein in the bolt model modeling step and the nut model modeling step, a material MAT9 is given to a bolt shell element and a nut shell element; and the beam element generated in the bolt modeling step is given MAT100 material.
According to another specific embodiment of the invention, the embodiment of the invention discloses a finite element modeling method for simulating bolt collision fracture failure, the size of a beam unit is not less than 2mm, and the size of a bolt shell unit is 3 mm.
According to another specific embodiment of the invention, the embodiment of the invention discloses a finite element modeling method for simulating bolt collision fracture failure, in the external contact setting step, when the actual nut is a welded nut, the nut model is set as a welding simulation connection.
The invention has the beneficial effects that:
according to the invention, through a reasonable modeling method, the appearance of the bolt is considered, bolt contact is accurately simulated, preloading of the bolt is considered, and failure setting is carried out on the bolt. The model established by the modeling method is used for simulating collision response, can accurately simulate the real loading condition of the bolt in the collision environment of the whole vehicle, and can accurately simulate fracture failure after exceeding the allowable range. The invention improves the simulation precision of bolt connection, is beneficial to improving the reliability of the collision simulation of the whole vehicle, and can reduce the times of development and test, shorten the development period and reduce the development cost.
Drawings
FIG. 1 is a flow diagram of a finite element modeling method for simulating bolt collision fracture failure according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a beam element of a finite element modeling method for simulating bolt collision fracture failure according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a bolt housing unit of a finite element modeling method for simulating bolt collision fracture failure according to an embodiment of the invention;
FIG. 4 is a schematic structural diagram of a bolt model of a finite element modeling method for simulating bolt collision fracture failure according to an embodiment of the invention;
FIG. 5 is a schematic structural diagram of a nut shell element of a finite element modeling method for simulating bolt collision fracture failure according to an embodiment of the invention;
FIG. 6 is a schematic structural diagram of a bolt model and nut model connection of a finite element modeling method for simulating bolt collision fracture failure according to an embodiment of the present invention;
FIG. 7 is a schematic structural diagram of a bolt model and nut model connection of a finite element modeling method for simulating bolt collision fracture failure according to an embodiment of the present invention;
FIG. 8 is a schematic assembly diagram of a bolt model and a nut model of a finite element modeling method for simulating bolt collision fracture failure according to an embodiment of the present invention;
fig. 9 is an exploded structure diagram of a bolt model and a nut model of a finite element modeling method for simulating bolt collision fracture failure according to an embodiment of the present invention.
Description of reference numerals:
a: a moving direction of the first external part model;
b: a moving direction of the second outer-part model;
1: a bolt model;
2: a nut model;
3: a first external component model;
4: a second outer part model.
Detailed Description
The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure. While the invention will be described in conjunction with the preferred embodiments, it is not intended that features of the invention be limited to these embodiments. On the contrary, the invention is described in connection with the embodiments for the purpose of covering alternatives or modifications that may be extended based on the claims of the present invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may be practiced without these particulars. Moreover, some of the specific details have been left out of the description in order to avoid obscuring or obscuring the focus of the present invention. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
It should be noted that in this specification, like reference numerals and letters refer to like items in the following drawings, and thus, once an item is defined in one drawing, it need not be further defined and explained in subsequent drawings.
In the description of the present embodiment, it should be noted that the terms "upper", "lower", "inner", "bottom", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings or orientations or positional relationships that are conventionally placed when the products of the present invention are used, and are only used for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the devices or elements indicated must have specific orientations, be configured in specific orientations, and operate, and thus, should not be construed as limiting the present invention.
The terms "first," "second," and the like are used solely to distinguish one from another and are not to be construed as indicating or implying relative importance.
In the description of the present embodiment, it should be further noted that, unless explicitly stated or limited otherwise, the terms "disposed," "connected," and "connected" are to be interpreted broadly, e.g., as a fixed connection, a detachable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present embodiment can be understood in specific cases by those of ordinary skill in the art.
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Examples
A finite element modeling method for simulating bolt collision fracture failure is provided, and analytical software is LS-dyan, as shown in FIG. 1, and comprises the following steps:
modeling a bolt model: arranging points, establishing a bolt center unit by using a BEAM unit (the BEAM unit is shown as BEAM in the analysis software LS-dyan) shown in figure 2, arranging a bolt shell unit shown in figure 3 on the periphery of the bolt center unit, and giving material parameters to the bolt shell unit; the bolt center unit corresponds to the nodes of the bolt shell unit one by one, and rigid connection is arranged between the corresponding nodes of the bolt shell unit and the bolt center unit, so that a bolt model shown in fig. 4 is obtained.
In particular, in the bolt model modeling step, the bolt model is the most important part for modeling the whole bolt connection, and the deformation and the failure of the bolt model are influenced by the contact and load conditions. The bolt model modeling should first connect the two points with a plurality of beam units in the centers of the two ends of the bolt model, namely the two circle centers of the plane of the head of the bolt model and the plane of the head of the bolt model. And arranging a bolt shell unit on the periphery of the bolt center unit to simulate the basic appearance of the bolt model.
It should be noted that along the length direction of the bolt model, the grid nodes of each layer of bolt shell unit should correspond to each node of the beam unit one by one.
Further, each layer of nodes on the outer surface of the bolt model is connected with the corresponding beam unit nodes through one-dimensional rigid units (the rigid units are shown as Rigidbody in the analysis software LS-dyan). The bolt shell unit on the outer surface is a null unit, is endowed with MAT9 material, and mainly plays a role in bearing all contact of the bolt and the outside, and does not provide rigidity and strength.
This bolt pattern is in contact with other peripheral components through the shell elements of the outer surface, transferring the load to the connected beam elements through the central rigid element (rigidbody), which carry various loads.
Modeling a nut model: establishing a nut model, and dividing the outer surface of the nut model into nut shell units as shown in fig. 5; and, give the nut shell unit the material parameter, give the nut quality to the centroid of nut model.
In particular, the nut is generally not susceptible to breakage, where only the shell elements need to be divided over the outer surface of the nut model. The operation method in the analysis software LS-dyan is that the nut shell units on the outer surface of the nut model are also null units, the material parameter is MAT9 material, and the nut model mainly plays a role in bearing all contact between the nut and the outside. It is worth noting that the nut centroid needs to give the quality of a real nut its real dynamics.
Connecting the bolt model and the nut model: rigid connections are established between the corresponding nodes of the bolt housing unit and the nut housing unit, and models as shown in fig. 6 and 7 are obtained.
An external contact setting step: the bolt housing unit and the nut housing unit are added to the contact of the external part so that the bolt housing unit and the nut housing unit are in contact with the external part mold.
The specific operation method is that all the shell units are made into a set and added into the contact of the whole vehicle, so that the contact of the bolt model and the nut model with other parts is completed.
Bolt preloading adding step: a preload is placed on each beam element generated in the bolt modeling step.
Bolt failure criterion setting step: and giving material parameters to the beam unit in the bolt modeling step, adding corresponding failure force and failure moment limit values to the material parameters, and when the load of the bolt exceeds the limit values, the beam unit of the bolt fails.
Specifically, the beam unit generated in the bolt model modeling step is a main loaded part of the bolt, and material parameters are given. For example, the operation method in the analysis software LS-dyan is to give the material MAT100, the parameter NRR/MRR in the material MAT100 represents the limit of the axial tension/torsion moment that the bolt can bear, the parameters NRS/MSS and NRT/MTT represent the limit of the transverse shear force/bending moment that the bolt can bear, the load limit of the bolt is obtained by a table look-up or bolt load test method, and the corresponding failure force and failure moment limit value are added to the material control card. When calculated by simulation, the bolted beam unit will be disabled if the bolt is loaded beyond the above limits.
As shown in fig. 8 and 9, the first and second outer member models 3 and 4 of fig. 8 are in contact with the bolt model, and one end of the bolt model 1 is connected to the nut model 2. The one-dimensional cells of the present invention are used to transmit forces and moments, evaluated from a contact perspective. The two-dimensional shell element is used to simulate the actual contact of the bolt. The one-dimensional unit and the two-dimensional unit are connected through a rigid unit (rigidbody), and the force and the moment generated by contact can be directly transmitted to the one-dimensional unit of the main loaded unit. And evaluating from the aspect of external load sensitivity, most of the fracture failures of the bolt in the collision process are shear fractures, and if the bolt model 1 is connected with the first external part model 3 and the second external part model 4 in the whole vehicle collision process after the modeling is completed. The first outer member model 3 moves towards the direction a, the second outer member model 4 moves towards the direction b, and the first outer member model 3 and the second outer member model 4 are in contact with the bolt model 1, so that the shearing force generated on the bolt by the contact between the real bolt and the peripheral member can be accurately simulated. In the aspect of evaluation of the fracture position, the bolt model 1 is divided into a plurality of layers, a plurality of one-dimensional units simulate different positions of the bolt, and the actual fracture position can be observed in actual simulation. Because the bolt model 1 can be connected with two simple sheet metal models, also can be connected with a plurality of different part models. After the bolt is broken under the complex connecting ring environment, accurate simulation of the broken position of the bolt can provide a good guide for solving the actual engineering problem.
By adopting the scheme, the bolt appearance is considered through a reasonable modeling method, bolt contact is accurately simulated, preloading of the bolt is considered, and failure setting is carried out on the bolt. The model established by the modeling method is used for simulating collision response, can accurately simulate the real loading condition of the bolt in the collision environment of the whole vehicle, and can accurately simulate fracture failure after exceeding the allowable range. The invention improves the simulation precision of bolt connection, is beneficial to improving the reliability of the collision simulation of the whole vehicle, and can reduce the times of development and test, shorten the development period and reduce the development cost.
According to another specific embodiment of the invention, in the bolt modeling step, points are distributed at two circle centers of a bolt head plane and a screw head plane respectively, at least one beam unit is used for connecting the two circle centers and establishing a bolt central unit, a layer of bolt shell unit is arranged on the outer surface of the bolt central unit, and each node of the bolt shell unit is connected with the corresponding node of the bolt central unit by a rigid unit; wherein the bolt center unit is defined as a threaded portion and an unthreaded portion according to the cross-sectional diameters, respectively; and the section diameter of the thread part is the diameter at the thread bottom, and the section diameter of the thread-free part is the real diameter of the screw.
Specifically, the bolt center, and particularly the threaded portion of the bolt center, is the location where failure at break is most likely to occur. The cross-sectional definition of the beam element needs to be differentiated in two sections according to the threaded and unthreaded parts. The diameter of the beam unit section should be the diameter of the thread minor diameter, i.e. the diameter at the thread root, and the non-threaded part should be the true diameter of the screw.
It should be understood that at least one beam unit means that the more beam units, the better the simulation effect, and those skilled in the art can select the number of beam units according to the design requirement.
According to another specific embodiment of the invention, the finite element modeling method for simulating the bolt collision fracture failure is disclosed in the embodiment of the invention, in the bolt preloading adding step, the friction coefficient between the bolt and the external component is determined according to the actual material properties of the bolt and the external component, and the mounting moment calculated according to the friction coefficient is converted into the axial force to be applied to each beam unit of the bolt central unit.
In particular, in practice, the bolts are usually mounted with a corresponding mounting torque. The method of operation in the analysis software LS-dyan is such that, depending on the different coefficients of friction of the bolt mounting surface, the moment should be converted into an AXIAL FORCE applied to each BEAM element generated in the bolt model modeling step by the INITIAL _ AXIAL _ FORCE _ BEAM key.
Further, in the bolt preload adding step, after the axial force is applied to each beam unit of the bolt center unit, the advancing action is dynamically released at the beginning of the actual calculation condition, and the preload is stably applied to the bolt model.
That is, the operation method in the analysis software LS-dyan is that, in the present embodiment, after the preload addition is completed, a CONTROL _ DYNAMIC _ hierarchy key is added for DYNAMIC release before the actual calculation operation starts, and the preload is stably applied to the bolt model.
According to another specific embodiment of the invention, the embodiment of the invention discloses a finite element modeling method for simulating bolt collision fracture failure, in the connecting step of the bolt model and the nut model, a node at the upper part of the bolt model, which exceeds the upper surface of the nut model, and a node at the uppermost surface of the nut model are connected through a rigid unit so as to rigidly connect the bolt model and the nut model.
In particular, the threaded portion of the bolt, which is beyond the height of the nut, is generally considered not to be loaded, where the model can be simplified to handle the entire bolt model without being affected by loading. The connection between the bolt model and the nut model can be realized by connecting a node of the upper part of the bolt model, which exceeds the upper surface of the nut model, with a node of the uppermost surface of the nut model through a rigid unit (rigidbody).
According to another embodiment of the present invention, a finite element modeling method for simulating a bolt collision fracture failure is disclosed in which in the step of connecting a bolt model to a nut model, a nut shell element on an upper surface of the nut model is made into a first rigid body element, a bolt shell element on an upper portion of the bolt model exceeding the nut portion is made into a second rigid body element, and the first rigid body element and the second rigid body element are rigidly connected to rigidly connect the bolt model to the nut model.
In particular, the threaded portion of the bolt beyond the height of the nut is generally considered not to bear load, and the model processing can be simplified here so that the whole bolt model is not affected by load. The operation method in the analysis software LS-dyan is that the nut shell unit on the upper surface of the nut model is made into a RIGID body, the bolt shell unit on the upper part of the bolt model exceeding the nut model is made into another RIGID body, and the two RIGID BODIES are rigidly connected through a structured _ RIGID _ BODIES keyword.
According to another specific embodiment of the invention, the finite element modeling method for simulating the bolt collision fracture failure is disclosed in the embodiment of the invention, the cell sizes of the beam cell, the bolt shell cell, the nut shell cell and the rigid cell all satisfy the condition that: the three-dimensional solid unit characteristic degree is not less than 3.5mm, the two-dimensional shell unit characteristic length is not less than 3mm, and the one-dimensional unit characteristic length is not less than 2 mm.
In particular, cell size is a very important factor affecting crash simulation modeling, and the following mainly explains the influence of cell size on the overall vehicle crash simulation, and thus has a corresponding influence on the bolt modeling manner. In order to fully express the appearance, the preloading, the contact and the like of the bolt, if the full-solid grid modeling is adopted, a plurality of fine grids are generated by involving relatively fine features such as a threaded screw. In light of the foregoing, too small a cell in the prior art would result in additional mass increase, affecting the model simulation accuracy.
In the existing whole vehicle collision simulation process, because the whole vehicle is involved, parts are numerous, and the number of units in a finite element simulation model is far more than one million. Collision simulation usually uses a central difference algorithm, so that there is a definition of a time step in model calculation. The smaller the time step is, the more accurate the algorithm is, the more stable the model is, and the higher the accuracy is, however, the total calculation time is also increased correspondingly, and the development period is required to be prolonged correspondingly.
In general, the calculation accuracy and the total calculation time are compromised, and each calculation time step in a general model is 5E-4ms to 7E-4 ms. The calculation time step is proportional to the cell size and inversely proportional to the material density. When the cell size is too small to meet the time step requirement, the computer will amplify the cell material density to make its time step meet the calculation requirement.
Density amplification means an increase in mass, and in kinetics, an increase in mass means an increase in energy. Unreasonable energy increase and mass change inevitably change the motion posture and stress condition of parts, thereby directly causing the distortion of the collision simulation result of the whole vehicle.
Therefore, all the cells in the entire vehicle model have reasonable cell sizes. Corresponding to the definition of the time step of the whole vehicle, the preferable unit size requirements are that the three-dimensional entity unit characteristic degree is not less than 3.5mm, the two-dimensional shell unit characteristic length is not less than 3mm, and the one-dimensional unit characteristic length is not less than 2 mm. In addition, most types of connecting bolts for passenger cars are generally between M8 and M16, namely the major diameter of the thread is 8mm to 16mm, and the connecting bolts can be selected by a person skilled in the art according to actual needs.
According to another specific embodiment of the present invention, the embodiment of the present invention discloses a finite element modeling method for simulating a bolt collision fracture failure, wherein in the bolt model modeling step and the nut model modeling step, a material MAT9 is given to a bolt shell element and a nut shell element; and, the beam unit generated in the bolt modeling step is given MAT100 material.
Specifically, the material given MAT9, which is primarily responsible for assuming all contact with the outside world, does not provide rigidity and strength. In MAT100 material, the parameter NRR/MRR represents the limit of axial tension/torsional moment that the bolt can bear, and the parameters NRS/MSS and NRT/MTT represent the limit of transverse shear force/bending moment that the bolt can bear.
According to another specific embodiment of the invention, the embodiment of the invention discloses a finite element modeling method for simulating bolt collision fracture failure, the size of a beam unit is not less than 2mm, and the size of a bolt shell unit is 3 mm.
The beam units are used for establishing bolt center units, bolt shell units are arranged on the peripheries of the bolt center units, material parameters are given to the bolt shell units, the bolt center units correspond to the nodes of the bolt shell units one to one, and rigid connection is arranged between the corresponding nodes.
According to another specific embodiment of the invention, the embodiment of the invention discloses a finite element modeling method for simulating bolt collision fracture failure, in the external contact setting step, when the actual nut is a welded nut, the nut model is set as a welding simulation connection.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing is a more detailed description of the invention, taken in conjunction with the specific embodiments thereof, and that no limitation of the invention is intended thereby. Various changes in form and detail, including simple deductions or substitutions, may be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims (10)
1. A finite element modeling method for simulating bolt collision fracture failure, characterized by comprising the steps of:
modeling a bolt model: arranging points, establishing a bolt central unit by using a beam unit, arranging a bolt shell unit on the periphery of the bolt central unit, and giving material parameters to the bolt shell unit; the bolt central unit corresponds to the nodes of the bolt shell unit one by one, and rigid connection is arranged between the corresponding nodes of the bolt shell unit and the bolt central unit;
modeling a nut model: establishing a nut model, and dividing the outer surface of the nut model into nut shell units; and, endowing the nut shell unit with material parameters, and endowing the centroid of the nut model with nut quality;
connecting the bolt model and the nut model: establishing rigid connection between the corresponding nodes of the bolt shell unit and the nut shell unit;
an external contact setting step: adding the bolt housing unit and the nut housing unit into contact with an external component to bring the bolt housing unit and the nut housing unit into contact with an external component mold;
bolt preloading adding step: setting a preload on each of the beam units generated in the bolt modeling step;
bolt failure criterion setting step: and giving material parameters to the beam unit in the bolt modeling step, and adding corresponding failure force and failure moment limit values to the material parameters.
2. The finite element modeling method for simulating bolt impact fracture failure of claim 1,
in the bolt modeling step, respectively arranging points at two circle centers of a bolt head plane and a screw head plane, connecting the two circle centers by using at least one beam unit and establishing a bolt center unit, arranging a layer of bolt shell unit on the outer surface of the bolt center unit, and connecting each node of the bolt shell unit with a corresponding node of the bolt center unit by using a rigid unit; wherein
The bolt center unit is defined as a threaded part and an unthreaded part according to the cross-sectional diameter, respectively; and is
The cross-sectional diameter of the threaded part is the diameter at the bottom of a thread ridge, and the cross-sectional diameter of the unthreaded part is the true diameter of the screw.
3. A finite element modeling method for simulating bolt collision fracture failure according to claim 2, characterized in that in the bolt preload addition step, a friction coefficient between a bolt and the outer component is determined according to actual material properties of the bolt and the outer component, and an installation moment calculated according to the friction coefficient is converted into an axial force to be applied to each of the beam elements of the bolt center unit.
4. A finite element modeling method for simulating bolt collision fracture failure according to claim 3, characterized in that in the bolt preload addition step, after the axial force is applied to each of the beam elements of the bolt center element, the advancing action is dynamically released at the start of actual calculation conditions, and preload is stably applied to the bolt model.
5. A finite element modeling method for simulating a bolt collision fracture failure according to claim 3, characterized in that in the connecting step of the bolt model and the nut model, a node of the upper portion of the bolt model exceeding the upper surface of the nut model and a node of the uppermost surface of the nut model are connected by a rigid element to rigidly connect the bolt model and the nut model.
6. A finite element modeling method for simulating a bolt collision fracture failure according to claim 3, characterized in that in the connecting step of the bolt model and the nut model, the first rigid body element and the second rigid body element are rigidly connected by making a nut shell element of an upper surface of the nut model a first rigid body element, making a bolt shell element of an upper portion of the bolt model exceeding the nut portion a second rigid body element, and rigidly connecting the bolt model and the nut model.
7. A finite element modeling method for simulating bolt collision fracture failure according to any of claims 2-6, characterized in that the cell sizes of the beam cell, the bolt housing cell, the nut housing cell and the rigid cell all satisfy the condition:
the three-dimensional solid unit characteristic degree is not less than 3.5mm, the two-dimensional shell unit characteristic length is not less than 3mm, and the one-dimensional unit characteristic length is not less than 2 mm.
8. A finite element modeling method for simulating a bolt collision fracture failure according to claim 7, characterized in that in the bolt model modeling step and the nut model modeling step, MAT 9-number material is given to the bolt housing element and the nut housing element; and is
The beam element produced in the bolt modeling step is given MAT100 material.
9. A finite element modeling method for simulating bolt impact fracture failure as claimed in claim 8 wherein the beam element size is no less than 2mm and the bolt housing element size is 3 mm.
10. A finite element modeling method for simulating bolt collision fracture failure according to claim 9, characterized in that in the external contact setting step, when the actual nut is a weld nut, the nut model is set as a weld simulation connection.
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