CN113051780A - Method for judging axial compression buckling load of flat plate structure - Google Patents
Method for judging axial compression buckling load of flat plate structure Download PDFInfo
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- CN113051780A CN113051780A CN201911366008.9A CN201911366008A CN113051780A CN 113051780 A CN113051780 A CN 113051780A CN 201911366008 A CN201911366008 A CN 201911366008A CN 113051780 A CN113051780 A CN 113051780A
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Abstract
The invention belongs to the field of aviation structure design, and particularly relates to a method for judging local buckling load during axial compression nonlinear analysis of a flat plate structure.
Description
Technical Field
The invention belongs to the field of aviation structure design, and particularly relates to a method for judging local buckling load during nonlinear analysis of axial compression of a flat plate structure.
Background
Under the action of axial compression load, when the flat plate structure is partially bent, the compression stiffness of the flat plate structure is changed within the plate width range, so that the compression load is redistributed at the middle position and the side supporting position of the flat plate structure, but the total compression stiffness of the flat plate structure is not changed greatly, and the bending load of the flat plate structure cannot be visually judged through a load-displacement curve.
The method mainly comprises two methods for judging the axial compression buckling load of the flat plate structure at home and abroad, wherein the buckling load is judged by a bifurcation point of strain gauges on the upper surface and the lower surface of the flat plate structure in the first method; the second method adopts a Digital Image Correlation (DIC) technique, also called DIC method, and determines the buckling load by whether the slab structure is fluctuating.
Due to possible geometrical defects of the flat plate structure, the strain bifurcation point judgment method may begin to bifurcate at the initial stage of loading, and the axial compression buckling load of the flat plate structure cannot be obtained; the DIC method is more in judgment of the buckling load according to engineering judgment of designers, and lacks necessary judgment criteria.
Disclosure of Invention
The application aims to provide a method capable of accurately judging the axial compression buckling load of a flat plate structure.
A method for judging axial compressive buckling load of a flat plate structure is disclosed, wherein the geometric parameters and material parameters of the flat plate structure are known, and the method is characterized by comprising the following steps of:
step one, adopting a linear four-node shell reducing unit to establish a finite element model of the flat plate structure;
and secondly, prefabricating the geometric defects of the flat plate structure on the finite element model by adopting linear combination of the buckling modes of the first three orders.
Thirdly, applying constraints to four sides of the flat plate structure on the finite element model, and applying opposite axial compression displacement loads to two ends of the flat plate structure to obtain an axial compression buckling finite element model of the flat plate structure;
step four, carrying out nonlinear solution on the axial compression buckling finite element model of the flat plate structure to obtain the counter force at the midpoint position of one end of the flat plate structure, which is subjected to the axial displacement load;
and step five, drawing a curve of the counter force and the axial pressure displacement according to the counter force at the midpoint position of one end of the flat plate structure subjected to the axial displacement load, which is obtained in the step four, and obtaining the buckling load of the flat plate structure through the inflection point of the curve.
The method can also be used for carrying out nonlinear solving on the axial compression buckling finite element model of the flat plate structure, obtaining the out-of-plane displacement change rate of the maximum position of the out-of-plane displacement of the flat plate structure, drawing the out-of-plane displacement change rate and axial compression displacement curve, and obtaining the buckling load of the flat plate structure through the inflection point of the curve.
The beneficial effect of this application lies in: the invention takes the physical phenomenon in the axial compression process of the flat plate structure as the basis, is not interfered by external factors such as initial defects and the like, and can accurately judge the axial compression buckling load of the flat plate through the axial compression reaction force curve and the out-of-plane displacement change rate curve.
The present application is described in further detail below with reference to the accompanying drawings of embodiments.
Drawings
FIG. 1 is a schematic diagram of a finite element model of a flat plate structure;
FIG. 2 is a schematic diagram of a prefabricated geometric defect of a flat plate structure in a finite element model.
FIG. 3 is a schematic diagram of a variation curve of the counter force and the axial pressure displacement at the midpoint position of one end of the flat plate structure subjected to the axial displacement load;
FIG. 4 is a graph showing the reaction force variation of the loaded end before and after the buckling of the flat plate structure.
FIG. 5 is a graph showing the variation rate of the out-of-plane displacement at the maximum position of the out-of-plane displacement of the flat plate structure and the variation of the axial pressure displacement.
The numbering in the figures illustrates: 1 flat plate structure finite element model, 2 geometric defects, 3 counterforce and axial pressure displacement curve, 4 curve inflection points, 5 out-of-plane displacement change rate and axial pressure displacement curve
Detailed Description
Referring to the attached drawings, the method for judging the axial compression buckling load of the flat plate structure provided by the application is based on the physical phenomenon in the axial compression process of the flat plate structure, and can accurately judge the axial compression buckling load of the flat plate through an axial compression reaction force curve and an out-of-plane displacement change rate curve without being interfered by external factors such as initial defects. Knowing the geometrical and material parameters of the flat structure, comprising the steps of:
step one, adopting a linear four-node shell reducing unit to establish the finite element model 1 with the flat plate structure. The grid size of the finite element model 1 of the flat plate structure is ensured to smoothly and accurately describe the buckling mode of the flat plate. As shown in fig. 1.
And secondly, prefabricating the geometric defect 2 on the flat plate structure on the finite element model 1 of the flat plate structure by adopting linear combination of the buckling modes of the first three stages. As shown in fig. 2.
In order to ensure that the expected buckling phenomenon occurs to the finite element model of the flat plate structure under the action of the uniform axial compression displacement load, for the prefabricated geometric defect 2 of the flat plate structure, a more ideal calculation result can be obtained by adopting the linear combination of the buckling modes of the first three orders under the common condition. For a flat structure, geometric defects are preformed, the magnitude of which is typically 1% to 5% of the thickness of the flat structure.
Thirdly, applying constraints to four sides of the flat plate structure on the finite element model, and applying opposite axial compression displacement loads to two ends of the flat plate structure to obtain an axial compression buckling finite element model of the flat plate structure;
in practice, the constraint imposed on the four sides of the flat plate structure may be simple or rigid.
Step four, carrying out nonlinear solution on the axial compression buckling finite element model of the flat plate structure to obtain the counter force at the midpoint position of one end of the flat plate structure, which is subjected to the axial displacement load;
for the nonlinear analysis method, after the flat plate structure is bent, the two sides of the flat plate can be continuously loaded, and the load-displacement curve of the whole flat plate structure has no obvious inflection point phenomenon, so that the bending load of the flat plate cannot be intuitively judged through the load-displacement curve in the prior art.
And step five, drawing a curve 3 of the counter force and the axial pressure displacement by taking the counter force as a vertical coordinate and the axial pressure displacement as a horizontal coordinate according to the counter force at the midpoint position of one end of the flat plate structure subjected to the axial displacement load, which is obtained in the step four, and obtaining the buckling load of the flat plate structure through a curve inflection point 4. As shown in fig. 3.
The counter forces of the loading ends of the flat plate structure are basically the same under the action of axial compression displacement load before buckling occurs; when flexion occurs, that is, the flat plate generates out-of-plane displacement, the axial compression stiffness of the flat plate changes. Due to the change of the axial compression stiffness of the flat plate, the counter force of the loading end is changed to be small in the middle and large on two sides, and the trend is gradually increased along with the increase of the load, as shown in fig. 4.
The application also provides a method for solving the buckling load of the flat plate structure according to the out-of-plane displacement change rate and the axial compression displacement curve of the flat plate structure subjected to the axial displacement load. And performing nonlinear solution on the axial compression buckling finite element model of the flat plate structure to obtain the out-of-plane displacement change rate at the maximum position of the out-of-plane displacement of the flat plate structure, drawing an out-of-plane displacement change rate and axial compression displacement curve 5 by taking the out-of-plane displacement change rate of the flat plate structure as a vertical axis and the axial compression displacement borne by the flat plate structure as a horizontal axis, and obtaining the buckling load of the flat plate structure through the curve inflection point 4. As shown in fig. 5.
Claims (4)
1. A method for judging axial compressive buckling load of a flat plate structure is disclosed, wherein the geometric parameters and material parameters of the flat plate structure are known, and the method is characterized by comprising the following steps of:
step one, adopting a linear four-node shell reducing unit to establish a finite element model of the flat plate structure;
and secondly, prefabricating the geometric defects of the flat plate structure on the finite element model by adopting linear combination of the buckling modes of the first three orders.
Thirdly, applying constraints to four sides of the flat plate structure on the finite element model, and applying opposite axial compression displacement loads to two ends of the flat plate structure to obtain an axial compression buckling finite element model of the flat plate structure;
step four, carrying out nonlinear solution on the axial compression buckling finite element model of the flat plate structure to obtain the counter force at the midpoint position of one end of the flat plate structure, which is subjected to the axial displacement load;
and step five, drawing a curve of the counter force and the axial pressure displacement according to the counter force at the midpoint position of one end of the flat plate structure subjected to the axial displacement load, which is obtained in the step four, and obtaining the buckling load of the flat plate structure through the inflection point of the curve.
2. The method for determining the buckling load of the flat plate structure in the axial compression manner as claimed in claim 1, wherein in the fourth step, the axial compression buckling finite element model of the flat plate structure is subjected to nonlinear solution to obtain the out-of-plane displacement change rate at the position of the maximum out-of-plane displacement of the flat plate structure, and an out-of-plane displacement change rate and axial compression displacement curve is drawn to obtain the buckling load of the flat plate structure through the inflection point of the curve.
3. The method for judging the axial compressive buckling load of the flat plate structure as claimed in claim 1 or 2, wherein in the second step, the flat plate structure is prefabricated with the geometric defect, and the amplitude of the geometric defect is 1% -5% of the thickness of the flat plate structure.
4. The method for determining the axial compressive buckling load of the flat plate structure as claimed in claim 1, wherein in the third step, the constraint applied to the four sides of the flat plate structure can be a simple support or a fixed support.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113720682A (en) * | 2021-08-19 | 2021-11-30 | 中国航空工业集团公司西安飞机设计研究所 | Method for determining local buckling load of test piece |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109507040A (en) * | 2018-12-12 | 2019-03-22 | 中国航空工业集团公司西安飞机设计研究所 | A kind of honeycomb sandwich construction panel compression stress appraisal procedure |
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Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109507040A (en) * | 2018-12-12 | 2019-03-22 | 中国航空工业集团公司西安飞机设计研究所 | A kind of honeycomb sandwich construction panel compression stress appraisal procedure |
Non-Patent Citations (1)
| Title |
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| 刘洪权;谭申刚;张建刚;杜正兴;: "几何缺陷对复合材料加筋平板轴压屈曲影响研究", 机械科学与技术, vol. 37, no. 12, pages 1964 - 1968 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113720682A (en) * | 2021-08-19 | 2021-11-30 | 中国航空工业集团公司西安飞机设计研究所 | Method for determining local buckling load of test piece |
| CN113720682B (en) * | 2021-08-19 | 2024-05-03 | 中国航空工业集团公司西安飞机设计研究所 | Method for determining local buckling load of test piece |
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