Composite shell plate truss connection fatigue strength test method

Abstract

The application discloses a kind of composite material surrounding shell panel frame connecting structure fatigue strength test methods, comprising the following steps: finite element modeling is carried out to composite material surrounding shell typical panel frame connecting structure, the size of each part of composite material surrounding shell typical panel frame and structure are preliminarily determined, the model built at this time is original structure model;According to the size of each part of composite material surrounding shell typical panel frame and structure that are preliminarily determined, design two kinds of connecting joint test models;According to the two kinds of connecting joint test models designed, finite element modeling is carried out, and load is applied on connecting joint test model, fatigue test load is determined by adjusting load size;The fatigue test is carried out by applying the fatigue test load determined on the two joint test models built in entity.This composite material surrounding shell panel frame connecting structure fatigue strength test method makes fatigue test more in line with actual use environment, so as to facilitate the size of composite material surrounding shell panel frame connecting structure to be designed accurately.

Description

Technical Field

[0001] This invention relates to the field of material performance testing technology, and in particular to a method for testing the fatigue strength of a composite material shell-plate connection structure. Background Technology

[0002] According to the relevant provisions of a national standard regarding "Calculation of Command Room Enclosure Structure," the strength of the command room enclosure structure is checked using a static load Pc borne by the top and one side. When considering wave impact loads, Pc is 0.098 MPa. Considering that wave impact loads are periodic loads, the enclosure will frequently experience wave impact loads in actual use environments; therefore, fatigue strength issues exist in the enclosure structure. When composite material shell plates are used in the enclosure structure, the connection structure between the composite material and the steel frame is relatively weak, and the fatigue problem of the connection structure must be considered during structural design.

[0003] The composite material in the shell structure is bolted to the steel frame, and the fatigue strength of this connection is generally verified by testing. Currently, the general approach to fatigue testing of composite material joints is as follows: first, an ultimate strength test is performed on the joint to determine its ultimate load; then, the fatigue test load is taken as 30% of the ultimate load. This testing method does not consider the actual service environment of the joint. For certain specific joints, when the measured ultimate load is too high, the fatigue test load also becomes high, potentially leading to situations where the joint's fatigue performance meets the service requirements, but the fatigue test fails to meet the standards. Summary of the Invention

[0004] The main objective of this invention is to provide a fatigue strength test method for composite material shell plate frame connection structures, aiming to make fatigue testing more consistent with actual use environments, so as to more accurately design the dimensions and structure of composite material shell plate frame connection structures.

[0005] To achieve the above objectives, the present invention provides a method for testing the fatigue strength of a composite material shell-plate connection structure, comprising the following steps: Finite element modeling is performed on a typical plate frame connection structure of composite material shell, and the strength is calculated by applying the load. The size and structure of each part of the typical plate frame of composite material shell are initially determined. The model built at this time is the original structural model. Based on the preliminary determination of the dimensions and structure of each part of the typical composite material shell frame, two test models of connection joints were designed to be equivalent to the stress states of the symmetrical boundary and free boundary of the typical composite material shell frame. Finite element modeling was performed based on the two designed connection joint test models, and loads were applied to the two connection joint test models and the original structural model. The fatigue test load was determined by adjusting the load magnitude. Fatigue tests were conducted on two types of joint test models constructed in physical form, with determined fatigue test loads applied, to determine whether the design of typical plate frame connection structure of composite material shell was reasonable.

[0006] Preferably, the two connection joint test models include a straight joint test model equivalent to the stress state of a typical composite shell plate frame at the free boundary and a T-joint test model equivalent to the symmetrical boundary of a typical composite shell plate frame. The test model of the straight joint includes a first test shell plate, which is equivalent to the composite material shell plate of the original structural model, a first bolt installed in the first test shell plate, and a first test clamping plate installed on the contact end surface of the first bolt and the first test shell plate. The T-joint test model includes a second test shell plate equivalent to the original structural model composite material shell plate, a second bolt installed inside the second test shell plate, a test connecting strip installed on the contact end face of the second bolt and the second test shell plate, and a second test clamping plate installed on the end face of the test connecting strip opposite to the second bolt.

[0007] Preferably, the original structural model includes an original composite material shell plate, original bolts, original connecting strips, and an original steel frame connected to the original connecting strips at one end away from the original composite material shell plate. The original steel frame includes a web plate and a face plate. The web plate is connected to the original connecting strips. The first test clamping plate and the test connecting strips are made of the same material as the original connecting strips, and the second test clamping plate is made of the same material as the original steel frame.

[0008] Preferably, the dimensions and materials of the first and second test shell plates are the same as those of the original composite material shell plate.

[0009] Preferably, the thickness of the first test clamping plate is greater than the thickness of the original connecting strip, and the thickness of the second test clamping plate is greater than the thickness of the original steel frame web.

[0010] Preferably, the panel at the clamping end of the original composite material shell plate is beveled for a transition.

[0011] Preferably, in the step of performing finite element modeling based on two connection joint test models and applying tensile stress loads to both the connection joint test model and the original structural model, and determining the fatigue test load by adjusting the load magnitude, the fatigue test load is determined by ensuring that the typical stress of each structure in the two connection joint test models is just not less than the typical stress of the corresponding structure in the original structural model.

[0012] Preferably, when applying tensile stress load to the I-shaped joint test model, the direction of tensile stress is parallel to the first test clamping plate, and when applying tensile stress load to the T-shaped joint test model, the direction of tensile stress is parallel to the second test clamping plate.

[0013] Preferably, when determining the fatigue test load for the I-shaped joint test model, the typical stresses of the corresponding structures of the original structural model include: the tensile stress, compressive stress, and shear stress of the original composite material shell plate, and the Mises stress of the original bolt; the typical stresses of each structure of the I-shaped joint test model include: the tensile stress, compressive stress, and shear stress of the first test shell plate, and the Mises stress of the first bolt. When determining the fatigue test load for the T-joint test model, the typical stresses of the corresponding structures in the original structural model include: tensile stress, compressive stress, and shear stress of the face plate and core material of the original composite shell plate; the typical stresses of each structure in the T-joint test model include: tensile stress, compressive stress, and shear stress of the face plate and core material of the second test shell plate.

[0014] Preferably, the step of applying a determined fatigue test load to the original structural model to conduct fatigue tests to determine whether the design of the typical plate-frame connection structure of the composite material shell is reasonable specifically includes: If the fatigue test results do not meet the standards, the process returns to modify the typical plate frame structure parameters and executes the steps of performing finite element modeling of the typical plate frame connection structure of the composite material shell and initially determining the size and structure of each part of the typical plate frame of the composite material shell until the fatigue test results meet the standards. When the fatigue test results meet the standards, it indicates that the dimensions and structural design of each structure in the original structural model are reasonable.

[0015] The fatigue strength test method for composite material shell plate frame connection structure proposed in this invention, by rationally designing the stress state of the free boundary and symmetrical boundary of the original structure corresponding to two test models, and using the ultimate design load determined by the test model as the fatigue test load, makes the fatigue test more in line with the actual use environment, the technical route is more reasonable, and the shell structure determined based on this test method is more reliable. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the fatigue strength test method for the composite material shell plate frame connection structure of the present invention; Figure 2 This is a schematic diagram of a typical original structural model of the composite material shell plate frame connection structure of the present invention; Figure 3 for Figure 2 A schematic diagram of the cross-sectional structure along the AA direction; Figure 4 This is a schematic diagram of the planar structure of the test model of the straight joint in the fatigue strength test method of the composite material shell plate frame connection structure of the present invention; Figure 5 for Figure 4A schematic diagram of the cross-sectional structure along the BB direction; Figure 6 This is a schematic diagram of the planar structure of the T-joint test model in the fatigue strength test method for composite material shell plate frame connection structure of the present invention; Figure 7 for Figure 6 The diagram shows a cross-sectional view along the CC direction.

[0017] Figure 8 A schematic diagram of the loading method for the test model of the straight-type joint; Figure 9 This is a schematic diagram of the loading method for the T-joint test model.

[0018] In the figure, 1-original composite material shell plate; 11-first test shell plate; 12-second test shell plate; 2-original steel frame; 3-original connecting strip; 4-original bolt; 41-first bolt; 42-second bolt; 5-original nut; 51-first nut; 52-second nut; 6-first test clamping plate; 7-test connecting strip; 8-second test clamping plate; 9-clamp hole.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] Reference Figure 1 In this preferred embodiment, a fatigue strength test method for a composite material shell frame connection structure includes the following steps: Step S10: Perform finite element modeling on the typical plate frame connection structure of the composite material shell, apply the load to perform strength calculation, and preliminarily determine the size and structure of each part of the typical plate frame of the composite material shell. The model built at this time is the original structural model. Step S20: Based on the preliminary determination of the dimensions and structure of each part of the typical composite material shell frame, design two connection joint test models to be equivalent to the stress states of the symmetrical boundary and free boundary of the typical composite material shell frame. Step S30: Perform finite element modeling based on the two designed connection joint test models, and apply loads to the two connection joint test models and the original structural model. Determine the fatigue test load by adjusting the load magnitude. Step S40: Apply the determined fatigue test load to the two joint test models constructed in the physical environment to conduct fatigue tests in order to determine whether the design of the typical plate frame connection structure of the composite material shell is reasonable.

[0022] Reference Figure 2 and Figure 3 ( Figure 2 and Figure 3 Taking a typical plate frame of this type of shell structure as an example, the original structural model includes an original composite shell plate 1 (the original composite shell plate 1 includes an upper panel, a lower panel, and a core material located in the connection area), original bolts 4, original connecting strips 3, and an original steel frame 2 connected to the original connecting strips 3 at one end away from the original composite shell plate 1. The original steel frame 2 includes a web and a panel, and the web is connected to the original connecting strips 3.

[0023] Specifically, the two connection joint test models include a straight-line joint test model equivalent to the free boundary stress state of a typical composite shell frame and a T-joint test model equivalent to the symmetrical boundary of a typical composite shell frame. Each joint test model contains no fewer than two bolts, with the bolt spacing being the same as that of the actual shell structure.

[0024] Based on the stress distribution in the static strength simulation calculation of the shell structure, there are two main types of stress within the composite shell connection structure, referring to... Figure 1 : The first is the shear force at the free boundary of the plate grid along the direction of the composite shell plate. To address this stress characteristic, a one-piece joint test model was designed, and tensile stress loads were applied to both ends of the joint to mainly represent the stress state at the free boundary of the plate grid.

[0025] Secondly, there is the compressive stress perpendicular to the shell plate direction at the symmetrical boundary of the plate grid. To address this stress characteristic, a T-joint test model was designed. The two ends of the composite material are clamped and fixed. The web of the T-joint test model is loaded along the direction perpendicular to the composite material. Due to the inherent characteristics of the connection structure, when compressive stress is applied, the load is largely converted into contact force between the composite material and the connecting strips, making it difficult to test the performance of the composite material and bolts / nuts in the connection area. Therefore, a tensile stress load perpendicular to the composite material direction is applied to the T-joint. This loading method is more stringent than actual working conditions and yields relatively conservative results. The T-joint is primarily equivalent to the symmetrical boundary between two composite material plates.

[0026] Fatigue tests were conducted on both joint models to jointly verify the fatigue performance of composite material connection joints for shell structures.

[0027] Reference Figure 4 and Figure 5 Specifically, the test model of the straight joint includes a first test shell plate 11, which is equivalent to the original structural model composite material shell plate, a first bolt 41 (with a first nut 51) installed in the first test shell plate 11, and a first test clamping plate 6 installed on the contact end face of the first bolt 41 and the first test shell plate 11. Reference Figure 6 and Figure 7 The T-joint test model includes a second test shell plate 12, which is equivalent to the original structural model composite material shell plate; a second bolt 42 (with a matching second nut 52) ​​installed inside the second test shell plate 12; a test connecting strip 7 installed on the contact end face of the second bolt 42 and the second test shell plate 12; and a second test clamping plate 8 installed on the end face of the test connecting strip 7 facing away from the second bolt 42. Similarly, the first test shell plate 11 and the second test shell plate 12 of the two connection joint test models are also provided with a three-layer structure, namely an upper panel, a lower panel, and a core material located in the connection area.

[0028] Furthermore, the materials of the first test clamping plate 6 and the test connecting strip 7 are the same as those of the original connecting strip 3, and the material of the second test clamping plate 8 is the same as that of the original steel frame 2 (specifically, the same as the web material). The dimensions and materials of the first test shell plate 11 and the second test shell plate 12 are the same as those of the original composite material shell plate 1.

[0029] To prevent fatigue failure of the test clamping plate before the composite material connection area, appropriate reinforcement should be applied to the test clamping plate and the composite material clamping end for both joint models. Therefore, the thickness of the first test clamping plate 6 is set to be greater than the thickness of the original connecting strip 3, and the thickness of the second test clamping plate 8 is greater than the thickness of the original steel frame reinforcing rib web. Furthermore, referring to Figure 5 and Figure 7 The original composite material shell plate clamping end panel (i.e. the junction of the upper panel and the lower panel with the core material) is beveled to improve the stress distribution at this location.

[0030] In step S30, the fatigue test load is determined by ensuring that the typical stress of each structure in the two connection joint test models is just not less than the typical stress of the corresponding structure in the original structural model.

[0031] Reference Figure 8 and Figure 9 When applying tensile stress load to the I-shaped joint test model, the direction of tensile stress is set parallel to the first test clamping plate 6. When applying tensile stress load to the T-shaped joint test model, the direction of tensile stress is set parallel to the second test clamping plate 8.

[0032] In step S30, when determining the fatigue test load for the I-shaped joint test model, the typical stresses of the corresponding structures of the original structural model include: the tensile stress, compressive stress, and shear stress of the panels (including the upper and lower panels) of the original composite material shell plate 1, and the Mises stress of the original bolt 4; the typical stresses of each structure of the I-shaped joint test model include: the tensile stress, compressive stress, and shear stress of the first test shell plate 11, and the Mises stress of the first bolt 41. When determining the fatigue test load for the T-joint test model, the typical stresses of the corresponding structures in the original structural model include: the tensile stress, compressive stress, and shear stress of the original composite shell plate 1, and the tensile stress, compressive stress, and shear stress of the core material; the typical stresses of each structure in the T-joint test model include: the tensile stress, compressive stress, and shear stress of the face plate and core material of the second test shell plate 12.

[0033] This composite material is more complex than conventional composite materials, and is roughly divided into three layers, including the upper and lower shell plates and the core material. Since they are different composite materials, they need to be checked separately in the strength and fatigue strength calculations.

[0034] For the test model of the straight joint, a finite element model is established based on the stress state of the main equivalent plate free boundary. Tensile loads are applied at both ends. By continuously adjusting the load size, the typical stresses of the two parts of the test model, such as the composite material panel and bolts, are not less than the typical stresses of the free boundary of the shell structure. The minimum load at this time is the ultimate design load of the straight joint model, which can be used as the fatigue test load.

[0035] For the T-joint test model, a finite element model is established based on the stress state of the main equivalent plate grid symmetry boundary. A tensile stress load perpendicular to the composite material direction is applied. By continuously adjusting the load magnitude, the typical stress of the composite material panel and core material on the test model is not less than the typical stress of the shell structure symmetry boundary. The minimum load at this time is the ultimate design load of the T-joint model, which can be used as the fatigue test load.

[0036] Specifically, step S40 includes: Step S41: If the fatigue test results do not meet the standards, return to modify the typical plate frame structure parameters and execute step 10 until the fatigue test results meet the standards. Step S42: When the fatigue test results meet the standards, it indicates that the dimensions and structural design of each structure in the original structural model are reasonable.

[0037] The following details the implementation process of the fatigue strength test method for the composite material shell plate frame connection structure.

[0038] If the test results do not meet the standards, the connection structure needs to be strengthened to improve the stress distribution of the connection joint. Based on the stress distribution characteristics of the strengthened connection structure, the joint model should be redesigned and the test load determined, and the test should be repeated for verification.

[0039] Step 1: Design of the original structural model Using ABAQUS software, for Figure 1 Finite element modeling was performed on a typical composite material enclosure frame to check its structural strength and fatigue strength. Based on the check results, the connection structure was preliminarily determined (see...). Figure 2 and Figure 3 The parameters are as follows: The original steel frame 2 has a web thickness of t1=10mm and a panel thickness of t2=12mm; The thickness of the connecting strip is t3 = 8mm; The original bolt 4 and the original nut were both M20.

[0040] Step 2: Design of the joint test model A load of Pc = 0.098 MPa was applied to the original structural model to obtain typical stress values ​​at various locations in the connection region between the symmetrical boundary and the free boundary (that is, the left side of Table 1 and Table 2 below).

[0041] Calculations were performed on the "I"-shaped joint test model. By continuously adjusting the load magnitude and comparing it with the stress state of the free boundary connection region, the stress comparison between the test model and various parts of the original structure when the load was 19.3 kN is shown in the table below: Table 1. Stress Comparison between the Original Structural Model and the Test Model with a Straight Joint

[0042] As shown in Table 1, the bolt stress is comparable to that of the original structural model, while the stress of the composite material panels is greater than that of the original structure. Therefore, the ultimate design load of the I-shaped joint model is taken as 19.3 kN, and the fatigue test load is also taken as 19.3 kN.

[0043] The T-joint test model was calculated, and the load was continuously adjusted and compared with the stress state of the symmetrical boundary connection region. When the load was 60.0 kN, the stress comparison of each component of the T-joint test model and the original structural model is shown in Table 2 below: Table 2. Stress Comparison between Original Structural Model and T-Joint Test Model

[0044] As can be seen from the table, the compressive stress of the composite panel is comparable to that of the original structural model, while other stresses are greater than those of the original structure. Therefore, the ultimate design load of the T-joint is taken as 60.0 kN, and the fatigue test load is taken as 60.0 kN.

[0045] Step 3: Modifying the connection structure parameters Based on the two fatigue test loads determined above, fatigue tests were conducted on two types of joint test models constructed in solid form (two test models of the same size were constructed in solid form based on the results of finite element analysis).

[0046] If the test results do not meet the standards, the connection structure needs to be strengthened to improve the stress distribution of the connection joint. Based on the stress distribution characteristics of the strengthened connection structure, the joint model should be redesigned and the test load determined, and the test should be repeated for verification. When the test results meet the standards, it is considered that the connection structure parameters such as the thickness of the connecting strip, the bolt specifications, and the bolt spacing meet the usage requirements and do not need to be modified.

[0047] In this example, the fatigue test results of the joint model meet the usage requirements, indicating that the joint design is reasonable and requires no modification.

[0048] The fatigue strength test method for composite material shell plate frame connection structure proposed in this invention, by rationally designing the stress state of the free boundary and symmetrical boundary of the original structure corresponding to two test models, and using the ultimate design load determined by the test model as the fatigue test load, makes the fatigue test more in line with the actual use environment, the technical route is more reasonable, and the shell structure determined based on this test method is more reliable.

[0049] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for testing the fatigue strength of a composite material shell-frame connection structure, characterized in that, Includes the following steps: Finite element modeling is performed on a typical plate frame connection structure of composite material shell, and the strength is calculated by applying the load. The size and structure of each part of the typical plate frame of composite material shell are initially determined. The model built at this time is the original structural model. Based on the preliminary determination of the dimensions and structure of each part of the typical composite material shell frame, two test models of connection joints were designed to be equivalent to the stress states of the symmetrical boundary and free boundary of the typical composite material shell frame. Finite element modeling was performed based on the two designed connection joint test models, and loads were applied to the two connection joint test models and the original structural model. The fatigue test load was determined by adjusting the load magnitude. Fatigue tests were conducted on two types of joint test models constructed in reality, with determined fatigue test loads applied to determine whether the design of typical plate frame connection structure of composite material shell was reasonable. Two types of connection joint test models include a straight joint test model that is equivalent to the stress state of a typical composite shell frame at the free boundary and a T-joint test model that is equivalent to the symmetrical boundary of a typical composite shell frame. The test model of the straight joint includes a first test shell plate, which is equivalent to the composite material shell plate of the original structural model, a first bolt installed in the first test shell plate, and a first test clamping plate installed on the contact end surface of the first bolt and the first test shell plate. The T-joint test model includes a second test shell plate, which is equivalent to the original structural model composite material shell plate, a second bolt installed in the second test shell plate, a test connecting strip installed on the contact end face of the second bolt and the second test shell plate, and a second test clamping plate installed on the end face of the test connecting strip opposite to the second bolt.

2. The fatigue strength test method for composite material shell-plate connection structure as described in claim 1, characterized in that, The original structural model includes an original composite shell plate, original bolts, original connecting strips, and an original steel frame connected to the original connecting strips at one end away from the original composite shell plate. The original steel frame includes a web plate and a face plate. The web plate is connected to the original connecting strips. The first test clamping plate and the test connecting strips are made of the same material as the original connecting strips. The second test clamping plate is made of the same material as the original steel frame.

3. The fatigue strength test method for composite material shell-plate connection structure as described in claim 2, characterized in that, The dimensions and materials of the first and second test shell plates are the same as those of the original composite material shell plate.

4. The fatigue strength test method for composite material shell-plate connection structure as described in claim 1, characterized in that, The thickness of the first test clamping plate is greater than the thickness of the original connecting strip, and the thickness of the second test clamping plate is greater than the thickness of the original steel frame web.

5. The fatigue strength test method for composite material shell-plate connection structure as described in claim 1, characterized in that, The original composite material shell plate clamping end panel is beveled for transition.

6. The fatigue strength test method for composite material shell-plate connection structure as described in claim 2, characterized in that, Based on the design of two connection joint test models, finite element modeling is performed, and tensile stress loads are applied to both the connection joint test model and the original structural model. In the step of determining the fatigue test load by adjusting the load magnitude, the fatigue test load is determined by ensuring that the typical stress of each structure in the two connection joint test models is just not less than the typical stress of the corresponding structure in the original structural model.

7. The fatigue strength test method for composite material shell-plate connection structure as described in claim 6, characterized in that, When applying tensile stress load to the I-shaped joint test model, the direction of tensile stress is set parallel to the first test clamping plate. When applying tensile stress load to the T-shaped joint test model, the direction of tensile stress is set parallel to the second test clamping plate.

8. The fatigue strength test method for composite material shell-plate connection structure as described in claim 6, characterized in that, When determining the fatigue test load for the I-shaped joint test model, the typical stresses of the corresponding structures in the original structural model include: the tensile stress, compressive stress, and shear stress of the original composite shell plate, and the Mises stress of the original bolt; the typical stresses of each structure in the I-shaped joint test model include: the tensile stress, compressive stress, and shear stress of the first test shell plate, and the Mises stress of the first bolt. When determining the fatigue test load for the T-joint test model, the typical stresses of the corresponding structures in the original structural model include: the tensile stress, compressive stress, and shear stress of the face plate and core material of the original composite shell plate; the typical stresses of each structure in the T-joint test model include: the tensile stress, compressive stress, and shear stress of the face plate and core material of the second test shell plate.

9. The fatigue strength test method for composite material shell-plate connection structure according to any one of claims 1 to 8, characterized in that, The specific steps for determining the rationality of the typical plate-frame connection structure design of the composite material shell by applying determined fatigue test loads to the original structural model and conducting fatigue tests include: If the fatigue test results do not meet the standards, the process returns to modify the typical plate frame structure parameters and executes the steps of performing finite element modeling of the typical plate frame connection structure of the composite material shell and initially determining the size and structure of each part of the typical plate frame of the composite material shell until the fatigue test results meet the standards. When the fatigue test results meet the standards, it indicates that the dimensions and structural design of each structure in the original structural model are reasonable.

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