Connection strength analysis method for stitched joints of sandwich parts

Abstract

The method for analyzing the connection strength of the stitched joint of sandwich parts involves using one-dimensional elements to simulate the seam and calculating the shear strength of a first finite element model; obtaining the test results of the shear strength test of the material-level hard sandwich, or obtaining the calculation results of a second finite element model with a solid seam for stitching; comparing and analyzing the test results or calculation results with the calculation results of the first finite element model to characterize the stitching strength of the one-dimensional element and establish a model failure criterion; obtaining a third finite element model of a plate-level hard sandwich, using one-dimensional elements to simulate the seam, establishing the stitching connection between the plates, and performing impact simulation calculations; determining the failure area of ​​the seam connection during impact, comparing it with the impact test results, and adjusting the model failure criterion; establishing a fourth finite element model of a part-level hard sandwich, using one-dimensional elements to simulate the seam, performing impact simulation calculations, and determining the blade failure area based on the model failure criterion.

Description

Technical Field

[0001] This invention relates to a method for strength analysis of structural components, and more particularly to a method for strength analysis of interface connections in sandwich components. Background Technology

[0002] Composite materials, due to their superior mechanical properties, have found widespread application in aero-engines. Existing composite blades abroad utilize titanium alloy edging structures to enhance their impact resistance, with the titanium alloy edging bonded to the composite blade body via adhesive bonding. This places high demands on the mechanical properties of the interface between the metal and composite materials, especially as interface splitting can easily occur under impact, leading to metal-composite material separation. Composite titanium alloy hybrid fan blades, through the application of additive manufacturing and woven composite material technologies, allow for designs that break free from the constraints of traditional processing techniques. This enables the use of a more flexible titanium core structure as the blade's impact-resistant structure, achieving a better balance between strength and weight reduction, making lightweight, high-bypass-ratio fan blades a very promising development direction.

[0003] The interface connection of the composite material-titanium alloy hybrid structure fan blade is a composite material-titanium alloy connection. Due to the existence of a large number of connection interfaces, and the interface connection as the main load-bearing part, in order to ensure that the blade will not suffer from large-area interface failure or even blade disintegration under severe loads such as impact, the various parts are connected by a composite material-titanium alloy-composite material stitching method.

[0004] Current research primarily focuses on experimental studies and microscopic models of composite or single-metal material stitching, such as "Research on the Influence of Stitching on the Performance of Carbon Fiber Composites" and "Analysis of the Influence of Microstructure on the Mechanical Properties of Stitched Composites." Background technology-related patents protect stitching processes, structural features of stitching, and related technologies and designs, such as CN105937506A and US20080053070. However, for the hard sandwich stitching method of composite-titanium alloy-composite materials used in actual composite titanium alloy hybrid fan blades, and its connection strength analysis method, no effective analysis method has yet been found. Using traditional mechanical solid modeling and calculation methods would involve a huge workload of modeling and computation. Therefore, a complete set of detailed analysis models down to the macroscopic simulation method at the blade component level is needed to address the design requirements of pre-analysis and stitching parameter optimization. Summary of the Invention

[0005] The purpose of this invention is to provide a method for analyzing the connection strength of stitched connections in sandwich parts, thereby improving analysis efficiency.

[0006] In one embodiment, the method for analyzing the connection strength of the stitched joint of sandwich parts includes:

[0007] Step 1. Obtain the first finite element model of the material-grade rigid sandwich, wherein the material-grade rigid sandwich includes a first material and a second material sandwiched by the first material. Use one-dimensional elements that can only withstand tensile force to simulate the suture and calculate the shear strength of the first finite element model.

[0008] Step 2. Obtain the test results of the shear strength test of the material-grade rigid sandwich, or obtain the calculation results of the shear strength of the second finite element model of the suture connection of the material-grade rigid sandwich established by solid sutures;

[0009] Step 3. Compare and analyze the experimental results or the calculation results of the second finite element model with the calculation results of the first finite element model to characterize the stitching strength of the one-dimensional unit that can only withstand tensile force and establish the model failure criterion of the one-dimensional unit.

[0010] Step 4. Obtain the third finite element model of the flat plate hard sandwich core, which includes two layers of first material plates and a second material plate sandwiched between the two layers of first material plates. Use the one-dimensional element to simulate the suture, establish the suture connection between each plate, and then perform impact simulation calculation.

[0011] Step 5. Obtain the calculation results of the third finite element model, determine the failure area of ​​the suture connection during the impact process, and compare it with the impact test results of the flat plate hard sandwich to adjust the model failure criterion of the one-dimensional element.

[0012] Step 6. Establish a fourth finite element model of the part-level hard sandwich in the simulation software. The part-level hard sandwich corresponds to the sandwich structure of the part. The one-dimensional element is used to simulate the seam, and impact simulation calculation is performed. The failure area of ​​the seam connection of the blade during the impact is determined according to the model failure criterion of the adjusted one-dimensional element.

[0013] Optionally, in step one, a first finite element model is established using the first simulation software to calculate the shear strength; in step two, a second finite element model is established using the second simulation software, and the shear strength is calculated.

[0014] Optionally, the first material is a composite material, and the second material is a titanium alloy.

[0015] Optionally, the feature is that, in the fourth finite element model of step six, the one-dimensional element shares nodes with the solid elements of the composite material and the titanium alloy.

[0016] Optionally, the sandwich component is a composite material titanium alloy hybrid structure fan blade.

[0017] The aforementioned connection strength analysis method is applicable to the stitched connections of sandwich parts. It breaks through the limitations of traditional mechanical solid modeling and calculation methods, avoiding enormous modeling and computational workloads, and achieving accurate characterization of stitched connections on parts, thus greatly improving the efficiency of stitched connection analysis. Furthermore, the proposed method can be calibrated using material-level experiments, maintaining high accuracy even when applied to plate and part scales. This enables the systematic application of the method across multiple simulation levels and has achieved excellent results in practical engineering applications. Attached Figure Description

[0018] The above and other features, properties and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, wherein:

[0019] Figure 1 This is a schematic diagram of a fan blade with a composite titanium alloy hybrid structure.

[0020] Figure 2 It is along Figure 1 A cross-sectional view along line AA.

[0021] Figure 3 This is a schematic diagram of the stitching method for a composite titanium alloy hybrid structure fan blade.

[0022] Figure 4 This is a schematic diagram of the connection strength analysis method for the stitched joint of a composite titanium alloy hybrid fan blade at each level.

[0023] Figure 5 This is a flowchart of the connection strength analysis method for the stitched joint of a composite titanium alloy hybrid structure fan blade.

[0024] Figure 6 This is a graph showing the measured and analyzed values ​​of the strain response at the first stitching position of a composite titanium alloy hybrid fan blade.

[0025] Figure 7 This is a graph showing the measured and analyzed values ​​of the strain response at the second stitching position of a composite titanium alloy hybrid structure fan blade.

[0026] Figure 8 This is a graph showing the measured and analyzed values ​​of the strain response at the third stitching position of a composite titanium alloy hybrid structure fan blade. Detailed Implementation

[0027] The following discloses various implementation methods or embodiments of the described subject matter. To simplify the disclosure, specific examples of the elements and arrangements are described below. Of course, these are merely examples and are not intended to limit the scope of protection of the present invention.

[0028] The following embodiments use a composite titanium alloy hybrid structure fan blade as an example to illustrate the connection strength analysis method for the stitched connection of sandwich parts. Through this embodiment, the analysis method for other sandwich parts can also be understood.

[0029] like Figure 1 and Figure 2 An example of a composite titanium alloy hybrid structure fan blade is provided, comprising a titanium alloy leading edge 2, a composite material blade body 1, and a titanium alloy core 6. For example... Figure 2 As shown, the composite material blade 1 includes an upper composite material part 3 and a lower composite material part 4. The area circled by the frame line 7 is the stitching area. The upper composite material part 3 and the lower composite material part 4 sandwich a titanium alloy core 6. The leading edge 2 of the titanium alloy is fixed to the contact position between the front end of the upper composite material part 3 and the lower composite material part 4 by adhesive bonding. Similarly, the contact position between the titanium alloy core 6 and the opposite surfaces of the upper composite material part 3 and the lower composite material part 4 is fixed by adhesive bonding. Figure 3 The interface is stitched using suture 8 as shown in the diagram to improve the bonding strength.

[0030] Figure 4 This paper illustrates a three-level analysis method for the connection strength of stitched joints in sandwich components. The first level is the material-level analysis, which involves calculating the shear strength of the rigid sandwich structure at the material level. The second level is the plate-level analysis, which involves impact simulation calculations for the rigid sandwich structure at the plate level. Finally, the third level is the blade-level analysis, which involves impact simulation calculations for the rigid sandwich structure at the component level.

[0031] Figure 5 The flowchart for the first level of analysis is shown, including the following process:

[0032] 1) Based on the geometric model of the material-grade hard sandwich, finite element models of the composite material-titanium alloy hybrid structure with and without slots were established in ANSYS (an implicit finite element analysis software) with slots and LS-DYNA (a general explicit dynamic analysis program). The material-grade hard sandwich includes the composite material and the titanium alloy sandwiched by the composite material.

[0033] 2) Establish solid stitches for the solid mesh with slots. For the solid mesh without slots, establish one-dimensional elements that can only withstand tensile forces between the titanium alloy and the composite material, such as cable elements or anchor cable elements. The characteristic parameters of the one-dimensional elements are mainly density, radius or area, material modulus, etc. The number of stitches is much less than the number of stitches on the blade.

[0034] 3) Assign material properties to the solid suture and the composite material, titanium alloy and suture in the finite element model of the above one-dimensional element respectively;

[0035] 4) Apply boundary conditions to the finite element models of the solid seam and the aforementioned one-dimensional element, respectively;

[0036] 5) Apply displacement loads to the solid suture and the finite element model of the one-dimensional element mentioned above, respectively;

[0037] 6) Apply calculation settings to the finite element models of the solid suture and the aforementioned one-dimensional element respectively;

[0038] 7) Analyze the finite element model calculation results of the solid suture and the above one-dimensional element respectively, and characterize the strength of the suture connection of the material-level hard sandwich established by the above one-dimensional element, such as the failure quantity of the one-dimensional element and its value. The failure quantity can be strain, stress or other, that is, the parameter calibration of the above one-dimensional element.

[0039] 8) Propose failure criteria for the above one-dimensional element model. For example, use one type of parameter in the failure quantity as the criterion. If it is not ideal, first adjust the value of the failure quantity. If it is still not ideal, replace it with other failure quantities, such as stress. And by comparing it with the solid element seam model, ensure the analysis accuracy and failure criterion reliability of the above one-dimensional element model.

[0040] Different levels of hard sandwich panels have different shapes and different numbers of stitches, with the complexity level being: part level > flat panel level > material level.

[0041] In another embodiment, in addition to the characterization and comparison performed using a finite element model with solid sutures, the characterization and comparison can also be performed based on the test results and failure modes of the shear strength test of the sutured connection of the material-grade hard sandwich.

[0042] Similarly, refer to Figure 5 The simulation analysis method for the impact of stitching in a flat, rigid sandwich structure can be understood, and it includes:

[0043] A finite element model of a flat-plate rigid sandwich structure was obtained. The flat-plate rigid sandwich structure includes two layers of composite material plates and a titanium alloy plate sandwiched between the two layers of composite material plates. The sutures were simulated using one-dimensional elements that can only withstand tensile forces, and the suture connections between the plates were established. Considering the modeling and computational complexity of the impact model of the higher-scale flat-plate hybrid structure, based on LS-DYNA, the model uses the aforementioned one-dimensional elements to simulate the sutures. The aforementioned one-dimensional elements share nodes with the composite material and titanium alloy solid elements.

[0044] Then repeat steps 3)-6) above to perform finite element setup and calculation;

[0045] Extract the finite element model calculation results of the above one-dimensional unit, analyze them according to the failure criteria obtained in step 8), and determine the failure area of ​​the suture connection during the impact of the flat plate hard sandwich suture.

[0046] By comparing the physical test results with those of the flat-plate hard sandwich, the failure criteria of the above one-dimensional element were adjusted according to the mesh size.

[0047] Similarly, refer to Figure 5 Furthermore, it can be understood that the simulation analysis method for the stitching impact of blade-level hard sandwich structures can be used to realize the impact on macroscopic components such as composite titanium alloy hybrid structure fan blades, which utilizes a reasonably simplified stitching connection analysis model. Figure 2 The analysis of the connection strength and determination of the failure criterion of the hard sandwich joint interface circled by the frame 7 shown.

[0048] First, a finite element model of the stitched blade is established based on LS-DYNA, for example... Figure 2 The model of the area circled by the middle frame line 7 uses the above one-dimensional element to simulate the seam, and shares nodes with the composite material 3 and 4 and the titanium alloy 6 solid element;

[0049] Then, repeat steps 3)-6) to perform finite element setup and calculation;

[0050] Finally, the finite element model calculation results of the above one-dimensional unit are extracted and analyzed according to the aforementioned adjusted failure criteria to determine the failure area of ​​the suture connection during the blade-level hard sandwich stitching impact process.

[0051] Figures 6 to 8 It shows Figure 2 The measured and analyzed values ​​of strain response at three locations on the seam interface are circled by the middle frame line 7. Curve 31 is the strain detected by the corresponding strain gauge, and curve 32 is the strain curve analyzed. It can be seen that the measured and analyzed values ​​of the blade-level strain response are in good agreement.

[0052] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the invention, fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for analyzing the connection strength of stitched joints in sandwich components, characterized in that, include: Step 1. Obtain the first finite element model of the material-grade rigid sandwich, wherein the material-grade rigid sandwich includes a first material and a second material sandwiched by the first material. Use one-dimensional elements that can only withstand tensile force to simulate the suture and calculate the shear strength of the first finite element model. Step 2. Obtain the test results of the shear strength test of the material-grade rigid sandwich, or obtain the calculation results of the shear strength of the second finite element model of the suture connection of the material-grade rigid sandwich established by solid sutures; Step 3. Compare and analyze the experimental results or the calculation results of the second finite element model with the calculation results of the first finite element model to characterize the stitching strength of the one-dimensional unit that can only withstand tensile force and establish the model failure criterion of the one-dimensional unit. Step 4. Obtain the third finite element model of the flat plate hard sandwich core, which includes two layers of first material plates and a second material plate sandwiched between the two layers of first material plates. Use the one-dimensional element to simulate the suture, establish the suture connection between each plate, and then perform impact simulation calculation. Step 5. Obtain the calculation results of the third finite element model, determine the failure area of ​​the suture connection during the impact process, and compare it with the impact test results of the flat plate hard sandwich to adjust the model failure criterion of the one-dimensional element. Step 6. Establish a fourth finite element model of the part-level hard sandwich in the simulation software. The part-level hard sandwich corresponds to the sandwich structure of the part. The one-dimensional element is used to simulate the seam, and impact simulation calculation is performed. The failure area of ​​the seam connection of the blade during the impact is determined according to the model failure criterion of the adjusted one-dimensional element.

2. The connection strength analysis method as described in claim 1, characterized in that, In step one, a first finite element model is established using the first simulation software to calculate the shear strength; in step two, a second finite element model is established using the second simulation software to calculate the shear strength.

3. The connection strength analysis method as described in claim 1, characterized in that, The first material is a composite material, and the second material is a titanium alloy.

4. The connection strength analysis method as described in claim 3, characterized in that, In the fourth finite element model of step six, the one-dimensional element shares nodes with the solid elements of the composite material and titanium alloy.

5. The connection strength analysis method as described in claim 1, characterized in that, The sandwich component is a composite material titanium alloy hybrid structure fan blade.

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