A method for prestress application for composite material analysis

Abstract

The application discloses a prestress applying method considering transverse deformation of composite materials. In order to solve the technical problem that the calculation efficiency and calculation accuracy of the prestress applying method of the prior art are difficult to balance, the application adopts an equivalent method to fuse multi-step analysis and thermal analysis method. Firstly, the multi-step analysis of a simple model is used to obtain the equivalent transverse thermal expansion coefficient of fibers, so as to consider the transverse deformation of the composite material under the prestress load, and then the prestress is equivalent to an equivalent temperature load, so as to realize efficient application of the prestress in the finite element analysis of the composite material. The prestress applying method for the composite material analysis effectively guarantees the accuracy and efficiency of the analysis of the prestressed composite material, and has strong engineering practical significance.

Description

TECHNICAL FIELD

[0001] The application relates to a finite element analysis method of a composite material, in particular to a prestress applying method for composite material analysis. BACKGROUND

[0002] Prestressed composite materials are widely used in engineering. However, due to the complex internal structure of the composite material, the great difference in mechanical properties between the fiber and the matrix, the complex molding process and other reasons, complex residual stress states will be generated in the material. The existence of residual stress will change the damage initiation and development process of the composite material, and ultimately affect its strength, so it is necessary to accurately predict the residual stress state in the material. The finite element method is an important tool for predicting the residual stress state of prestressed composite materials, but there is still a lack of efficient prestress applying method.

[0003] In order to ensure the accuracy of the analysis of prestressed composite materials, the existing prestress applying method is the equivalent temperature method, which is widely used in the study of the internal stress state of prestressed reinforced concrete members. It is based on the prestress value and the longitudinal thermal expansion coefficient and elastic modulus of the steel bar to calculate the equivalent temperature load applied to the steel bar. However, in reinforced concrete members, the volume content of steel bars accounts for a small proportion, and the transverse deformation of steel bars can be ignored. However, with the improvement of the preparation process, the design fiber volume content of fiber reinforced composites can be higher and higher. Due to the Poisson's ratio effect, there will be shrinkage deformation in the transverse direction of the fiber, which cannot be reflected in the equivalent temperature method. In addition, most fiber reinforced composites need a static high-temperature curing process, which will also cause residual stress in the material. However, the equivalent temperature method cannot consider the coupling effect of temperature and prestress on the residual stress state.

[0004] In order to improve the efficiency of the analysis, the common equivalent method in the prestress applying process is to calculate the equivalent temperature load of the prestress according to a certain equivalent formula, and to realize the application of the prestress by applying the equivalent temperature load. However, this method does not consider the transverse deformation between the fiber and the matrix of the composite material during the prestress applying process, although it improves the analysis efficiency, but it will lead to poor accuracy of the finite element analysis results of the prestressed composite material. Based on this, the application proposes a prestress applying method considering the transverse deformation of the fiber of the composite material, which effectively ensures the analysis accuracy of the finite element analysis of the prestressed composite material, and effectively controls the calculation amount of the finite element analysis, ensuring the calculation efficiency. SUMMARY

[0005] In order to solve the technical problems existing in the prior art, the application provides a prestress applying method for composite material analysis, which improves the accuracy and efficiency of the analysis of prestressed composite materials.

[0006] The application realizes the technical scheme as follows:

[0007] A prestress applying method for composite material finite element analysis, characterized in that the method comprises the following steps:

[0008] Step 1: a unit cell model of the composite material is established, and a fiber model and a matrix model of the unit cell model are respectively established;

[0009] Step 2: prestress applied on the fiber in the unit cell model is calculated σ pre , and equivalent temperature load Δ T of the prestress is calculated;

[0010] Step 3: prestress σ pre is applied on the fiber model, finite element analysis is carried out, and finite element analysis result of the fiber model is obtained;

[0011] Step 4: the finite element analysis result of the fiber model is applied to the unit cell model, finite element analysis is carried out on the unit cell model, and finite element analysis result of the unit cell model is obtained;

[0012] Step 5: according to the finite element analysis result of the unit cell model, equivalent transverse thermal expansion coefficient α ft of the composite material fiber is calculated;

[0013] Step 6: equivalent transverse thermal expansion coefficient α ft of the composite material is taken as input value of the unit cell model, equivalent temperature load Δ T is applied to the unit cell model, and prestress applying of the composite material analysis is realized.

[0014] Further, the calculation formula of prestress σ pre on the unit cell model is: σ pre = F pre / A f ; wherein F pre is prestress load of the unit cell model, A f is cross-sectional area of the fiber in the unit cell model.

[0015] Further, the calculation formula of equivalent temperature load Δ T of the prestress is: ΔT = σ pre / (α f E f ; wherein, α f is the coefficient of thermal expansion of the fiber, E f is the elastic modulus of the fiber.

[0016] Further, the equivalent transverse thermal expansion coefficient of the composite fiber α ft is calculated by the formula: α ft = ε ft / Δ T ; wherein, ε ft is the transverse expansion strain of the fiber in the step 4 analysis result.

[0017] Further, the transverse expansion strain of the composite fiber under the equivalent temperature load ε ft is calculated by the formula: ε ft =Δ d / l ; wherein, Δ d is the average transverse deformation of the fiber at the fiber-matrix interface of the unit cell model, l is the average diameter of the fiber cross section in the unit cell model.

[0018] Compared with the prior art, the beneficial effects of the present application are: 1. The composite prestress application method of the present application realizes the application of prestress in the composite finite element analysis through the prestress equivalent method, which improves the efficiency of the prestressed composite finite element analysis. 2. The composite prestress application method of the present application considers the transverse deformation of the composite material while equivalent prestress, which ensures the model accuracy after prestress equivalent, and makes the corresponding prestressed composite material model have higher engineering reference value when doing subsequent structure analysis. 3. The composite prestress application method of the present application can be applied to more complex composite material analysis, including finite element analysis of different fiber volume content or woven composite material, which has obvious advantages compared with the traditional prestressed composite material analysis method. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0020] Figure 1 is the unit cell model used to apply prestress load.

[0021] Figure 2 The invention discloses a stress distribution model of a fiber of a unit cell model after prestressing is applied by using the stress distribution model method of the fiber after prestressing of the present invention.

[0022] Figure 3 It is the residual stress state of the unit cell model after the fiber prestress value of the present invention is applied to the unit cell model.

[0023] Figure 4 is the transverse expansion strain distribution of the fiber after prestressing.

[0024] Figure 5 It is a stress distribution model of a unit cell model after adopting the prestressing method of the present invention.

[0025] Figure 6 It is a stress distribution model of a fiber random distribution unit cell model after prestress is applied by the prestress applying method of the present invention.

[0026] Figure 7 This is a transverse strain distribution model of a matrix of a unit cell model with random fiber distribution after prestress is applied by the prestress applying method of the present invention. DETAILED DESCRIPTION

[0027] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0028] Example 1

[0029] Use Figure 1 The unit cell model shown is used to prestress the composite material. The indoor temperature difference of this model is δT =2.4℃, the prestress applied per unit area is 60MPa. In the establishment of the unit cell model of the composite material, the elastic modulus of the matrix of the unit cell model is E m is 3.35GPa, Poisson's ratio μ m is 0.35, and the thermal expansion coefficient of the substrate is 5.8×10 -6 / ℃; elastic modulus of fiber E f is 74GPa, Poisson's ratio μf 0.2, the thermal expansion coefficient of the fiber α f 4.9x10 -6 / ℃.

[0030] Setting up the equivalent prestress to the unit cell model shown in the figure, specifically including the following steps: Figure 1

[0031] Step 1: Establishing a unit cell model of the composite material, and respectively establishing a fiber model and a matrix model of the unit cell model;

[0032] Step 2: Calculating the prestress applied to the unit cell model σ pre = 60MPa, and calculating the equivalent temperature load Δ T = σ pre / ( α f E f ) = 165.5℃;

[0033] Step 3: Applying the prestress σ pre to the fiber model, and performing finite element analysis to obtain the stress distribution model of the composite material fiber as shown in the figure; Figure 2

[0034] Step 4: Applying the finite element analysis result of the fiber model to the unit cell model, and performing finite element analysis on the unit cell model to obtain the finite element analysis result of the unit cell model as shown in the figure; Figure 3

[0035] Step 5: Calculating the equivalent transverse thermal expansion coefficient of the composite material fiber through the fiber transverse strain distribution result in the unit cell model as shown in the figure, which is Figure 4 α ft = ε ft / Δ T =-9.5e -7 / ℃;

[0036] Step 6: Using the longitudinal thermal expansion coefficient and the equivalent transverse thermal expansion coefficient of the fiber to obtain the stress distribution model of the composite material as shown in the figure. Figure 5

[0037] Example 2

[0038] A composite material finite element model with random distribution of fibers is established by using a random method, and a prestress is applied by using the prestress application method proposed in the application, and the specific application method is the same as that in Example 1. Figure 6-7 ​​​​​The stress distribution of the fiber random distribution composite finite element model cell and the matrix transverse strain distribution model are shown, the embodiment verifies that the method can be applied to the finite element analysis of the irregular fiber arrangement composite material, and illustrates the universality of the prestress application method for the composite material analysis. In the analysis step, the method does not need to further adopt steps 3-5.

Claims

1. A prestressing method for composite material analysis, characterized in that: The method comprises the following steps: Step 1: Establish a unit cell model of the composite material, and establish the fiber model and matrix model of the unit cell model respectively; Step 2: Calculate the prestress σ applied to the fibers of the unit cell model pre , and calculate the equivalent temperature load ΔT of the prestress; Step 3: Apply prestress σ to the fiber model pre , perform finite element analysis and obtain the finite element analysis results of the fiber model; Step 4: applying the finite element analysis results of the fiber model to the unit cell model, performing finite element analysis on the unit cell model, and obtaining the finite element analysis results of the unit cell model; Step 5: Calculate the equivalent transverse thermal expansion coefficient α of the composite fiber based on the finite element analysis results of the unit cell model ft : a ft =e ft / ΔT Among them, ε ft is the transverse expansion strain of the fiber in the analysis result of step 4, and the ε ft The calculation formula is: e ft =Δd / l Wherein, Δd is the average transverse deformation of the fiber at the interface between the fiber and the matrix of the unit cell model, and l is the average diameter of the fiber cross section in the unit cell model; Step 6: The equivalent transverse thermal expansion coefficient α of the composite material ft As an input value of the unit cell model, an equivalent temperature load ΔT is applied to the unit cell model to achieve prestressing of the composite material analysis.

2. A prestressing method for composite material analysis according to claim 1, characterized in that: The prestress σ on the unit cell model pre The calculation formula is: pre =F pre / A f ; Among them, F pre is the prestress load of the unit cell model, A f is the cross-sectional area of ​​the fiber in the unit cell model.

3. A prestressing method for composite material analysis according to claim 1, characterized in that: The calculation formula of the equivalent temperature load ΔT of the prestress is: ΔT=σ pre / (α f E f ); Among them, α f is the thermal expansion coefficient of the fiber, E f is the elastic modulus of the fiber.

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