Method for predicting service life of high-capacity tube bundle type fully-wound composite hydrogen bottle by considering pre-deformation

Abstract

According to the method for predicting the service life of the high-capacity tube bundle type fully-wound composite hydrogen cylinder considering the pre-deformation, the influence of the pre-deformation on the tensile strength and the fatigue performance of a gas cylinder liner material is fully considered, and the accuracy of a calculation result is improved. The method comprises the following steps: performing stress prefabrication on a liner aluminum alloy material tensile sample, then unloading, and finally performing a tensile test to obtain a stress-strain curve; prefabricating stress for the fatigue sample, performing surface treatment, and performing strain control on the fatigue sample to obtain an aluminum alloy S-N curve with pre-deformation influence; a gas cylinder liner model is established based on the real stress-strain curve after stress prefabrication, and a composite winding layer model is established based on the winding method, the winding layer thickness and the like of the gas cylinder; applying an internal pressure alternating load to the finite element model, extracting the strain of the dangerous point of the liner material in each direction, and calculating equivalent stress amplitude and average stress correction; and calculating the fatigue life of the winding gas cylinder according to the corrected equivalent stress amplitude and the pre-deformed aluminum alloy S-N curve.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure vessel safety, and in particular to a life prediction method for a large-capacity tube bundle type fully wound composite hydrogen bottle taking pre-deformation into consideration. Background Art

[0002] Composite carbon fiber wrapped hydrogen storage cylinders consist of a carbon fiber composite wrapping layer on the outer surface and a metal liner material. The outer surface uses a carbon fiber composite wrapping layer with high specific strength, which has the advantages of strong load-bearing capacity, light weight, and strong fatigue resistance. The inner liner of the gas cylinder is made of aluminum alloy, which has the advantages of excellent processing performance, good corrosion resistance, high toughness, no deformation after processing, dense and defect-free material, etc. During the filling and deflation process of the wrapped gas cylinder, alternating loads will be applied to the metal liner, causing fatigue damage, thereby limiting the service life of the gas cylinder. In order to ensure safety and reliability during service, the life of the gas cylinder is currently set according to the design service life, but there is a lack of specific filling cycles. Therefore, it is necessary to conduct fatigue life assessment on the designed and produced wrapped gas cylinders.

[0003] During the production process of composite carbon fiber fully wound tube bundle hydrogen storage cylinders, a large load is pre-loaded on the cylinders and then unloaded, so that the aluminum alloy liner and the carbon fiber winding layer fit closely together, and the carbon fiber is tightened at the same time, so that the carbon fiber is in a high stress state to improve the bearing capacity of the cylinder. This production process is called the self-tightening process. However, this process will impose a large prestress on the liner material, that is, cause a large amount of deformation of the cylinder, thereby changing the tensile and fatigue properties of the material.

[0004] Among the currently available technologies, the fatigue life prediction of most carbon fiber wrapped gas cylinders is carried out through water pressure cycle tests. Although the experiments are highly reliable and convincing, they are time-consuming and costly. The few methods that use finite element analysis to calculate the fatigue life of gas cylinders do not consider the effect of pre-deformation on the tensile strength and fatigue performance of the gas cylinder liner material, which limits the accuracy of the calculation results. Summary of the invention

[0005] The purpose of the present invention is to provide a life prediction method for a large-capacity tube bundle fully wound composite hydrogen cylinder taking pre-deformation into consideration, by simulating the performance changes of materials in an actual working environment through pre-deformation, and using these data to predict the fatigue life of the cylinder, which can significantly improve the prediction accuracy of the fatigue life of the cylinder.

[0006] According to one object of the present invention, the present invention provides a life prediction method for a large-capacity tube bundle type fully wound composite hydrogen bottle taking into account pre-deformation, comprising the following steps:

[0007] S1: Pre-stress the aluminum alloy tensile specimen, then unload it, and then conduct a tensile test to obtain the stress-strain curve, elastic modulus, and yield strength;

[0008] S2: Prestress the aluminum alloy fatigue specimen, then perform surface treatment, and then perform strain-controlled fatigue testing to obtain the aluminum alloy SN curve with pre-deformation effect;

[0009] S3: Obtain engineering constants and failure stress material parameters of carbon fiber composite material layers;

[0010] S4: Input the property parameters of the liner material and the composite winding layer after prefabrication stress in the finite element; establish the liner finite element model and the composite winding layer finite element model, divide the mesh, and apply boundary conditions and balance surface loads;

[0011] S5: Apply loads to the inside of the gas cylinder according to the analysis step and perform finite element calculation;

[0012] S501: Apply a lower limit of the cyclic load (generally 2 MPa) to the analysis step 1 of the finite element model;

[0013] S502: applying a cyclic load upper limit of 1.25 times the working pressure (allowable pressure) to the analysis step 2 of the finite element model;

[0014] S503: Repeat the cyclic load analysis step for a certain number of cycles;

[0015] S6: Check whether the calculation results are stable, and regard the node with the maximum strain of the inner liner under the upper limit of 1.25 times the working pressure cycle load as a dangerous point, and output the strain data in all directions of this point;

[0016] S7: Calculate the equivalent strain according to the output directional strain;

[0017] S8: Since the average value of the alternating load received by the cylinder is not 0, the equivalent stress amplitude is corrected using the Goebel equation;

[0018] S9: Using the calculated equivalent stress amplitude and comparing it with the SN curve of the material with pre-deformation effect, the fatigue life of the wrapped gas cylinder considering the pre-deformation effect can be obtained.

[0019] Further, in S4, a finite element model of the composite winding layer is established according to the winding layer thickness, winding angle and winding order.

[0020] Furthermore, in S4, the finite element model of the composite winding layer needs to consider the changes in the winding angle, thickness and winding starting position of the winding layer at the head.

[0021] Furthermore, in S4, the inner liner finite element model and the composite winding layer finite element model are connected by binding connection.

[0022] Furthermore, in S4, the Abaqus-wcm plug-in or the ANSYS-Acp module is used to establish a finite element model of the carbon fiber wrapped gas cylinder to achieve variable angle, thickness, and position of the carbon fiber at the head.

[0023] Further, in S4, according to the production process in the actual production process, the finite element model of the carbon fiber winding composite material layer is established layer by layer according to the winding layer thickness, winding start and end positions, winding angle and winding order.

[0024] Furthermore, in S4, the lower bottle mouth is completely fixed, and the upper bottle mouth applies a balance surface load that changes with the internal pressure, and the two sides of the gas cylinder are cyclically symmetrical.

[0025] Furthermore, in S5, the steps of finite element calculation are as follows:

[0026] S501: Apply a lower limit of the cyclic load (generally 2 MPa) to the analysis step 1 of the finite element model;

[0027] S502: applying a cyclic load upper limit of 1.25 times the working pressure (allowable pressure) to the analysis step 2 of the finite element model;

[0028] S503: Repeat the cyclic load analysis step for a certain number of cycles.

[0029] Furthermore, in S7, half of the equivalent strain multiplied by the elastic modulus is the equivalent stress amplitude, which is calculated as follows:

[0030] Δε xi =ε xi -ε xo ;

[0031] Δε yi =ε yi -ε yo ;

[0032] Δε zi =ε zi -ε zo ;

[0033] Δγ xyi =γ xyi -γ xyo ;

[0034] Δγ yzi =γ yzi -γ yzo ;

[0035] Δγ zxi =γ zxi -γ zxo ;

[0036] In the formula,

[0037] V * - is the Poisson’s ratio of the material;

[0038] Δε equiv,i -Equivalent strain range under cycle type i;

[0039] Δε xi - x-direction strain under cycle type i;

[0040] Δε yi - y-direction strain under cycle type i;

[0041] Δε zi - z-direction strain under cycle type i;

[0042] Δγ xyi , Δγ yzi , Δγ zxi - Shear strain under cycle type i.

[0043] Furthermore, in S8, the Goebel equation is as follows:

[0044]

[0045] In the formula,

[0046] S f' is the equivalent stress amplitude when the mean stress is not 0;

[0047] S f is the equivalent stress amplitude when the mean stress is 0;

[0048] S m is the mean stress;

[0049] S u For tensile strength.

[0050] The technical solution of the present invention establishes a fatigue life prediction method for type III gas cylinders that takes into account the influence of pre-deformation, fully considers the influence of pre-deformation on the tensile strength and fatigue performance of the gas cylinder liner material, and improves the accuracy of the calculation results. The present invention can more accurately predict the fatigue life of type III gas cylinders under the influence of pre-deformation, which is of great significance for improving the reliability and safety of gas cylinders. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0052] Figure 1 This is a flow chart of a method for predicting fatigue life of a carbon fiber wrapped gas cylinder according to an embodiment of the present invention;

[0053] Figure 2 A finite element model of an embodiment of the present invention;

[0054] Figure 3 The most dangerous point of the finite element calculation result of the embodiment of the present invention;

[0055] Figure 4 This is the SN curve of the liner aluminum alloy considering the influence of pre-deformation according to an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0058] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0059] Example 1

[0060] like Figure 1 As shown, a life prediction method for a large-capacity tube bundle type fully wound composite hydrogen bottle considering pre-deformation includes the following steps:

[0061] S1: Prestress the aluminum alloy tensile specimen, then unload it, and then perform a tensile test to obtain the stress-strain curve, elastic modulus, yield strength, etc. after prestressing; This embodiment first prestresses the aluminum alloy material of the liner, which helps to simulate the pre-deformation that the material will experience in actual use, and then performs a tensile test to obtain parameters such as the stress-strain curve. In this way, the behavior of the material in actual use can be simulated more accurately.

[0062] S2: Process aluminum alloy fatigue specimens according to the standard, pre-stress the specimens, then perform surface treatment, and then perform strain-controlled fatigue testing to obtain the aluminum alloy SN curve with pre-deformation effect;

[0063] S3: Obtain material parameters such as engineering constants and failure stress of carbon fiber composite material layers. Generally, relevant data can be found from composite material manufacturers.

[0064] S4: Input the real strain curve of the liner material after prestressing and the engineering constant property parameters of the composite winding layer in the finite element; based on the actual calculation amount and computing power, this embodiment establishes a 1 / 36 liner model. The Abaqus-wcm plug-in or the ANSYS-Acp module can be used to establish a finite element model of a carbon fiber wrapped gas cylinder, both of which can achieve variable angles, thicknesses, and positions of carbon fibers at the head. According to the production process in the actual production process, the finite element model of the carbon fiber wrapped composite material layer is established layer by layer according to the thickness of the winding layer, the starting and ending positions of the winding, the winding angle, and the winding order. The liner model and the composite material model are connected by binding, the lower bottle mouth is completely fixed, and the upper bottle mouth is applied with a balanced surface load that changes with the internal pressure. Circular symmetry is applied on both sides of the gas cylinder to divide the grid. The finite element model of this embodiment is as follows Figure 2 shown.

[0065] In this embodiment, it is also considered to establish a complete gas cylinder model or at least increase the subdivision level of the model to improve the accuracy of the analysis. At the same time, more advanced meshing technology and more sophisticated contact analysis are used.

[0066] S5: Apply loads to the inside of the gas cylinder according to the analysis step and perform finite element calculation;

[0067] S501: When using a hydrogen cylinder, generally, the hydrogen cannot be completely used up. A certain amount of residual gas must be left to keep the cylinder under positive pressure to ensure the purity of the hydrogen in the cylinder and the safe use of the cylinder. The residual pressure is generally 2MPa. Apply the lower limit of the cyclic load (2MPa) to the analysis step 1 of the finite element model;

[0068] S502: When conducting fatigue tests on hydrogen cylinders, the upper limit of the general pressure is 1.25 times the working pressure. The working pressure of the cylinder in this embodiment is 52MPa, so the upper limit of the cycle pressure is 65MPa. Apply a cycle load upper limit of 1.25 times the working pressure (allowable pressure) to the analysis step 2 of the finite element model; by simulating different load conditions, the performance of the cylinder under different working conditions can be predicted.

[0069] S503: Apply a cyclic load of 2MPa-65MPa for a certain number of cycles to the inner liner of the gas cylinder according to the analysis step. The specific number of cycles is determined based on the calculation amount and the stability of the simulation calculation results. In this embodiment, the load loading is: 0MPa-2MPa (lower limit of cyclic pressure)-65MPa (upper limit of cyclic pressure)

[0070] —2MPa—65MPa—2MPa—65MPa.

[0071] S6: The finite element model under the upper limit of the last cycle pressure is analyzed. In terms of fatigue, the composite material has good tolerance, and the degree of damage and the slope of the SN curve are low. Therefore, the carbon / epoxy composite material has good fatigue resistance in the fiber direction. The fatigue behavior of the metal liner is considered to be elastic-plastic and damageable. In contrast to the composite material, the liner is more sensitive to fatigue. Therefore, when performing fatigue life analysis on the wrapped gas cylinder, only the fatigue life of the liner needs to be considered. The most dangerous point of the liner in this calculation example is as follows Figure 3 As shown in Figure 2. Extract the strains in all directions of the last cyclic load analysis step at this point.

[0072] S7: Calculate the equivalent strain according to the output directional strain. Half of the equivalent strain multiplied by the elastic modulus is the equivalent stress amplitude, and the calculation method is as follows:

[0073] Δε xi =ε xi -ε xo

[0074] Δε yi =ε yi -ε yo

[0075] Δε zi =ε zi -ε zo

[0076] Δγ xyi =γ xyi -γ xyo

[0077] Δγ yzi =γ yzi -γ yzo

[0078] Δγ zxi =γ zxi -γ zxo

[0079] In the formula,

[0080] V * - is the Poisson’s ratio of the material;

[0081] Δε equiv,i -Equivalent strain range under cycle type i;

[0082] Δε xi - x-direction strain under cycle type i;

[0083] Δε yi - y-direction strain under cycle type i;

[0084] Δε zi - z-direction strain under cycle type i;

[0085] Δγ xyi , Δγ yzi , Δγ zxi - shear strain under cycle type i;

[0086] The strain values ​​in each direction of the cyclic loading analysis step are as follows:

[0087] ε xo =0.00555637;ε yo =-0.000150634; ε zo =-0.00715682; γ xyo =-0.0031282; γ yzo =0.00420733; γ zxo =-0.003064;

[0088] ε xi =0.00987268; ε yi =0.000321199;ε zi =-0.00954404; γ xyi =-0.00677022; γ yzi =0.00863858; zxi =-0.005418;

[0089] The Poisson's ratio of 6061Al alloy is 0.33, the elastic modulus is 70000 MPa, and the calculated equivalent strain is 0.005957243. The equivalent stress amplitude is obtained by multiplying half of the equivalent strain by the elastic modulus, and the value in this embodiment is: 208.5034968.

[0090] S8: Because Figure 4 It is the SN curve under symmetrical cyclic load conditions, but the alternating load of filling and degassing borne by the wrapped gas cylinder is asymmetrical, so the calculated equivalent stress amplitude needs to be corrected.

[0091] Although the Goodman equation is widely used in mean stress correction, 6061Al has high yield strength and tensile strength, so the Goodman equation is not applicable. In this embodiment, the Goebel equation with better correction effect is used to correct the mean stress. The mean stress is: (2+65) / 2=33.5MPa, the tensile strength of the liner material is: 350MPa, and the equivalent stress amplitude after correction by the Goebel equation is 206.5933495.

[0092] The Goodman equation is: The Goebel equation is:

[0093] In the formula,

[0094] S f' is the equivalent stress amplitude when the mean stress is not 0;

[0095] S f is the equivalent stress amplitude when the mean stress is 0;

[0096] S m is the mean stress;

[0097] S u is the tensile strength;

[0098] S9: Using the calculated equivalent stress amplitude and comparing it with the SN curve of the deformed material, the fatigue life of the wrapped gas cylinder considering the effect of pre-deformation can be obtained. Substituting the equivalent stress amplitude, the fatigue life of the carbon fiber wrapped gas cylinder is obtained as N = 13375 times.

[0099] In view of the shortcomings of the existing technology, the present invention establishes a fatigue life prediction method for type III gas cylinders that takes into account the influence of pre-deformation, fully considers the influence of pre-deformation on the tensile strength and fatigue performance of the gas cylinder liner material, and improves the accuracy of the calculation results. The core of the present invention is to simulate the performance changes of materials in the actual working environment through pre-deformation, and use these data to predict the fatigue life of the gas cylinder.

[0100] The present invention pre-stresses a tensile specimen of an aluminum alloy material of an inner liner, then unloads it, and then performs a tensile test to obtain a stress-strain curve; pre-stresses a fatigue specimen, performs a strain-controlled fatigue specimen after surface treatment, and obtains an aluminum alloy SN curve with pre-deformation influence; based on the real stress-strain curve after pre-stressing, a gas cylinder inner liner model is established, and based on the winding method and winding layer thickness of the gas cylinder, a composite winding layer model is established; an internal pressure alternating load is applied to the finite element model, strains in all directions of dangerous points of the inner liner material are extracted, and an equivalent stress amplitude and an average stress correction are calculated; and according to the corrected equivalent stress amplitude and the aluminum alloy SN curve containing pre-deformation, the fatigue life of the wound gas cylinder is calculated.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A life prediction method for a large-capacity tube bundle fully wound composite hydrogen bottle considering pre-deformation, characterized in that: The following steps are involved: S1: Pre-stress the aluminum alloy tensile specimen, then unload it, and then conduct a tensile test to obtain the stress-strain curve, elastic modulus, and yield strength; S2: Prestress the aluminum alloy fatigue specimen, then perform surface treatment, and then perform strain-controlled fatigue testing to obtain the aluminum alloy SN curve with pre-deformation effect; S3: Obtain engineering constants and failure stress material parameters of carbon fiber composite material layers; S4: Input the property parameters of the liner material and the composite winding layer after prefabrication stress in the finite element; establish the liner finite element model and the composite winding layer finite element model, divide the mesh, and apply boundary conditions and balance surface loads; S5: Apply loads to the inside of the gas cylinder according to the analysis step and perform finite element calculation; S5 01: Apply the lower limit of cyclic load to the analysis step 1 of the finite element model; S502: applying a cyclic load upper limit of 1.25 times the working pressure to the analysis step 2 of the finite element model; S503: Repeat the cyclic load analysis step for a certain number of cycles; S6: Check whether the calculation results are stable, and regard the node with the maximum strain of the inner liner under the upper limit of 1.25 times the working pressure cycle load as a dangerous point, and output the strain data in all directions of this point; S7: Calculate the equivalent strain according to the output directional strain; S8: Since the average value of the alternating load received by the cylinder is not 0, the equivalent stress amplitude is corrected using the Goebel equation; S9: Using the calculated equivalent stress amplitude and comparing it with the SN curve of the material with pre-deformation effect, the fatigue life of the wrapped gas cylinder considering the pre-deformation effect can be obtained.

2. The life prediction method of a large-capacity tube bundle type fully wound composite hydrogen bottle considering pre-deformation according to claim 1 is characterized in that: In S4, a finite element model of the composite winding layer is established according to the winding layer thickness, winding angle and winding order.

3. The life prediction method of a large-capacity tube bundle type fully wound composite hydrogen bottle considering pre-deformation according to claim 1 is characterized in that: In S4, the finite element model of the composite winding layer needs to consider the changes in the winding angle, thickness and winding starting position of the winding layer at the head.

4. The life prediction method of a large-capacity tube bundle fully wound composite hydrogen bottle considering pre-deformation according to claim 1 is characterized in that: In S4, the inner liner finite element model and the composite winding layer finite element model are connected by binding connection.

5. The life prediction method of a large-capacity tube bundle fully wound composite hydrogen bottle considering pre-deformation according to claim 1 is characterized in that: In S4, the Abaqus-wcm plug-in or ANSYS-Acp module is used to establish a finite element model of the carbon fiber wrapped gas cylinder to achieve variable angle, thickness and position of the carbon fiber at the head.

6. The life prediction method of a large-capacity tube bundle fully wound composite hydrogen bottle considering pre-deformation according to claim 1 is characterized in that: In S4, according to the production process in the actual production process, the finite element model of the carbon fiber winding composite material layer is established layer by layer according to the winding layer thickness, winding start and end positions, winding angle and winding order.

7. The life prediction method of a large-capacity tube bundle type fully wound composite hydrogen bottle considering pre-deformation according to claim 1 is characterized in that: In S4, the lower bottle mouth is completely fixed, and the upper bottle mouth is applied with a balance surface load that changes with the internal pressure, and the load is applied cyclically symmetrically on both sides of the gas cylinder.

8. The life prediction method of a large-capacity tube bundle fully wound composite hydrogen bottle considering pre-deformation according to claim 1 is characterized in that: In S5, the steps of finite element calculation are as follows: S501: applying a lower limit of the cyclic load to the analysis step 1 of the finite element model; S502: applying a cyclic load upper limit of 1.25 times the working pressure to the analysis step 2 of the finite element model; S503: Repeat the cyclic load analysis step for a certain number of cycles.

9. The life prediction method of a large-capacity tube bundle type fully wound composite hydrogen bottle considering pre-deformation according to claim 1 is characterized in that: In S7, half of the equivalent strain multiplied by the elastic modulus is the equivalent stress amplitude, which is calculated as follows: No xi =e xi -e xo ; No yi =e yi -e yo ; No zi =e zi -e zo ; Dg xyi =c xyi -c xyo ; Dg yzi =c yzi -c yzo ; Dg zxi =c zxi -c zxo ; In the formula, V * - is the Poisson’s ratio of the material; Δε equiv，i -Equivalent strain range under cycle type i; Δε xi - x-direction strain under cycle type i; Δε yi - y-direction strain under cycle type i; Δε zi - z-direction strain under cycle type i; Δγ xyi , Δγ yzi , Δγ zxi - Shear strain under cycle type i.

10. The life prediction method of a large-capacity tube bundle fully wound composite hydrogen bottle considering pre-deformation according to claim 1 is characterized in that: In S8, the Goebel equation is as follows: In the formula, S f′ is the equivalent stress amplitude when the mean stress is not 0; S f is the equivalent stress amplitude when the mean stress is 0; S m is the mean stress; S u For tensile strength.

Images