Aging / creep coupled analysis method for long-term storage solid propellant grains

Abstract

The present invention discloses a method for analyzing the aging / creep coupling of solid propellant grains in long-term storage, including: constructing an aging model with constant stress influence; performing parameter identification on the aging model, and constructing a constitutive model based on the aging module and creep model after parameter identification, and performing aging / creep coupling analysis on the propellant grains based on the constitutive model. The present invention is applied to the field of energetic material analysis, and not only takes into account the influence of stress on the aging rate of the propellant in the process of constructing the aging model, which can effectively match the actual situation that the propellant is subjected to small stress alternating loads for more time during storage, but also couples the influence of aging and creep, which can effectively predict the structural integrity analysis of the propellant after long-term storage and natural aging, and provide a basis for its life estimation.

Description

Technical Field

[0001] The invention relates to the technical field of energetic material analysis, in particular to an aging / creep coupling analysis method for long-term storage solid propellant grains. Background Art

[0002] Solid rocket engines have the advantages of simple structure, strong maneuverability and rapid response. They are widely used in aviation, aerospace and other fields. They have the characteristics of single use and long-term storage. During storage, due to the instability of physical and chemical properties, the mechanical properties of the propellant are significantly deteriorated under the dual factors of creep and aging, which directly affects the storage life of the engine. Under different stress states, the mechanical properties parameters of the propellant material such as elastic modulus, maximum elongation, and strength limit change to varying degrees after aging. In addition, the creep phenomenon of the propellant is also affected by aging, which brings great difficulties to the consideration of the creep phenomenon of long-term storage of solid propellants and the accurate prediction of structural integrity.

[0003] Most of the existing constitutive models only study aging or creep, but there are few studies on the constitutive models under the combined effects of aging and creep. Therefore, it is an urgent problem for engine design and use departments to establish a constitutive model that accurately characterizes the entire process of propellant creep and reveals the creep characteristics before and after aging.

[0004] Currently, the existing finite element simulation tools do not have the function of creep damage constitutive model considering aging effect, and it is difficult to use them directly. Therefore, it is necessary to use the secondary development interface of commercial software to realize the development and application of propellant constitutive model that couples aging and creep.

[0005] The existing technology is to carry out high temperature accelerated aging test according to the relevant provisions of the aerospace industry standard QJ 2328A-2005 "High Temperature Accelerated Aging Test Method for Composite Solid Propellants". After reaching the predetermined aging time, the mechanical properties characterization test after aging is carried out to obtain the propellant performance at different temperatures. According to the aging test results, three types of mathematical equations are used to fit the change law of mechanical performance parameters with aging time. According to the aging test results, the following three types of mathematical equations are used to fit the change law of mechanical performance parameters with aging time:

[0006] ;

[0007] ;

[0008] ;

[0009] in, P For time t The corresponding performance, P 0 is the initial value of the performance (usually a constant), Kis the rate constant of performance change related to temperature, t is the aging time in days. The performance change rate constant related to temperature is obtained K After that, substitute The least squares method was used for fitting, and then the curve of the change of the mechanical properties of the propellant at room temperature with the storage time was obtained by extrapolation.

[0010] According to the above three methods of fitting mechanical property parameters, the existing aging model does not consider the influence of constant stress on the aging rate, and the uniaxial tensile test can only study the ultimate destructive performance of the propellant, while the propellant is subjected to small stress alternating loads for more time during storage. Summary of the invention

[0011] In view of the above-mentioned deficiencies in the prior art, the present invention provides an aging / creep coupling analysis method for long-term storage solid propellant grains, which not only takes into account the influence of stress on the aging rate of propellant grains, but also couples creep and aging, and can effectively predict the structural integrity analysis of the propellant after long-term storage and natural aging.

[0012] To achieve the above object, the present invention provides a method for analyzing the aging / creep coupling of long-term stored solid propellant grains, comprising the following steps:

[0013] Step 1: construct an aging model with constant stress influence, which is:

[0014] ;

[0015] in, is the mechanical property parameter of the propellant, is the initial value of the mechanical properties of the propellant, is the rate of change of mechanical properties, is a given constant stress value, is the aging characteristic stress, is the aging time;

[0016] Step 2: Perform aging experiments on the propellant grains at N aging temperatures, M stress states, and K aging times to obtain different propellant samples. ,in, For the i Aging temperature, j stress state, k After the propellant sample was aged at aging time, i =1~N, j =1~M, k= 1~K;

[0017] Step 3, performing a mechanical property characterization experiment on all propellant samples after the aging test to obtain the mechanical property parameters corresponding to each propellant sample;

[0018] Step 4: Perform the first fitting of the mechanical property change rate with the mechanical property parameters under the same stress state, the same aging temperature and different aging time as a group, and obtain the mechanical property change rate after the first fitting of M×N groups. ;

[0019] Step 5: Perform a second fitting on the mechanical property change rate under the same stress state and different aging temperatures as a group to obtain the mechanical property change rate after the second fitting of group M. ;

[0020] Step 6: Perform a third fitting based on the mechanical property change rate under different stress states of group M to obtain the final mechanical property change rate and aging characteristic stress , complete the parameter identification of the aging model;

[0021] Step 7: construct a constitutive model based on the aging module and the creep model, and perform aging / creep coupling analysis on the propellant grain based on the constitutive model.

[0022] In one embodiment, the process of step 4 is:

[0023] Step 401, obtaining an aging model without considering the influence of stress, which is ;

[0024] Step 402, pair Taking the logarithm of both sides, we get ;

[0025] Step 403, let , , , , will be Convert to Line Equation ;

[0026] Step 404, taking the mechanical property parameters under the same stress state, the same aging temperature and different aging times as a group of data, and calculating the mechanical property parameters in the same group of data , and its corresponding aging time is ,Will , Substituting into the equation of the line , and the least squares method is used to fit , , that is, the corresponding ;

[0027] Step 405, traverse the data of N aging temperatures and M stress state combinations to perform step 404, and obtain M×N groups .

[0028] In one embodiment, the process of step 5 is:

[0029] Step 501, obtaining the mechanical property change rate constant K The Arrhenius equation related to the thermodynamic temperature T is:

[0030] ;

[0031] in, Z is the frequency factor, E is the apparent activation energy, R is the molar gas constant;

[0032] Step 502, let , , , , will be Convert to Line Equation ;

[0033] Step 503, using the same stress state and different aging temperatures As a set of data, Calculated , calculated based on its corresponding aging temperature ,Will , Substituting into the equation of the line , and the least squares method is used to fit , , the fitted , Substitution , get the corresponding ;

[0034] Step 504, traverse the data under M stress states and perform step 503 to obtain M groups .

[0035] In one embodiment, the process of step 6 is:

[0036] Step 601: Introduce intermediate parameters ;

[0037] Step 602: Take the reciprocal and split it, and we get ;

[0038] Step 603, let , , , , will be Convert to Line Equation ;

[0039] Step 604, based on a set of data corresponding to Calculated , and its corresponding constant stress value is ,Will , Substituting into the equation of the line , and the least squares method is used to fit , , that is, the final mechanical property change rate and aging characteristic stress .

[0040] In one embodiment, the mechanical properties characterization experiment is performed on all propellant samples after the aging test, specifically:

[0041] All propellant samples after the aging test were subjected to a uniaxial constant-speed tensile test at a test temperature of 25°C ± 2°C and a tensile speed of 100 mm / min.

[0042] In one embodiment, the mechanical performance parameter is the maximum elongation, initial modulus or tensile strength of the propellant.

[0043] Compared with the prior art, the present invention has the following beneficial technical effects:

[0044] 1. The present invention takes into account the influence of stress on the aging rate of propellant in the process of constructing the aging model, which can effectively match the actual situation that the propellant is subjected to small stress alternating loads for more time during storage, making the calculation results of the aging model more accurate and true;

[0045] 2. The present invention considers the effects of aging and creep at the same time and couples them in the process of analyzing the propellant grain, which can effectively predict the structural integrity analysis of the propellant after long-term storage and natural aging, and provide a basis for its life estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0047] Figure 1 The figure is a flow chart of the aging / creep coupling analysis method of long-term storage solid propellant grains in an embodiment of the present invention.

[0048] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not 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.

[0050] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0051] The present embodiment discloses an aging / creep coupling analysis method for solid propellant grains in long-term storage. The method considers the influence of stress on the aging rate of the propellant in the process of constructing the aging model, thereby matching the actual situation that the propellant is subjected to small stress alternating loads for more time during the storage process. At the same time, in the process of analyzing the propellant grains, the influence of aging and creep are considered and coupled, thereby effectively predicting the structural integrity analysis of the propellant after natural aging in long-term storage, and providing a basis for its life estimation.

[0052] refer to Figure 1 In this embodiment, the long-term storage solid propellant grain aging / creep coupling analysis method specifically includes the following steps:

[0053] Step 1: Construct an aging model with constant stress effect, which includes the change rate of mechanical properties to be identified. and aging characteristic stress ;

[0054] Step 2, conducting aging experiments on the propellant grains at N aging temperatures, M stress states, and K aging times to obtain different propellant samples;

[0055] Step 3, performing a mechanical property characterization experiment on all propellant samples after the aging test to obtain the mechanical property parameters corresponding to each propellant sample;

[0056] Step 4: Perform the first fitting of the mechanical property change rate with the mechanical property parameters under the same stress state, the same aging temperature and different aging time as a group, and obtain the mechanical property change rate after the first fitting of M×N groups. ;

[0057] Step 5: Perform a second fitting on the mechanical property change rate under the same stress state and different aging temperatures as a group to obtain the mechanical property change rate after the second fitting of group M. ;

[0058] Step 6: Perform a third fitting based on the mechanical property change rate under different stress states of group M to obtain the final mechanical property change rate and aging characteristic stress , complete the parameter identification of the aging model;

[0059] Step 7: construct a constitutive model based on the aging module and the creep model, and perform aging / creep coupling analysis on the propellant grain based on the constitutive model.

[0060] In the specific implementation of step 1, the aging model including the influence of constant stress is:

[0061] ;

[0062] in, is the mechanical property parameter of the propellant (such as the maximum elongation, initial modulus or tensile strength of the propellant), is the initial value of the mechanical properties of the propellant, is the rate of change of mechanical properties, is a given constant stress value, is the aging characteristic stress, is the aging time.

[0063] This embodiment introduces aging characteristic stress into the aging model , constant stress value The larger the mechanical performance parameters The faster it falls. When .like It represents The aging limit is reached at that moment. Although the material has already been destroyed due to exceeding the strength limit, such a definition is still made to phenomenologically characterize the impact of aging on material properties.

[0064] In the specific implementation process of step 2, a high-temperature accelerated aging test is carried out on the propellant grain in an oil bath incubator, with a temperature accuracy of ±1°C and a relative humidity of the test environment of less than 50%RH. Specifically, according to QJ 2328A-2005 "High-temperature Accelerated Aging Test Method for Composite Solid Propellants", aging experiments are carried out on the propellant grain at N different aging temperatures, M different stress states, and K different aging times to obtain different propellant samples. ,in, For the i Aging temperature, j stress state, k After the propellant sample was aged at aging time, i =1~N, j =1~M, k= 1~K, that is, a total of M×N×K propellant samples after aging tests can be obtained.

[0065] In the specific implementation process of step 3, the mechanical properties characterization experiment is carried out on all the propellant samples after the aging test. Specifically, all the propellant samples after the aging test are subjected to a uniaxial constant speed tensile test using an electronic universal testing machine, the test temperature is 25°C ± 2°C, and the tensile speed is 100mm / min. After the uniaxial constant speed tensile test, the mechanical properties parameters corresponding to each propellant sample can be measured, and the mechanical properties parameters are the maximum elongation, initial modulus, tensile strength or other parameters that can characterize the mechanical properties of the propellant.

[0066] During the specific implementation of step 4, the rate of change of mechanical properties The specific fitting process is as follows:

[0067] Step 401, obtaining an aging model without considering the influence of stress, which is ;

[0068] Step 402, pair Taking the logarithm of both sides, we get ;

[0069] Step 403, let , , , , will be Convert to Line Equation ;

[0070] Step 404, taking the mechanical property parameters under the same stress state, the same aging temperature and different aging times as a group of data, and calculating the mechanical property parameters in the same group of data , and its corresponding aging time is ,Will , Substituting into the equation of the line , and the least squares method is used to fit , , that is, the corresponding , where the least squares method is used to fit , The process is:

[0071] ;

[0072] ;

[0073] Intermediate parameters , , , Specifically:

[0074] ;

[0075] ;

[0076] ;

[0077] ;

[0078] Step 405, traverse the data of N aging temperatures and M stress state combinations to perform step 404, and obtain M×N groups .

[0079] During the specific implementation of step 5, the rate of change of mechanical properties The specific fitting process is as follows:

[0080] Step 501, obtaining the mechanical property change rate constant K The Arrhenius equation related to the thermodynamic temperature T is:

[0081] ;

[0082] in, Z is the frequency factor; E is the apparent activation energy, expressed in joules per mole (J / mol); R is the molar gas constant, with the unit of joule per Kelvin mole [J / (K·mol)]; T is the unit of Kelvin (K);

[0083] Step 502, let , , , , will be Convert to Line Equation ;

[0084] Step 503, using the same stress state and different aging temperatures As a set of data, Calculated , calculated based on its corresponding aging temperature is ,Will , Substituting into the equation of the line , and the least squares method is used to fit , , the fitted , Substitution , get the corresponding , where the least squares method is used to fit , The process is basically the same as step 404, so this embodiment will not be described in detail;

[0085] Step 504, traverse the data under M stress states and perform step 503 to obtain M groups .

[0086] During the specific implementation of step 6, the rate of change of mechanical properties and aging characteristic stress The specific fitting process is as follows:

[0087] Step 601: Introduce intermediate parameters ;

[0088] Step 602: Take the reciprocal and split it, and we get ;

[0089] Step 603, let , , , , will be Convert to Line Equation ;

[0090] Step 604, based on a set of data corresponding to Calculated , and its corresponding constant stress value is ,Will , Substituting into the equation of the line , and the least squares method is used to fit , , that is, the final mechanical property change rate and aging characteristic stress , where the least squares method is used to fit , The process is substantially the same as step 404, and therefore will not be described in detail in this embodiment.

[0091] After completing the parameter identification of the aging model, the constitutive model can be constructed based on the aging module and the creep model, and the aging / creep coupling analysis of the propellant grain can be performed based on the constitutive model. In the specific implementation process of step 7, the process of constructing the constitutive model based on the aging module and the creep model, and performing the aging / creep coupling analysis of the propellant grain based on the constitutive model is as follows:

[0092] The influence coefficient of constant stress on propellant in the aging model is introduced and combined with the time hardening creep model, and the UMAT material subroutine is obtained by writing Fortran language. The user material UMAT subroutine is connected to ABAQUS for simulation analysis, and the uniaxial constant speed tensile test of the propellant is numerically simulated. The finite element simulation results are compared with the actual test results to verify the feasibility and accuracy of the numerical simulation. UMAT is used in ABAQUS to perform numerical simulation of solid rocket engines. In the numerical simulation: constant stress affects the aging of the propellant and thus affects the elastic displacement. The elastic displacement is combined with the creep displacement to obtain the total displacement, and the aging / creep are coupled with each other.

[0093] The above description is only a preferred embodiment of the present invention, and does not limit the protection scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the protection scope of the present invention.

Claims

1. A method for analyzing the aging / creep coupling of long-term stored solid propellant grains, characterized in that: The steps include: Step 1: construct an aging model with constant stress influence, which is: in, is the mechanical property parameter of the propellant, is the initial value of the mechanical properties of the propellant, is the rate of change of mechanical properties, is a given constant stress value, is the aging characteristic stress, is the aging time; Step 2: Perform aging experiments on the propellant grains at N aging temperatures, M stress states, and K aging times to obtain different propellant samples. ,in, For the i Aging temperature, j stress state, k After the propellant sample was aged at aging time, i =1~N, j =1~M, k= 1~K; Step 3, performing a mechanical property characterization experiment on all propellant samples after the aging test to obtain the mechanical property parameters corresponding to each propellant sample; Step 4: Perform the first fitting of the mechanical property change rate with the mechanical property parameters under the same stress state, the same aging temperature and different aging time as a group, and obtain the mechanical property change rate after the first fitting of M×N groups. ; Step 5: Perform a second fitting on the mechanical property change rate under the same stress state and different aging temperatures as a group to obtain the mechanical property change rate after the second fitting of group M. ; Step 6: Perform a third fitting based on the mechanical property change rate under different stress states of group M to obtain the final mechanical property change rate and aging characteristic stress , complete the parameter identification of the aging model; Step 7: construct a constitutive model based on the aging module and the creep model, and perform aging / creep coupling analysis on the propellant grain based on the constitutive model.

2. The method for analyzing the aging / creep coupling of long-term stored solid propellant grains according to claim 1, characterized in that: The process of step 4 is: Step 401, obtaining an aging model without considering the influence of stress, which is ; Step 402, pair Taking the logarithm of both sides, we get ; Step 403, let , , , , will be Convert to Line Equation ; Step 404, taking the mechanical property parameters under the same stress state, the same aging temperature and different aging times as a group of data, and calculating the mechanical property parameters in the same group of data , and its corresponding aging time is ,Will , Substituting into the equation of the line , and the least squares method is used to fit , , that is, the corresponding ; Step 405, traverse the data of N aging temperatures and M stress state combinations to perform step 404, and obtain M×N groups .

3. The method for analyzing the aging / creep coupling of long-term stored solid propellant grains according to claim 1, characterized in that: The process of step 5 is: Step 501, obtaining the mechanical property change rate constant K The Arrhenius equation related to the thermodynamic temperature T is: in, Z is the frequency factor, E is the apparent activation energy, R is the molar gas constant; Step 502, let , , , , will be Convert to Line Equation ; Step 503, using the same stress state and different aging temperatures As a set of data, Calculated , calculated based on its corresponding aging temperature ,Will , Substituting into the equation of the line , and the least squares method is used to fit , , the fitted , Substitution , get the corresponding ; Step 504, traverse the data under M stress states and perform step 503 to obtain M groups .

4. The method for analyzing the aging / creep coupling of long-term stored solid propellant grains according to claim 1, characterized in that: The process of step 6 is: Step 601: Introduce intermediate parameters ; Step 602: Take the reciprocal and split it, and we get ; Step 603, let , , , , will be Convert to Line Equation ; Step 604, based on a set of data corresponding to Calculated , and its corresponding constant stress value is ,Will , Substituting into the equation of the line , and the least squares method is used to fit , , that is, the final mechanical property change rate and aging characteristic stress .

5. The method for analyzing the aging / creep coupling of long-term stored solid propellant grains according to any one of claims 1 to 4, characterized in that: The mechanical properties characterization experiment is carried out on all propellant samples after the aging test, specifically: All propellant samples after the aging test were subjected to a uniaxial constant-speed tensile test at a test temperature of 25°C ± 2°C and a tensile speed of 100 mm / min.

6. The method for analyzing the aging / creep coupling of long-term stored solid propellant grains according to any one of claims 1 to 4, characterized in that: The mechanical performance parameter is the maximum elongation, initial modulus or tensile strength of the propellant.

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