An evaluation method for slow cook-off of explosives

Abstract

The present invention discloses an evaluation method for slow cook-off of explosives, and the specific steps are as follows: Establish a calculation model in proportion to the test projectile according to the slow cook-off test device for simulation; Conduct slow cook-off calculation of the charge to obtain the temperature contour map at the ignition moment of the calculated charge in the calculation model; Adjust the heating rate until the heating rate at this time is the critical heating rate of slow cook-off; Change the charge diameter of the calculated charge to obtain the relationship of the critical heating rate of slow cook-off under different charge diameters; According to any charge diameter of the calculated charge and the corresponding critical heating rate, load the critical heating rate onto the calculated heating wall for calculation, obtain the internal temperature change, ignition time and ignition temperature of the calculated charge, and evaluate the slow cook-off characteristics of the explosive; The present invention can solve the problems of non-standard slow cook-off in existing cook-off tests and calculations, as well as the problem that the heating rate and charge geometric size jointly affect the ignition position.

Description

Technical Field

[0001] The present invention belongs to the technical field of explosive safety assessment, and particularly relates to an assessment method for slow cook-off of explosives. Background Art

[0002] During the manufacturing, storage, transportation, and use of weapons and ammunitions, they may be subjected to accidental thermal stimuli, resulting in uncontrollable combustion or explosion, and even causing serious losses of life and property. Therefore, studying the cook-off response characteristics and laws of explosives under thermal stimuli is of great significance for their safety assessment.

[0003] Currently, the commonly used methods for studying and assessing the safety of explosives under thermal stimuli include cook-off tests and numerical simulation calculations. Cook-off tests can directly obtain response characteristics, but cannot obtain information on the internal temperature distribution of explosives, and the test costs are relatively high; therefore, numerical simulation calculations have become the main method for studying the cook-off characteristics of explosives. Cook-off is divided into rapid cook-off and slow cook-off. Slow cook-off simulates a slowly heating environment, and it has been found that slow cook-off poses a more serious threat to the safety of ammunitions. Many studies have been conducted at home and abroad, and the charge size and heating rate are the most important influencing factors for slow cook-off. The military standard for insensitive explosives in the United States (MIL-STD-2015D) [SWIERK T. IM Testing and Assessments[J]. Naval Surface Warfare Center, US. 2014.] stipulates that the slow cook-off test standard for ammunitions is to slowly heat the ammunitions at a heating rate of 3.3 K / h until the ammunitions react and the reaction intensity is not greater than combustion, then the test is passed. Due to the long test time at a heating rate of 3.3 K / h, the heating rates in current domestic slow cook-off tests and numerical simulation calculations are mostly 1 - 3 K / min. Zeng Jia et al. [ZENG Jia, ZHI Xiaoqi, HAO Chunjie, et al. Thermal Cook-off Study of DNAN-based Cast Explosives at Different Heating Rates[J]. Journal of Projectiles, Rockets, Missiles and Guidance, 2018, 38(6): 129 - 134.] studied the influence of the heating rate on the ignition position through experiments and numerical calculations. As Figure 1 shown, when the size of the projectile body is fixed, as the heating rate increases, the ignition position moves from the center to the wall surface. WU Hao [WU Hao. Study on the Thermal-Ignition Response Characteristics of DNAN-based Explosives[D]. Beijing Institute of Technology, 2021.] studied the influence of size effect on the ignition position through numerical calculations. As Figure 2 shown, at a heating rate of 3.3 K / h, as the size increases, the ignition position moves from the center to both ends, and when the size continues to increase, the ignition position will move to the surface of the charge.

[0004] The existing domestic evaluation method for slow cook-off of explosives conducts cook-off tests and simulation calculations at a heating rate of 1 - 3 K / min, and the ignition position is mostly located on the surface of the charge; the foreign slow cook-off standard with a heating rate of 3.3 K / h is applicable to small-sized cook-off projectiles, and the ignition position of large-sized test projectiles is also on the surface of the charge, which is not a standard slow cook-off. The ignition position of slow cook-off should be at the geometric center of the charge. Therefore, the existing evaluation methods have certain limitations.

[0005] In addition, when studying the influence of heating rate and geometric size on the ignition position of slow cook-off charges, the existing analysis methods only study the influence of a single factor. In fact, the ignition position is affected by both of them. Summary of the Invention

[0006] In view of this, the present invention provides an evaluation method for slow cook-off of explosives, which can solve the problems of non-standard slow cook-off in existing cook-off tests and calculations, and the problem that the ignition position is jointly affected by the heating rate and the geometric size of the charge.

[0007] The present invention is realized through the following technical solutions:

[0008] An evaluation method for slow cook-off of explosives, the specific steps are as follows:

[0009] Step 1, establish a calculation model proportional to the test projectile according to the slow cook-off test device for simulation, and calibrate the reaction kinetic parameters; the calculation model includes: a calculation shell, a calculation charge, a calculation heating wall surface and an adiabatic wall surface;

[0010] Step 2, conduct slow cook-off calculation of the charge, load the preset heating rate on the outer wall surface of the calculation shell as a boundary condition onto the calculation heating wall surface; load the reaction kinetic equation into the calculation charge for calculation, and according to the calibrated reaction kinetic parameters, calculate the temperature cloud map at the ignition moment of the calculation charge; one or two ignition points are formed in the calculation charge at the ignition moment;

[0011] Step 3, according to the formula judge whether the calculation charge is slow cook-off, where when there is only one ignition point, Δx = 0, when there are two ignition points, Δx is the distance between the two ignition points, which can be obtained from the temperature cloud map, and L is the charge length; if it satisfies then the calculation charge is slow cook-off, if it does not satisfy then the calculation charge is not slow cook-off;

[0012] Adjust the heating rate until At this time, the heating rate is the critical heating rate of slow cook-off;

[0013] And so on. Since the length-diameter ratio of the calculated charge is a fixed value, by changing the charge length of the calculated charge, that is, the charge diameter, the scatter points of the critical heating rate of slow cook-off at different charge diameters can be obtained. After fitting these scatter points, the relationship between the critical heating rate R and the charge diameter D of the calculated charge can be obtained;

[0014] Step 4: According to any charge diameter D of the calculated charge, the corresponding critical heating rate R of slow cook-off can be obtained. This critical heating rate R is the heating rate boundary. Load this heating rate boundary onto the calculated heating wall for calculation, obtain the internal temperature change, ignition time, and ignition temperature of the calculated charge, and evaluate the slow cook-off characteristics of the explosive.

[0015] Further, in Step 1, the slow cook-off test device includes: an annular heater, a test bomb, a temperature controller, a central temperature-measuring thermocouple, and a wall temperature-measuring thermocouple; the test bomb includes: a test shell and a test charge; the test charge is installed in the test shell, and the length-diameter ratio of the test charge is 1;

[0016] The annular heater is sleeved on the outer wall of the test bomb and is used to heat the test bomb; the wall temperature-measuring thermocouple is placed between the annular heater and the test shell and is electrically connected to the temperature controller through a wire, and is used to measure the outer wall temperature of the test bomb and feedback it to the temperature controller to achieve temperature control; the central temperature-measuring thermocouple is placed at the geometric center of the test charge and is electrically connected to the temperature controller through a wire, and is used to measure the central position temperature inside the test charge;

[0017] When conducting the slow cook-off test, the annular heater operates to heat the test bomb, and the test charge inside the test bomb heats up. When the highest temperature of the test charge is higher than its ignition point, the test charge ignites; during this process, the wall temperature-measuring thermocouple measures the outer wall temperature of the test bomb in real time and obtains the change curve of the outer wall temperature of the test over time; the central temperature-measuring thermocouple measures the central position temperature inside the test charge in real time and obtains the change curve of the central position temperature of the test over time.

[0018] Further, in Step 1, the calculated shell is exactly the same as the test shell, and the calculated charge is exactly the same as the test charge; the calculated charge is located inside the calculated shell, the outer wall of the calculated shell is the calculated heating wall, and both the upper and lower end faces of the calculated shell are adiabatic walls;

[0019] Perform numerical simulation calculations on the calculation model. Use the curve of the outer wall temperature of the test over time as the curve of the outer wall temperature of the calculation shell over time, and use the curve of the outer wall temperature of the calculation shell over time as the boundary condition to be loaded onto the calculation heating wall. Write the reaction kinetics equation as a subroutine and load it into the calculation charge for calculation. Based on the initial reaction kinetics parameters and physical properties parameters of the calculation charge, calculate the curve of the temperature at the center position of the calculation charge over time.

[0020] Compare the curve of the temperature at the center position of the calculation charge obtained from this calculation over time with the curve of the temperature at the center position of the test over time. If the difference in ambient temperature at the same time point between the two is within the set range, the initial reaction kinetics parameters do not need to be corrected. If the difference in ambient temperature at the same time point between the two is not within the set range, the initial reaction kinetics parameters need to be corrected until the difference in ambient temperature at the same time point between the curve of the temperature at the center position of the calculation charge obtained from the calculation over time and the curve of the temperature at the center position of the test over time is within the set range, thereby obtaining the calibrated reaction kinetics parameters.

[0021] Further, in step three, when the length-diameter ratio L / D of the calculation charge is 1, the relational expression between the critical heating rate R and the charge diameter D of the calculation charge obtained by fitting is:

[0022]

[0023] Further, in step one, after changing the length-diameter ratio of the calculation charge, obtain the relational expression between the critical heating rate R and the charge diameter D of the calculation charge at different length-diameter ratios.

[0024] Further, in step two, when performing the slow cook-off calculation of the charge, by adjusting the heating rate, make the ignition position of the calculation charge located on the central axis of the calculation charge, and use the XY plot data processing function in the Fluent software to extract the temperature distribution on the central axis of the calculation charge at the ignition moment of the calculation charge, then the value of Δx can be obtained.

[0025] Further, in step one, the reaction kinetics parameters include: activation energy E and pre-exponential factor A.

[0026] Further, in step three, use the single-phase exponential decay function in the Origin software to fit the scatter points.

[0027] Further, in step three, use the Matlab software to fit the scatter points.

[0028] Beneficial effects:

[0029] (1) The present invention utilizes the XY plot data processing function in Fluent software to extract the temperature distribution on the central axis of the calculated charge at the ignition moment. When two ignition points are formed on the central axis of the calculated charge, the formula is used as the basis for slow cook-off judgment; if is satisfied, then the calculated charge is slow cook-off, and if is not satisfied, then the calculated charge is not slow cook-off; therefore, the present invention takes the central ignition of the calculated charge as the evaluation criterion for slow cook-off, solving the problem that the existing evaluation criterion for slow cook-off only based on the heating rate has limitations. and uses the formula as the basis for slow cook-off judgment; if is satisfied, then the calculated charge is slow cook-off, and if is not satisfied, then the calculated charge is not slow cook-off; therefore, the present invention takes the central ignition of the calculated charge as the evaluation criterion for slow cook-off, solving the problem that the existing evaluation criterion for slow cook-off only based on the heating rate has limitations.

[0030] (2) The present invention establishes a multi-dimensional influencing factor evaluation mechanism, considering the combined effect of the heating rate and the geometric size of the calculated charge on the slow cook-off of the calculated charge. Compared with the existing single-factor evaluation method, the evaluation mechanism is more comprehensive.

[0031] (3) The existing slow cook-off evaluation methods are all qualitative analyses. The present invention can use the single-phase exponential decay function in Origin software to fit the relationship between the heating rate and the geometric size of the calculated charge, which can provide a basis for the slow cook-off test. According to the geometric size of the test projectile, the corresponding heating rate can be determined, reducing the number of tests, saving costs, and improving efficiency. Description of the Drawings

[0032] Figure 1 shows the ignition positions at different heating rates.

[0033] Figure 2 shows the influence of geometric size on the ignition position of the explosive (heating rate 3.3 K / h);

[0034] Figure 3 shows the composition diagram of the slow cook-off test device;

[0035] Figure 4 shows the composition diagram of the calculation model scaled with the test projectile;

[0036] Figure 5 shows the comparison diagram of the temperature curves of the test and calculation;

[0037] Figure 6 shows the temperature distribution nephogram of the calculated charge at the ignition moment;

[0038] Figure 7 shows the temperature distribution diagram on the central axis of the calculated charge;

[0039] Figure 8 shows the relationship diagram between the slow cook-off critical heating rate and the charge diameter;

[0040] Among them, 1 - annular heater, 2 - test shell, 3 - test charge, 4 - temperature controller, 5 - central temperature - measuring thermocouple, 6 - wall - temperature - measuring thermocouple, 7 - bolt, 8 - calculation shell, 9 - calculation charge, 10 - calculation heating wall, 11 - adiabatic wall. Specific implementation mode

[0041] The present invention will be described in detail below with reference to the accompanying drawings and by way of examples.

[0042] This embodiment provides a method for evaluating the slow cook - off of explosives, and the specific steps are as follows:

[0043] Step 1: Establish a slow cook - off test device and conduct a slow cook - off test on the test projectile. As Figure 3 shown, the slow cook - off test device includes: an annular heater 1, a test projectile, a temperature controller 4, a central temperature - measuring thermocouple 5, and a wall - temperature - measuring thermocouple 6; the test projectile includes: a test shell 2, a test charge 3, and a bolt 7.

[0044] Both the test charge 3 and the test shell 2 are split - body structures in upper and lower parts, and the upper and lower parts of the test shell 2 are connected into one body by bolts 7; the test charge 3 is installed in the test shell 2, the length - diameter ratio of the test charge 3 is 1, and the charge diameter is 50 mm; the wall thickness at both upper and lower ends of the test shell 2 is 15 mm, and the side - wall thickness is 25 mm.

[0045] The annular heater 1 is sleeved on the outer wall of the test projectile and is used to heat the test projectile; the wall - temperature - measuring thermocouple 6 is placed between the annular heater 1 and the test shell 2 and is electrically connected to the temperature controller 4 through a wire, and is used to measure the outer - wall temperature of the test projectile and feed it back to the temperature controller 4 to achieve temperature control; the central temperature - measuring thermocouple 5 is placed at the geometric center of the test charge 3 and is electrically connected to the temperature controller 4 through a wire, and is used to measure the central - position temperature inside the test charge 3.

[0046] When conducting the slow cook - off test, the annular heater 1 operates to heat the test projectile, and the test charge 3 inside the test projectile heats up. When the highest temperature of the test charge 3 is higher than its ignition point, the test charge 3 ignites; during this process, the wall - temperature - measuring thermocouple 6 measures the outer - wall temperature of the test projectile in real time and obtains the change curve of the outer - wall temperature of the test with time, as Figure 5 shown by the circular dotted solid line; the central temperature - measuring thermocouple measures the central - position temperature inside the test charge 3 in real time and obtains the change curve of the central - position temperature of the test with time, as Figure 5 shown by the solid line.

[0047] Step 2: Establish a calculation model that is proportional to the test projectile according to the slow roasting combustion test device for simulation, and calibrate the reaction kinetic parameters; the reaction kinetic parameters include: activation energy E and pre-exponential factor A; see Appendix Figure 4 , the calculation model includes: calculation shell 8, calculation charge 9, calculation heating wall surface 10 and adiabatic wall surface 11;

[0048] The calculation shell 8 is exactly the same as the test shell 2, and the calculation charge 9 is exactly the same as the test charge 3; the calculation charge 9 is located inside the calculation shell 8, the outer wall surface of the calculation shell 8 is the calculation heating wall surface 10, and both the upper and lower end surfaces of the calculation shell 8 are adiabatic wall surfaces 11;

[0049] Use the computational fluid dynamics software ANSYS Fluent to perform numerical simulation calculations on the calculation model. During the numerical simulation calculations, the reaction kinetic equation is required. The reaction kinetic equation contains the reaction kinetic parameters (i.e., activation energy E and pre-exponential factor A) and physical property parameters of the calculation charge 9; the initial activation energy E, pre-exponential factor A and physical property parameters of the calculation charge 9 can be obtained according to the literature [Ma Xin. Research on the Thermal Reaction Characteristics and Laws of High-Energy Mixed Explosives [D]; Beijing: Beijing Institute of Technology, 2014.];

[0050] Take the curve of the outer wall surface temperature of the test over time as the curve of the outer wall surface temperature of the calculation shell 8 over time, and load the curve of the outer wall surface temperature of the calculation shell 8 over time as a boundary condition onto the calculation heating wall surface 10; write the reaction kinetic equation as a subroutine and load it into the calculation charge 9 for calculation. According to the initial reaction kinetic parameters and physical property parameters of the calculation charge 9, calculate the curve of the temperature at the center position of the calculation charge 9 over time, that is Figure 5 dotted line;

[0051] Compare the calculated curve of the temperature at the center position of the calculation charge 9 over time with the curve of the temperature at the center position of the test over time (i.e., Figure 5 solid line). If the two basically coincide (i.e., the difference in ambient temperature at the same time point between the dotted line and the solid line is within the set range), then the initial reaction kinetic parameters, that is, the initial activation energy E and pre-exponential factor A do not need to be corrected. If the two differ greatly (i.e., the difference in ambient temperature at the same time point between the dotted line and the solid line is not within the set range), then the initial activation energy E and pre-exponential factor A need to be corrected until the calculated curve of the temperature at the center position of the calculation charge 9 over time basically coincides with the curve of the temperature at the center position of the test over time, so as to obtain the calibrated activation energy E and pre-exponential factor A;

[0052] Step 3: Simplify the calculation model in Step 2 and conduct slow cook-off calculation for the charge; that is, after changing the size of the calculated charge 9 and the thickness of the calculated casing 8 to form a simplified model, conduct slow cook-off calculation for the charge. The length-diameter ratio L / D of the calculated charge 9 in the simplified model is 1, the charge diameter is 40 mm, and the wall thickness at both the upper and lower ends and the side wall thickness of the calculated casing 8 are all 6 mm (adjustable);

[0053] When conducting slow cook-off calculation for the charge, load the preset heating rate on the outer wall surface of the calculated casing 8 as a boundary condition onto the calculated heating wall 10; write the reaction kinetic equation as a subroutine and load it into the calculated charge 9 for calculation. According to the calibrated activation energy E and pre-exponential factor A in Step 2, calculate the temperature contour at the ignition moment of the calculated charge 9. By adjusting the heating rate, make the ignition position of the calculated charge 9 located on the central axis of the calculated charge 9, as Figure 6 shown; among them, one or two ignition points can be formed on the central axis of the calculated charge 9;

[0054] Step 4: Use the XY plot data processing function in Fluent software to extract the temperature distribution diagram on the central axis of the calculated charge 9 at the ignition moment of the calculated charge 9, as Figure 7 shown, Figure 7 the X-axis of which is the direction vector, that is, the distance from any point on the central axis of the calculated charge 9 to the bottom surface of the calculated charge 9, Figure 7 the Y-axis of which is the temperature on the central axis of the calculated charge 9. According to Figure 7 it can be known that two ignition points are formed on the central axis of the calculated charge 9, that is, Figure 7 the two points with the highest and the second highest temperatures in

[0055] According to the formula judge whether the calculated charge 9 is slow cook-off. Among them, when there is only one ignition point, Δx = 0; when there are two ignition points, Δx is the distance between the two ignition points, and L is the charge length. If it satisfies then the calculated charge 9 is slow cook-off; if it does not satisfy then the calculated charge 9 is not slow cook-off. Since the length-diameter ratio L / D of the calculated charge 9 in the simplified model is 1 and the charge diameter is 40 mm, therefore, adjust the heating rate again until At this time, the heating rate is 16 K / h; the heating rate at this time is the critical heating rate of slow cook-off;

[0056] And so on, when the length-diameter ratio L / D of the calculated charge 9 is 1, by changing the charge diameter of the calculated charge 9, the critical heating rates of slow cook-off under different charge diameters can be obtained, as Figure 8 the scatter points in

[0057] Step 5: Use the single-phase exponential decay function in Origin software or Matlab software to fit the Figure 8 scattered points as shown by the solid line in Figure 8 to obtain the relationship between the critical heating rate R and the charge diameter D of the calculated charge 9 when the length-diameter ratio L / D of the calculated charge 9 is 1 as

[0058]

[0059] Step 6: In Step 3, after changing the length-diameter ratio of the calculated charge 9, repeat Steps 3 to 5 to obtain the relationship between the critical heating rate R and the charge diameter D of the calculated charge 9 at different length-diameter ratios;

[0060] Step 7: According to the length-diameter ratio and the charge diameter D of the calculated charge 9, the corresponding critical heating rate of slow cook-off can be obtained from formula (1) or the relationship in Step 6. This critical heating rate is the heating rate boundary. Load this heating rate boundary onto the calculated heating wall 10 for calculation to obtain information such as the internal temperature change, ignition time, and ignition temperature of the calculated charge 9, and evaluate the slow cook-off characteristics of the explosive.

[0061] In summary, the above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An evaluation method for slow cook-off of explosives, characterized in that, The specific steps are as follows: Step 1: Establish a calculation model with the same ratio as the test projectile according to the slow cook-off test device for simulation, and calibrate the reaction kinetic parameters; the calculation model includes: a calculation shell (8), a calculation charge (9), a calculation heating wall (10), and an adiabatic wall (11); Step 2: Conduct slow cook-off calculation of the charge. Load the preset heating rate on the outer wall surface of the calculation shell (8) as a boundary condition onto the calculation heating wall (10); load the reaction kinetic equation into the calculation charge (9) for calculation. According to the calibrated reaction kinetic parameters, calculate the temperature contour map at the ignition moment of the calculation charge (9); one or two ignition points are formed in the calculation charge (9) at the ignition moment; Step 3: According to the formula judge whether the calculated charge (9) is slow cook-off. Wherein, when there is only one ignition point, Δx = 0; when there are two ignition points, Δx is the distance between the two ignition points, which can be obtained from the temperature contour map, and L is the charge length. If is satisfied, then the calculated charge (9) is slow cook-off; if is not satisfied, then the calculated charge (9) is not slow cook-off; Adjust the heating rate until the heating rate at this time is the critical heating rate for slow roasting combustion; And so on. Since the length-diameter ratio of the calculation charge (9) is a fixed value, by changing the charge length of the calculation charge (9), that is, the charge diameter, scatter points of the critical heating rates of slow cook-off at different charge diameters can be obtained. After fitting the scatter points, the relationship between the critical heating rate R and the charge diameter D of the calculation charge (9) can be obtained; Step 4: According to any charge diameter D of the calculation charge (9), the corresponding critical heating rate R of slow cook-off can be obtained. This critical heating rate R is the heating rate boundary. Load this heating rate boundary onto the calculation heating wall (10) for calculation to obtain the internal temperature change, ignition time, and ignition temperature of the calculation charge (9), and evaluate the slow cook-off characteristics of the explosive; The slow cook-off test device includes: an annular heater (1), a test projectile, a temperature controller (4), a central temperature measurement thermocouple (5), and a wall temperature measurement thermocouple (6); the test projectile includes: a test shell (2) and a test charge (3); the test charge (3) is installed in the test shell (2), and the length-diameter ratio of the test charge (3) is 1; The annular heater (1) is sleeved on the outer wall surface of the test projectile for heating the test projectile; the wall temperature measurement thermocouple (6) is placed between the annular heater (1) and the test shell (2) and is electrically connected to the temperature controller (4) through a wire for measuring the outer wall surface temperature of the test projectile and feeding it back to the temperature controller (4) to achieve temperature control; the central temperature measurement thermocouple (5) is placed at the geometric center of the test charge (3) and is electrically connected to the temperature controller (4) through a wire for measuring the central position temperature inside the test charge (3); When conducting a slow cook-off test, the annular heater (1) operates to heat the test projectile, and the test charge (3) inside the test projectile heats up. When the highest temperature of the test charge (3) is higher than its ignition point, the test charge (3) ignites; during this process, the wall temperature measurement thermocouple (6) measures the outer wall surface temperature of the test projectile in real time and obtains the change curve of the outer wall surface temperature of the test over time; the central temperature measurement thermocouple measures the central position temperature inside the test charge (3) in real time and obtains the change curve of the central position temperature of the test over time; In Step 1, the reaction kinetic parameters include: activation energy E and pre-exponential factor A.

2. The evaluation method for slow cook-off of an explosive according to claim 1, characterized in that, In Step 1, the calculation shell (8) is exactly the same as the test shell (2), and the calculation charge (9) is exactly the same as the test charge (3); the calculation charge (9) is located inside the calculation shell (8), the outer wall surface of the calculation shell (8) is the calculation heating wall surface (10), and both the upper and lower end surfaces of the calculation shell (8) are adiabatic wall surfaces (11). Perform numerical simulation calculations on the calculation model. Use the curve of the outer wall surface temperature change over time in the test as the curve of the outer wall surface temperature change over time of the calculation shell (8), and apply the curve of the outer wall surface temperature change over time of the calculation shell (8) as a boundary condition to the calculation heating wall surface (10); write the reaction kinetic equation as a subroutine and load it into the calculation charge (9) for calculation. According to the initial reaction kinetic parameters and physical property parameters of the calculation charge (9), calculate the curve of the temperature change over time at the center position of the calculation charge (9). Compare the curve of the temperature change over time at the center position of the calculated calculation charge (9) with the curve of the temperature change over time at the center position in the test. If the environmental temperature difference at the same time point between the two is within the set range, the initial reaction kinetic parameters do not need to be corrected. If the environmental temperature difference at the same time point between the two is not within the set range, the initial reaction kinetic parameters need to be corrected until the environmental temperature difference at the same time point between the curve of the temperature change over time at the center position of the calculated calculation charge (9) and the curve of the temperature change over time at the center position in the test is within the set range, thereby obtaining the calibrated reaction kinetic parameters.

3. The evaluation method for slow cook-off of an explosive according to claim 2, characterized in that In Step 3, when the length-diameter ratio L / D of the calculation charge (9) is 1, the fitted relationship between the critical heating rate R and the charge diameter D of the calculation charge (9) is:[ 4. The evaluation method for slow cook-off of an explosive according to claim 3, characterized in that, In Step 1, after changing the length-diameter ratio of the calculation charge (9), obtain the relationship between the critical heating rate R and the charge diameter D of the calculation charge (9) at different length-diameter ratios.

5. An evaluation method for slow cook-off of an explosive according to any one of claims 1-4, characterized in that, In Step 2, when performing slow cook-off calculations for the charge, by adjusting the heating rate, make the ignition position of the calculation charge (9) located on the central axis of the calculation charge (9), and use the XY plot data processing function in Fluent software to extract the temperature distribution on the central axis of the calculation charge (9) at the ignition moment of the calculation charge (9), then the value of Δx can be obtained.

6. A method for evaluating the slow cook-off of an explosive according to any one of claims 1-4, characterized in that, In Step 3, use the single-phase exponential decay function in Origin software to fit the scatter points.

7. A method for evaluating the slow cook-off of an explosive according to any one of claims 1-4, characterized in that, In Step 3, use Matlab software to fit the scatter points.

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