A method for checking strength of an energetic material pressing tool

Abstract

This invention discloses a method for strength verification of a propellant loading fixture for energetic materials, comprising: identifying the weak components of the propellant loading fixture for strength verification, wherein the weak components are the pressure bar and the upper pressure block; the strength verification includes verifying the crush strength and stability of the pressure bar, quantitatively evaluating the stress distribution of the pressure bar and the upper pressure block under axial load, examining the mechanical behavior at the contact point between the pressure bar and the upper pressure block, and determining the strength from a numerical simulation perspective; using an analysis method combining theoretical calculation and finite element simulation, the strength verification and validation of the pressure bar and the upper pressure block of the dedicated propellant loading fixture are completed. This method can confirm that the stress and deformation of the propellant loading fixture are within the elastic range, and the structural integrity meets the requirements.

Description

Technical Field

[0001] This invention belongs to the field of mechanical strength verification, and in particular, it is a method for verifying the strength of a tooling for pressing energetic materials. Background Technology

[0002] The compression molding of energetic materials (such as explosives, gunpowder, and propellants) is a core technological step in the field of ammunition loading. This process typically involves applying axial pressure of tens to hundreds of megapascals to the powder under quasi-static loading conditions using compression tooling (punches, molds, pads, etc.) to achieve the specified density and geometric dimensions. The structural strength of the tooling directly determines production safety, product quality, and loading efficiency.

[0003] Currently, for strength verification of tooling under quasi-static propellant loading conditions, the engineering and academic communities mainly use analytical formulas based on materials mechanics or general finite element simulation methods. Among these, the strength criterion is generally based on the von Mises yield criterion, using the material's yield strength as the allowable stress benchmark, focusing on preventing plastic deformation failure of the tooling. This criterion system has good applicability to conventional propellant loading tooling made of carbon tool steel and low-alloy die steel, and the relevant safety factor values ​​and verification procedures have become mature engineering practices. However, as modern weapon propellants develop towards high damage and high reliability, the requirements for material performance in propellant loading tooling are becoming increasingly stringent. High-hardness die steels (such as Cr12MoV and DC53) and high-strength wear-resistant materials such as cemented carbide are increasingly widely used in propellant loading tooling. These materials have high yield strength but low plasticity reserve, and their failure mode often manifests as brittle cracking without significant plastic deformation. The existing strength verification system is severely inadequate in its ability to warn of such failure risks. Furthermore, the widespread adoption of precision propellant loading structures imposes rigid constraints on tooling stiffness. Traditional strength verification methods only focus on "whether it is damaged" and do not include "whether the deformation exceeds the tolerance" in the verification system. This results in some tooling having sufficient strength but insufficient rigidity, leading to batch scrap and requiring repeated trial molding and correction.

[0004] In summary, existing methods for verifying the strength of propellant presses have significant shortcomings in terms of failure mode criteria: a single criterion system based on plastic yielding is insufficient to cover the fracture risk of high-strength brittle materials. Currently, there are no publicly reported dedicated quasi-static strength verification methods for propellant presses made of energetic materials that integrate strength verification with stiffness constraints. Summary of the Invention

[0005] The purpose of this invention is to provide a method for strength verification of tooling for pressing energetic materials, in order to solve the technical problem in the prior art where inaccurate or improper strength verification of tooling design during the pressing and molding process of energetic materials leads to tooling deformation, cracking, or even safety accidents.

[0006] The technical solution to achieve the purpose of this invention is as follows:

[0007] A method for strength verification of a propellant loading tool for energetic materials includes:

[0008] Weak components of the energetic material compression tooling were identified for strength verification. The weak components were the pressure bar and the upper pressure block.

[0009] The strength verification includes verifying the crush strength and stability of the pressure bar, as well as quantitatively evaluating the stress distribution of the pressure bar and the upper pressure block under axial load, examining the mechanical behavior at the contact point between the pressure bar and the upper pressure block, and determining the strength from the perspective of numerical simulation. Using an analysis method that combines theoretical calculation and finite element simulation, the strength verification and validation of the pressure bar and upper pressure block of the special-purpose press tool were completed.

[0010] The significant advantages of this invention compared to existing technologies are:

[0011] The present invention provides a method for strength verification of a propellant pressing fixture for energetic materials. Using an analytical method combining theoretical calculation and finite element simulation, the strength verification and validation of the pressure bar and upper pressure block of the special propellant pressing fixture were completed. This method confirms that the stress and deformation of the propellant pressing fixture are within the elastic range and the structural integrity meets the requirements, thus laying a reliable hardware foundation for subsequent propellant pressing tests. Attached Figure Description

[0012] Figure 1 This is a 3D model of a special-purpose press tool.

[0013] Figure 2 This is a 3D model of the compression bar.

[0014] Figure 3 This is the equivalent stress cloud diagram of the upper pressure block.

[0015] Figure 4 This is the equivalent stress contour diagram of the compression member.

[0016] Figure 5 This is a displacement contour map of the upper pressure block and pressure rod.

[0017] Figure 6 This is the equivalent plastic strain contour plot of the compression bar. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0019] This embodiment describes a method for strength verification of a propellant loading tool for energetic materials, using the strength verification of a propellant loading tool with a diameter of 5 mm as an example.

[0020] To meet the requirements for pressing and testing Φ5 mm × 5 mm JO-8 explosive charges, a specialized pressing fixture with a modular mold and matching pressure bar was designed. (See attached image.) Figure 1 The pressing fixture, from top to bottom, comprises an upper pressing block 1, a pressing rod 2, a mold sleeve 3, and a pad block 4. Before using this fixture for pressing, the strength of the weakest components must be checked. According to the design, the pressing rod and the upper pressing block are identified as the weakest components. The pressing rod of this pressing fixture adopts an integrated design of an arc-shaped ball head and a cylindrical rod, see... Figure 2 The pressure bar is a Φ5 mm cylinder with a height of 30 mm. The top of the pressure bar is designed as an arc-shaped ball head with a certain curvature (the diameter of the curvature circle is 8 mm) to ensure safe and stable pressure. The pressure bar is made of Cr12MoV material.

[0021] Strength verification theoretical calculation:

[0022] Strength verification of cylindrical compression members: crushing and stability

[0023] ① Crushing strength verification

[0024] This is the most direct check to ensure that the cylindrical rod will not collapse under pressure.

[0025] Calculate compressive stress :

[0026]

[0027] , ,

[0028]

[0029] in denoted as compressive stress; F is the maximum working load of the press; d is the diameter of the cylinder; and A is the base area of ​​the cylinder.

[0030] Strength requirements:

[0031]

[0032] This represents the yield strength of the material. For safety factor, take (For static loads, it is usually taken as 1.5~2).

[0033] The pressure bar material is Cr12MoV mold steel, after quenching and tempering. .

[0034]

[0035] in conclusion: The crushing strength fully meets the requirements.

[0036] ② Stability check

[0037] Because the injection column is slender, it needs to be checked whether it will bend like a chopstick, i.e., become unstable.

[0038] Calculate the slenderness ratio:

[0039] Length of the compression bar : .

[0040] Cross-sectional radius of inertia For a circular cross-section, .

[0041] Slenderness ratio : .

[0042] Determine the failure mode:

[0043] For slender steel rods, when When this occurs, Euler's formula needs to be used to calculate the critical instability load.

[0044] In this example It belongs to the category of low slenderness compression members, and its failure is mainly caused by insufficient strength rather than instability.

[0045] Conclusion: The stability requirements are met.

[0046] Strength verification by finite element analysis:

[0047] To verify the structural integrity of the pressure bar under the maximum working load (2000N) of the press, a detailed static finite element analysis was performed. By quantitatively evaluating the stress distribution of the pressure bar and the upper pressure block under axial load, the strength of the bar body and the mechanical behavior at the contact point between the arc-shaped ball head and the upper pressure block were examined, and its strength was determined from the perspective of numerical simulation.

[0048] Create a 3D geometric model of the pressure bar and upper pressure block in SolidWorks. Key features of the model are: the cylindrical bar has a diameter of 5 mm, and its head is an arc-shaped spherical head with a radius of curvature of 8 mm. The upper pressure block has a rectangular base of 25 × 8 mm and a thickness of 14 mm. After importing the entire model into ABAQUS finite element analysis software, perform the following preprocessing settings:

[0049] Material properties: The materials of the pressure bar and the upper pressure block are both set to Cr12MoV mold steel. The model adopts the Joshon-Cook constitutive model with damage. The parameters are shown in Table 1.

[0050] Table 1 Constitutive model parameters of Cr12MoV mold steel with damage (Joshon-Cook)

[0051]

[0052] Mesh generation: All elements are C3D8R (8-node hexahedral linear reduced integral element). The pressure bar has 27,423 meshes and 30,400 nodes. The upper pressure block has 9,537 meshes and 11,016 nodes. The entire model uses a total of 36,960 meshes and 41,416 nodes for calculation.

[0053] Loads and constraints: Simulating actual working conditions, loads are applied to the upper surface area of ​​the upper pressure block. The concentrated load is linked to the upper surface using motion coupling. The amplitude curve is set as a smooth analysis step, and the time is set to 120 seconds to load up to an amplitude of 2000 N to simulate the load applied during the test. All degrees of freedom of the lower end face of the cylindrical compression bar are fully constrained, i.e., fixed end constraint.

[0054] After the calculations are completed, the equivalent stress contour plot and the total deformation contour plot (3-6) of the model are extracted and analyzed. The equivalent stress contour plot (see...) Figure 3 , Figure 4 The data shows that the maximum equivalent stress occurs in the central region of the contact surface between the curved ball head and the upper pressure block, and its value is σ. max = 1512 MPa, lower than the yield strength of Cr12MoV die steel (1600 MPa), indicating no plastic yielding or structural failure under static load. Stress decreases rapidly from the contact center towards the edge of the curved ball head and the shaft. The maximum equivalent stress on the cylindrical shaft is approximately 100 MPa, located in the root region where the shaft connects to the fixed end, due to local stiffness changes caused by constraints. Stress in most areas of the shaft is between 80 and 100 MPa, with a relatively uniform force distribution, exhibiting axial compressive stress. Comparing the maximum stress of the shaft with the yield strength of Cr12MoV material (≥ 1600 MPa), its safety factor is much greater than 1, indicating that the shaft has sufficient strength margin under a 2000 N load, operates in a fully elastic state, has no risk of yielding, and fully meets the strength requirements. Regarding deformation (see...), Figure 5 , Figure 6 The entire structure undergoes elastic compressive deformation along the load direction. The maximum displacement occurs at the load application point (upper pressure block), with a value of U. max =0.044 mm, and U=0.034 mm at the contact point between the center of the rod and the upper pressure block. The deformation is small and it is in a fully elastic working state.

[0055] Conclusion: To meet the requirements for pressing and testing Φ5 mm × 5 mm JO-8 explosive charges, a combination of theoretical calculations and finite element simulation was used to verify the strength of the pressure bar and upper pressure block of the dedicated pressing fixture. The results show that the maximum stress of the pressure bar and upper pressure block under a 2000 N load is below the material strength limit, confirming that the stress and deformation of the pressing fixture are within the elastic range, and that the structural integrity meets the requirements, laying a reliable hardware foundation for subsequent pressing tests.

Claims

1. A method for strength verification of a tooling system for pressing energetic materials, characterized in that, include: Weak components of the energetic material compression tooling were identified for strength verification. The weak components were the pressure bar and the upper pressure block. The strength verification includes verifying the crush strength and stability of the pressure bar, as well as quantitatively evaluating the stress distribution of the pressure bar and the upper pressure block under axial load, examining the mechanical behavior at the contact point between the pressure bar and the upper pressure block, and determining the strength from the perspective of numerical simulation. Using an analysis method that combines theoretical calculation and finite element simulation, the strength verification and validation of the pressure bar and upper pressure block of the special-purpose press tool were completed.

2. The method for strength verification of energetic material propellant loading fixtures according to claim 1, characterized in that, In the crush strength check, the compressive stress of the column is first calculated, and the crush strength is then determined to meet the requirements using the strength criterion. The strength criterion is as follows: in It is compressive stress. For the material's yield strength, This is for the safety factor.

3. The method for strength verification of a propellant loading fixture for energetic materials according to claim 2, characterized in that, The method for calculating compressive stress is as follows: Where F is the maximum working load of the press; d is the diameter of the cylinder of the pressure bar; and A is the base area of ​​the cylinder of the pressure bar.

4. The method for strength verification of a propellant loading fixture for energetic materials according to claim 1, characterized in that, In stability verification, the failure mode is determined by calculating the slenderness ratio of the compression bar.

5. The method for strength verification of a propellant loading fixture for energetic materials according to claim 4, characterized in that, The method for calculating the slenderness ratio of a compression member is as follows: in slenderness ratio, The length of the compression bar The radius of inertia of the cross section of the compression member, where d is the diameter of the cylindrical compression member.

6. The method for strength verification of a propellant loading fixture for energetic materials according to claim 1, characterized in that, In finite element simulation, a three-dimensional geometric model of the pressure bar and the upper pressure block is first established. After importing the entire model into the finite element analysis software, material properties are set, meshing is performed, loads and constraints are added, and equivalent stress cloud map and total deformation cloud map are extracted and analyzed to obtain the location and value of the maximum equivalent stress. The strength is then checked by comparing it with the yield strength of the material.

7. The method for strength verification of a propellant loading fixture for energetic materials according to claim 1, characterized in that, In the load and constraint section, a concentrated load equal to the maximum working load of the press is applied to the upper surface area of ​​the upper pressure block. Motion coupling is used to link the concentrated load to the upper surface of the upper pressure block. The amplitude curve is set as a smoothing analysis step to simulate the load applied during the test. All degrees of freedom of the lower end face of the pressure bar are fully constrained, i.e., fixed end constraint.

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