Method for characterizing shear sensitivity of material

Abstract

The invention provides a method for characterizing the shear sensitivity of a material. The method specifically comprises the following steps: (1) establishing a dynamic relationship and an energy relationship of material shear band evolution; (2) obtaining a dynamic result of material shear band evolution according to the dynamic relationship and the energy relationship; (3) solving evolutionary dissipated energy of the material shear band according to a dynamic result; and (4) obtaining critical dissipated energy according to a minimum energy principle, and providing an index for evaluating the shear sensitivity of the material by combining a shear modulus and a shear zone toughness index. The method is reasonable in conception, fully considers various factors influencing the shear sensitivity of the material, can be widely applied to various materials, and can efficiently and accurately characterize the shear sensitivity of the material at low cost.

Description

Technical Field

[0001] The invention relates to the technical field of testing dynamic mechanical behavior of materials, and in particular to a method for characterizing shear sensitivity of materials. Background Art

[0002] In the process of continuous development of weapons and equipment technology, kinetic penetration, as a crucial damage mode, plays a core role in many military application scenarios. As a typical weapon and equipment for achieving kinetic penetration, the performance of armor-piercing projectiles directly affects combat effectiveness. At present, in the material system used for armor-piercing projectiles, 93 tungsten alloy has become the mainstream armor-piercing material due to its relatively good comprehensive performance. However, in the actual penetration process, 93 tungsten alloy exposed obvious defects. When subjected to high-speed impact loads, the head of the 93 tungsten alloy armor-piercing projectile will be upset and gradually form a mushroom-like shape. This change in the shape of the head greatly increases the resistance during the penetration process, resulting in a significant reduction in its penetration depth and penetration effect, making it difficult to meet the increasingly stringent combat requirements for the penetration performance of armor-piercing projectiles. In sharp contrast, depleted uranium materials have shown unique advantages in terms of penetration characteristics. Depleted uranium materials have the property of "self-sharpening", and can maintain a sharp head shape when subjected to impact penetration. This feature enables armor-piercing projectiles made of depleted uranium materials to effectively reduce penetration resistance and significantly improve penetration capability during the penetration process. A deeper exploration of the reasons shows that depleted uranium materials have low shear sensitivity, and shear bands are easily formed inside them during the impact process. The formation mechanism of this shear band prompts the material to adjust its structure in a way that is conducive to keeping the head sharp during the deformation process, thereby achieving a "self-sharpening" effect. However, depleted uranium materials have a serious limitation. Due to their radioactivity, they can cause potential huge harm to the environment and human health. Therefore, they are strictly restricted and controlled worldwide, which greatly hinders the widespread application of depleted uranium materials in the field of weapons and equipment. In view of the problems existing in 93 tungsten alloy and depleted uranium materials, the development of a new type of environmentally friendly penetrating material with "self-sharpening" properties has become a research hotspot and urgent need in the field of weapons and equipment materials. In this research and development process, a key and long-standing problem needs to be solved, that is, how to quantitatively characterize the shear sensitivity of the material. In existing engineering practice, the critical shear strain is usually used to determine whether the material is shear instability. However, this method has obvious limitations. It can only predict whether the material will form a shear band, but it is difficult to effectively capture and analyze the subsequent evolution and development behavior after the shear band is formed. The "self-sharpening" property of the material is actually closely related to the complex evolution and development behavior after the shear band is formed. For example, the expansion direction, expansion rate and morphological changes of the shear band under different load conditions all play a decisive role in whether the material can continue to maintain the "self-sharpening" characteristics. At present, the quantitative characterization research in this key field is still in a completely blank stage, which seriously restricts the development process of new penetrating materials and the improvement of the performance of related weapons and equipment. Therefore, if relevant research can be carried out in depth and quantitative characterization of material shear sensitivity can be successfully achieved, it will be of inestimable value. On the one hand, this will fill the key gaps in the current material performance evaluation system, and provide a more accurate and reliable theoretical basis for engineering designers to select suitable penetration materials. It will help them to fully consider the shear characteristics of materials in the design process of weapons and equipment, optimize the structure and performance of equipment, and thus significantly improve the safety and reliability of engineering structures in actual combat environments. On the other hand, this research result will also inject strong impetus into the development of materials science, promote materials science to move towards higher performance and more complex systems, and help develop more advanced materials that meet the needs of future wars. To sum up, in order to overcome the many problems existing in the existing technology and meet the urgent demand for high-performance penetrating materials in the field of weapons and equipment, further innovation of the existing technology is imperative. Summary of the invention

[0003] In view of the technical problems existing in the above-mentioned background technology, the present invention proposes a method for quantitatively characterizing the shear sensitivity of materials. The method has a reasonable concept, fully considers the influence of various material parameters, can be widely applied to various materials, and can obtain shear instability criteria at low cost, high efficiency and accuracy.

[0004] In order to solve the above technical problems, the present invention provides a method for characterizing the shear sensitivity of a material, which specifically comprises the following steps: (1) Establish the dynamic relationship and energy relationship of material shear band evolution: ; In the above formular is the density, is the shear strain rate, is the rigid-plastic interface position, is the flow stress, is the boundary slip of the shear zone, is the stress in the shear band, i is the temperature, β is the work-to-heat conversion coefficient, x is the thermal diffusion coefficient, a is the shear band width, d is the differential operator and need not be explained, t is the time, and c is the specific heat; (2) Obtain the dynamic results of the shear band evolution of the material based on the dynamic relationship and energy relationship; (3) Determine the dissipated energy of shear band evolution based on the dynamic results; (4) Based on the minimum energy principle, the critical dissipated energy is obtained and combined with the shear modulus, an index of shear band toughness is proposed to evaluate the shear sensitivity of the material.

[0005] The method for characterizing the shear sensitivity of a material, wherein the specific process of obtaining the dynamic result of the shear band evolution of the material in step (2) is: Compatibility equations incorporating rigid regions of materials , the kinetic solution is obtained as: ; in is the critical slip of the shear band boundary; Assume that the material is linearly thermally softened ,in α is the thermal softening coefficient. Combined with the kinetic solution, the relationship between temperature and time is obtained as follows: .

[0006] The method for characterizing the shear sensitivity of a material, wherein the process of solving the shear band evolution dissipated energy in step (3) is: The temperature i Substituting into the energy equation and integrating over the entire time domain, we obtain: ; in It is critical time; Definition of Dissipated Energy , the implicit relationship between the shear band evolution dissipation energy and the shear band width is obtained as: .

[0007] The method for characterizing the shear sensitivity of a material, wherein the specific process of step (4) is as follows: According to the minimum energy principle, the critical dissipated energy is obtained: ; Modeled after fracture toughness, combined with shear modulus G The following expression of shear band toughness is given to quantitatively characterize the shear sensitivity: .

[0008] By adopting the above technical solution, the present invention has the following beneficial effects: The method for characterizing the shear sensitivity of materials of the present invention is reasonably conceived, fully considers the influence of various material parameters, can be widely applied to various materials, and can obtain shear instability criterion at low cost, efficiently and accurately to characterize the shear sensitivity of materials.

[0009] The present invention can not only quantitatively characterize the shear sensitivity of materials, but also be used to screen materials with better self-sharpening effects. On the other hand, it provides a wide range of material parameters that can be used to guide material design. The present invention fills the gap in the prior art, increases the phase space of material design, and provides a clear direction for the design and preparation of related materials.

[0010] The present invention also has the following characteristics and advantages: (1) Evaluating material safety: It can quantitatively describe the material's ability to resist shear instability, helping engineers accurately evaluate the safety of structures under dynamic loads and effectively prevent catastrophic accidents. For example, in the aerospace field, by characterizing the shear sensitivity of materials, it is possible to ensure that key aircraft components will not suddenly fail due to shear instability when subjected to complex stresses, thereby ensuring flight safety.

[0011] (2) Guiding material selection: When designing engineering structures, the shear sensitivity index can be used to select the most suitable materials for different working conditions. For example, when selecting high-performance armor-piercing materials, if self-sharpening properties are required, materials with high shear sensitivity can be selected to achieve this.

[0012] (3) Optimizing process design: The processing technology of a material will affect its shear sensitivity. By studying the parameters that affect shear sensitivity, the process parameters can be optimized. For example, during the heat treatment of metal materials, adjusting parameters such as heating temperature and cooling rate can reduce the shear sensitivity of the material and improve material performance.

[0013] (4) Promote the research and development of new materials: Quantitative characterization of shear sensitivity provides important performance indicators and directions for the research and development of new materials, prompting researchers to develop more advanced new materials to meet the requirements of high-performance materials in high-end fields such as aerospace and new energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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 in the following description 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.

[0015] Figure 1 Flow chart of the method for quantitatively characterizing the shear sensitivity of a material according to the present invention. DETAILED DESCRIPTION

[0016] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. 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.

[0017] The present invention is further explained below in conjunction with specific implementation modes.

[0018] like Figure 1 As shown, this embodiment provides a method for quantitatively characterizing the shear sensitivity of a material, and the specific process is as follows: (1) First, the kinetic equation and energy equation for the evolution of the shear band of the material are established: ; In the above formula r is the density, is the shear strain rate, is the rigid-plastic interface position, is the flow stress, is the boundary slip of the shear zone, is the stress in the shear band, i is the temperature, β is the work-to-heat conversion coefficient, x is the thermal diffusion coefficient, a is the shear band width, d is the differential operator and need not be explained, t is the time, and c is the specific heat; (2) Coordination equations combined with the rigid region of the material , and obtain the kinetic solution: ; in is the critical slip of the shear band boundary; (3) Assuming that the material is linearly thermally softened ,in α is the thermal softening coefficient (the inverse of the melting point), combined with the kinetic solution, the relationship between temperature and time is obtained: ; (4) Temperature i Substituting into the energy equation and integrating over the entire time domain, we obtain: ; in It is critical time; (5) Definition of dissipated energy , we can obtain the implicit relationship between the shear band evolution dissipation energy and the shear band width: ; (6) According to the minimum energy principle, the critical dissipated energy is obtained: ; 7) Based on fracture toughness, combined with shear modulus G The following expression for shear band toughness is given to quantitatively characterize shear sensitivity: .

[0019] This embodiment first obtains the basic parameters of the material: shear modulus G ,density r , work-to-heat conversion coefficient β , thermal diffusivity x , specific heat c , shear yield strength , thermal softening coefficient α ; Then, the loading strain rate is set and the material parameters are substituted into the proposed shear sensitivity characterization method to obtain the specific value of the shear band toughness.

[0020] The following is further explained using copper and 304 stainless steel as materials.

[0021] copper: The shear modulus is 47.1 GPa and the density is 8.9 g / cm 3 , the work-to-heat conversion coefficient is 0.9, and the thermal diffusion coefficient is 1.15×10 -4 m 2 / s, specific heat is 390J / kg K, shear yield strength is 60MPa, and thermal softening coefficient is 7.47×10 -4 K -1 .

[0022] 304 Stainless Steel: The shear modulus is 190GPa and the density is 7.8g / cm 3 , the work-to-heat conversion coefficient is 0.9, and the thermal diffusion coefficient is 4.18×10 -6 m 2 / s, specific heat is 477J / kg K, shear yield strength is 200MPa, and thermal softening coefficient is 5.9×10-4 K -1 .

[0023] The loading strain rate was set to 5×10 3 s -1 , the shear band toughness of copper is calculated to be 561 MPa√m, and the shear band toughness of 304 stainless steel is 170 MPa√m. It can be seen that the shear band toughness of 304 stainless steel is less than that of 304 stainless steel, and it has stronger shear sensitivity, and it is easier to produce shear bands in actual engineering.

[0024] The invention has a reasonable conception and proposes a method for quantitatively characterizing the shear sensitivity of materials based on basic material parameters. The method can be widely applied to various materials and can characterize the shear sensitivity of materials with low cost, high efficiency and accuracy.

[0025] 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 method for characterizing the shear sensitivity of a material, characterized in that: The specific steps include: (1) Establish the dynamic relationship and energy relationship of material shear band evolution: ； In the above formula ρ is the density, is the shear strain rate, is the rigid-plastic interface position, is the flow stress, is the boundary slip of the shear zone, is the stress in the shear band, θ is the temperature, β is the work-to-heat conversion coefficient, χ is the thermal diffusion coefficient, a is the shear band width, d is the differential operator and need not be explained, t is the time, and c is the specific heat; (2) Obtain the dynamic results of the shear band evolution of the material based on the dynamic relationship and energy relationship; (3) Determine the dissipated energy of shear band evolution based on the dynamic results; (4) Based on the minimum energy principle, the critical dissipated energy is obtained and combined with the shear modulus, an index of shear band toughness is proposed to evaluate the shear sensitivity of the material.

2. The method for characterizing the shear sensitivity of a material according to claim 1, characterized in that: The specific process of obtaining the dynamic results of the material shear band evolution in step (2) is as follows: Compatibility equations incorporating rigid regions of materials , the kinetic solution is obtained as: ； in is the critical slip of the shear band boundary; Assuming linear thermal softening of the material ,in α is the thermal softening coefficient. Combined with the kinetic solution, the relationship between temperature and time is obtained as follows: 。 3. The method for characterizing the shear sensitivity of a material according to claim 2, characterized in that: The solution process of the shear band evolution dissipated energy in step (3) is: The temperature θ Substituting into the energy equation and integrating over the entire time domain, we obtain: ； in It is critical time; Definition of Dissipated Energy The implicit relationship between the shear band evolution dissipated energy and the shear band width is obtained as follows: 。 4. The method for characterizing the shear sensitivity of a material according to claim 1, characterized in that: The specific process of step (4) is as follows: According to the minimum energy principle, the critical dissipated energy is obtained: ； Modeled after fracture toughness, combined with shear modulus G The following expression of shear band toughness is given to quantitatively characterize the shear sensitivity: 。

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