A method for characterizing the shear sensitivity of materials

Abstract

The present invention provides a method for characterizing the shear sensitivity of a material, which specifically includes: (1) establishing a kinetic relationship and an energy relationship for the evolution of a shear band in the material; (2) obtaining a kinetic result of the evolution of the shear band in the material based on the kinetic relationship and the energy relationship; (3) solving the dissipated energy of the shear band evolution in the material based on the kinetic result; and (4) obtaining the critical dissipated energy based on the minimum energy principle and proposing an index of shear band toughness in combination with the shear modulus to evaluate the shear sensitivity of the material. The present invention is rationally conceived, fully considers various factors that affect the shear sensitivity of a material, can be widely applied to various materials, and can characterize the shear sensitivity of a material in a low-cost, efficient, and accurate manner.

Description

Technical Field

[0001] The present 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] As weapons technology continues to evolve, kinetic penetration, as a crucial damage mode, plays a core role in numerous military applications. Armor-piercing projectiles, as a typical weapon capable of kinetic penetration, have a direct impact on combat effectiveness. Currently, 93 tungsten alloy has become the mainstream material for armor-piercing projectiles due to its relatively good overall performance. However, during actual penetration, 93 tungsten alloy has exposed significant flaws. When subjected to high-speed impact loads, the head of a 93 tungsten alloy armor-piercing projectile undergoes upsetting, gradually developing a mushroom-like shape. This change in head shape significantly increases penetration resistance, significantly reducing penetration depth and effectiveness, making it difficult to meet the increasingly stringent penetration performance requirements of armor-piercing projectiles.

[0003] In stark contrast, depleted uranium exhibits unique advantages in terms of penetration properties. Depleted uranium possesses a self-sharpening property, maintaining a sharp tip when subjected to impact. This property effectively reduces penetration resistance and significantly improves penetration capability in armor-piercing projectiles made from depleted uranium. A deeper dive into the reasons for this reveals that depleted uranium has low shear sensitivity, and shear bands easily form within it during impact. This shear band formation mechanism causes the material to adjust its structure during deformation in a manner that helps maintain a sharp tip, thus achieving the self-sharpening effect. However, depleted uranium has a serious limitation. Due to its radioactivity, it poses a potentially significant threat to the environment and human health. Therefore, it is subject to strict restrictions and controls worldwide, significantly hindering its widespread use in weaponry.

[0004] Given the respective challenges of 93 tungsten alloy and depleted uranium materials, the development of a new environmentally friendly penetrating material with "self-sharpening" properties has become a research hotspot and a pressing need in the field of weapons and equipment materials. A key and long-standing issue in this research and development process is the quantitative characterization of the material's shear sensitivity. In existing engineering practice, the critical shear strain is often used to determine whether a material is experiencing shear instability. However, this method has significant limitations. It only indicates whether a shear band will form, but it struggles to effectively capture and analyze the subsequent evolution of the shear band after formation. The self-sharpening property of a material is closely related to the complex evolution of the shear band after formation. For example, the shear band's propagation direction, rate, and morphological changes under different loading conditions all play a decisive role in whether the material can maintain its self-sharpening properties. Currently, quantitative characterization research in this critical area remains completely unresolved, severely hindering the development of new penetrating materials and the improvement of the performance of related weapons and equipment.

[0005] Therefore, if relevant research can be carried out in depth and the quantitative characterization of material shear sensitivity can be successfully achieved, it will be of immeasurable value. On the one hand, this will fill the key gaps in the current material performance evaluation system, and provide engineering designers with a more accurate and reliable theoretical basis when selecting suitable penetrating materials. It will help them to fully consider the shear properties 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 continuously move towards higher performance and more complex systems, and help develop more advanced materials that meet the needs of future warfare.

[0006] 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

[0007] In response to 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 and fully considers the influence of various material parameters. It can be widely applied to various materials and can obtain shear instability criteria at low cost, high efficiency and accuracy.

[0008] To solve the above technical problems, the present invention provides a method for characterizing the shear sensitivity of a material, which specifically includes the following steps:

[0009] (1) Establish the dynamic and energy relationships of shear band evolution:

[0010] ;

[0011] In the above formula r is the density, is the shear strain rate, is the position of the rigid-plastic interface, 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 diffusivity, a is the shear band width, d is the differential operator and is not explained, t is the time, and c is the specific heat;

[0012] (2) Obtain the dynamic results of shear band evolution of materials based on dynamic and energy relationships;

[0013] (3) Determine the dissipated energy of shear band evolution based on the dynamic results;

[0014] (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.

[0015] The method for characterizing the shear sensitivity of a material, wherein the specific process of obtaining the dynamic results of the shear band evolution of the material in step (2) is as follows:

[0016] Compatibility equations combining rigid regions of materials , the kinetic solution is obtained as:

[0017] ;

[0018] in is the critical slip at the shear zone boundary;

[0019] 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:

[0020] .

[0021] The method for characterizing the shear sensitivity of a material, wherein the process for solving the shear band evolution dissipation energy in step (3) is as follows:

[0022] The temperature i Substituting into the energy equation and integrating over the entire time domain, we obtain:

[0023] ;

[0024] in It is critical time;

[0025] Definition of dissipated energy , the implicit relationship between the shear band evolution dissipation energy and the shear band width is obtained as:

[0026] .

[0027] The method for characterizing the shear sensitivity of a material, wherein the specific process of step (4) is:

[0028] According to the minimum energy principle, the critical dissipated energy is obtained:

[0029] ;

[0030] Modeled after fracture toughness, combined with shear modulus G The following expression of shear band toughness is given to quantitatively characterize the shear sensitivity:

[0031] .

[0032] By adopting the above technical solution, the present invention has the following beneficial effects:

[0033] The method for characterizing the shear sensitivity of materials of the present invention is rationally 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.

[0034] 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.

[0035] The present invention also has the following characteristics and advantages:

[0036] (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.

[0037] (2) Guiding material selection: When designing engineering structures, the most suitable materials can be selected for different working conditions based on the shear sensitivity index; 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.

[0038] (3) Optimize process design: The processing technology of the material will affect its shear sensitivity. By studying the parameters affecting shear sensitivity, the process parameters can be optimized. For example, in the heat treatment process of metal materials, adjusting parameters such as heating temperature and cooling rate can reduce the shear sensitivity of the material and improve the material performance.

[0039] (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 high performance requirements of materials in high-end fields such as aerospace, new energy, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 Flow chart of the method for quantitatively characterizing the shear sensitivity of a material according to the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0043] The present invention will be further explained below with reference to specific embodiments.

[0044] 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:

[0045] (1) First, the kinetic equation and energy equation for the evolution of the shear band of the material are established:

[0046] ;

[0047] In the above formula r is the density, is the shear strain rate, is the position of the rigid-plastic interface, 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 diffusivity, a is the shear band width, d is the differential operator and is not explained, t is the time, and c is the specific heat;

[0048] (2) Coordination equations combined with the rigid region of the material , and obtain the kinetic solution:

[0049] ;

[0050] in is the critical slip at the shear zone boundary;

[0051] (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:

[0052] ;

[0053] (4) Set the temperature i Substituting into the energy equation and integrating over the entire time domain, we obtain:

[0054] ;

[0055] in It is critical time;

[0056] (5) Definition of dissipated energy , we can obtain the implicit relationship between the shear band evolution dissipation energy and the shear band width:

[0057] ;

[0058] (6) Obtain critical dissipated energy according to the minimum energy principle:

[0059] ;

[0060] 7) Based on fracture toughness, combined with shear modulus G The following expression for shear band toughness is given to quantitatively characterize shear sensitivity:

[0061] .

[0062] 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 coefficientα ; 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.

[0063] The following is further explained using copper and 304 stainless steel as materials.

[0064] copper:

[0065] 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 390 J / kg K, shear yield strength is 60 MPa, and thermal softening coefficient is 7.47×10 -4 K -1 .

[0066] 304 stainless steel:

[0067] The shear modulus is 190 GPa and the density is 7.8 g / 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 477 J / kg K, shear yield strength is 200 MPa, and thermal softening coefficient is 5.9×10 -4 K -1 .

[0068] The loading strain rate was set to 5×10 3 s -1 , the calculated shear band toughness of copper is 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 is more likely to produce shear bands in actual engineering.

[0069] 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 in a low-cost, efficient and accurate manner.

[0070] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 and energy relationships of shear band evolution: ； In the above formula ρ is the density, is the shear strain rate, is the position of the rigid-plastic interface, 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 diffusivity, a is the shear band width, d is the differential operator and is not explained, t is the time, and c is the specific heat; (2) Obtain the dynamic results of shear band evolution of materials based on dynamic and energy relationships; (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, wherein: The specific process of obtaining the dynamic results of the material shear band evolution in step (2) is as follows: Assuming the stress in the shear band The linear softening law with boundary slip is: ； Compatibility equations combining rigid regions of materials , the kinetic solution is obtained as: ； in is the critical slip at the shear zone boundary; Assuming linear thermal softening of the material ,in α is the thermal softening coefficient. Combining the kinetic solution and the linear softening law of boundary slip, 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, wherein: The solution process of the shear band evolution dissipated energy in step (3) is: The temperature θ Substituting the energy relationship in step (1) 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: 。 4. The method for characterizing the shear sensitivity of a material according to claim 1, 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: 。

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