Resistance Performance of Grooved Metal Target Subjected to Projectile Impact

TONG Zong-Bao WANG Jin-Xiang LIANG Li QIAN Ji-Sheng TANG Kui

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Resistance Performance of Grooved Metal Target Subjected to Projectile Impact

    作者简介: TONG Zong-Bao(1988—), male, assistant engineer, major in warhead design.E-mail:asnyxun@163.com;
    通讯作者: WANG Jin-Xiang, wjx@njust.edu.cn
  • 基金项目: National Natural Science Foundation of China 11672138
    Foundation of Science and Technology on Transient Physics Laboratory 9140C300405150C30005
    National Natural Science Foundation of China 11272158

  • 中图分类号: O385

Resistance Performance of Grooved Metal Target Subjected to Projectile Impact

    Author Bio: TONG Zong-Bao(1988—), male, assistant engineer, major in warhead design.E-mail:asnyxun@163.com;
    Corresponding author: WANG Jin-Xiang, wjx@njust.edu.cn ;
  • Fund Project: National Natural Science Foundation of China 11672138Foundation of Science and Technology on Transient Physics Laboratory 9140C300405150C30005National Natural Science Foundation of China 11272158

    CLC number: O385

  • 摘要: 采用弹道实验和数值模拟的方法研究了带环形预裂槽的金属靶在射弹冲击下的毁伤模式和防护性能,分析了弹头形状、预裂槽直径及深度等因素对靶板防护性能的影响。结果表明:对带有环形预裂槽的金属靶板,存在两种主要毁伤模式,即环形槽内部的侵彻和环形槽底的冲击断裂;临界毁伤速度与毁伤模式密切相关,随着环形槽深度的增大或半径的变小,临界毁伤速度变小;与尖头弹相比,平头弹的临界毁伤速度更小;微观分析表明,在射弹冲击作用下,环形槽底部产生绝热剪切带,更容易形成充塞剪切破坏。
  • Figure 1.  Schematics of tandem warhead and target

    Figure 2.  Schematic and photo of experimental setup

    Figure 3.  Projectile size and grooved steel target

    Figure 4.  FEM calculation model(1/2)

    Figure 5.  Comparison of experimental and numerical results

    Figure 6.  Results of numerical simulation about CDV under different conditions

    Figure 7.  Typical experimental results of targets for different incidence velocities of projectile

    Figure 8.  Typical damage modes of pre-split targets (experimental results)

    Figure 9.  Numerical simulation of stress distribution

    Figure 10.  Microstructure analysis of damage zone near plug edge

    Table 1.  Various experimental conditions

    Projectile D/(mm) L/(mm) Projectile D/(mm) L/(mm)
    Oval projectile 15 4.0
    5.5
    7.0
    Oval projectile 30 4.0
    5.5
    7.0
    20 4.0
    5.5
    7.0
    Flat nose projectile 20 4.0
    5.5
    7.0
    下载: 导出CSV

    Table 2.  Material model parameters of projectile (304L steel) and target (45 steel)[16-17]

    Material A/
    (MPa)
    B/
    (MPa)
    N C M D1 D2 D3 D4 D5
    304L steel 792 510 0.260 0.014 1.03 -0.8 2.10 -0.50 0.002 0.61
    45 steel 507 320 0.064 0.280 1.06 0.1 0.76 1.57 0.085 -0.84
    下载: 导出CSV

    Table 3.  Equation of state parameters of projectile (304L steel) and target (45 steel)[16-17]

    Material ρ0/(g/cm3) S1/(MPa) S2/(MPa) S3/(MPa) γ0 a
    304L steel 7.83 164 294 500 1.16 0.46
    45 steel 7.81 153 271 483 1.12 0.44
    下载: 导出CSV

    Table 4.  Numerical simulation results of damage modes and CDV

    Projectile D/(mm) L/(mm) v0/(m/s) Damage mode
    Oval projectile 0 624 Penetrate
    15 4.0
    5.5
    7.0
    438
    352
    225
    Penetrate
    Penetrate
    Fracture
    20 4.0
    5.5
    7.0
    516
    409
    288
    Penetrate
    Fracture
    Fracture
    30 4.0
    5.5
    7.0
    543
    502
    356
    Penetrate
    Penetrate
    Fracture
    Flat nose projectile 20 4.0
    5.5
    7.0
    386
    377
    358
    Penetrate
    Fracture
    Fracture
    下载: 导出CSV

    Table 5.  Experimental results

    Projectile D/(mm) L/(mm) Mass/(g) v/(m/s) Damage model
    Oval projectile 15 4.0
    5.5
    5.5
    7.0
    7.0
    9.65
    9.65
    9.65
    9.65
    9.65
    396.0
    378.0
    305.0
    260.0
    174.5
    No penetrate
    Fracture
    No fracture
    Fracture
    No fracture
    20 4.0
    4.0
    5.5
    5.5
    9.65
    9.65
    9.65
    9.65
    390.6
    535.0
    523.0
    341.0
    No penetrate
    Penetrate
    Fracture
    No fracture
    30 4.0
    4.0
    5.5
    7.0
    7.0
    9.65
    9.65
    9.65
    9.65
    9.65
    558.0
    471.7
    492.0
    341.0
    374.0
    Penetrate
    No penetrate
    Penetrate
    No fracture
    Critical fracture
    Flat nose projectile 20 4.0
    5.5
    7.0
    7.81
    7.81
    7.81
    374.0
    375.0
    363.0
    No fracture
    Critical fracture
    Fracture
    下载: 导出CSV
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  • 收稿日期:  2016-04-26
  • 录用日期:  2016-06-28
  • 刊出日期:  2017-04-25

Resistance Performance of Grooved Metal Target Subjected to Projectile Impact

    作者简介:TONG Zong-Bao(1988—), male, assistant engineer, major in warhead design.E-mail:asnyxun@163.com
    通讯作者: WANG Jin-Xiang, wjx@njust.edu.cn
  • 1. Science and Technology on Transient Physics Laboratory, Nanjing University of Science and Technology, Nanjing 210094, China
  • 2. Jiangnan Industries Group Co.LTD, Xiangtan 411207, China
  • 3. Jinxi Industries Group Co.LTD, Taiyuan 030027, China
基金项目:  National Natural Science Foundation of China 11672138Foundation of Science and Technology on Transient Physics Laboratory 9140C300405150C30005National Natural Science Foundation of China 11272158

摘要: 采用弹道实验和数值模拟的方法研究了带环形预裂槽的金属靶在射弹冲击下的毁伤模式和防护性能,分析了弹头形状、预裂槽直径及深度等因素对靶板防护性能的影响。结果表明:对带有环形预裂槽的金属靶板,存在两种主要毁伤模式,即环形槽内部的侵彻和环形槽底的冲击断裂;临界毁伤速度与毁伤模式密切相关,随着环形槽深度的增大或半径的变小,临界毁伤速度变小;与尖头弹相比,平头弹的临界毁伤速度更小;微观分析表明,在射弹冲击作用下,环形槽底部产生绝热剪切带,更容易形成充塞剪切破坏。

English Abstract

    • The failure models of the metal plate during projectile penetration have been a concern of researchers.The steel plate with high hardness is not easy to appear plastic deformation under penetration.With the increase of strength and hardness of the metal target, the kinetic energy of the projectile is easier to be concentrated in one part of the plate, forming a shear plug[1-4].Generally the microscopic failure models of the metal target are micro cracks, micro holes and adiabatic shear band (ASB) which are the precursors of the material damage.About ASB, a lot of research has been done on its formation mechanism, development process and relationship with the micro cracks.Zhang et al.[5] studied the microstructure evolution process of 2519A-T87 aluminum alloy during projectile penetration.Balakrishnan et al.[6] analyzed the microstructure of welded armor steel joints after ballistic tests.Duan et al.[7] studied the microstructure and ASB formed by ballistic impact in steels and tungsten alloys.Zou et al.[8] analyzed the characterization of ASB in AM60B magnesium alloy under ballistic impact.Atapek et al.[9] discussed the ballistic impact behavior of tempered bainitic steel against 7.62 mm armor piercing projectile.Hu et al.[10] analyzed the ballistic performance and microstructure of modified rolled homogeneous armor steel.Sastry et al.[11] studied the ballistic impact of the composite panels.The above researches mainly focus on the intact metal target and the formation of ASB caused by strain hardening[12-15].

      In this research, the resistance performance of the grooved metal target was studied.As shown in Fig. 1(a), a tandem warhead was composed by a following projectile right behind a shaped charge circulus.The circular jet formed by the shaped charge circulus will pre-cut the metal target and the circular groove will form on the target, and then the following projectile will impact on the target within the groove, as shown in Fig. 1(b).Ballistic experiments and numerical simulation by the finite element method (FEM) code LS-DYNA 2D were adopted to analyze the damage mechanism and the resistance performance of the pre-cut metal target.Because the depth and the diameter of the groove will be affected by the circular shaped charge jet, 9 kinds of grooves with different depths and diameters were considered in this study.Also, our emphasis is on the impact of the projectile on the grooved target, so the influence of the shaped charge on the following projectile was ignored in this study.The microstructure near the failure area was examined to analyze the damage mechanism of the target.The effect of the groove diameter and depth as well as the projectile nose shape on the resistance performance and failure modes were also discussed.Our research results will be helpful for the design of the tandem warhead composed by shaped charge circulus and a following projectile.

      Figure 1.  Schematics of tandem warhead and target

    • The projectile with an oval nose shape was launched by a 7.62 mm slip chamber gun.To analyze the effect of projectile nose shape, a 14.5 mm slip chamber gun was adopted to launch the flat nose projectile.The incidence velocity of the projectile was controlled between 300-600 m/s by adjusting the charge weight.Two groups of light meshes test equipments in front and back of the target were used to measure the incidence and residual velocities of the projectile respectively, and sabots after penetrating the target were caught by a sabot catcher.Schematic and photo of the experimental setup are shown in Fig. 2.

      Figure 2.  Schematic and photo of experimental setup

    • The projectiles adopted in the experiment are standard oval bullets and flat nose projectiles with the diameters of 7.62 and 8.00 mm respectively.The material of the target is 45 steel and the thickness is 8 mm.The annular groove diameters D is 15, 20 and 30 mm, respectively.The depths of the annular groove L is 4.0, 5.5 and 7.0 mm, respectively.The width of the groove d=2 mm and the thickness of the target H=8 mm.The projectile size and pre-cut target are shown in Fig. 3.

      Figure 3.  Projectile size and grooved steel target

    • To analyze the influence of the projectile nose shape, the diameter and depth of the groove on the damage modes and resistance performance of the grooved target, ballistic experiments were carried out for different conditions.The projectile initial velocity was controlled by adjusting the charge weight.Various experimental conditions are shown in Table 1.

      Projectile D/(mm) L/(mm) Projectile D/(mm) L/(mm)
      Oval projectile 15 4.0
      5.5
      7.0
      Oval projectile 30 4.0
      5.5
      7.0
      20 4.0
      5.5
      7.0
      Flat nose projectile 20 4.0
      5.5
      7.0

      Table 1.  Various experimental conditions

    • In order to make up for the deficiency of the experiment data and analyze the stress change of the pre-split annular groove impacted by projectiles, Fig. 4 FEM calculation model (1/2)LS-DYNA finite element code was adopted to simulate the impact process of the annular grooved target in comparison with the intact target.The size of the projectile was a higher order small value compared with that of the target, so the non-reflection boundary constraints were applied to target edges and the target was considered as an infinite domain.

      Figure 4.  FEM calculation model(1/2)

      As shown in Fig. 4, a two-dimensional half model is established.The projectile and target were meshed with 2D Solid 162 elements and the Lagrange algorithm was adopted.The Contact_2D_Automatic_Single_Suface contact algorithm was used to describe the interaction of the projectile and the target.

    • During the impact process, the stress state of materials was complex, so the equivalent stress σe was used to describe the multi-axial stress state, defined in terms of the equivalent plastic strain εe, equivalent plastic strain rate ${\mathit{\dot \varepsilon }_{\rm{e}}}$, and temperature T as

      $ {\mathit{\sigma }_{\rm{e}}} = f\left( {{\mathit{\varepsilon }_{\rm{e}}}, {{\mathit{\dot \varepsilon }}_{\rm{e}}}, T} \right) $

      The Johnson-Cook constitutive relation was adopted to describe the deformation and failure of both the projectile and the target here for it can reflect the effects of strain, strain rate and temperature

      ${\sigma _{\rm{e}}} = \left[ {A + B{{\left( {\sigma _{\rm{e}}^{\rm{p}}} \right)}^N}} \right]\left( {1 + C\ln \dot \varepsilon *} \right)\left[ {1 - {{\left( {{T^*}{\rm{\;\;}}} \right)}^M}} \right] $

      where σep is the effective plastic stress; ${\mathit{\dot \varepsilon }^*} = \mathit{\dot \varepsilon }_{\rm{e}}^{\rm{p}}/{\mathit{\dot \varepsilon }_{\rm{0}}}$ is the effective plastic strain rate for ${\mathit{\dot \varepsilon }_{\rm{0}}}$=1 s-1; T* is the homologous temperature, T*=(T-Tr)/(TmTr), where Tr is the room temperature and Tm the melting temperature; A, B, N, C and M are material constants.

      The Grüneisen equation of state with the cubic us (shock wave velocity)-up (particle velocity) curve defines the pressure p for the compressed materials as the following

      $ \mathit{p = }\frac{{{\mathit{\rho }_{\rm{0}}}{c^2}\;\mathit{\mu }\left[ {1 + \left( {1 - \frac{{{\mathit{\gamma }_{\rm{0}}}}}{2}} \right)\mathit{\mu } - \frac{{a{\mathit{\mu }^2}}}{2}} \right]}}{{{{\left[ {1 - \left( {{S_{\rm{1}}} - 1} \right)\mathit{\mu } - {\mathit{S}_{\rm{2}}}\frac{{{\mathit{\mu }^2}}}{{\mathit{\mu + }{\rm{1}}}} - {S_{\rm{3}}}\frac{{{\mathit{\mu }^{\rm{3}}}}}{{{{\left( {\mathit{\mu + }{\rm{1}}} \right)}^2}}}} \right]}^2}}} + \left( {{\mathit{\gamma }_{\rm{0}}} + a\mathit{\mu }} \right)E \mathit{p} = \\ \frac{{{\mathit{\rho }_{\rm{0}}}{c^2}\;\mathit{\mu }\left[ {1 + \left( {1 - \frac{{{\mathit{\gamma }_{\rm{0}}}}}{2}} \right)\mathit{\mu } - \frac{{a{\mathit{\mu }^2}}}{2}} \right]}}{{{{\left[ {1 - \left( {{S_{\rm{1}}} - 1} \right)\mathit{\mu } - {\mathit{S}_{\rm{2}}}\frac{{{\mathit{\mu }^2}}}{{\mathit{\mu + }{\rm{1}}}} - {S_{\rm{3}}}\frac{{{\mathit{\mu }^{\rm{3}}}}}{{{{\left( {\mathit{\mu + }{\rm{1}}} \right)}^2}}}} \right]}^2}}} + \left( {{\mathit{\gamma }_{\rm{0}}} + a\mathit{\mu }} \right)E $

      where c is the intercept of the us-up curve; γ0 is the Grüneisen coefficient; a is the first order volume correction to γ0; S1, S2 and S3 are the coefficients of the slope of the us-up curve; μ=ρ/ρ0-1 is the change rate of volume; ρ0 is the initial density; E is the internal energy.

      Fracture of materials in the Johnson-Cook constitutive relation occurs according to the following cumulative damage law

      ${\varepsilon _{\rm{f}}} = \left[ {{D_1} + {D_2}\exp \left( {{D_3}{\sigma ^*}{\rm{\;}}} \right)} \right]\left( {1 + {D_4}{{\dot \varepsilon }^*}{\rm{\;}}} \right)\left( {1 + {D_5}{T^*}{\rm{\;}}} \right) $

      where D1, D2, D3, D4 and D5 are material constants; σ*=p/σe, p and σe is the mean stress and von Mises equivalent stress, respectively.

      The failure criterion is based on damage evolution, where the damage parameter D of a material element is defined as

      $D = \sum {\Delta \mathit{\varepsilon }/{\mathit{\varepsilon }_{\rm{f}}}} $

      where Δε is the increment of effective plastic strain.Materials parameters used in the numerical simulation are shown in Table 2 and Table 3.

      Material A/
      (MPa)
      B/
      (MPa)
      N C M D1 D2 D3 D4 D5
      304L steel 792 510 0.260 0.014 1.03 -0.8 2.10 -0.50 0.002 0.61
      45 steel 507 320 0.064 0.280 1.06 0.1 0.76 1.57 0.085 -0.84

      Table 2.  Material model parameters of projectile (304L steel) and target (45 steel)[16-17]

      Material ρ0/(g/cm3) S1/(MPa) S2/(MPa) S3/(MPa) γ0 a
      304L steel 7.83 164 294 500 1.16 0.46
      45 steel 7.81 153 271 483 1.12 0.44

      Table 3.  Equation of state parameters of projectile (304L steel) and target (45 steel)[16-17]

    • The experimental and numerical results show that there mainly exist two kinds of damage modes of the grooved targets, the penetration of the inner part of the target groove and the fracture of the bottom of the groove.Generally, the two kinds of damage modes occur simultaneously.Here we define the lower incidence velocity at which one of the damage modes occurs as the critical damage velocity (CDV) v0.By "up-down" method, the CDV could be identified by experimental and numerical results.

    • The annular grooved target with the diameter of 20 mm and depth of 5.5 mm impacted by a standard oval nose projectile with the incidence velocity of 523 m/s was taken as an example to analyze the effectiveness of the numerical simulation.The results of the numerical simulation and experiments are shown in Fig. 5.It can be found that the projectile embeds into the target and the plug is formed.The results of the numerical simulation accord well with the experimental results.

      Figure 5.  Comparison of experimental and numerical results

    • To study the influence of the pre-split groove on the damage modes and resistance performance of the target, the impact process of the projectile on pre-split annular groove targets and the intact target were studied numerically.The results were shown in Table 4 and Fig. 6.It can be found that with the same projectile nose shape, the CDV of the annular grooved target is lower than that of the intact target, indicating that the grooved target is easier to be damaged by the penetration of projectiles.

      Figure 6.  Results of numerical simulation about CDV under different conditions

      Projectile D/(mm) L/(mm) v0/(m/s) Damage mode
      Oval projectile 0 624 Penetrate
      15 4.0
      5.5
      7.0
      438
      352
      225
      Penetrate
      Penetrate
      Fracture
      20 4.0
      5.5
      7.0
      516
      409
      288
      Penetrate
      Fracture
      Fracture
      30 4.0
      5.5
      7.0
      543
      502
      356
      Penetrate
      Penetrate
      Fracture
      Flat nose projectile 20 4.0
      5.5
      7.0
      386
      377
      358
      Penetrate
      Fracture
      Fracture

      Table 4.  Numerical simulation results of damage modes and CDV

    • The ballistic experiments of the metal target with an annular groove were carried out.The experimental results are shown in Table 5 and the typical experimental results of the targets for different incidence velocities (v) of the projectile are shown in Fig. 7.According to Table 4, Table 5, Fig. 6 and Fig. 7, it can be seen that with the same projectile and groove depth, the CDV increases with the diameter of the groove.It is because that the larger the annular groove diameter, the closer the target is to the intact target, and the greater the consumption of the projectile kinetic energy.From Table 4, Table 5, Fig. 6 and Fig. 7 it can also be found that with the same projectile and annular groove diameter, the CDV decreases as the groove depth increases.The reason is that for the deeper groove the plug is easier to be formed and the consumption of the projectile kinetic energy is smaller.

      Figure 7.  Typical experimental results of targets for different incidence velocities of projectile

      Projectile D/(mm) L/(mm) Mass/(g) v/(m/s) Damage model
      Oval projectile 15 4.0
      5.5
      5.5
      7.0
      7.0
      9.65
      9.65
      9.65
      9.65
      9.65
      396.0
      378.0
      305.0
      260.0
      174.5
      No penetrate
      Fracture
      No fracture
      Fracture
      No fracture
      20 4.0
      4.0
      5.5
      5.5
      9.65
      9.65
      9.65
      9.65
      390.6
      535.0
      523.0
      341.0
      No penetrate
      Penetrate
      Fracture
      No fracture
      30 4.0
      4.0
      5.5
      7.0
      7.0
      9.65
      9.65
      9.65
      9.65
      9.65
      558.0
      471.7
      492.0
      341.0
      374.0
      Penetrate
      No penetrate
      Penetrate
      No fracture
      Critical fracture
      Flat nose projectile 20 4.0
      5.5
      7.0
      7.81
      7.81
      7.81
      374.0
      375.0
      363.0
      No fracture
      Critical fracture
      Fracture

      Table 5.  Experimental results

    • To study the influence of the projectile nose shape on the damage modes of the target, the standard oval projectile and flat nose projectile were adopted in the ballistic experiments.The nonparallelism of the projectile front face with the target surface was neglected in the following analysis because its influence was proved small by experiments.With the annular groove diameter D=20 mm and the groove depth L=5.5 mm, the plug will form for both the flat nose projectile and the oval projectile.The CDV of the target is lower for the flat nose projectile (377 m/s) than that of the oval projectile (409 m/s).This is because part of the kinetic energy of the oval projectile is consumed by penetrating into the target and the other consumed by the adiabatic shear during the formation of the plug.While for the flat nose projectile, almost all of the kinetic energy is consumed by the formation of the plug.

    • The typical damage effects of the target impacted by the projectile with different incidence velocities (v) are shown in Fig. 8, which exhibits typical damage modes of the annular grooved steel target impacted by oval and flat nose projectiles, respectively.Two failure modes can be found from Fig. 8 as the objective influence of elliptic parabolic, one being the internal part of the infiltration of the tank and the other the fracture along the bottom of the annular groove.With the decrease of the diameter and increase of the depth of the annular groove, the annular groove is easier to fracture and form the plug.This is because during the impact of the projectile on the target, the stress concentration mainly exists at two points, one is the interface of the projectile and target which will lead to the large deformation of the target and projectile during penetration, and the other is the bottom along the annular groove which may cause the formation of the plug.The typical stress distribution during the impact of the projectile on the annular grooved target are shown in Fig. 9, from which it can also be found that the typical damage modes of the target are in good agreement with the experimental results.The influence of the depth as well as the diameter of the groove on the damage modes also accords well with the experimental results.

      Figure 8.  Typical damage modes of pre-split targets (experimental results)

      Figure 9.  Numerical simulation of stress distribution

      As shown in Fig. 8(d), for the projectile with a flat nose shape, there also exist two kinds of energy consumption mentioned above.The difference here is that more energy will be transferred to the annular groove and the plug of the whole pre-cut block is easier to form because it is more difficult for the projectile with a flat nose to penetrate the target.

    • The target with a pre-split annular groove (D=20 mm, L=4.0 mm) impacted by the oval projectile at the velocity of 535 m/s was taken as an example to be cut along the axis to analyze the microstructure.We used 5% nitric acid alcohol (5% HNO3+95% CH3CH2OH) to corrode the metal interface after the mechanical polishing and observed the morphology of the adiabatic shear band (ASB) by stereo microscope.Then we observed the organizational structure of ASB by the metallographic microscope and examined the internal micro characteristics of ASB by scanning electron microscope (SEM).

      Fig. 10(a) shows the morphology of ASB found by stereo microscope and Fig. 10(b) shows the organizational structure near ASB observed by metallographic microscope and obvious organizational deformation can be found.Fig. 10(c) gives the 800 times magnified micro structure of ASB observed by SEM and Fig. 10(d) shows the 3 200 times magnified micro structure of ASB, from which it can be found that the width of ASB is about 4.5 μm and its angle to the penetration direction is about 45°.

      Figure 10.  Microstructure analysis of damage zone near plug edge

      The internal strain of the ASB was large and nonuniform, which can easily cause the micro cracks and micro holes.As shown in Fig. 10(d), the micro cracks were formed inside ASB.When the micro cracks inside ASB are mutually joined or connected to the cracks, ASB becomes the connection between the cracks inside the material.The micro cracks grow and expand gradually and eventually become large cracks along the entire ASB, which will lead to the formation of the plug damage.

    • (1) The pre-cut target was more likely to be damaged than the intact target.With the same projectile nose shape, the CDV of the annular grooved target is lower than that of the intact target.According to the numerical results, when the projectile nose shape is oval and the annular groove diameter D=15 mm, depth L=4.0, 5.5, 7.0 mm, the CDV of the grooved targets decreased by 29.81%, 43.59% and 63.94% respectively compared to that of the intact target.When D=20 mm, L=4.0, 5.5, 7.0 mm, the CDV of the grooved targets decreased by 17.31%, 34.46% and 53.85% respectively compared to that of the intact target.When D=30 mm, L=4.0, 5.5, 7.0 mm, the CDV of the grooved targets decreased by 12.98%, 19.55% and 42.95% respectively compared to that of the intact target.Similarly, for the flat nose shaped projectile with the annular groove diameter of 20 mm and depth of 5.5 mm, the CDV decreased by 47.26% compared to the intact target.

      (2) The CDV is closely related to the damage modes of the target.Generally, there mainly exist two kinds of damage modes for the annular grooved target, one being the penetration of the inner part of the groove and the other the fracture along the bottom of the annular groove.With the decreasing of the diameter and increasing of the depth of the annular groove, the annular groove is easier to fracture and the plug is easier to be formed.Accordingly, the CDV increases for the target with a groove of larger diameter and smaller depth.As to the influence of the projectile nose shape, the CDV of the target is smaller for the flat nose projectile than the oval nose projectile.

      (3) The microscopic analysis of the annular grooved target gives the reason of the plug formation.When ASB is formed inside of the target, the plug is easier to be formed, and the target is easier to be damaged.

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