Proceedings of the ACMFMS 2012

Third Asian Conference on MECHANICS OF FUNCTIONAL MATERIALS AND STRUCTURES

December 5-8, 2012, IIT Delhi, INDIA [ISBN 978-81-8487-248-4]

Impact of Double Nose Blunt Projectile on Ductile Target

S.H. Khan1, M. Azeem

2 and R. Ansari

3

Department of Mechanical Eng. Aligarh Muslim University, Aligarh, 202002, India

In this study dual-nose projectile was prepared by two blunt noses along the length of projectile and

then made to impact on aluminium plates of 0.82 mm thickness to observe its deformation behavior. The

diameter of first blunt nose was 6.4 mm while second blunt nose was on the shank of the projectile having

12.8 mm diameter. Impact on target plate by double nose projectile was made by gas gun experimentally

and then verified numerically on Abaqus FEM code. Mesh convergence study was done to choose the

correct elements size in the impact area. It was observed that blunt-blunt projectile perforates the target by

producing one plug and one ring while speed of the first plug was higher than the speed of the projectile.

Blunt-blunt projectile takes more time to perforate the target than single blunt projectile. Experimental

and numerical value agrees to each other.

Keywords: blunt-blunt projectile, Abaqus, plugging

1 Introduction

Nose shape of the projectile decides the perforation

mechanism of the target. Perforation by different nose

projectile has been studied by various people in the past

decade [1-3]. They all emphasized that the failure

mechanism leading to the final perforation of a target

could be ductile hole enlargement with petaling for a

sharp nose while plugging or adiabatic shearing for a

blunt nose projectile. For blunt nose projectile,

Awerbuch [4] divided the penetration of a target into

two stages. In the first stage, only inertia and

compressive forces are introduced to decelerate the

effective mass of the projectile while the second stage is

initiated when a shear plug of the target material is

formed, during which the compressive resistance is

replaced by the surrounding shear force. Kane et al. [5]

studied the mesh sensitivity issues during perforation

and penetration of blunt nose projectiles on steel targets.

In this study attempt is being made to model the

projectile which contains two blunt noses along its

length. Then comparison is made between the single

and double nose projectile by keeping their mass and

shank diameter same and impacting them on aluminium

targets 0.82 mm thin. Experiments and numerical

simulation is carried out to observe the effect of dual

nose of this projectile.

2 Experimental and Numerical Execution

Aluminium 1100-H14 is used as a target plate while

EN-31 alloy steel with density as dual

nose and single nose blunt projectiles. Circular plates of

255 mm diameter were cut out from these Al sheets in

which 8 holes of ø 7.93 mm at p.c.d of 230 mm were

drilled in each specimen for fixing it rigidly to a fixture.

The material properties of Al 1100-H14 such as density

( ), modulus of elasticity ( ), engineering ultimate stress

poison’s ratio ( ) were obtained

from the uniaxial tensile tests carried out on standard

test specimen prepared as per ANSI I ASTM-B557M as

shown in Fig 1 (a). These specimens were cut from

rolling and transverse direction of the sheets, however

no sign of anisotropy was observed in them. Fig 2

shows the engineering stress-strain response of the

material obtained during the test.

Figure 1: Line diagram of (a) test specimen (b)

fractured specimen, after the tensile test.

0

50

100

150

0.000 0.005 0.010

Str

ess (

MP

a)

Strain

stress-strain curve

0.2 % offset

Figure 2: Engineering stress-strain response for the

fractured specimen

1 Research Scholar, shkhan@iitk.ac.in

2Assistant Professor, er.azeem@gmail.com

3 Professor, ruansari@rediffmail.com

While for the projectile a circular rod is cut off and its

temperature is raised to 920°C. Then, it was oil

quenched at this temperature. The material was tested

on hardener tester and found 64-65 RHN. Then

tempering is done and hardness value is reduced to 47-

50 RHN to minimize plastic deformation during impact.

Finally, the material is shaped as shown in Fig 3(a)

blunt-blunt nose (double nose) and 3(b) as blunt nose.

Both the projectiles were so designed that their mass

and diameter remains same. To do this, projectiles

diameter was kept 12.8 mm (corresponding to the 13

mm barrel diameter) and total volume of both

projectiles was kept constant by altering their shank

length which produces mass of 29.7g for both

projectiles. Experiments were performed by gas gun and

its details can be found in [6].

Figure 3: Line sketch of (a) Blunt-Blunt nose (b) Blunt-

nose projectiles

2.2 Numerical Investigation

Abaqus Explicit is used to perform the numerical

simulation of the problem. Projectiles were constructed

as analytical rigid while target as deformable body with

impact zone at center. Surface to surface contact was

assigned between projectile and plate by the kinematic

contact algorithm [8] while the plate was curtailed at its

periphery with respect to all degree of freedom by using

encastre boundary condition [9] of the code.

Meshing of target is done by maintaining aspect ratio

of elements close to unity in the impact zone and

varying elements along the thickness from 2 to 8. Mesh

convergence study was also carried out as shown in Fig

5 by taking number of elements along the thickness

direction. It was observed that close to 6th

element with

mesh size (0.13 0.13 0.13) mm3

the residual velocity

(36.11m/s) is closest to experimental value based on

computational feasibility. Thus 6 elements were chosen

which has generated 59052 elements in the impact zone

and 373996 elements for the whole target plate.

Figure 4: Section view of the mesh at impact zone

Figure 5: Mesh convergence study

2.3 Material Modeling

Johnson-Cook (J-C) model is used to capture the

impact behavior of the projectile by using flow surface

as [10]

[ ][ ][ ] (1)

Where A, B, C, n and m are constants and is non-

dimensional temperature. And failure strain at the onset

of damage [11]

[ ][ ][

](2)

Where D1-D5 are damage parameters.

To reduce mesh dependency upon the results

damage evolution is used based on Hillerborg's [12]

fracture energy proposal which creates a stress-

displacement response. He defines the energy required

to open a unit area of crack, as a material parameter.

(3)

Before damage initiation, however, after

damage initiation i.e. damage evolution,

where L is the characteristic length of the element

The Johnson cook hardening parameters has been calculated from the data of the

tensile test discussed in section 2.1 as done by Gupta et

al [13]. Parameter, and

effective plastic strain were taken from

Vermint Al’s [14] website corresponding to aluminum

alloy 1100-H14. While all others parameters given in

Table 1, including Johnson-Cook damage parameters

were assumed equivalent to those of Al 1100-

H12 used by Gupta et al. [10].

3. Results

It was observed from the experimental and numerical

work that the deformation by Blunt-Blunt projectile was

in the form of two different plugs and dishing in the rest

part of the plate. The first plug was created due to the

initial indentation of the “first blunt part” of the

projectile by the process of shear plugging. The second

plug (ring) was created by the collar of the “second

blunt part” of the same projectile and by the same

phenomenon. The first indentation of the projectile

propagates the forward movement of the material.

9.43

19.45

27.47

32.88 36.11 36.61 36.69

0

10

20

30

40

0 2 4 6 8 10

Resid

ual V

elo

city (

m/s

)

Number of elements along the thickness(n)

Experimental Vr ( 37.61 m/s)

Numerical Convergence

Table 1: Material parameters used for numerical

simulation of the problem

Modulus of elasticity, E (GPa) 68.948 Poison’s ratio, ν 0.33 Density, (kg/m

3 ) 2712.6

Yield stress, A (MPa) 102.82 Hardening constant, B (MPa) 49.79 Strain hardening constant, n 0.197 Strain rate sensitivity, C 0.001 Reference strain rate, ( ) 1 Temperature sensitivity, m 0.859 Melting temperature (k) 893 Transition temperature, (k) 293 Specific heat, (J/kg-K) 920

Inelastic heat fraction, 0.9 Thermal conductivity, k (W/m-°C) 222

D1 0.071

D2 1.248 D3 -1.142 D4 0.147 D5 0

Effective plastic strain,

Fracture Energy, (KJ) 5.7

(yielding) in front of the tip of the projectile in the

impact zone Also the “red color zone” shows the

maximum stress concentration and contour of failure for

the material. The diameter of the first plug is equal to

the diameter of the nose of the projectile (first blunt

part), while the second plug is in the form of ring having

two diameters. The inside diameter is equal to the nose

diameter of the projectile while the outside diameter is

equal to the diameter of the projectile itself. The speed

of the first plug was found higher than the speed of the

projectile. This is depicted while performing numerical

simulations. This may be due to the reason that the blunt

nose of the projectile is like an impulsive force on the

plate, which after the ejection of plug, pushes it in

forward direction. For the case of second plug or ring,

there wasn’t any speed found in the plug, as it may have

hooked up around the nose of the projectile.

Table 2: Comparison of the experimental and numerical

results in terms of residual velocity (Vr), maximum

deformation (Dmax) and Absorbed energy (Eab) against

impact velocities (Vi).

Specimen no.

Vi

(m/s)

Experimental Numerical

Vr

(m/s)

Dmax

(mm)

Eab

(J)

Vr

(m/s)

Dmax

(mm)

Eab

(J)

BB-A52 34.85/37.4 0 - 18.04 0 - 20.77

BB-A45 55.79 38.23 10.6 24.52 37.61 9.9 25.21

BB-A38 71.4 59.62 10.3 22.92 58.1 9.6 25.58 BB-A2-11 86.2 77.1 10.1 22.07 75.72 9.1 25.20

BB-A719 103.6 97.95 9.7 16.91 96.54 8.3 20.98

B-10 33.2/34.5 0 - 16.37 0 - 17.67 B-12 42.21 26.19 9.3 15.70 23.76 9.7 18.07

B-16 65.75 57.19 8.1 15.63 54.23 8.6 20.52

B-19 83.31 77.35 7.4 14.22 74.46 7.9 20.73 B-22 104.2 101.02 6.6 9.69 98.67 7.1 16.66

BB-for blunt-blunt projectile, B-for blunt projectile

While performing experiments also, this effect was

noticed as the recovered projectile (after perforation)

always caps itself with the “ejected ring” (or plug).

Table 2 shows the experimental and numerical data. The

experimental ballistic limit for blunt-blunt projectile

was 34.85 m/s and for blunt projectile were 33.2 m/s. In

the present study, ballistic limit is interpreted as the

maximum impact velocity at which zero residual

velocity is first encountered. Also, it was observed that

the maximum deformation (Dmax) decreases as the

impact velocity is increased for both the cases. However

blunt-blunt projectile produces larger deformation

throughout the increasing velocities. Fig 7 shows

increasing residual velocity with an increase in impact

velocity while Fig 8 depicts larger energy absorption for

blunt-blunt projectile. Fig 9 shows the time duration of

both the projectile while travelling through the target

plate. Blunt-blunt projectile takes larger time to

perforate the target due to its two blunt noses. When

projectile was propelled with 103.6 m/s velocity, the

first blunt nose eats up 2.31m/s while the second blunt

nose absorbs 4.75 m/s velocity, which is almost double.

4. Conclusion

Double nose blunt-blunt projectile has been prepared

and made to impact on 0.82 mm thin aluminium plate to

observe its ballistic strength and perforation mechanism.

Figure 6: (a-c) Shows the perforation mechanism of blunt-blunt projectile in Abaqus while (d) shows the experimental

view.

(a) (b) (c) (d)

Table 3: Evidences obtained during experimental and

numerical investigation.

Figure 7: Variation of residual velocity with increasing

impact velocity.

Figure 7: Variation of Absorbed energy with increasing

impact velocity.

Figure 9: Variation of residual velocity during

projectile perforation.

The perforation process produces 1 plug and 1 ring.

Speed of the first plug was found higher than projectile

itself and its diameter was same as nose diameter while

the ring does not experiences any speed and its outer

diameter was same as projectile shank diameter. Energy

absorbed and time taken during the perforation by the

double nose projectile was higher than single blunt nose

projectile.

References

[1] Corbett GG, Reid SR, Johnson W. Impact loading

of plates and shells by free-flying projectiles: a

review. Int. J Impact Eng. 1996; 18:141–230.

[2] Backman ME, Goldsmith W. The mechanics of

penetration of projectiles into targets. Int. J Eng.

Sci. 1978; 16: 1–99.

[3] Woodward RL. The interrelation of failure modes

observed in the penetration of metallic targets. Int.

J Impact Eng. 1984; 2:121–9.

[4] Awerbuch J. A mechanics approach to projectile

penetration. Israel J Tech. 1970; 8: 375–83.

[5] Kane A., Borvik T., Hopperstad OS. and Langseth

M. Finite Element Analysis of Plugging Failure in

Steel Plates Struck by Blunt Projectiles. J. Appl.

Mech. 2009;76, Issue5, 051302

http://dx.doi.org/10.1115/1.3129722

[6] Ansari R, Khan SH and Khan AH. Oblique impact

of cylindro-conical projectile on thin aluminum

plates CD Proceedings ICTACEM 2010, Dec 27-29

IIT Kharagpur, India 361-63.

[7] Khan SH. Impact of dual nose projectiles on thin

Aluminium plates: Experimental and Numerical

Study. M.Tech Thesis, Aligarh Muslim University

(AMU). 2011

[8] Iqbal M.A. Gupta G. Gupta N.K. 3D numerical

simulations of ductile targets subjected to oblique

impact by sharp nosed projectiles. Int. J. Solids and

Structure 2010; 47: 224-37

[9] Version 6.11 ABAQUS analysis user’s manual,

vol. 2; 2011

[10] Johnson GR., Cook WH. A constitutive model and

data for metals subjected to large strains, high strain

rates and high temperatures, Proceedings of the

Seventh International Symposium on Ballistics,

The Hague, The Netherlands, 1983 541-547.

[11] Johnson GR and Cook WH. Fracture

Characteristics of Three Metals Subjected to

Various Strain, Strain Rates, Temperatures and

Pressures. Eng. Fract. Mech. 1985, 21, 31-8.

[12] Hillerborg A, Modeer M, and Petersson PE.

Analysis of Crack Formation and Crack Growth in

Concrete by Means of Fracture Mechanics and

Finite Elements. Cem. and Conc. Research, 1976,

6, 773-82.

[13] Gupta NK, Iqbal MA, Sekhon GS. Effect of

projectile nose shape, impact velocity and target

thickness on deformation behavior of aluminum

plates. Int. J. Solids Struct. 2007 44, 3411–39.

[14] http://www.varmintal.com/aengr.htm

0

20

40

60

80

100

120

0 50 100 150

Vr

(m/s

)

Vi (m/s)

B-B (Exp.)B-B (Num.)B (Exp.)B (Num.)

0

5

10

15

20

25

30

0 50 100 150

Eab (

J)

Vi (m/s)

B-B (Exp.)

B (Exp.)

B-B (Num.)

B (Num.)

96

98

100

102

104

106

0 0.1 0.2 0.3

Vr

(m/s

)

Time (ms)

Blunt-Blunt (vi=103.6 m/s)

Blunt (vi=104.2 m/s)

Experimental Evidence Numerical evidence