Layer Configuration of Composite Armor

Sudeep Kumar Department of Mechanical Engineering

Moradabad Institute of TechnologyMoradabad, U.P., INDIA

S.S. SamantDepartment of Mechanical Engineering

G.B. Pant Engineering CollegePauri Garhwal, U.K., INDIA

ABSTRACTPresently, world is under the danger of terrorist attacks and wars. This problem is going to be very serious because advanced weapons (guns, bullet) have been developed by the scientists for the awesome attacks. So, protection of soldiers and army vehicle has become the subject of great concern. Armors are used for providing protection to soldiers and army vehicles in defence applications. Basically, weight is a major factor of selecting armor material. So, composites are used as material in latest armors due to their less density. In this work, ballistic performance of composite armors has been examined by using Ansys Autodyn in order to find out an excellent configuration of composite armor in terms of layer. Keywords: Mass reduction, Striking velocity, Residual velocity, Layer configuration and Ballistic resistance.

1. INTRODUCTIONArmors are used for providing protection in deferent defense applications such as personal protection, vehicle protection and tank protection. Conventional materials have been used in the production of armor since 17th century. But it is beneficial to use composites as armor material because these possess high strength and high toughness at low weight. Jacobs and Dingenen [1] suggest that in battle field, light and fast vehicle is desired which can provide an adequate protection to the solders. The excess weight results in engine and suspension system failure and also reduces mobility of vehicle, which makes them an easier target to enemy.

Teng and Wierzbicki [2] evaluated the ballistic resistance of double layered steel shields against projectile impact at subordinate velocity using finite element simulation. They found that a double layered shield of the same metal possess 7 to 25% more ballistic resistance than monolithic plate of the same weight. In that work, they used various material combinations to analyze double layered shields. They found that the armor configuration with upper layer of high ductile material and lower layer of high strength material possess 25% more ballistic resistance than simple double layered shield.

All the calculations carried out in the present work are done using ANSYS AUTODYN. AUTODYN is a Non-Linear explicit dynamics software package used in modern days. Almost all dynamic high speed analyses can be modeled in AUTODYN. AUTODYN falls into a group of computer programs known as ‘‘hydro-codes’’, which are particularly

suited for modeling explosion, blast, impact and penetration events. Within the code, the appropriate mass, momentum and energy conservation equations coupled with the material modeling equations, subjected to initial and boundary conditions are solved.

In this work armor and bullet are used of following specifications.

Table 1: Armor specifications

Material Thickness (mm)

Length (mm)

Width (mm)

Kevlar-epoxy 8 120 120

Table 2: Bullet specifications

Material Velocity (m/s) Mass (gram) ShapeLead Variable 9.5 Ogive

2. NUMERICAL SIMULATIONS For numerical simulations two types of configuration (single layered and double layered) of armor were modeled in Ansys Autodyn software. In single layered configuration 8 mm thick Kevlar – Epoxy layer was used and in case of double layered configuration, two layers of Kevlar Epoxy, each of 4mm thickness were used. For both the armor configurations, impacts were performed by same type of bullet for different striking velocities.

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Table 3: Simulation 1 data

Sr. No. Type of armor

Initial weight (mg)

Thickness(mm)

VS(m/s)

Vr(m/s)

VS-Vr(m/s)

Final weight (mg)

%of weight

reduction

Remark

1 Single layered

190074 8 423.8 58.9 364.9 189830 0.127 Incomplete penetration

Fig. 4: Material status of armor after impact

Fig. 5: Variation of mass with time

Figure 2 shows the variation of armor mass with time. For this striking velocity % of armor mass reduction is 0.127 and residual velocity of bullet is 58.9 m/s. Figure 1 shows the incomplete penetration of armor.

2.1 For striking velocity 477.8 m/sFor 477.8 m/s striking velocity, mass reduction of armor is 0.144% and residual velocity of bullet is 148.2 m/s. and material status of armor after impact suggests the incomplete penetration of armor.

Fig. 1: Material status of armor after impact

Fig. 2: Variation of mass with time

Fig. 3: Average X velocity versus time

Table 4: Simulation 2 data

Sr. No. Type of armor

Initial weight (mg)

Thickness(mm)

VS(m/s)

Vr(m/s)

VS-Vr(m/s)

Final weight (mg)

%of weight reduction

Remark

1 Single layered

190074 8 477.8 148.2 329.6 189800 0.144 Incomplete penetration

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Fig. 6: Average X-Velocity versus time

2.2 For Striking Velocity 594.8 m/s.Figure 8 shows the variation of armor mass with time for striking velocity 594.8 m/s. And in this case % of armor mass reduction is 0.63 and residual velocity of bullet is 310.4 m/s. Figure 7 suggests that shot lodging occurred.

Figure 7: Material status of armor after impact

Figure 8: Variation of mass with time

Figure 9: Average X-Velocity versus time

Table 5: Simulation 3 data

Sr. No.

Type of armor

Initial weight (mg)

Thickness(mm)

VS(m/s)

Vr(m/s)

VS-Vr(m/s)

Final weight (mg)

%of weight reduction

Remark

1 Single layered

190074 8 594.8 310.4 284.4 188870 0.63 Shot lodging

3. SIMULATION FOR DOUBLE LAYERED CONFIGURATION

3.1 For Striking Velocity 423.8 m/s.

Table 6: Simulation 4 data

Sr. No. Layer of armor

Initial weight (mg)

Thickness (mm)

VS(m/s)

Vr(m/s)

VS-Vr(m/s)

Final weight (mg)

%of weight

reduction

Remark

1 First layer 95037 4 423.8 — — 95037 0.0 —

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Table 5: Simulation 3 data

Sr. No. Type of armor

Initial weight (mg)

Thickness(mm)

VS(m/s)

Vr(m/s)

VS-Vr(m/s)

Final weight (mg)

%of weight

reduction

Remark

2 Second layer 95037 4 — -10 — 95010 0.028 —

3 As a double layered armor

190074 8 423.8 -10 433.8 190047 0.014 Very little penetration

Fig. 12: Variation of 2nd layer mass

Fig. 13: Average x-velocity versus time

Fig. 10: Material status after impact

Fig. 11: Variation of 1st layer mass

3.2 For Striking Velocity 477.8 m/s.Table 7: Simulation 5 data

Sr. No.

Layer of armor

Initial weight (mg)

Thickness (mm)

VS(m/s)

Vr(m/s)

VS-Vr(m/s)

Final weight (mg)

% of weight

reduction

Remark

1. First layer 95037 4 477.8 — — 95037 0.0 —

2. Second layer 95037 4 — 5 — 94920 0.123 —3. As a double

layered armor190074 8 477.8 5 472.8 189957 .061 Incomplete

penetration

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Fig. 14: Material status after impact

Fig. 15: Variation of 1st layer mass

Fig. 16: Variation of 2nd layer mass

Fig. 17: Average x-velocity versus time

Table 8: Simulation 6 data

Sr. No. Layer of armor

Initial weight (mg)

Thickness (mm)

VS(m/s)

Vr(m/s)

VS-Vr(m/s)

Final weight (mg)

%of weight reduction

Remark

1. First layer 95037 4 594.8 — — 95010 .028 —

2. Second layer 95037 4 — 91 — 94984 .055 —3. As a double

layered armor190074 8 594.8 91 503.8 189994 .042 Incomplete

penetration

3.3 For Striking Velocity 594.8 m/s.

Fig. 18: Material status after impact Fig. 19: Variation of 1st layer mass

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Fig. 20: Variation of 2nd layer mass Fig. 21: Average X-velocity versus time

Figure 11 shows that no mass reduction of first layer takes place and only .028 % mass reduction of second layer takes place. For the first case residual velocity of bullet is found -10 m/s. And for the second case, residual velocity is found 5 m/s and incomplete penetration of armor takes place. For

striking velocity 594.8 m/s, mass removal of both the layers takes place. From first layer % of mass reduction is .028 and from second layer % of mass reduction is .055 and as a double layered armor .042% of mass reduction takes place. For third case, residual velocity is found 91 m/s.

4. RESULT AND DISCUSSIONTable 9: Summary

Sr. No. Type of armor

Thickness (mm)

Vs (m/s)

Vr(m/s)

Vs-Vr (m/s)

% of mass reduction

Remark

1. Single layer 8 423.8 58.9 364.9 0.127 Incomplete penetration

2. Double layer 8(4+4)

423.8 -10 433.8 0.014 Very little penetration

3. Single layer 8 477.8 148.2 329.6 0.144 Incomplete penetration

4. Double layer 8 (4+4)

477.8 5 472.8 0.061 Incomplete penetration

5. Single layer 8 594.8 310.4 284.4 0.63 Shot lodging6. Double layer 8

(4+4)594.8 91 503.8 0.042 Incomplete

penetration

Above mentioned statistics show that % of mass removal of double layered armor is less than that of single layered armor, for all the simulations. For double layered armor, not only % of mass removal but residual velocities (bullet) are also lees than that of single layered armor. Less % of mass removal (armor) indicates the less damage of armor and small value of residual velocity (bullet) indicates the higher degree of ballistic resistance of armor. The combined result of “residual velocities (bullet) and % of mass removal (armor)” determine the ballistic performance of armor.

5. CONCLUSIONSThe present work analyzed the material status of armor after bullet impact.

This work compares the ballistic resistance of single layered armor and double layered armor.

Mass removal of single layered armor decreases with the increment in the difference value of striking velocity and residual velocity (Vs-Vr).

Doubled layered armor possesses better ballistic resistance than single layered armor.

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