27TH INTERNATIONAL SYMPOSIUM ON BALLISTICS FREIBURG, GERMANY, APRIL 22–26, 2013
EXPERIMENTAL TESTS OF SUBCALIBRE PROJECTILES WITH SEGMENTED PENETRATORS FOR TANK GUNS M. Magier Military Institute of Armament Technology, Prymasa Wyszynskiego 7 st., 05-220 Zielonka, Poland
[email protected] During 25th ISB in China a poster was presented with a conception of segmented kinetic energy penetrators for tank guns. The penetrator is composed of two tungsten alloy pieces connected by screwed steel muff. The axial deformation of the connecting muff during penetration process results in decreasing of the distance between tungsten segments. For this reason the rear segment can hit the front segment to give it some additional kinetic energy enhancing penetration depth. A new concept called “forced segmented penetration” was presented in Journal of Applied Mechanics [1]. A numerical optimization of the new concept kinetic energy penetrator and its influence to the penetration process was presented in the paper [2] (26th ISB in Miami). In this paper firing tests of some variants of subcalibre projectiles with segmented penetrators are presented. This examination was crucial for the completion of this research work and making the synthesis of theoretical results with numerical analyses and experimental tests.
1. INTRODUCTION During 25th ISB in China a poster with conception of segmented kinetic energy penetrators for tank guns was presented. The penetrator is composed of two tungsten alloy pieces connected by screwed steel muff. The axial deformation of the connecting muff during penetration process results in decreasing of the distance between tungsten segments. For this reason the rear segment can hit the front segment to give it some additional kinetic energy enhancing penetration depth. During simulation process it was established that for one of the developing variants the penetration depth increased by 10% in comparison with penetration depth of the real penetrator with the same weight and dimension. A new concept called “forced segmented penetration” was presented in Journal of Applied Mechanics [1]. This kind of segmented penetration phenomena wasn’t presented before (Fig. 1).
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Figure 1. The time sequences of equivalent plastic strain in magnification for connecting muff - the phenomena of the forced segmented penetration.
Next the author focused on the problem of increasing the penetration depth by optimizing the distance between penetrator’s segments (established by the length of connecting muff) and transforming the penetration process from a one-stage into a few-stages. A numerical optimization of the new concept kinetic energy penetrator and its influence to the penetration process was presented in the paper [2]. According to simulation results author decided to develop and produce the subcalibre projectiles with segmented penetrators in variants A and B (Fig. 2). Additionally with aim of the wider comparison of the results also projectiles were made with segmental penetrators in the basic W2 variant (the distance about 2 mm between tungsten segments [3]).
Figure 2. Segmented penetrators in variants A and B, from the left: A (distance between tungsten segments 2 cm), B (distance between tungsten segments 4 cm).
2. RESULTS OF PENETRATION TESTS This examination was crucial from the point of seeing the completion of this research work, and its results allowed making a synthesis of numerical theoretical results and experimental tests.
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The comparative firing tests of penetration depth was conducted with 125 mm APFSDS-T projectiles having the segmented penetrator W2 variant (distance between tungsten segments - about 2 mm) and the penetrator variant A (distance between tungsten segments of 2 cm) and the penetrator B variant (distance between tungsten segments of 4 cm). There were used for examinations models of APFSDS-T with penetrators W2 variant in the amount of 4 pieces, variant A (3 pieces) and the B (3 pieces) because of high costs of making a new cartridge. In examinations of segmented penetrators bullets it was used 125 mm subcalibre projectile APFSDS-T with the structure where a special four-parts sabot was applied (being characterized by a higher strength in the comparison to three-parts sabot of 120 mm APFSDS-T projectile), enabling the assembling of penetrators with different lengths (fig. 3).
Figure 3. 125 mm subcalibre projectiles with segmented penetrators in variants (from left) W2, A, B.
Next these projectiles were fixed with propellant charges at the Centre of Dynamic Tests of the Military Institute of Armament Technology in Stalowa Wola. The weight of charges was selected to establish the hitting velocity of the penetrators at about 1520 m/s (that corresponds to the point-blank range of 2300 m). The test was conducted by using 125 mm ballistic cannon 2A46 installed on the mounting (fig. 4) and firing to the RHA armour plate having the thickness of 275 mm that was placed on the stand at the distance of 150 m from the firing position and using cartridges seasoned in temperature 288 K (fig. 5).
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Figure 4. 125 mm ballistic gun 2A46.
Figure 5. RHA armour plate (the thickness of 275 mm) at angle 52° from vertical at the distance 150 m from firing position.
The firing test was conducted at the simultaneous measurements of muzzle and hitting velocities of the penetrator by using the ballistic radar SL 520 and pictures of the projectile leaving the barrel muzzle were taken by the camera Phantom V710. Achieved results are presented in table 1.
Shot No.
Type of penetrator
Muzzle velocity V0 [m/s]
Hit velocity Vu [m/s]
Target
Results
Table 1.
1
OF-19 EC
817
802
Hill at dist. 1000 m
warming up the gun tube
2
BM-15
1773
1750
cardboard shield at dist. 150 m
correct stabilization of the projectile
3
W2
1531
1522
cardboard shield at dist. 150 m
correct stabilization of the projectile
4
W2
1515
V100=1509 V150 =1507
275 mm plate RHA – at angle 52°
Full penetration– penetration depth (447 mm RHA)
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Muzzle velocity V0 [m/s]
Hit velocity Vu [m/s]
1528
1520
6
A
7
A
1538
1521
Non full penetration – measured depth of penetration channel - 310 mm RHA
8
B
1496
1484
penetrated previous holes of earlier shots
9
B
1516
1503
penetrated previous holes of earlier shots
10
11
12
B
A
W2
Non full penetration – measured depth of penetration channel - 300 mm RHA
lack of lack of measurem measurement ent
1509
1534
1525
1496
Results
Type of penetrator W2
Target
Shot No. 5
penetrated previous holes of earlier shots
275 mm plate RHA – at angle 60°
Non full penetration – measured depth of penetration channel - 310 mm RHA
1520
Non full penetration – measured depth of penetration channel - 320 mm RHA, penetration of the plate in contact areas of the armour plate with supports of the stand
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Non full penetration – measured depth of penetration channel - 325 mm RHA, penetration of the plate in contact areas of the armour plate with supports of the stand
The shot No. 1 (warming up the gun tube) was fired with 125 mm training projectile OF-19EC cartridge to the hill at 1000 m distance. Next two shots were fired (shot No. 2 with cartridge with the BM-15 projectile, shot No. 3 with cartridge with W2 projectile) to a cardboard shield placed by the armour plate in order to check putting the average point of the direct hit relative to the aiming point and to check the correct stabilization of the projectile. The first shot to the 275 mm RHA armour plate (shot No. 4) at the angle 52 ° (it means the penetration depth of 447mm RHA) was carried out by using the projectile with the W2 penetrator. The hit velocity was 1507 m/sec and fully penetration was achieved. During qualification tests conducted in previous years it was checked, that this projectile had achieved the penetration depth of 500 RHA mm for the hit velocity 1550 m/sec. In order to make the comparison of depths of examined craters for different penetrators the tilt angle of the armour plate was increased to 60 ° (what corresponds
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to the full penetration distance of 550 RHA mm) with the aim of getting the effect of the incomplete penetration. In this configuration all 8 other rounds were fired. At the picture No.6 the RHA plate was presented with numbered penetrations holes. Based on data compared in table 1 and holes presented at the picture No. 6 the selection of the results was performed. For the comparative analysis of the penetration depth for different penetrators the representative shots were chosen: No. 5 (W2 variant), No. 7 (variant A) and No. 10 (B variant). Taking into account the shots which penetrated previous holes of earlier shots No. 6, 8, 9 results were rejected. Moreover for the penetration of the plate in contact areas of the armour plate with supports of the stand (where the plate bends less than in the centre what influences the penetration depth) results for shots 11 and 12 were also rejected.
12
5 7 4
911
8 10
6
Figure 6. RHA armour plate with numbered penetration holes. Green – correct results, red –incorrect results, penetration of previous holes.
In table 2 the analysis of the results of checking comparative depths of piercing for shots with No. 5, 7, 10 is presented. To compare the results of analysed shots the conversions of the penetration depth were made by taking the real penetration depth of the basic variant of the W2 penetrator being 500 RHA mm as a point of reference. For this operation a special following formula was developed: 2
V P Po = uW 2 maxW 2 × P Vu PW 2 where: – penetration depth with reference to maximum penetration depth of the Po variant W2, equals 500 mm RHA, PmaxW2 – maximum penetration depth of the variant W2, equals 500 mm RHA, PW2 – measured depth of penetration channel of the variant W2 for shot No. 5, equals 300 mm RHA, P – measured depth of penetration channel of the analysed penetrators variant, VuW2 – hit velocity of the variant W2, – hit velocity of the analysed penetrator variant. Vu
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(1)
7
A (z=2cm)
1521
10
B (z=4cm)
1496
Relative growth of penetration (P0PmaxW2)/Pma xW2 [%]
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Penetration depth Po[mm]
Hit velocity Vu [m/s]
W2
Measured depth of penetration channel P [mm]
Type of penetrator
5
Target
Shot No.
Table 2.
300
500
0
310
516
3,2
310
533
6,6
275 mm plate RHA – at angle 60°
Based on made calculations there is an evident increase of the penetration depth by the 3.2% for the penetrator variant A (distance between segments z=2 cm) and by the 6.6% for the variant B (distance between segments z=4 cm). Because the penetrators variants A and B have higher weight (about 40 g for variant A, and 80 g for variant B) in the relationship to the basic W2 penetrator an additional comparison was made. The modification of the formula (1) to the form (2) was made to take into account the difference of weights in the aspect of the penetration depth of segmented penetrators analysed in shots No. 5, 7, 10.
m Po* = W 2 m
2
VuW 2 PmaxW 2 ×P Vu PW 2
(2)
where: – weight of penetrator variant W2 (kg), mW2 m – weight of analysed penetrator (kg).
The calculation results (taking into account the weight differences) are presented in the table 3.
3,597
7
A (z=2cm)
1521
3,635
10
B (z=4cm)
1496
3,672
275 mm plate RHA – at angle 60°
Relative growth of penetration (P0PmaxW2)/Pma xW2 [%]
Weight of penetrator [kg]
1520
Penetration depth P0*[mm]
Hit velocity Vu [m/s]
W2
Measured depth of penetration channel P [mm]
Type of penetrator
5
Target
Shot No.
Table 3.
300
500
0
310
511
2,2
310
522
4,4
Finally based on calculations taking differences of mass into account and the hit velocities of segmented penetrators in analysed variants the growth of penetration depth was stated at 2.2% for penetrator A (for distance between segments z= 2 cm)
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and at 4.4% for B penetrator (for distance between segments z= 4 cm).
3. COMPARATIVE ANALYSIS OF FIRING TESTS WITH NUMERICAL SIMULATIONS RESULTS Comparing results of numerical simulations of the penetration process in a few variants introduced by segmented penetrators [3] and above results of dynamic tests one difference which could affect values of penetration depths must be taken into account. This is the configuration of RHA armour plate. In case of numerical simulations it was used the plate for thicknesses from 500 to 700 mm placed vertically to the axis of penetrating projectile in the two-dimensional system. Such system was applied because of software and hardware restrictions which didn't let the simulations run in the full-scale and three-dimensional system, where the penetrator would hit the armour plate places at the any angle. Instead for the firing experiment it was used 275 mm thick armour plate that was declined at angles 52° and 60 ° from the vertical in order to match conditions of examinations with requirements of the firing against armoured targets in accordance with standards NATO ("angle NATO 60 °") and in accordance with the requirements of used methodologies [4]. Moreover such position of the armour plate allowed checking the concept of segmented penetrator in solving a problem of resistance against ricocheting, bending (or decay) of extended penetrators while hitting the armour at a lowered angle. In paper [2] penetrators A (distance between segments 2 cm) and B (distance between segments 4 cm) were accepted to comparative tests of segmented penetrators. Results of the simulation are presented in the picture 7.
Figure 7. The results of penetration depth simulations for variants A-468 mm RHA (left) and B-443 mm RHA (right).
In numerical simulations of processes of the penetration depths for vertical armour plate appropriately were achieved following results: 468 mm for the variant A and 443 mm for the B variant. Results of experimental firing tests and simulated for A and B penetrator variants show opposite relation between the length of the steel connecting muff and the length of the penetration channel. Comparison of single results (tables 2 ÷ 4) of individual variants reflecting
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penetration depths of segmental penetrators shows a tendency to increasing the penetration depth of the lowered armour plate along with the larger separation distances between segments of the penetrator. A difference in penetration processes of the vertical and lowered plate is a reason for differences between the simulations and experiment. A phenomenon of observed increase of penetration depth at low angle armour comparing to the vertical armour is known. This phenomenon is based on bending the penetration channel to the external surface of the lowered armour plate (fig. 8). This phenomenon is clearly visible particularly in case of penetration tests of plates placed under the low angle for the conditions of the penetration of the projectile similar to value of the velocity V50 (e.g. some producers of the subcalibre ammunition give the thickness of penetrated angled armour plates to 0 ° and 60° where the value for the plate at 0° is lower than doubled thickness of the angled plate 60 °[5]).
Figure 8. A phenomenon of ostensible penetration depth increasing of low angle armour.
This effect was also observed during conducted firing tests. In this case at testing the lowered RHA plate this phenomenon was supported by a process of the axial deforming on the steel connecting muff linking tungsten segments of the penetrator, causing the incurvation of the channel of the penetration what caused the increase of the penetration depth. Thanks to increased susceptibility to bending stresses (by using an elastic-plastic connection muff) the structure of the segmented penetrators is characterised by itself as having greater resistance to damage (fracture) in the process of the penetration of the armour. This resistance supports the process of the incurvation (changing the channel of penetration with an effect of increased penetration depth at lowered angle comparing to a vertical plate having the same thickness. Moreover segments of the penetrator with two times reduced length comparing to the homogenous penetrator are characterised by an increased resistance against bending. There is also a no small importance fact that applying steel connecting muff that links tungsten segments of the penetrator can cause simpler "skid" on the joint with material of the armour plate what results in smaller forces of the resistance.
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4. SUMMARY Author's concept of increasing the penetration depth with the increase in the distance between segments of the penetrator initially was verified (on the available number of rounds) during comparative firing tests verifying the penetration depth of analysed variants of penetrators. Based on calculations taking into account differences of weight and hit velocities of segmented penetrators it was revealed that there is an increase in the penetration depth by the 2.2% for the penetrator A (distance between segments z= 2 cm) and by the 4.4% for the B penetrator (distance between segments z= 4 cm) in relation to basic W2 penetrator (the little gap between tungsten segments). Of course conducting the comparative analysis on such small population of results (because of reduced funds and the high individual cost only 10 pieces of cartridges for testing the penetration were prepared) doesn't allow for presenting the problem in a statistical sense and they don't constitute total confirmation of an assumption made in the introduction of the paper. However the received results indicate in terms of physics that there is a possibility for increasing the penetration depth thanks to applying the segmented construction of penetrators with appropriate distances between tungsten elements. Moreover it has to be emphasized that none of rounds fired to the armour plate with segmental penetrators suffered a fracture (destruction) in the process of penetration. It is an experimental proof that assumptions made at this work concerning the minimization of probability for ricocheting and destruction of penetrator in the process of hitting and penetration of armour plate at a low angle were sensible. This R&D is supported by the Polish Ministry of Science and High Education - project No O N501052937. REFERENCES [1] [2]
[3]
[4] [5]
Magier, M., 2010, “The Conception of the Segmented Kinetic Energy Penetrators for Tank Guns”, Journal of Applied Mechanics, Vol. 77, pp.051802-1-10. Magier M., 2011, “The numerical optimization of the novel kinetic energy penetrator for tank guns” , DEtech Publications, Inc, USA, 26 International Ballistics Symposium, Miami 12–16 September 2011, Vol.2, pp. 1171–1080. Jach, K., Świerczyński, R., Magier, M., 2009, “ Numerical analyzes of armors penetration by subcalibre projectiles with monolith and segmented penetrators” in Polish. Bulletin WAT Vol. LVIII3, 123–140. STANAG 4164 (land) –Test procedures for armour perforation test of anti-armour ammunition. www.russianarmor.ru.
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