Wednesday 18 May 2016

IS-3 Prototype Penetration Testing

"Resilience of main hull components

Part
Thickness (mm)
Plate Angle (deg)
Shell type
Angle
Impact velocity
Range (m)
Damage type
Caliber
Type
Upper front plate
120
60
88
AP
0
965
350
No penetration
Upper front plate
120
60
122
AP
0
758
690
No penetration
Side with spaced armour
85/16
60/35
88
AP
90
982
150
No penetration
Side without spaced armour
85
60
88
AP
90
983
159
Limit of dangerous penetration
Side with spaced armour
85/16
60/35
75
Subcaliber
60
1051
100
No penetration
Side (upper belt)
100
0
75
AP
45
905
500
No penetration
Side (upper belt)
100
0
75
AP
60
720
1600
Penetration
Side (rear part)
60
0
75
AP
35
780
1500
Limit of rear plate
Bottom with spaced armour
20/30
60
75
AP
35
607
2200
Only spaced armour is penetrated
Bottom with spaced armour
20/30
60
75
AP
35
660
1900
Same

Resilience of main turret components

Part
Thickness (mm)
Angle of plate
Shell type
Impact velocity (m/s)
Range (m)
Damage type
Caliber
Type
Turret front
175
Sphere
88
AP
967
350
Penetration less than shell caliber
2nd belt
120
51
88
AP
900
1000
Penetration within +/- 15 degrees of normal
3rd belt
90-100
58
88
AP
900
1000
4th belt
175
15
88
AP
900
1000
2nd belt
120
51
88
AP
965
350
Penetration within +/- 30 degrees of normal
3rd belt
90-100
58
88
AP
966
350
4th belt
175
15
88
AP
975
300

Figure #35: Diagram of the damage to the turret.

Recommendations on improvement of the IS-3 tank design

Hull and turret

1. Replace the sides of the hull with a single bent 75 mm thick plate of medium hardness with a 45 mm high hardness screen in the middle part, according to the attached diagram.

Figure #9: Diagram of the hull side armour.

2. Thicken the front part of the hull roof, not protected by the turret, to 45-60 mm.
3. Increase the thickness of the front of the turret to 230 mm.
4. Remove the sudden change from the fourth belt (175 mm) to the third belt (90 mm) by changing the slope of the fourth belt according to the attached diagram.

Figure #10. Diagram of the changes to the turret armour.

RGASPI 644-2-464

It's worth noting that the designers took the results of these trials seriously and upgraded the turret armour significantly,

2 comments:

  1. This is a very interesting document. It indirectly sheds light on the performance of cast armour in comparison to RHA as well.

    German official penetration data based upon the G(D) criterium (5 out of 5 successes, no failures) indicates that the 88mm PzGr.39/43 does penetrate reliably only 80mm german RHA at 60° obliquity and 1000m/s.

    The penetration data against the soviet cast turret show a somehow better performance:

    at 59.2° compound netto obliquity (composed of 58° vertical at 15° horizontal component) the 8.8cm penetrates 90-100mm cast armour already at 900m/s.

    at 62.3° compound netto obliquity (composed of 58° vertical and 30° horizontal component) the 8.8cm penetrates 90-100mm cast armour at 965m/s.

    From this comparison it appears that either the WaPrüf penetration data of the 88mm are overly conservative, or alternatively, the soviet 100mm cast armour at high obliquity appear to be significantly inferior to their test RHA.

    interesting, thanks for posting.

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  2. High hardness is a disadvantage at high obliquity impact. The harder the plate, and the lower the velocity, the more normalization occurs. At 60° the nose shape hardly ever is important because projectile break up occurs almost all the time, creating a rather blunt nose -if the projectile doesn´t shatter completely. More important is the deepness of the cap over the nose and it´s hardness, as it rightens up the projectile a bit, and digs out a piece of metal from the plate, allowing easier passage of whatever follows.

    Cast armour is certainly less effective than RHA due to the lack of cross rolling used to work out impurities and gas bubbles present in the cast.

    Take also notice that german penetration definitions are harder. 0 out of 5 failures allowed can at high obliquity turn to significantly degrading results if a single projectile undergoes complete rather than nose-only break up.

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