Slope Effects for Thin Plates

[rexford]

The following web site has some penetration vs angle curves for German 380mm APCBC ammo, which brings up an interesting aspect of slope effect analysis.

http://www.warships1.com/W-INRO/INRO_Hood_p2.htm

Our base data for APCBC slope effects is limited to a range where the T/D ratio ranges from low to high figures, but does not really reach very low ratio's. I have read where thin plate gains added resistance from stretching, which suggests that our slope multiplier vs T/D ratio's for each angle may not work well at very low T/D.

Here is an analysis of 380mm APCBC slope effects vs T/D ratio with comparison to estimates using our equations;

380mm APCBC at 250 m/s

penetrates 200mm at vertical and 80mm at 57 degrees from vertical

2.50 slope multiplier when T/D = 0.211 (80mm/380mm)

If U.S. 75mm APCBC hit 16mm at 57 degree armor (T/D = 0.211), the slope effect would be about 1.88 from our equations.

380mm APCBC at 170 m/s

penetrates 120mm at vertical and 40mm at 67 degrees from vertical

3.00 slope multiplier when T/D = 0.105 (40mm/380mm)

If U.S. 75mm APCBC hit 8mm plate at 67 degrees (T/D = 0.105), the slope effect would be 2.13 from our equations.

380mm APCBC at 120 m/s

penetrates 80mm at vertical and 40mm at 57.5 degrees from vertical

2.00 slope multiplier when T/D = 0.105 (40mm/380mm)

U.S. 75mm APCBC against 8mm at 57.5 (T/D = 0.105) would have a slope effect of 1.63 from our equations.

It may be that our models don't consider hits on very thin armor where the stretching of the plate comes into play. Our base data may not go to really low T/D ratio's.

[rexford]

Robert Livingston has noted that scale effects may lead to greater resistance of an 80mm plate as opposed to 16mm armor.

U.S. analysis of firing test results theorized that the surfaces on a plate offer less resistance than the interior areas, since the outer surfaces are not tightly supported and are relatively free to move vertically and laterally. This would suggest that an 80mm plate would outperform a 16mm plate when both were hit at the same angle and T/D ratio.

The above explanation appears to offer a reasonable explanation of the deviations from our curves.

[Paul Lakowski]

I would think that a 80mm plate of the same hardness would be stiffer while a 16mm plate would be more bendable under impactloading , reguardless of the actual t/d of the impact event?