Revised High Hardness Multipliers and 37mm Pak

[rexford]

New information on German penetration data from a British BIOS report allowed for a more accurate analysis of German tests against T34 like armor.

Against a 45mm high hardness plate (about 440 Brinell Hardness) as found on a T34, the armor is ocnverted to an equivalent thickness of 240 Brinell Hardness armor using the following multipliers:

37mm AP ammo, 1.25 (45mm resists like 56mm)

47mm AP or APC ammo, 0.99 (45mm resists like 45mm)

50mm AP or APC ammo, 0.93 (45mm resists like 42mm)

57mm AP, APC or APCBC amm0, 0.82 (45mm resists like 37mm)

The above data is based on analysis of German firing tests against T34 like armor with 37mm AP projectiles, where the 37mm AP penetration against 240 Brinell plate was estimated at:

0000m, 66mm

0100m, 61mm

0500m, 47mm

1000m, 32mm

When 37mm AP hits the 45mm high hardness mantlet on T34 at 0 degrees impact from vertical, the 45mm plate will resist like 56mm of 240 Brinell plate.

The above multipliers only tell part of the story, as shatter gap will cause hits to shatter and fail when they overpenetrate the armor. Shatter gap is dependent on the armor thickness/projectile diameter ratio, the impact angle and the ratio of the penetration divided by the equivalent armor resistance.

Next week I will post some advanced information on shatter gap that will help to explain the relative ineffectiveness of German 37mm and 50mm ammo at various ranges where penetration did not occur despite what appeared to be adequate penetration.

The following equations describe the multipliers that convert high hardness armor to an equivalent thickness of 240 Brinell plate (T/D is plate thickness divided by projectile diameter):

37mm

1.130 x (T/D) ratio raised to 0.502 power

47mm

1.002 x (T/D) ratio raised to 0.383 power

50mm

0.961 x (T/D) ratio raised to 0.351 power

57mm

0.879 x (T/D) ratio raised to 0.282 power

For 50mm against 65mm high hardness, multiplier would be 0.961 x (65/50) raised to 0.351 power, or 0.961 x 1.3 raised to 0.351 power, or 1.05.

[flamingknives]

If you'll excuse my ignorance, is 240 Brinell hardness what you'd expect of RHA?

[John D Salt]

Originally posted by flamingknives:

If you'll excuse my ignorance, is 240 Brinell hardness what you'd expect of RHA?

For thick plates, yes; thinner plates would be likely to be harder.

PRO document WO 185/171, "Armour plate experiments", includes a table giving typical ranges of hardness for British and German plates of different thicknesses, based on information collected up to June 1944:

German plate:

Thickness Hardness

40mm_____280-335

60mm_____270-320

80mm_____250-300

100mm____220-290

thicker____215-250

British plate:

40mm_____262-302

60mm_____255-293

80mm_____248-277

100mm____240-269

thicker____240-269

All the best,

John.

[ April 14, 2003, 07:59 AM: Message edited by: John D Salt ]

[PzKpfw 1]

The Watertown Arsenal(WAL 710/542) on the Tiger E armor, points out instances where the armor was ballisticly not up to par with other German plate examined previuosly Ie, the PzKpfw III, and indicated a decline in German quality control. The Report was done on an Tiger E from Tunisia.

Ie:

Hull Side plate: 3.2in thick 352 BHN.

'All Plates except one, the hull side plate, were of acceptable quality steel. Excessively large ammount of segregated nonmetallic inclusions, which appeared as laminations in the fracture test, were observed on examination of this plate'.

Main Front plate 4.0in 321BHN

'Improper heat treatment of the main front plate and the hull side plate wa1s reflected in poor notched bar impact strength which,in turn, would be associated with poor resistance to cracking under ballistic attack.

Heat-treating tests were conducted which revealed that approximately the same notch bar impact strength could be obtained by a normalize and draw of a small section as was observed in the 4" main front plate as recieved."

The report goes into detail on German welding practices as well:

Welding and Joint design:

'The Joint design is characterized by grooves machined in the heavy section of each weld joint to give a fitted or mortised joint which is in compression on impact from the direction of principal ballistic attack. Fit-up is fairly good.'

'Rough surface appearence, severe undercutting, and failure to completely fill the joint grooves with weld material indicate inexperience or carelessness on the part of the welders.'

'All welds were made up of multiple overlapping beads and appear to have been deposited, without preheat, on the armor in the final heat-treated condition. Very extensive base metal cracks were present in the heat affected zones of the three weld joint samples and sections from the samples break through these cracks on light impact with a hammer'.

This examination revealed an amazeing lack of concern by German fabrication and inspection facilites, for base metal cracks which (1) would ordinarily be expected in welding of this high carbon armor plate, (2) must have occured soon after welding and were so extensive that they probably could have been detected by any of the usual inspection methods,and (3) are universally recognized to have a very serious effect on shock ressistance of the welded structure.'

The Plates examined were:

Hull Roof Plate - 1.0in 363BHN

Turret Roof Plate - 1.0in 321BHN

Hull Side Plate - 3.2in 352BHN

Turret Side Plate - 3.2in 352BHN

Main Front Plate - 4.0in 321BHN

Front Glacis Plate - 2.4in 352BHN

Regards, John Waters

[PzKpfw 1]

Below is the BHN data for the T-34-76 Model 1942 from the British report on the T-34-76 42:

Glacis - 354 - 400

Pannier side plate (nearside) - 388 - 434

"" " " (offside) - 387 - 398

Upper tail plate (outside) - 400 - 410

" " " (inside) - 389 - 406

Engine cover plate (cast) - 405 - 407

Turret escape hatch (pressing) - 390

Encasement for buffer and recuperator - 416

Gun mantlet - 407

Regards, John Waters

[rexford]

Originally posted by PzKpfw 1:

Below is the BHN data for the T-34-76 Model 1942 from the British report on the T-34-76 42:

Glacis - 354 - 400

Pannier side plate (nearside) - 388 - 434

"" " " (offside) - 387 - 398

Upper tail plate (outside) - 400 - 410

" " " (inside) - 389 - 406

Engine cover plate (cast) - 405 - 407

Turret escape hatch (pressing) - 390

Encasement for buffer and recuperator - 416

Gun mantlet - 407

Regards, John Waters

Above hardness figures probably derived from portable Poldi testing machine, which is notorious for underestimating hardness.

If the glacis were 354 Brinell it would increase the resistance relative to the majority of T34 (440 Brinell would be much more brittle acting against 75mm hits with 45mm plate). Maybe that explains how some T34 were alot more resistant than others in the Jentz Panzertruppen reports.

Germans measured T34 armor and found it to consistently be around 440 Brinell.

[ April 14, 2003, 07:20 PM: Message edited by: rexford ]

[PzKpfw 1]

Originally posted by rexford:

Above hardness figures probably derived from portable Poldi testing machine, which is notorious for underestimating hardness.

Germans measured T34 armor and found it to be around 440 Brinell.

The US data on the same T-34-76 (useing an portable poldi) obtained 10% higher BHN results on the same samples as the British. Same goes for the Tiger E, all BHN data we have was obtained with an portable poldi, Ie, the Tiger E live freings etc, same with the WAL reports.

What BHN measureing device did the Germans use that the US/UK didn't ? & Can you list the German BHN results on the same pieces Lorrin, from the German report?.

Regards, John Waters

[ April 14, 2003, 07:29 PM: Message edited by: PzKpfw 1 ]

[rexford]

When 37mm PaK AP hits T34 turret side at 100m, there is 45mm high hardness armor at 30 degrees from vertical multiplied by 1.25 for 72mm equivalent vertical resistance at 240 Brinell Hardness. 37mm Pak will not penetrate that armor at any range.

If 37mm PaK AP hits vertical 45mm gun mantlet at 15 degrees side angle, resistance would equal 45mm x 1.25 conversion to 240 Brinell x 1.02 or 57mm vertical equivalent. If 37mm made that shot at 100m where penetration equaled about 60mm, shot could still fail due to shatter gap because penetration exceeds armor resistance by 5.3%.

So 37mm PaK AP will not penetrate a 45mm vertical mantlet on T34 at an angle of 15 degrees at any range.

Good quality 240 Brinell is the test plate that the Americans used and has about the same resistance as good quality German, British and Russian test plate and armor.

Using published German penetration figures at range and 30 degrees for 50mm AP and APC (L42 and L60 guns), the following figures were derived for production rounds at 0 degrees from vertical against 240 Brinell plate:

50mm L42

========

0000m, 77mm with APC, 81mm with AP

0100m, 73mm with APC, 74mm with AP

0500m, 59mm with APC, 58mm with AP

1000m, 45mm with APC, 41mm with AP

1500m, 35mm with APC, 28mm with AP

50mm L60

========000m, 101mm with APC, 105mm with AP

0100m, 97mm with APC, 097mm with AP

0500m, 80mm with APC, 080mm with AP

1000m, 62mm with APC, 059mm with AP

1500m, 47mm with APC, 043mm with AP

German tests during early 1942 with 50mm PaK 38 against KV-I driver plate (75mm at 30 degrees from vertical) resulted in penetrations at 100m and ricochets at 200m.

50mm L60 penetration at 100m is:

97mm with APC and AP

KV-I driver plate resistance is 99mm against AP and 97mm against APC

50mm L60 penetration at 200m is:93mm with AP and 91mm with APC

KV-I resistance is 99mm vs AP and 97mm vs APC

So above penetration figures are consistent with test results if APC was fired by PaK 38, which is likely.

KV-I driver plate resisted 50mm PaK like U.S. 240 Brinell plate, nothing super about the armor.

With 75mm hull side armor on KV-I, 50mm Pak 38 firing APC would be expected to defeat the armor at 584m.

[rexford]

What happens when German 50mm AP rounds hit Russian T34 side hull armor during 1941?

T34 side hull is 45mm high hardness at 40 degrees from vertical, for 72mm equivalent vertical resistance against 50mm AP. Conversion to 240 Brinell plate resistance used multiplier of 0.93, for 67mm.

Early German AP appears to be softer than APC and more prone to shatter failure. Classical shatter gap theory has AP rounds failing when they overpenetrate armor by 5% to 30%, so German 50mm should fail to penetrate T34 side hull when penetration varies from 70mm to 87mm, and when penetration falls below 67mm.

Following are theoretical failure ranges for 50mm AP against 45mm T34 side hull at 40 degrees from vertical:

50mm L42 AP

===========

000m to 210m

272m to 2000m

50mm L60 AP

===========

321m to 692m

767m to 2000m

If classical shatter gap theory holds for 1941 hits by 50mm AP against T34 side hull, 50mm L42 gun would only be effective fron 210m to 272m and 50mm L60 would be effective from 0m to 321m and from 692m to 767m.

Anecdotes in Jentz Panzertruppen are somewhat consistent with above estimates. U.S. tests with high hardness armor showed that the shatter gap failure ratio's were not as wide as the above estimates assume.

[rexford]

Originally posted by PzKpfw 1:

The Watertown Arsenal(WAL 710/542) on the Tiger E armor, points out instances where the armor was ballisticly not up to par with other German plate examined previuosly Ie, the PzKpfw III, and indicated a decline in German quality control. The Report was done on an Tiger E from Tunisia.

Ie:

Hull Side plate: 3.2in thick 352 BHN.

'All Plates except one, the hull side plate, were of acceptable quality steel. Excessively large ammount of segregated nonmetallic inclusions, which appeared as laminations in the fracture test, were observed on examination of this plate'.

Main Front plate 4.0in 321BHN

'Improper heat treatment of the main front plate and the hull side plate wa1s reflected in poor notched bar impact strength which,in turn, would be associated with poor resistance to cracking under ballistic attack.

Heat-treating tests were conducted which revealed that approximately the same notch bar impact strength could be obtained by a normalize and draw of a small section as was observed in the 4" main front plate as recieved."

The report goes into detail on German welding practices as well:

Welding and Joint design:

'The Joint design is characterized by grooves machined in the heavy section of each weld joint to give a fitted or mortised joint which is in compression on impact from the direction of principal ballistic attack. Fit-up is fairly good.'

'Rough surface appearence, severe undercutting, and failure to completely fill the joint grooves with weld material indicate inexperience or carelessness on the part of the welders.'

'All welds were made up of multiple overlapping beads and appear to have been deposited, without preheat, on the armor in the final heat-treated condition. Very extensive base metal cracks were present in the heat affected zones of the three weld joint samples and sections from the samples break through these cracks on light impact with a hammer'.

This examination revealed an amazeing lack of concern by German fabrication and inspection facilites, for base metal cracks which (1) would ordinarily be expected in welding of this high carbon armor plate, (2) must have occured soon after welding and were so extensive that they probably could have been detected by any of the usual inspection methods,and (3) are universally recognized to have a very serious effect on shock ressistance of the welded structure.'

The Plates examined were:

Hull Roof Plate - 1.0in 363BHN

Turret Roof Plate - 1.0in 321BHN

Hull Side Plate - 3.2in 352BHN

Turret Side Plate - 3.2in 352BHN

Main Front Plate - 4.0in 321BHN

Front Glacis Plate - 2.4in 352BHN

Regards, John Waters

Thanks for a great post.