Wednesday 17 June 2020

Waste Not, Want Not

A number of defective hulls and turrets that were rejected by QA were still put to good use by the GABTU. The parts were rejected due to cracking, particularly around the welds, but the question of how cracks affected the performance of the armour remained. There was only one way to find out.

"Effect of cracks and weld seam tears around welding areas on resistance to shells

Before trials began, all cracks and tears around the weld seams were marked on sketches and their length and type recorded (figs. 27-43). The edges of the cracks were marked.

Analysis of test materials showed the following:
  1. No matter the conditions of firing (at normal or at an angle) or types of 37, 45, or 76 mm shells, the cracks did not result in a reduction of the limit of partial or complete penetration of 40 and 45 mm thick armour plates. Results of the trials of a 45 mm shell (blueprint 2-04830) against component 29-006 of alloy batch 507302 with especially many cracks (46) that had a limit of partial penetration in the middle of 750 m/s and a limit of partial penetration near the edges (100 mm from the weld seam) of 755 m/s. No difference in resistance was established on components with fewer cracks.
  2. The size of the cracks increases only a small amount when a shell strikes, even if it hits in the vicinity of the crack. There were only a few cases where a crack increased 2-3 times in size after a great many hits. The formation of new cracks in the vicinity of the weld was not frequent.
    For instance, item 29-006 of alloy batch 507302  had 46 cracks before the trials on the outer and inner surface of the welding area. After 16 hits with 45 mm shells, the following condition of the cracks was recorded:
    1. No change: 36 cracks
    2. Increase by 70-75 mm: 10 cracks
    3. New cracks up to 40 mm in length: 3
    4. One old 20 mm crack opened up
      Note: see attachment #1 from Ilyich factory regarding the quality of alloy batch 507302.
      The amount and size of cracks before and after are recorded in figures ##56, 57, and 62. The behaviour of cracks after being hit with 45 and 76 mm rounds are shown in figures ## 77-81, which show that the cracks do not change notably even in areas where the armour is deformed, and do not pose an additional danger to the crew.
  3. The robustness of weld seams in the area of cracking does not significantly differ from the robustness of the seams on parts without cracking. However, the failure in the weld seam tends to coincide with the location of the cracks.
  4. Cracks in the vicinity of weld seams in the pannier floor showed a noticeable increase after shells or fragments struck the side of the tank, even though they were not hit directly. If there were enough cracks, they resulted in breaches, spalling, and through cracks.
The commission considers the presence of cracks in the armour in the vicinity of weld seams to be  an undesirable defect, caused by the quality of the armour and welding. In connection with this, factory #183 and the Ilyich factory must take action to completely correct these defects."

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