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发表于 2013-1-16 13:24
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本帖最后由 seven_nana 于 2013-1-16 13:30 编辑
Nathan Okun的文章里也有提到Scaling这一参数，没有理由认为他在计算VH时，忽略了这一特性
Scaling的定义：在射弹与装甲的冶金属性，射弹形状，命中角度，射弹受损情况等因素均保持一致，仅射弹弹径与装甲厚度以给定程度发生增长时，弹道极限出现降低的情况。
弹道极限的定义：对于给定类型/厚度/倾斜度设置的装甲，给定类型的射弹达成穿透所需的速度。
也就是说，在其他条件不变的情况下，3寸弹击中2寸甲，与6寸弹击中4寸甲，达成穿透所需的速度是不同的
SCALING - Reduction in the ballistic limit of an armor type when all metallurgical properties of the plate and projectile, the projectile shape, the impact obliquity, projectile damage, and so forth are kept constant, but the size of both the projectile and the plate are increased by a given amount (i.e., a 3" (7.62 cm) projectile versus a 2" (5.08 cm) plate is replaced by, say, a 6" (15.2 cm) projectile and a 4" (10.16 cm) plate, both identical scale models of the first projectile and plate). Face-hardened armors have a scaling effect that increases rapidly with a decrease in the percentage thickness of the plate's unhardened back layer when the back layer goes below about 65% of the total plate thickness (due to brittle fracture of the hard face layers being a surface phenomenon, increasing only with the square of the scale (much slower than increased projectile and armor plug weight increase), while ductile deformation and tearing of the soft back is a volume-related phenomenon which increases with the cube of the scale, in step with increased projectile weight). The most ductile homogeneous armors only have a very tiny scale effect, but this increases as they get less and less ductile (due to reduced ability to stretch sideways to get out of the projectile's path before the armor splits apart, which is an increasing problem for the plate material near the impact center as the projectile gets wider), as measured by a decrease in the "Percent Elongation" (see page 1) from the circa 25% of the best ductile homogeneous armors, such as U.S. Navy World War II BuShips "Special Treatment Steel" (STS), to, for example, 18% Elongation for German World War II "Wotan Härte" (Wh) armor, which has a roughly 13.2% drop in the Navy BL for Wh plates when otherwise-identical projectile diameter increases from 8" (20.3 cm) to 14.96" (38 cm) against otherwise-identical plates scaled from, say, 6" to 11.22" (28.5 cm), compared to only a 1.4% drop for similar STS plates, though both plate types have virtually the same Navy BL (scale effects identical) against smaller projectiles. For homogeneous armors, the optimum ductility increases with absolute scale--due to the sideways stretch problem just mentioned, largely caused by factors such as the metal's speed of sound and crystal size that do not change with scale--and the 25% Elongation value seems to be the minimum to allow the minimum scale effects when against projectiles over 8". Relative scale effects due to a thicker or more oblique plate having a greater Navy BL at any scale also require that the plate have increased toughness for a maximum Navy BL, usually obtained by reduced hardness and increased Percent Elongation, on top of the absolute scale effects applicable to all plates. (See "SCALING" under FACTORS AFFECTING HOMOGENEOUS, DUCTILE PLATE RESISTANCE, below, for more information.) |
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