Materials mimicking complex railgun armatures [experimental]
May 15, 2017 16:14:18 GMT
apophys, bigbombr, and 7 more like this

### Post by omnipotentvoid on May 15, 2017 16:14:18 GMT

As most of you are probably aware, railguns armatures/projectiles in the game are assumed to be flat disks. This is a fair assumption, but causes huge problems with high performance accelerators, because flat armatures suffer from acceleration differences across the projectile, causing shear forces that limit the maximum acceleration:

Force across the rail bore:

As result we see following acceleration across a flat projectile, vs one with a parabolic cut out (cut out geometry can be vastly improve, I used a rough guestimate here for simplicities sake):

The differences in acceleration lead to the following shear forces across the projectile (rough approximation via mean acceleration:

As is clear by the graph, the peak shear forces at the edges have been reduced by nearly 4/5 and the central shear force has been more than halved. This means that the maximum acceleration the projectile can endure has been tripled with the more complex geometry, despite it being a rough estimate. Theoretically, this can be used to create projectiles that can withstand infinite acceleration, given infinite length. Practically it means that projectiles, that can withstand at least 20 times the force that a flat projectile can withstand, should be fairly easy to design. With advanced simulation software, it might be possible to push that 20 times an order of magnitude or so higher.

This isn't implemented into the game yet and might never be, due to the inherent complexity of complex armatures. It is, however, possible to emulate this effect to some extent by simply increasing the ultimate tensile strength of a material (which is what the game uses to calculate at what acceleration a projectile shatters) and decreasing density. To test this, I drafted up following materials (UTS*20,density /2):

note: only use these as railgun projectiles. The increase in tensile strength and decrease in density makes no sense in any other context.

Force across the rail bore:

As result we see following acceleration across a flat projectile, vs one with a parabolic cut out (cut out geometry can be vastly improve, I used a rough guestimate here for simplicities sake):

The differences in acceleration lead to the following shear forces across the projectile (rough approximation via mean acceleration:

As is clear by the graph, the peak shear forces at the edges have been reduced by nearly 4/5 and the central shear force has been more than halved. This means that the maximum acceleration the projectile can endure has been tripled with the more complex geometry, despite it being a rough estimate. Theoretically, this can be used to create projectiles that can withstand infinite acceleration, given infinite length. Practically it means that projectiles, that can withstand at least 20 times the force that a flat projectile can withstand, should be fairly easy to design. With advanced simulation software, it might be possible to push that 20 times an order of magnitude or so higher.

This isn't implemented into the game yet and might never be, due to the inherent complexity of complex armatures. It is, however, possible to emulate this effect to some extent by simply increasing the ultimate tensile strength of a material (which is what the game uses to calculate at what acceleration a projectile shatters) and decreasing density. To test this, I drafted up following materials (UTS*20,density /2):

`Material Railgun Armature Vanadium Chromium Steel`

Elements Fe V Cr C Mo Si Mn S

ElementCount .79 .10 .05 .025 .017 .011 .006 .001

Density_kg__m3 3725

YieldStrength_MPa 5171

UltimateTensileStrength_MPa 104100

YoungsModulus_GPa 190

ShearModulus_GPa 81

MeltingPoint_K 1494

SpecificHeat_J__kg_K 460

ThermalConductivity_W__m_K 24.7

ThermalExpansion__K 10.72e-6

Resistivity_Ohm_m 520e-9

RefractiveIndex Vanadium

RoughnessCoefficient 0.7

Material Railgun Armature Zirconium Copper

Elements Cu Zr

ElementCount .94 .06

Density_kg__m3 2866

YieldStrength_MPa 1008

UltimateTensileStrength_MPa 27320

YoungsModulus_GPa 128.9

ShearModulus_GPa 45

SpecificHeat_J__kg_K 385

MeltingPoint_K 1373

ThermalConductivity_W__m_K 366.9

ThermalExpansion__K 16.92e-6

Resistivity_Ohm_m 1.8e-8

RefractiveIndex Copper

RoughnessCoefficient .1

note: only use these as railgun projectiles. The increase in tensile strength and decrease in density makes no sense in any other context.