References:
Depleted Uranium and Uranium Alloys by Northwest National Laboratory
Properties and Applications of Heat-Treated Uranium Alloys
U.S. Patent 5,273,711: High Strength and Ductile Depleted Uranium Alloy
BRL Memorandum Report 2703: Quasi Static Tensile Stress Strain Curves II: Rolled Homogenous Armor by Ralph F. Benck (1~ MB)

Properties of Armor/Penetrator Materials

Before we begin looking at the various armor materials available to us; a word must be said about hardness and tensile stress levels.

While the ultimate goal of any military armor/penetrator system is to score a decisive overmatch versus the opposing armor; e.g. the penetrator material having a tensile stress of 900 MPa versus the opposing armor's tensile stress rating of 400 MPa; there is a key ingredient that is often overlooked in comparing materials.

Ductility (or Elongation).

Put simply, you can age, quench, and harden steels to increase their hardness and strength ratings. However, the more you treat the material to raise those qualities, the lower the ductility of the material becomes.

The ideal penetrator/armor material should have a ductility of around 10-15% percent. This allows a penetrator to “bend” so it can absorb the stress of striking a hard surface at high velocities without shattering. For armor, this allows it to absorb the hit without shattering, preventing spalling of the armor inside the fighting compartment, and preserving multi-hit capability in the same spot.

This is why tool steel, despite looking very attractive as a penetrator/armor material because of it's high strength levels, is not suited to the task because of it's very low ductility.

The same goes for Depleted Uranium (0.75% Ti) Alloys which have been Gamma quenched and aged for 6 hours at 450C. While their yield strength is 1,215 MPa and their tensile strength 1,660 MPa; their ductility is below 2%, meaning they're worthless as armor material outside of extremely specialized applications such as external shatter plates intended to shatter small caliber projectiles and absorb some of the energy of larger caliber projectiles before they strike the main ductile armor plate.

Metallic Alloys (arranged by Density)

Depleted Uranium U-0.75Ti Alloy

Elongation: 19%
Treatment: Gamma Quenched, aged at 380C for 6 hours
Density: 18.6 g/cm3
Rockwell C Hardness: 42
Yield Strength: 965 MPa
Ultimate Tensile Strength: 1,565 MPa

Notes: Possibly the first generation of “Staballoy” used in Depleted Uranium Penetrators of the 1980s.

Depleted Uranium U-1%Mo-0.5%Ti-0.2%Zr (aged)

Elongation: 10%
Density: 18.5 g/cm3 (at least)
Yield Strength: 1,462 MPa
Ultimate Tensile Strength: 1,889 MPa

Notes: Possibly the second generation of “Staballoy” used in Depleted Uranium Penetrators of the 1990s.

Dual-Hardness Armor (DHA) (MIL-DTL-46099)

Notes: Developed to provide improved performance over HHA.

High Hardness Armor (HHA) (MIL-DTL-46100)

Notes: Developed during the Vietnam War for protection against ball ammunition. The LAV uses this above the belt-line, and plain RHA under the belt line.

½” Rolled Homogenous Armor (RHA) (MIL-DTL-12560) (1976)

Elongation: 12.1%
Density: 7.84 g/cm3
Rockwell C Hardness: 37
Yield Strength: 938 MPa
Ultimate Tensile Strength: 1,111 MPa

Composition (averages of allowable ranges)

94.58% Steel
0.265% Carbon
0.270% Manganese
0.001% Phosphorus
0.008% Sulfur
0.150% Silicon
3.250% Nickel
0.060% Copper
1.200% Chromium
0.010% Vanadium
0.175% Molybdenum
0.030% Aluminum

1½” Rolled Homogenous Armor (RHA) (MIL-DTL-12560) (1976)

Elongation: 15.9%
Density: 7.84 g/cm3
Rockwell C Hardness: 30.5
Yield Strength: 815 MPa
Ultimate Tensile Strength: 923 MPa

Composition (averages of allowable ranges)

94.58% Steel
0.265% Carbon
0.270% Manganese
0.001% Phosphorus
0.008% Sulfur
0.150% Silicon
3.250% Nickel
0.060% Copper
1.200% Chromium
0.010% Vanadium
0.175% Molybdenum
0.030% Aluminum

4” Rolled Homogenous Armor (RHA) (MIL-DTL-12560) (1976)

Elongation: 18%
Density: 7.84 g/cm3
Rockwell C Hardness: 26
Yield Strength: 688.5 MPa
Ultimate Tensile Strength: 842 MPa

Composition (averages of allowable ranges)

94.58% Steel
0.265% Carbon
0.270% Manganese
0.001% Phosphorus
0.008% Sulfur
0.150% Silicon
3.250% Nickel
0.060% Copper
1.200% Chromium
0.010% Vanadium
0.175% Molybdenum
0.030% Aluminum

Rolled Homogenous Armor (RHA) (MIL-DTL-12560) (1976) Curves

Density: 7.84 g/cm3
Rockwell C Hardness: RC Hard = 32.82 times (Thickness)^-0.17
Yield Strength: MPa = 950 times (Thickness minus -0.56)^-0.21
Ultimate Tensile Strength: About 1.18 times that of Yield Strength.

Notes: Use these to calculate the strengths of your particular thickness of material. Thicknesses are in inches. Computed from the 0.5”, 1.5”, and 4” thickness results.

Cast Homogenous Armor (CHA) (MIL-DTL-11356)

Titanium Ti-6AL-4V (Grade 5) (MIL-T-9046J)

Elongation: 14%
Treatment: Annealed at 700-785C
Density: 4.43 g/cm3
Rockwell C Hardness: 36
Yield Strength: 880 MPa
Ultimate Tensile Strength: 950 MPa
Compressive Yield Strength: 970 MPa

Titanium Ti-5AL-2.5Sn (Grade 6)

Elongation: 15%
Treatment: Unknown
Density: 4.43 g/cm3
Rockwell C Hardness: 36
Yield Strength: 827 MPa
Ultimate Tensile Strength: 861 MPa
Compressive Yield Strength: 830 MPa

Notes: This alloy is used in airframes and jet engines due to its good weldability, stability and strength at elevated temperatures.

Titanium ATSM Grade 38 (aka ATI Wah Chang 425 Titanium Alloy)

Elongation: 12%
Treatment: Hot rolled and Annealed
Density: 4.48 g/cm3
Rockwell C Hardness: 32 to 36
Yield Strength: 1,020 MPa
Ultimate Tensile Strength: 1,140 MPa

Notes: Developed as armor plate for ballistic protection.

Aluminum 2519-T87 (MIL-DTL-46192)

Density: 2.823 g/cm3
Yield Strength: 400 MPa
Ultimate Tensile Strength: 455 MPa

Composition (averages of allowable ranges)

92.77% Aluminum
5.85% Copper
0.30% Iron
0.30% Manganese
0.25% Silicon
0.23% Magnesium
0.15% Other
0.10% Zinc
0.06% Titanium

Notes: Developed by Alcoa in cooperation with the U.S. Army to deliver a weldable material with better performance against fragmentation threats than 5083 Aluminum, and almost the same performance against Ball/AP threats as 7039 Aluminum. Very good resistance to stress corrosion cracking, but very poor resistance against general corrosion. A significant loss of ballistic properties near welds due to the heat-treated zone being much weaker; so special attention to joints is required to minimize this effect. The first vehicle to use this will be the USMC EFV/AAAV.

Aluminum 5083-H131 (MIL-DTL-46027)

Density: 2.768 g/cm3
Yield Strength: 241 MPa
Ultimate Tensile Strength: 303 MPa

Composition (averages of allowable ranges)

83.3% Aluminum
4.45% Magnesium
0.70% Manganese
0.40% Iron
0.40% Silicon
0.25% Zinc
0.20% Others
0.15% Titanium
0.15% Chromium

Notes: Very resistant to stress corrosion cracking. The M113, M109, and the lower half of the Bradley are made from this.

Aluminum 7039-T64 (MIL-DTL-46063)

Elongation: 13%
Density: 2.74 g/cm3
Brinell Hardness: 133
Rockwell A Hardness: 50
Rockwell B Hardness: 81
Yield Strength: 380 MPa
Ultimate Tensile Strength: 450 MPa
Compressive Yield: 410 MPa
Shear Strength: 260 MPa
Charpy Impact: 7.5J

Composition (averages of allowable ranges)

91.65% Aluminum
4% Zinc
2.8% Magnesium
0.40% Iron
0.30% Silicon
0.25% Manganese
0.20% Others
0.20% Chromium
0.10% Copper
0.10% Titanium

Notes: Exhibits better performance against ball/AP threats than 5083 Aluminum at some loss in fragmentation protection. However, it is very susceptible to stress corrosion cracking. The upper half of the Bradley is made from this.

Weldalite 049-T81

Elongation: 10%
Density: 2.6 g/cm3
Rockwell B Hardness: 76
Brinell Hardness: 123
Yield Strength: 350 MPa
Ultimate Tensile Strength: 460 MPa

Notes: Is Aluminum-Lithium Alloy 2195. Developed by Lockheed Martin for Space Shuttle External Tank.

Magnesium AZ31B-H24 (Hard Rolled Sheet)

Elongation: 15%
Density: 1.77 g/cm3
Yield Tensile Strength: 220 MPa
Ultimate Tensile Strength: 290 MPa
Compressive Yield Strength: 180 MPa

Notes: Tested by U.S. Army ARL for ballistic protection.

Ceramics

Alumina AD-90

Elongation: Virtually None
Density: 3.6 g/cm3
Rockwell C Hardness: 68
Tensile Strength: 221 MPa
Compressive Strength: 2,482 MPa

Alumina AD-995

Elongation: Virtually None
Density: 3.9 g/cm3
Rockwell C Hardness: Above 69~
Tensile Strength: 262 MPa
Compressive Strength: 2,600 MPa

Silicon Carbide (SiC)

Density: 3.13 g/cm3
Compressive Strength: 3,900 MPa

Polymers

Kevlar 29 Aramid Fiber by DuPont

Density: 1.44 g/cm3
Ultimate Tensile Strength: 2,920 MPa

Notes: Uses 1500 Denier with 1000 filaments. Used in ballistic protection.

Kevlar 49 Aramid Fiber by DuPont

Density: 1.44 g/cm3
Ultimate Tensile Strength: 3,000 MPa

Notes: Uses 1140 Denier with 768 filaments. Used in Aerospace.

Kevlar 149 Fiber by DuPont

Density: 1.47 g/cm3
Ultimate Tensile Strength: 3,450 MPa

Notes: Used in armor.