The ‘Bullet’ Project

By:Lucas Rhymes, Scott Parks, Brian Botteri12/12/06Engr 45, Santa Rosa Junior College, SRJC Younes Ataiiyan

What Exactly Happened?

• Supposedly a wife shot her husband through the back of a recliner with a bullet from .357 magnum. The chair absorbed enough energy to leave her husband nearly unharmed.

• How did this happen? Only material science can explain it!

Some .357 Magnum Background

Standard 125g ammunition propelled with 584ft·lbf of energy at a staggering 1450ft/s.

• Developed in 1930’s specifically to defeat car cover and early body armor in the ‘gangster period’. Early bullet proof vests only protected frombullets under 1000foot/second and the .357 Magnum rendered them utterly uselessInformation courtosey of Wikipedia

Body armor via LA-Z-BoyBody Armor Types

• Soft Body Armor – highly ductile material that will absorb energy, usually kevlar

• Body Armor - Thick metal plates, brittle and heavy.

• Combination - The best of both worlds!!

How is body armor rated?Chart from the National Institute of Defense.

Armor Level Protects Against Type I (.22 LR; .380 ACP)

This armor protects against .22 caliber Long Rifle Lead Round Nose (LR LRN) bullets, with nominal masses of 2.6 g (40 gr) at a reference velocity of 329 m/s (1080 ft/s ± 30 ft/s) and .380 ACP Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 6.2 g (95 gr) at a reference velocity of 322 m/s (1055 ft/s ± 30 ft/s).

Type IIA (9 mm; .40 S&W)

This armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) at a reference velocity of 341 m/s (1120 ft/s ± 30 ft/s) and .40 S&W caliber Full Metal Jacketed (FMJ) bullets, with nominal masses of 11.7 g (180 gr) at a reference velocity of 322 m/s (1055 ft/s ± 30 ft/s). It also provides protection against the threats mentioned in [Type I].

Type II (9 mm; .357 Magnum)

This armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) at a reference velocity of 367 m/s (1205 ft/s ± 30 ft/s) and 357 Magnum Jacketed Soft Point (JSP) bullets, with nominal masses of 10.2 g (158 gr) at a reference velocity of 436 m/s (1430 ft/s ± 30 ft/s). It also provides protection against the threats mentioned in [Types I and IIA].

Type IIIA (High Velocity 9 mm; .44 Magnum)

This armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) at a reference velocity of 436 m/s (1430 ft/s ± 30 ft/s) and .44 Magnum Semi Jacketed Hollow Point (SJHP) bullets, with nominal masses of 15.6 g (240 gr) at a reference velocity of 436 m/s (1430 ft/s ± 30 ft/s). It also provides protection against most handgun threats, as well as the threats mentioned in [Types I, IIA, and II].

Type III (Rifles)

This armor protects against 7.62 mm Full Metal Jacketed (FMJ) bullets (U.S. Military designation M80), with nominal masses of 9.6 g (148 gr) at a reference velocity of 847 m/s (2780 ft/s ± 30 ft/s) or less. It also provides protection against the threats mentioned in [Types I, IIA, II, and IIIA].

Type IV (Armor Piercing Rifle)

This armor protects against .30 caliber armor piercing (AP) bullets (U.S. Military designation M2 AP), with nominal masses of 10.8 g (166 gr) at a reference velocity of 878 m/s (2880 ft/s ± 30 ft/s). It also provides at least single hit protection against the threats mentioned in [Types I, IIA, II, IIIA, and III].

Type II Body Armor is equivalent to 17 Layers of Kevlar

• Each web of the material named kevlar disperses the impact thereby making good use of its high yield strength.

(To the right, a drawing of how a layer of kevlar looks, and a kevlar bullet proof jacket after absorbing a .357 Magnum, courtosey of sciencemaster.com)

High Speed Video of Kevlar Impact

More Fun Facts on Kevlar...DuPont Kevlar® 149 Fiber, diam. 12µm (used for armour). Facts according to MatWeb (Online Material Property Date for over 61,000 materials)

– Density = 1.47 g/cc– Tensile Strength, Ultimate = 3450 M.P.a. – Modulus of Elasticity = 179 G.P.a

In comparison with 1045 Steel... DuPont Kevlar AISI 1045 Steel,

hot rolled, 19-32 mm -Density =1.47g/cc - Density = 7.87 g/cc

-UTS = 3450 MPa - UTS= 565 MPa-Modulus of E= 170Gpa - Modulus of E= 200Gpa

Lets shoot some stuff

• Our experiment was to determine the effectiveness of various different types of armor.

• To gain further understanding a field study became necessary.

Set up #1

A brittle material represented by wood T.S. 31 MPa

Set up #2

A ductile material represented by rubber T.S. 28 MPa

Set up # 3

A combination of material alternating brittle to ductile

Set up #4

A combination of material, brittle then ductile.

How does a LA-Z-Boy match up to the experiment?

• Cushions are usually made of about 6 inch thick polyurethane, which has a Tensile Strength of 54-76 Mpa.

• Brittle wood backing and metal springs definitly played a crucial role as well.

• CONCLUSION: Parallels can be drawn between the combination of hard and soft body armor and the chair.