The ‘Bullet’ Project By:Lucas Rhymes, Scott Parks, Brian Botteri 12/12/06 Engr 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 from bullets under 1000foot/second and the .357 Magnum rendered them utterly useless Information courtosey of Wikipedia

Body armor via LA-Z-Boy Body Armor Types Body Armor - Thick metal plates, brittle and heavy. Soft Body Armor – highly ductile material that will absorb energy, usually kevlar Combination - The best of both worlds!!

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

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.

A brittle material represented by wood T.S. 31 MPa Set up #1 A brittle material represented by wood T.S. 31 MPa

A ductile material represented by rubber T.S. 28 MPa Set up #2 A ductile material represented by rubber T.S. 28 MPa

A combination of material alternating brittle to ductile Set up # 3 A combination of material alternating brittle to ductile

A combination of material, brittle then 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.