3 - SC Metals

Consider special environments (high temp, corrosion), specific strength and stiffness (avoid fracture and excessive deflection), and cost (acquisition cost and durability costs)

What should you consider for aerospace vehicle structures?

failure stress per unit mass

What is specific strength?

stiffness per unit mass

What is specific stiffness?

specific stiffness

Most metals have very similar _____

specific strengths

Milds steels, titanium, practical glass, and intermediate carbon fiber composites have similar _____

Specific stiffness

Carbon fiber composites have superior ______

heat treatments

All aircraft metals have special _______ to improve strength or ductility

quenched (cooled quickly to improve strength), tempered (reheated to improve ductility), martempering of large forgings (prolonged quenching in salt or oil to prevent residual stresses)

For special heat treatment, steels are:

typically air-cooled, often “aged” to improve strength, and sometimes refrigerated to prevent “over aging”

For special heat treatment, aluminums are:

crystal “grains”

Metals are made of ____

slip

_____ is the hallmark of ductile materials

a materials ability to undergo significant plastic deformation before fracture

What is ductility?

K (stress intensity factor)

Failure will not occur if _____ is less than the critical stress intensity factor, or fracture toughness (Kapp or Kic)

stress intensity factor

Cracks grow at a rate based on the ______ range during a load event

fatigue

failure due to repeated loading at levels significantly below the yield strength

The stress at which materials begin to deform plastically, meaning it won’t return to its original shape

What is yield strength?