Mechanical Properties: Review

l0

A0

F0

FA

0

0

l l

l

(str

ess

)

(strain)

Y

nominal (engineering)

00 0 0

lnl

totall

dl dl ld

l l l

true

i

FA

plastic – rearrange chemical bonds

elastic – stretch chemical bonds

stress

strain

true (, )

nominal (s, e)

(s

tre

ss)

(strain)

Y

plastic

elastic

y

load

Definitions

unload

0.2 %

y = yield strength 0.2% offset yield strength

y = elastic limit

strength – some value of stress

Definitions & Comparisons

P. L. Mangonon “Principles of Materials Selection for Engineering Design” Prentice Hall, Upper Saddle River, NJ 1999.

necking

necking

UTS = (ultimate) tensile strength

upper yield strength

lower yield strength

X

fracture without yield (ionic/colavent bonding)

Xfracture strength

ductility = strain at failure

y

= F/Ai

Definitions

(str

ess

)

(strain)y = elastic limit ductility

X

resilience = energy to plastic deformation0

y

RU d energy/vol

PdV energy

/ F A pressure

recall:

Elastic region: Y

0

y

RU Y d 2½ yY

½

2

½

y

Y

toughness = energy to failure

Shear stress from uniaxial tension

AF

FA force is normal to the planenormal stress

A′

n̂

consider what happens on some other plane, A′

need to know area of A′

A′ = A/cos()

consider shear force parallel to A′ along an arbitrary directionF′

need to know magnitude of F′

F′ = Fcos()

F′ can be along any direction parallel to A′ (each corresponds to a different )

Given and :

F

A cos sin

F

A cos sin res

Solute Hardening

Precipitate Hardening

coherent incoherent