Chap 03 - Mech Properties of Material

8/19/2019 Chap 03 - Mech Properties of Material

1/48

Mechanics of Materials ISKMM1113

MECHANICAL PROPERTIESOF MATERIALS

Instructor:

Dr Muhammad Adil Khattak

(PhD,ME,MBA,BE)

017-8272871

[email protected]


2/48

hat!s It "#out$

• %his lecture is a#out the mechanical&ro&erties of materials

• 'o( to measure them and use them.

• It!s im&ortant for any material (hichis )oin) to #e su#*ected tomechanical forces in use.

• %hese forces cause the material todeform +i.e. chan)e sha&e, and maycause it to fail +i.e. #rea,.


3/48

Mechanical ro&erties in/esi)n

• /esi)ners need to no( a#outmechanical &ro&erties

• to choose the ri)ht material for a)ien com&onent +e.). a car!scranshaft, or structure +e.). a dam,.

• %hey need to mae sure that there(on!t #e too much deection underload and that the forces (on!t #ehi)h enou)h to cause failure.


4/48

45am&les of 6ailures


5/48

45am&les of 6ailures


6/48

/enin) and Measurin) Mechanical

ro&erties

• %here are lots of mechanical&ro&erties in this lecture (e are *ust)oin) to loo at the sim&lest +and

most im&ortant, ones (hich (e callthe 9static &ro&erties.

• %hese can #e measured usin) ery

sim&le tests conducted on sam&lesof the material.

• %he most im&ortant test is the tensile

test


7/48

Sim&le %ensile %est


8/48

Some racticalities


9/48

%he Stress;Strain


10/48

%y&ical =esults


11/48

Stress Strain /ia)ram


12/48

%y&ical Stress Strain>ehaiour


13/48

Stress Strain /ia)ram


14/48

%ensile S&ecimen ? %he


15/48

6racture 6eatures:


16/48

Im&ortant Mechanical ro&ertiesfrom a %ensile %est


17/48

%erminolo)y


18/48

%he stress;strain cure in more

detail


19/48

ield Stren)th


20/48

%ensile Stren)th %S


21/48

StiAness


22/48

Bsin) StiAness


23/48

Bsin) StiAness


24/48

%ou)hness


25/48

%ou)hness


26/48

Strain hardenin)


27/48

Strain 'ardenin) +n K or <alues,


28/48

/uctility C4D


29/48


30/48

oisson 4Aect

• hen a material is com&ressed in one direction itusually tends to e5&and in the other t(o directions&er&endicular to the direction of com&ression.

• %his &henomenon is called the oisson eAect.

• oissonEs ratio +nu, is a measure of the oisson eAect.

• %he oisson ratio is the ratio of the fraction +or&ercent, of e5&ansion diided #y the fraction +or&ercent, of com&ression for small alues of these

chan)es.

long

lat vε

ε −=

long

lat vε

ε −=


31/48

4n)ineerin) Stress


32/48

Shear Stress-strain


33/48

6ailure of Materials due to


34/48

'i)h %em&erature Material ro#lem


35/48

hat is


36/48


37/48

F#*ectie:


38/48

The gradual deterioration of a material that issubjected to time-varying loads.

FTI!"#


39/48

Structures subjected to fatigue loading

Jack-up structure

Lifter (photo courtesy

P.M. Anderson)


40/48

$. The stresses have been repeated a

very large number of times

%. ctual ma&imum stresses were below

the ultimate strength (even below theyield strength) of the material

'. egins with a small crac at a point of

discontinuity in the material.

*. !ives no warning+ it is sudden and

fatal.

6ati)ue

failure


41/48


42/48

'o( to reco)niHe fati)ue in a

#roen &iece

• each mars on the fracture surface &$%

Indications of loading

changes

• /triations

01 (/how indiv.2ycles)


43/48

45am&le 1


44/48

Solution


45/48

Solution


46/48

45am&le 2


47/48


48/48

Solution

Chap 03 - Mech Properties of Material

Documents