strength of materials ch 1

8/9/2019 Strength of Materials Ch 1

1/27

STRENGTH OFMATERIALS

MOHAMMAD AIZRULSHAH BIN KAMARUDDIN

PPPTDH42M PRODUCT DESIGNDEPARTMENT OF MECHANICAL ENGINEERING

POLITEKNIK MUADZAM SHAH

BY

JJ310


2/27

CHAPTER 1

FORCES ONMATERIALS

JJ310

This topics will analyses the efect oorces on materials H!!"E#s $A%&&hear stress an' &hear an' &hear strain

Objective

s• E(plain the efect o orces on materials• )iferentiate *etween tensional compression an' shear orces• )e+ne stress strain an' Y!,-.#& /!),$,&


3/27

!,T$-E

orces on materials

• )ynamics

• &tatics• mpact• ati2e an' Alternatin2 loa's

Type o orces• Tensional• compression• shear

$!A)-.&

&TRE&& &TRA-• Tensile

• compressi4e

/o'ls o Elasticity


4/27

Efects orces on materials

orceF!ce is a "#$%tit$tive 'escription o thei%te!$cti% bet&ee% t& '()*ic$+ b,ie* sch asan o*5ect an' its en4ironment6 orce is proportional toacceleration6 n calcls terms orce is the 'eri4ati4eo momentm with respect to time6 ,nit in - or 82m9s:

%here

•

http://physics.about.com/od/glossary/g/acceleration.htmhttp://physics.about.com/od/glossary/g/momentum.htmhttp://physics.about.com/od/glossary/g/momentum.htmhttp://physics.about.com/od/glossary/g/acceleration.htm


5/27


loa'in2s)ynamics

The ri2i' *o'y in analysis is in motion6

&tatics

The ri2i' *o'y in analysis is in stationary state6

mpact

is a hi2h orce or shoc8 applie' o4er a shorttime perio' when two or more *o'ies colli'e

http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Shock_(mechanics)http://en.wikipedia.org/wiki/Shock_(mechanics)http://en.wikipedia.org/wiki/Force


6/27


ati2e

wea8enin2 o a material case' *yrepeate'ly applie' loa's; alternatin2 loa's<

Alternatin2 loa's• Load that is applied, removed and applied again, always acting on the same

direction

• Alternating load that reverse direction during every cycle of loading.

• Fluctuating load that varies about an average value.

commonly associated with machinery, engines, turbines, generators, shafts,

propellers, airplane parts, automobile parts..


7/27

TYPE ! !RCE&

Tensile Tensile is a orcethat ten's to stretch a material6

increase the len2th

E(ample=

CompressionCompressi4e is aorce that ten's tosqueeze or crush amaterial6

E(ample=

&hear&hear is a orce thatten's to slide oneace o the materialo4er an a'5acentace6

*en' sli'e or twist6

E(ample=

'ecrease the len2th


8/27

Pro*lem 1

i2re ;a< represents a crane an' i2re

;*< a transmission 5oint6 &tate the typeso orces actin2 la*ele' A to 6


9/27

&TRE&& > &TRA-

&TRE&&

• The intensity orces actin2 on a material innormal 'irection that case 'eormation or

chan2e o 'imension6• Ratio o applie' orce F, cross sectional area A o the material

• Tensile stress

• Compressi4e stress

1 Pa =

1N/m2

-


10/27

E(ample 1

i2re 16 &hows a steel *loc8 with crossarea o 1?000mm: s*5ecte' to loa'in2shown6 )etermine the normal stress

/@?00".

@ 3:000


11/27


12/27

&TRE&& > &TRA-

&train

• &train is the 'eormation per nit o the

ori2nal len2th

Where; δ = the deformation

L= original lengt h

• Percenta2e &train

(100

•

• Tensile strain• Compressi4e strain


13/27

E(ample 3

A *ar 160 m lon2 contracts a(ially *y 061mm when a compressi4e loa' is applie' toit6 )etermine the strain an' the percenta2e

strain6

St!$i%. @ @ @@

Percenta2e strain

•


14/27

E(ample D

A wire o len2th :6?0 m has apercenta2e strain o 0601: whenloa'e' with a tensile orce6 )etermine

the e(tension o the wire6


15/27

/o'ls o elasticity

• ratio o stress ;orce per nit area< alon2an a(is to strain ;ratio o 'eormation o4erinitial len2th< alon2 that a(is

• is a /e$*#!e 0 *ti%e** o an elasticmaterial6

• t is se' to 'escri*e the elastic propertieso o*5ects li8e wires ro's or colmns whenstretche' or compresse'6


16/27

• &i2n or Yon2#s mo'ls @ E

• ormla 2i4en

@ @ @

•

/o'ls o elasticity


17/27

• $aw o elasticity on'e' *y Ro*ertHoo8e

• &tate that – the e(tension o a material is

proportional to applie' orce6

HOOKE’S LAW

%here " is aconstantF 'istance


18/27

• actor o saety – Ratio o ma(imm stress that a

strctre or material can with stan' to

the ma(imm stress estimate' or it6

• /st *e 2reater than 160

•

HOOKE’S LAW


19/27

• %or8in2 stress G allowa*le stress – /a(imm &tress 4ale within the elastic

re2ion that mst not e(cee'

G

•

HOOKE’S LAW


20/27

• D#cti+it) is the a*ility o a material to *e plastically'eorme' *y elon2ation withot ractre6 This is a propertythat ena*les a material to *e 'rawn ot into wires6

• B!itt+e%e** is the property o a material manieste'*y ractre withot apprecia*le prior plastic 'eormation6Brittleness is a lac8 o 'ctility an' *rittle materials schas cast iron 2lass concrete *ric8 an' Ceramics6

• M$++e$bi+it) is the property o a material where*y it

can *e shape' when col' *y hammerin2 or rollin26 Amallea*le material is capa*le o n'er2oin2 plastic'eormation withot ractre6 E(amples o mallea*lematerials incl'e lea' 2ol' ptty an' mil' steel

HOOKE’S LAW

t t


21/27

t!e** t!$ %

Di$3!$/• ,ltimate tensile Test


22/27

&tress strain 'ia2ram

D

U C T I L

E

B R I T T L

E


23/27

)E-T!- • A ratio *etween lateral strain an'

lon2it'inal strain

• )imensionless• ,sally pro4i'e' *y the manactrer o

the material

• ormla 2i4en

where

POISSONS

RATIO


24/27

E(ample ?

A *ar ma'e o AI3 steel has the 'imension o shown in +2re*elow6 an a(ial orce o P @ 08- is applie' to the *ar

'etermine the chan2e in its len2th an' the chan2e in the

'imension o its cross section ater applyin2 the loa'6 The

material *eha4e elastically6.i4en

@ :00.Pa


25/27

)e+nition

• The ratio *etween sheer stress an' shearstrain

• Kale can *e o*taine' e(perimentallyrom the slope o &TRE&& &TRA-'ia2ram6

• 'enote' *y sym*ol L.# nit Pa6• ormla 2i4en

/o'ls o Ri2i'ity


26/27

&-.$E &HEAR


27/27

)!,B$E &HEAR

strength of materials ch 1

Documents