Fatigue Test

 

 Jordan University of Science Science and Technology Technology

Faculty of Engineering Industrial Engineering Department

Engineering Materials Laboratory Ep! "# Fatigue Test   Student$s name% Mateel &asser 'anna 'addad Student$s (o!% )*+,**)-*++

Teacher% Dr!  .mar /ataineh Teacher assistant % Mo$men 0babah

Date of the eperiment % -1,1)*+2 Due date %+21,1)*+2

section % #

1

 

% Table .f 3ontents 4age number

Description

4age +

.b5ective 6 introduction

4age )

Setups

4age ,

 procedure

4age #

3alculations

4age 9 4age 2 4age :

S1( curves for cold 7or8ed steel and aluminum Discussion 3onclusion and references

2

 

.b5ectives % 11-T To und unders ersta tand nd the beh behavi avior or of di dier erent ent mat materi erials als und under er uc uctua tuatin ting g (cyclic or periodic) loads in service. 2-To dierentiate the appearance of fatigue fracture from other types of  fractures.

% Introduction Fatigue is is a progressive and localized structural damage occurs hen the components are sub!ected to uctuating or cyclic loading such as suspended bridges" rails" or airplane ings. Though the uctuating load is normally less than the yield strength of the materials" it results in fracture behaviour hich is more severe than that achieved from static loading.

  #atigue atigue fai failur lures es are are the there refor fore e unp unpre redic dictab table" le" and pr provi ovide de hig high-r h-ris$ is$ situations" if the operators are not aare of material behaviour hen sub!ected to fatigue loading. #atigue failures can be easily observed from its uni%ue characteristics of  fracture surfaces" revealing as a beach mar$ pattern as shon in &g.1 (a)" fatigu fat igue e fai failur lures es ar are e als also o dri driven ven by sev sever ere e env envir ironm onment ent.. #or e' e'amp ample" le" corrosion fatigue is a combined situation of fatigue loading in a corrosive environment as illustrated in &g 1 (b). #atigue life is inuenced by a &nish" microstructure" microstructure" vari va riet ety y of fa fact ctor ors" s" such such as temperature" temperature " surface &nish" o'idizing   or inert  inert  che chemic micals als"" re resid sidual ual str stress esses" es" con contac tactt presence of o'idizing (fretting fretting)" )" etc.

#ig.1  a) # #atigue atigue surface b) corr corrosion osion   

 

% Setups % Fatigue testing machine1+ *ne of the machines used to determine the fatigue limit is the fatigue testing machine! +n this machine a standard specimen is used here it is supported in a rotating chuc$ at one end and at the other end ith a load (p) applied through a ball race. +n this type of cantilever loading each point innthe circumfer circumference ofpress the specimen is sub!ected to stres stress s bet betee een ten tensio sion n andence com compr ession ion. . To &nd the fat fatigu igue e alternate lim limit" it" di dier erent ent .specimens are tested at dierent loading till failure occurs

#ig.2 #atigue testing

)1 Test specimens %   T  To o materials ar are e tested " one shos a fatigue limit (ferr (ferrous ous metal" cold or$ steel ) and the other does not sho this limit (non-ferrous metal" cold or$ ,luminum ).

#ig. cold or$ aluminum

#ig.2 cold or$ steel



 

%4rocedure 1-elect to materials" one shos a fatigue limit (ferrous metal) and the other does not sho this limit (non-ferro (non-ferrous us metal). 2-Ta$e at least to standard specimens from each material. -/ount the specimen in the machine and &' it properly" then apply the re%uired re%uir ed load by the loading system. -/a$e sure" that the reading of the revolution counter is zero" and then start the machine. 0-hen the specimen is bro$en" read the number of revolutions (cycles)" as indicated by the revolution counter of the machine.  MY  σ  

=

 I 

-3eterm -3ete rmine ine the app applie lied d str stress ess from from the re relat lation ion   as e'plain e'plained ed above. 44-T Tabulat abulate e the obt obtain ained ed resul results" ts" tog togeth ether er it ith h the giv given en re resul sults ts fr from om previous tests. 5-#rom these results" plot the -6 diagram for each tested material" on the same graph paper. 7-8ompare the obtained -6 diagram ith the diagram given in the lab handout and 19-:'amine the appearance of   the fracture for each sample ith the pictures also provided in the handout .

#ig #atigue test procedure using fati ue testin machine 0

 



 

 3alculation ,fter performing the fatigue test" ma'imum stress that as obtained that caused the sample to brea$ ill be calculated using the formula M

σ   =

y

I

 

here / is the bending moment (6.m) and + is the second moment of  π    D

4

64

 ( m 4 )

) and y half the thic$n thic$ness ess of the s sample ample (y;3t >t have a de& de&nit nite e fatigu fatigue e limit   .

11

 

3onclusion % +1 #atigue is a normal phenomenon that ill cause a material to fail eventu eve ntuall ally y und under er alt alter ernat nate e loa loadin ding" g" re regar gardle dless ss of the num number ber of  cycles. )1 #atigue is tested using the fatigue testing machine and its value is obtained from plotting the -6 curve" here stress is calculated  MY  σ  

=

 I 

,1

#1 91 21

using the formula #ati atigue gue ae aecte cted d by des design ign" surfac face e %ua %ualit lity" y" materi material al typ type" e" gra grain in   " sur size" siz e" dir directi ection on of loa loadin ding" g" gra grain in siz size e and tem temper peratu aturre and oth other er factors. 8old or$ing increases the fatigue strength. 3uctile materials have a loer fatigue limit than brittle materials. #atigue fracture shape diers in structure from other fractures used from other types of failures" as it consist of three zones ( initial crac$ zone" propagation zone

:1 +annd &nal the is larger brittle

fruaccttiulere m zoante d e)rials propagation zone than that of the materials.

#ig.5 crac$ propagation

0eferences % g