Issue 14

B. Lo

bato da Silva et

alii, Frattura ed

Integrità Struttu

rale, 14 (2010)

17-26; DOI: 10

.3221/IGF-ESIS.

14.02

Mod

el

Equat

ion to estima

te the equiva

lent alternatin

g stress Eq

uation

a 

S



  

  

ar



Goodm

an

(17)

1



m

S

rt

a 

S



ar

2   

  

(18)

Gerb

er



1



m

S

rt

1 

   

  

2

Walk

er

(19)

S

  

ar

a

R

1



a       e

  



m

Kwo

fie

(20)



S

S

rt

ar

Table 4 : Equ f the Kwofi

ations used to e and Walke

estimate the e r’s models, 

quivalent alter and  , resp

nating stress. ectively, the

To res

estimate the pectively.

exponents o

Eqns. 21 an

d 22 were u

sed,

  





  m rt S N   





b 

'

S 

e

1    2 1 R     R f

(21)

1 R

a

     1 

(22) ab. 5 shows

b

' f S N

 

1 R 

a  e estimate of ained results

R

1



Levenberg-M

ethod [11]. T

the

Th obt

parameters .

 and  was

accomplish

ed using the

arquardt m

Expected stimate Sta 0.407 1.453 ameters that c

value ndard error 0.019 0.084 haracterize Kw

Confiden

ce intervals Standard erro 0.468 1.720 ker’s models.

P

arameter E   Table 5 : Par

Estimate 0.346 1.187 ofie and Wal

r

R E Tes F

SULTS AND

DISCUSSIO

NS

ts with ratio l or the ra 7 show t

oading, -1 tio loading e he statistic b

and

qual -1, 11 sp ehavior of th

ecimens wer e estimated f

e used of sam atigue lives fo

ple A and 2 r such stress

2 specimens level.

of sample B

. The Tab. 6

S a

(

MPa)

4

17

4

40

4

63

5

09

56

6 .3 e+03

S a / M Dev CV

S rt

(%)

4

6.9 4 e+05 3.51 e+05 5.73 6.7 1 tatistic behavi

9.4 52 e+05 1.99 e+04 4.92 6.3 0 or of fatigue li

.1 57 e+05 8.03 e+02 2.63 .2 32 ves ( R = -1 ) -

.2 63 e+04 9.38 e+04 * .7 * Sample A.

ean 9.63 iation 5.46 (%) 5 Table 6 : S

21