Crack Paths 2009

0 α is the normalized initial crack length, α

where W is the width of specimen,

is the

()

α

and are empirical constants of the Paris law and C m

normalized crack length,

f

is the shape factor of the stress intensity factor.

Furthermore, if two sensors of different properties are employed, two equations on the

cyclic number N can be obtained and the cyclic number and the stress amplitude can be

estimated as shown in Figures 2(a), 2(b).

106

6

10

(a)

(b)

10 12 34 5

5

10

4

10

3

10

2

10

0.5 0.55 0.6 0.65 0.7 0.75 0.8 Steel bar 3450MP

1

Steel bar

30MPa

1

40MPa

10

50MPa

1

0.5 0.55 0.6 0.65 0.7 0.75 0.8

Normalized crack length, α

Normalized crack length, α

Figure 2. (a) Cyclic number obtained from the crack lengths in 3 sensors As-received

104

STEEL σ = ()b) Cyclic num;ber obtained from the crack lengths in 3 M P a

and steel bar (

104 M P a

σ

sensors heat-treated and steel bar (

=

)

STEEL

Estimation of the MaximumStress

A Eevent is generated due to microcraking, slip deformation and so on when materials

is loaded. It is well known that microcracking and slip deformation are generally

irreversible phenomena.. After smart stress-memory patch is removed from the

structure, A E measurement is conduced during tensile loading. Then, the maximum

stress can be estimated as the onset stress when A E activity increases due to Kaiser

effect, as shown in Figure 3.

E X P E R I M E N TPARLO C E D U R E

Materials and Geometry

The patch was made of electrodeposited (ED) copper because of its good corrosion

resistance, stable crack growth and easily observation of the crack length. As-received

and heat-treated (400°C, 30 min) E DCu coupons with 0.1 m mthickness were prepared

for the fatigue test and A E measurement. Heat-treated (400°C, 30 min) rolled Cu

coupon with 0.2 m mthickness was also used for A Emeasurement. The mean grain size

was about 2 µ m for the As-received E DCu coupon, about 4 µ m for the heat-treated E D

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