Crack Paths 2009

3 2

)( ) 0.857 0 . 2 6 5 1

{

}

(

) ( 4

α − +

α α −

0.265 1

K W σ π α Δ = Δ ×

+

(2)(2)

A EMeasurement

A Ebehaviour was measured to obtain the maximumstress using Kaiser effect during

tensile loading. Three types of specimens were prepared. These were a smooth

specimen, a notched specimen with 0.5 normalized notch length and a cracked specimen

after fatigue crack growth. A E behaviour under monotonic loading was measured to

estimate the onset stress of AE, and A E behaviour after fatigue loading was also

investigated

investigated to examine Kaiser effect. A E sensor (M304, Fuji Ceramic Corp.) was Corp.)

attached to the surface of each specimen and A E waveform was recorded by C W M

(continuous wave memory) system. The cross-head speed for the tensile loading was

0.1 mm/minand 200 K H zhigh pass filter was employed in A Emeasurement.

R E S U L TASN DDISCUSSION

Fatigue Crack Growth Behaviour

The crack growth of each sample was obtained from the fatigue test. Results in the case

of 0.1 stress ratio are shown in Figures 4(a), 4(b). The crack growths was affected by

the maximumstress and the slope of Paris Law, m , is about 2.61 and 3.00 in As

received E D and heat-treated Cu specimen respectively. The crack growth also

depended on the stress ratio. It is found that the crack growth of this patch is

substantially affected by the maximumstress and the stress ratio.

10-9 -87 3 4 5 6 7 8 9 1 0 20 30 y = 6.1981e-11 * x^(2.6134) R= 0.796 Bar34kN(as) 68 Stress Intensity Factor range, Δ K(MPam½)

y = 6.9404e-11 * x^(2.9952) R= 0.97219 Stress Intensity Factor range, Δ K(MPam½)

(a)

(b)

10-9 -87 3 4 5 6 7 8 9 1 0 20 30

a te ,

/ c y c l e )

C r a c k g r o w t h r

m=2.61

m=3.00

( m

Bar34kN(400-30) 6

Figure 4. (a) Stress Intensity Factor under uniform displacement for steel bar (As

received) under the maximumstress of 80, 86 and 89 MPa; (b) Stress Intensity Factor

under uniform displacement for steel bar (heat-treated) under the maximumstress of 80

and 86 M P a

In these results, the crack growth rates are smaller than those of bulk specimens of

pure Cu in the same stress intensity factor range. Because the thicknesses of specimens

540