Crack Paths 2009

Tensile specimens have higher negative

cef T ,

range in comparison with bending

specimen. It means that constraint is less for tensile specimen. The D C Bspecimens

cef T , - s t r e s s values. These positive

cefT, -stress values have

exhibit particular positive

some influence on stability of crack propagation. The S E N Tand C T specimens have a

high negative value of the

cef T , -stress. For these specimens, crack extension is observed

along x direction, i.e. perpendicular to the principal tensile stress. This can be clearly

seen in Fig. 7a and b.

X20

X20

Figure 7a. Stable crack extension in SENT specimen. cefT, = -348 M P a

Figure 7b. Stable crack extension in

C T specimen.

cefT, = -328 M P a

X1

X20

Figure 7c. Crack bifurcation in D C B specimen. cefT, = + 78 MPa.

Figure 7 d. Stable crack extension in TR.

cefT, = - 111 MPa.

Crack bifurcation appears after initiation in D C B specimens, this well-known

phenomenon is an attribute of positive T-stress [10]. In order to prevent crack

bifurcation, it is recommended to use the tapered D C Bspecimen. In this case, we return

cefT, value, and for this reason the crack extension is

to a specimen with a negative

stable in x direction.

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