Crack Paths 2012

M E C H A N I CBAELH A V I O UORF A C E R A M ILCA M I N A TDEE S I G N E D

W I T HR E S I D U ASLTRESSES

The mechanical behaviour of a layered ceramic composed of thin layers of Al2O3 with

30%monoclinic ZrO2 (referred to as A M Zlayers), sandwiched between thicker layers

of Al2O3 with 5 % tetragonal ZrO2 (ATZ layers) was tested under the four–point

bending. The volume ratio between the A M Zand A T Zmaterial, i.e. VAMZ/VATZ, was ca.

1/6. The properties of both materials were determined in monolithic samples [19] and

are listed in Table 1.

Table 1. Material properties of the laminate components

Gc

[GEPa]

[MPKaIc.m 1/2 ]

Vf [MPa]

Q [-]

Dx106[K-1]

Material

[J/m2]

9.8r0.2

25r2

A T Z 390r10

0.22

422±30 3.2r0.1

A M Z 280r10

0.22

8r0.2

90±20

2.6r0.1

23r2

In order to investigate the crack propagation in the laminate, a sharp notch of depth

3 0 0 mand tip radius of ca. 25 m, was introduced in the first A T Zlayer following the

standard S E V N Bprocedure according to ISO 23146. Due to the tensile residual stresses

in the first layer a local stress intensity factor at the crack tip overcomed the fracture

toughness KIc of the A T Zlayer during the notching process. Thus, a crack between the

notch and the first A T Z / A M iZnterface originated without any additional mechanical

load (see close-up in Fig. 2a). This was the initial state of the specimen (i.e. crack

terminating at the first interface).

b)

B

a)

BxHxL=4.39x4.03x44.5mm

S o = 4 0 m m

S i

Si=20mm

H

L

S o

200Pm

Figure 2. a) Test configuration of the four-point bend experiment on a notched

specimen and b) load-displacement curve recorded during testing.

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