Issue 22

A. Brotzu et alii, Frattura ed Integrità Strutturale, 22 (2012) 20-25; DOI: 10.3221/IGF-ESIS.22.03

Figure 4 : SEM micrograph showing the fracture surface morphology.

In this work four CT specimens were used for toughness tests. The curves load vs. displacement (Fig. 5) were elaborated according to the ASTM E 399 standard in order to obtain the load values required to calculate the K IC . All the obtained data are reported in Tab. 2. For all the tested specimens the value of P 5 coincides with the value of P Q and the ratio P max / P Q , which is the first acceptance criterion established by the ASTM standard, is always lower than 1.10. It is then possible to calculate the K Q values. The calculated K Q values are: 16.9 MPa  m for specimen 1, 16.6 MPa  m for specimen 2, 15.56 MPa  m for specimen 3 and 23.8 MPa  m for specimen 4.

4500

Specimen 1

Specimen 2

Specimen 3

Specimen 4

4000

3500

3000

2500

2000

1500 Load (N)

1000

500

0

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

Displacement (mm)

Figure 5 : Load versus displacement curves obtained for the four specimens.

P max ( kN) 2.888 2.822 2.207 3.969

P 5

=P Q

K Q ( MPa  m)

Acceptance criteria

( kN) 2.888 2.800 2.207 3.850

P max

/ P Q

<1.10

R p

< 9.7 mm (B)

Specimen 1 Specimen 2 Specimen 3 Specimen 4

16.9 16.6 15.5 23.8

1.00 1.01 1.00 1.03

3.8 3.6 3.2 7.5

Table 2 : Data obtained from the load- crack displacement curves.

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