PSI - Issue 14

Arun Kumar Singh et al. / Procedia Structural Integrity 14 (2019) 720–728 Arun Kumar Singh et al./ Structural Integrity Procedia 00 (2018) 000–000

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In this work, single edge notch bend (SENB) specimens were used to determine the critical notch root radius and plane strain fracture toughness. Notches of different crack length have been developed in the test samples using diamond wafer blades mounted on a standard cutting machine. All the specimen dimensions were accurately measured using optical profile projector. Notches of constant length having crack length to width ratio of 0.45–0.55 and varying notch root radius (ρ) were introduced. The notches thus introduced were found to have finite root radius (ρ) typically of the orders varying from 110 to 750 µm. The crack lengths were maintained as per ASTM D 5045-99 for the determination of K Ic values. The load vs. displacement curves for different depth of cut to width (a/W) ratio have been shown in Fig. 2. In order to calculate apparent fracture toughness K Q , it is required to obtain a load and displacement diagram as given in the typical case as a Fig. 3. It is required to draw a best tangent line as shown by dotted line in Fig. 3 to determine the initial compliance (C). C is given by the reciprocal of the slope of tangent line.Another line with compliance 5% greater than that of tangent line has been drawn. It has been found that P max in all cases lies outside of both lines, hence, P Q has been considered for the calculation of K Q .

Fig. 3. Conditional load curve.

Table 3. Apparent fracture toughness (KQ, MPa√m) data of hybrid composite specimens. S No. Specimen Name Sample Size Depth of Cut (a) (mm) Notch root radius (ρ) (μm) a / W f(x) P Q

P max

K 1Q MPam 1/2

K max MPam 1/2

Width (W) (mm)

Thickness (B) (mm)

1

K Q _1

10.42

5.58

3.52

110.04

0.338

6.709 215.21

228.51

2.534

3.19

2

K Q _2

10.38

5.61

3.96

203.34

0.382

7.535 215.43

232.70

2.840

2.74

3

K Q _3

10.36

5.65

4.19

339.66

0.404

8.025 209.48

232.09

2.923

3.47

4

K Q _4

10.55

5.62

4.61

416.98

0.437

8.800 197.91

217.56

3.017

3.36

5

K Q _5

10.35

5.72

5.17

553.19

0.499

10.63 3

177.74

194.91

3.248

3.96

6

K Q _6

10.41

5.70

4.51

750.21

0.433

8.876 229.41

254.19

3.434

2.97

The data regarding notch root radius and specimen dimensions along with the obtained fracture toughness are given in Tables 3 and 4. The K IQ as a function of notch root radius and the data are summarized in Table 4. It can be clearly seen that specimens with lower notch root radius exhibits lower fracture toughness and the value increases