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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with increase in notch root radius. The presence of sharper notch facilitates the easy propagation of crack which results in lesser amount of energy absorption. Fig. 4 shows that a linear relationship between K IQ and ρ is obtained for hybrid composite reaching to a critical value of notch root radius (ρ o ) below which the apparent fracture toughness is invariant and such invariant K IQ is the material fracture toughness. The critical value of notch root radius (ρ o ) thus determined is approximately equal to340 µm. This implies that in composite, if notch root radius is below the critical value then the fracture toughness is solely a material property conditional to the fact that the criteria for linear elastic fracture mechanics (LEFM) and plane strain are satisfied.

Table 4. Effect of notch root radius on apparent fracture toughness of hybrid composite specimens. Specimen No. Thickness of isomet blade used (μm) Notch root radius (ρ)(μm Notch root radius (√ρ)(√μm)

Fracture toughness, (K Q ) MPa√m

K Q1

100

110.04

10.49

2.534

K Q2

150

203.34

14.26

2.840

K Q3

300

339.66

18.43

2.923

K Q4

300

416.98

20.42

3.017

K Q5

300

553.19

23.52

3.248

K Q6

300

750.21

27.39

3.434

Fig. 4. Variation of apparent fracture toughness with square root of notch root radius.

4.2. Linear elastic fracture toughness This part of the work describes the experimentally measured values of the Mode-I plane strain fracture toughness (K Ic ) of hybrid composite. This provides a quantitative measure of fracture toughness. The results are valid, if the plane strain conditions are satisfied (Xian et al. (2012)).The conditional plane strain fracture toughness (K IQ) is evaluated as per ASTM D 5045-99, the data is subjected to validation so that the K IQ values thus calculated are verified to be K IC . In all cases the values of (P max /P Q )<1.1 and also the thickness validity criterion B, a, W-a≥2.5 (K Q /σ f )2 has been found to be satisfied. Hence, the obtained results are valid and the values can be termed as K Ic . Further, though the specimens with varied a/W were tested, data corresponding to specimens with a/W values in between 0.45-0.55, as specified by the ASTM D 5045-99, were only used to arrive at K Ic . All the test samples exhibit valid K max /K IQ values (<1.1). In view of these observations, the K Q values derived from specimens with a/W of 0.45 to 0.55 are termed as K Ic . The K Ic values thus calculated for test specimens are given in Table 5.