PSI - Issue 14

M.K. Singh et al. / Procedia Structural Integrity 14 (2019) 475–481 M. K. Singh, R. Kitey / Structural Integrity Procedia 00 (2018) 000 – 000

478

3.2. Fracture test

Single edge notch beam (SENB) specimens of dimension 75 mm x 15 mm x 5 mm are machined following ASTM D5045-14 standards. To produce a natural crack, initially an edge notch of 4 mm is machined at the mid span of the sample. A sharp razor blade is placed into the machined notch and tapped gently by hammer. Care is being taken to initiate a straight natural crack with in specified range of a/w ratio (0.45 to 0.55) where a and w represent the initial crack length and width of the specimen, respectively, as illustrated in Fig. 2. The specimens are loaded symmetrically in a three-point bend fixture under displacement control mode by employing universal testing machine INSTRON 3345. Stress intensity factor (SIF), K I , is calculated by using linear fracture mechanics,

P

  

  

K

f ( ) 



(3)

I

1/ 2

BW

where

2

3/ 2 [1.99 (1 )(2.15 3.93 2.7 ) f ( ) 6 (1 2 )(1 )            

(4)

In the above equation f(ξ) is geometric parameter with ξ = (a/w). To find the critical stress intensity factor K IC the load P is replaced by the load corresponds to the fracture initiation.

Fig.2. SENB sample configuration for fracture test

4. Result and discussion

4.1 Flexural analysis of composites

Flexural stress vs. flexural strain data for the tested composites are plotted in Fig. 3. The plots show linearly varying stress-strain curves for all filler cases. Consistently increasing slope of the curves indicates that the composite’s stiffness increases with increasing filler size. Flexural moduli calculated from the data are tabulated in Table 1. The data shows that 1/4” fiber reinforcement has enhanced the composite’s flexural modulus by ~ 30% when compared to the neat epoxy case. Similarly, the composites exhibit more than 20% and 5% increase in the moduli for the 1/8” and 1/32” filler cases, respectively. While failure stress and failure strain values in neat epoxy are higher when compared to the composites, the plots exhibit nearly the same failure strain for all filler cases. Failure stress on the contrary shows increasing trend with increase in the filler size. The flexural strength of all tested samples are tabulated in Table 1.