PSI - Issue 60

A.B. Penurkar et al. / Procedia Structural Integrity 60 (2024) 355–363 A. B. Penurkar/ StructuralIntegrity Procedia 00 (2023) 000 – 000

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(a) (b) Fig. 3: (a) Universal testing machine used for experiments (b) Zoomed view of machine attachments.

3. Determination of scatter in fracture stress of glass specimen The maximum load at fracture of the glass for 4 mm and 8 mm thickness was obtained through three point bend testing. The typical load vs displacement plot for the 4mm thick and 8 mm thick specimen are shown in Fig.4. The load vs displacement behavior of glass is elastic till the maximum load reached. Then there is sudden drop in load from maximum value to zero value owing to its brittle fracture. The maximum load at which the glass specimen broke is noted and it is used for obtaining the failure distribution of glass samples. The maximum load required for 4 mm glass specimen to break was evaluated as 285 N as shown in Fig. 4(a). However, after observing the scatter of all glass samples for 4 mm thickness, it was observed that this test was an outlier evaluated using box plot and interquartile range approach. The box plot along with the interquartile range for both the specimen thickness is shown in Fig. 6 (a) and (b). It can be observed that only one outlier is obtained for 4 mm specimen thickness, however, no outliers were obtained for 8 mm specimen thickness. The maximum and minimum load for 4 mm glass samples was found out to be 255 N and 175 N respectively as shown in Fig. 5(a). The scatter in the load for 4 mm glass thickness was around 80 N. The median fracture load at which 50% of the failure occurs is around 211 N which is approximately the mean of maximum load and minimum load. The maximum load required for 8 mm glass specimen to break was evaluated as 977 N as shown in Fig. 4(b). The maximum and minimum load for 8 mm glass samples was found out to be 977 N and 633 N respectively as shown in Fig. 5(b). The scatter in the load for 8 mm glass thickness was around 300 N. An important observation can be noted from these plots is that there is substantial increase in median value of fracture load required for glass to break for 8 mm thick glass as compared to 4 mm glass. This is due to the increase in probability of finding a defect with simultaneous increase in thickness of the specimen. As probability of minor or major defects in the glass increases, the load shall increase or decrease substantially, as observed from the scatter in load at fracture of 8 mm thick glass. The median fracture load is around 780 N which is closer to minimum fracture load. This shows that nearly half of the 8 mm thick glass fails near to its minimum load as compared to the maximum load. This is not the case for 4 mm thick specimen where median fracture load occurs near to the mean of maximum and minimum load.