PSI - Issue 13

Stefan Reich et al. / Procedia Structural Integrity 13 (2018) 28–33 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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3. Ball drop tests to determine fracture energy 3.1. Idea

The application of the known techniques ( Error! Reference source not found. - Error! Reference source not found. ) needs a comprehensive preparation. It is unknown, how a simple, dynamic life scale test would produce similar results. Objective of the testing is to show, that there is a direct relation between impact energy of the impact body and crack area and furthermore, whether a specific surface energy, comparable to the known techniques were determined by the testing results. 3.2. Test set-up In Germany the production of laminated safety glass is continuously tested by a ball drop test according to DIN 52338, that is the most commonly performed ball drop test. The test-set up is shown in Figure 5.

Figure 5: Ball drop test set-up for 500 mm x 500 mm glasses according to DIN 52338 (used for production testing of laminated safety glass)

All specimens were made of annealed glasses, 8 mm thick and 500 mm x 500 mm size. The glass panes laid in a 5 mm rubber gasket between lower and upper frame of the test set-up (Figure 5). A steel ball of 1000 g weight served as impactor. Three different drop heights, 6.75 cm, 11.75 cm, and 16.75 cm were investigated, 10 specimens per drop height. A small, 5 cm long scratch in the centre of the lower surface performed as initial crack origin. 3.3. Results The fracture pattern was completely different at three drop heights. Error! Reference source not found. shows, that at a drop height of 6.75 cm the cracking of the scratched pane started and with higher drop height the number of cracks increased. Furthermore, at 6.75 cm drop height, almost no glass powder at the impact point exists, whereas at 16.75 cm much powder was created. The diagrams below in Figure 7 show the crack lengths in the glass panes at different drop heights. The lengths were optically measured and calculated by a computer routine.

Figure 7: Typical fracture pattern at drop heights of 6.75 cm

Figure 6: Crack length depending on the drop heights of 6.75 cm