PSI - Issue 13

Sheikh Muhammad Zakir et al. / Procedia Structural Integrity 13 (2018) 1244–1249 Sheikh Muhammad Zakir et al. / Structural Integrity Procedia 00 (2018) 000–000

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Figure 2 Schematic of dynamic compression test set-up.

The typical example of stress, strain-rate history and dynamic equilibrium coefficient R(t), of ALS glass specimens in dynamic compression tests, is also presented in figure 3(b).

Figure 3 (a) The typical oscilloscope record of the incident, transmitted and reflected wave signals, (b) The stress, strain-rate and stress equilibrium parameter against time for a dynamic compression test on ALS glass specimen.

After carefully controlling the dynamic equilibrium, the series of dynamic compression experiments were conducted on glass specimens. The representative static and dynamic stress-strain curves are presented in figure 4 (a), it is observed that glass specimens exhibited brittle elastic behavior and both at low and high strain-rates the peak compressive stress results show rate sensitivity (figure 4b). At low strain-rates, the rate sensitivity is seen because during static loading the strength of ALS glass is mostly controlled by the defects like surface flaws and scratches and it follows the weakest link theory. The glass debris also collected after tests to explain the strain-rate effect figure 4 (c, d), it can be seen that at axial static compression loading the ALS glass specimen split into columnar way due to its expansion in the lateral direction and low tensile strength in comparison to compression strength. However, in dynamic compression loading failure is reached when cracked/damaged specimen fully crushes and at high strain-rate the glass ruptures into a fine powder like debris. This explains the underlying phenomenon of increased compressive strength at higher strain-rates because of many failure surfaces generated which enhances the energy/load absorbing capacity of ALS glass at dynamic loading conditions. Figure 5 shows the failure process of ALS glass recorded during dynamic compression test and associated stress time history marked with points. The high-speed images match the five numerals points, captured during the dynamic compression test. The specimen is initially dark and when the crack starts to appear in specimen due to the reflection of the light from the crack surface a bright region can be seen. The two consecutive images were taken after a time interval of 5 μs. It was observed that after 35 μs of the loading process the first crack appears and before this specimen was dark which confirm the uniform deformation of glass specimen. The axial cracks marked in red dotted circle region starts to develop from the incident end and travels towards the transmitted end of the bar. At the time of 50 μs, the specimen was fully covered by the cracks and peak stress in the specimen was recorded, this corresponds to the point 4 on the stress-time curve. After this, the glass specimen loses its load carrying capacity and fails abruptly in fine particles. It can be seen from failure process that axial splitting of leads towards the failure of the ALS glass specimen and surface flaws originating from the impacting surfaces and propagate into the entire specimen. The