PSI - Issue 14

5 5 5

Neelanchali Asija Bhalla et al. / Procedia Structural Integrity 14 (2019) 564–570 Neelanchali et al/ Structural Integrity Procedia 00 (2018) 000–000 Neelanchali et al/ Structur Integrity Procedia 00 (2018) 000–00 Neelanchali et al/ Structural Integrity Procedia 00 (2018) 000–000

568

The Nitrogen gas triggering pressure was varied from 0.2 to 0.8 bar to provide a range of compressional strain rates. The specimen diameter was kept equal to the bar diameter, which was 15.5 mm, whereas the gap between the incident and transmission bars was kept fixed at 0.35 mm with the help of feeler gauge. 5. Results and Discussion 5.1. Effect of Specific Surface Area on the Low Shear Rate Rheology Fig.3 depicts the rheogram obtained from the low shear rate rheometric testing of FS dispersions. It is observed that as the particle size becomes finer with the increase in specific surface area, the severity of shear thickening increases. It is also observed that prior to the onset of shear thickening, the magnitude of shear thinning increases with the decrease in particle size. The Nitrogen gas triggering pressure was varied from 0.2 to 0.8 bar to provide a range of compressional strain rates. The specimen diameter was kept equal to the bar diameter, which was 15.5 mm, whereas the gap between the incident and transmission bars was kept fixed at 0.35 mm with the help of feeler gauge. 5. Results and Discussion 5.1. Effect of Specific Surface Area on the Low Shear Rate Rheology Fig.3 depicts the rheogram obtained from the low shear rate rheometric testing of FS dispersions. It is observed that as the particle size becomes finer with the increase in specific surface area, the severity of shear thickening increases. It is also observed that prior to the onset of shear thickening, the magnitude of shear thinning increases with the decrease in particle size. The Nitrogen gas triggering pressure was varied from 0.2 to 0.8 bar to provide a range of compressional strain rates. The specimen dia eter was kept equal to the bar diameter, w ich was 15.5 mm, whereas the gap between the incident and transmission bars was kept fixed at 0.35 mm with the help of feeler gauge. 5. Results and Discussion 5.1. Effect of Specific Surface Area on the Low Shear Rate Rheology Fig.3 de icts the rh ogram obtai d from the low sh ar rate rheometric testing of FS dispersions. It is obs rved that the particle size becomes finer wit the increase in specific surface area, the severity of shear thickening increases. It is also observed that prior to the onset of shear thickening, the magnitude of shear thinning increases with the decrease in particle size.

Fig.3: Rheogram for fumed silica dispersions Fig.3: Rheogram for fumed silica dispersions Fig.3: Rheogram for fumed silica dispersions

The critical shear required to trigger the onset of shear thickening was also found to be higher for A-150 FS dispersion (13 s -1 ), as compared to A-130 FS dispersion (11 s -1 ). Since the variation in the particle sizes for A-130 and A-150 FS grades is not much, so the difference in the post shear thickening viscosities for both the grades is not appreciable. It is 11.8 Pas for A-130 and 12.5 Pas for A-150 FS dispersions, respectively. The minimum viscosity exhibited just before the onset of shear thickening was found to be 1.37 Pas for A-130 and 0.4 Pas for A-150 dispersions, respectively. The critical shear required to trigger the onset of shear thickening was also found to be higher for A-150 FS dispersion (13 s -1 ), as compared to A-130 FS dispersion (11 s -1 ). Since the variation in the particle sizes for A-130 and A-150 FS grades is not much, so the difference in the post shear thickening viscosities for both the grades is not appreciable. It is 11.8 Pas for A-130 and 12.5 Pas for A-150 FS dispersions, respectively. The minimum viscosity exhibited just before the onset of shear thickening was found to be 1.37 Pas for A-130 and 0.4 Pas for A-150 dispersions, respectively. The critical shear required to trigger the onset of shear thickening was also found to be higher for A-150 FS dispersion (13 s -1 ), as compared to A-130 FS dispersion (11 s -1 ). Since the variation in the particle sizes for A-130 and A-150 FS grades is not much, so the difference in the post shear thickening viscosities for both the grades is not appreciable. It is 11.8 Pas for A-130 and 12.5 Pas for A-150 FS dispersions, respectively. The minimum viscosity exhibited just before the onset of shear thickening was found to be 1.37 Pas for A-130 and 0.4 Pas for A-150 dispersions, respectively.

5.2. Effect of Specific Surface Area on the High Strain Rate Rheology 5.2. Effect of Specific Surface Area on the High Strain Rate Rheology 5.2. Effect of Specific Surface Area on the High Strain Rate Rheology

Fig.4: Stress-Strain and Stress-Strain Rate plots for A-130 fumed silica dispersions Fig.4: Stress-Strain and Stress-Strain Rate plots for A-130 fumed silica dispersions Fig.4: Stress-Strain and Stress-Strain Rate plots for A-130 fumed silica dispersions