Dynamic Testing of Partially Saturated Porous Media

Exploring the dynamic response of porous media is of paramount importance across industrial sectors ranging from civil engineering to defense. However, the behavior of porous media under high strain rate loading is infrequently characterized and poorly understood. The incorporation of water giving rise to a partially saturated state further exacerbates the challenges in evaluating the response of such materials under dynamic conditions. We aim to address current deficiencies by exploring the compressive high strain rate behavior of partially saturated porous media via experimental testing using a modified split Hopkinson pressure bar. 

Materials consisting of Sydney sand and glass beads were examined under strain rates ranging from 800 s-1 to 2100 s-1 at saturations from 0% to 90%. It was identified that the stress-strain response is highly complex and sensitive to multiple controlled parameters including strain rate, grain shape, specimen gradation, initial dry density, and confinement environment, which are all in turn further influenced by the degree of saturation. Experimental results extracted as part of this study will aid in the development and calibration of multi-scale multi-phase constitutive mechanical models with the potential for implementation throughout engineering practice.

Relevant Publications

Wang, S., Shen, L., Nguyen, G.D., Maggi, F., El-Zein, A., Zheng, Y. (2019). An empirical approach for the quantification of uniaxial compressive stress-strain of partially saturated granular media under high strain rates. Soil Dynamics and Earthquake Engineering, 120, 245-256

Wang, S., Shen, L., Maggi, F., El-Zein, A., Nguyen, G.D., Zheng, Y., Zhang, H., Chen, Z. (2018). Influence of dry density and confinement environment on the high strain rate response of partially saturated sand. International Journal of Impact Engineering, 116, 65-78

Wang, S., Flores-Johnson, E.A., Shen, L. (2017). A Technique for the Elimination of Stress Waves Overlapping in the Split Hopkinson Pressure Bar. Experimental Techniques, 41, 345-355

Wang, S., Shen, L., Maggi, F., El-Zein, A., Nguyen, G.D. (2017). Uniaxial compressive behavior of partially saturated granular media under high strain rates. International Journal of Impact Engineering, 102, 156-168

Flores-Johnson, E.A., Wang, S., Maggi, F., El Zein, A., Gan, Y., Nguyen, G.D., Shen, L. (2016). Discrete element simulation of dynamic behavior of partially saturated sand. International Journal of Mechanics and Materials in Design, 12 (4), 495-507

Wang, S., Shen, L., Maggi, F., El-Zein, A. & Nguyen, G.D. (2016). High strain rate behavior of unsaturated sand. 10th International Conference on Structural Integrity and Failure (SIF-2016): Advances in Materials and Structures, University of Adelaide, Adelaide, Australia

Dynamic Testing of Crumpled Paper

The crumpling of precursor materials to form dense three-dimensional geometries offers an attractive route towards the utilization of minor-value waste materials. Crumple-forming results in a mesostructured system in which mechanical properties of the material are governed by complex cross-scale deformation mechanisms. Here, we investigate the physical and mechanical properties of dense compacted structures fabricated by the confined uniaxial compression of a cellulose tissue to yield crumpled mesostructuring.

Relevant Publications

Hanaor, D., Flores-Johnson, E.A., Wang, S., Quach, S., Dela-Torre, K., Gan, Y., Shen, L. (2017). Mechanical properties in crumple-formed paper derived materials subjected to compression. Heliyon, 3 (6)

Dynamic Testing of Shear-thickening Fluids

Shear-thickening fluids (STFs) exhibit solid-like behavior at high strain rates. This study focused on STFs with styrene/acrylate particles at 58% volume fraction. The microstructure and dispersion of the particles were measured, together with the rheological behavior of the STFs. Then, the high-strain-rate compressive responses of the STFs were studied using a split Hopkinson pressure bar (SHPB). Along with the implementation of high-speed photography at 100,000 FPS, the stress-strain relations of the STFs at high strain rates were determined.

Relevant Publications

Fu, K., Wang, H., Wang, S., Chang, L., Shen, L., Ye, L. (2018). Compressive behavior of shear-thickening fluid with concentrated polymers at high strain rates. Materials and Design, 140, 295-306

Pile Foundations in Liquefiable Soil

This research numerically simulates the response of raked pile foundations in liquefying ground through nonlinear finite element analysis. Experimental and analytical data confirmed that the backbone force density–displacement (p–y) curve simulating lateral pile response is of acceptable credibility for both vertical and raked piles. A parametric investigation on fixed-head piles subject to lateral spreading concluded that piles exhibiting positive inclination impart lower moment demands at the head while those inclined negatively perform better at liquefaction boundaries (relative to vertical piles). Further studies reveal substantial axial demand imposed upon negatively inclined members due to the transfer of gravity and ground-induced lateral forces axially down the pile. Extra care must be taken in the design of such members in soils susceptible to lateral spreading such that compressive failure (i.e., pile buckling) is avoided.

Relevant Publications

Wang, S., Orense, R.P. (2014). Modeling of raked pile foundations in liquefiable ground. Soil Dynamics and Earthquake Engineering, 64, 11-23

Wang, S.,  Orense, R.P. (2013). Modelling of pile response in laterally spreading liquefiable ground. Proceedings of the 19th NZGS Geotechnical Symposium, Queenstown, New Zealand