13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Mode-I Fracture Behaviors of a Shear Thickening Fluid as Adhesive Layer under Different Loading Rates Maisha Tabassum 1 , Lin Ye 1,* , Li Chang 1 , Klaus Friedrich 2,3 1 Center for Advanced Materials Technology, School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW, 2006, Australia 2 Institute for Composite Materials, University of Kaiserslautern, 67663 Kaiserslautern, Germany 3 College of Engineering, King Saud University, Riyadh, Saudi Arabia * Email: lin.ye@sydney.edu.au Abstract Shear thickening fluids (STFs) classified as Non-Newtonian fluids are fluidic composites of dense suspensions. These fluids display unusual phase transitions between liquid and “solid” phases due to recoverable changes in viscosity at a critical rate of shear. This study characterizes the fracture behavior of a STF with 58 vol.% dispersion of styrene/acrylate particles in ethylene glycol. Double cantilever beam (DCB) specimens with the STF as adhesive layer were utilized to investigate the Mode-I fracture energy of the STF. The fracture behavior of the STF of different thickness was evaluated in detail at different crack opening displacement rates, varying from 1 mm/s to 50 mm/s. The results indicate that the fracture behavior of the STF is very rate-sensitive. However, before the opening displacement rate reaches 5 mm/s, the STF is not showing any “solid” like behavior. The average Mode-I fracture energy of the STF increases with an increase in the opening displacement rate up to 30 mm/s, after that the values are plateaued and almost constant at 240 J/m 2 . This is comparable to the fracture toughness of a typical epoxy. The fracture energy of the STF also shows an inverse dependence on the thickness of the STF at low opening displacement rates, but at high rates such dependence was not observed. Keywords Fracture energy, Shear thickening fluid (STF), Rate effect, Double cantilever beam (DCB), Adhesive thickness 1. Introduction The ability to divert or dissipate dynamic energy during impact has many engineering challenges in industrial, biomedical and military applications. Shear thickening fluids (STFs) can play a vital role in engineering designs as energy shunting materials. STFs are mostly fluidic composites of dense suspensions that exhibit reversible shear thickening behavior, and STFs are non-Newtonian fluids, which can sometime display intriguing phase transitions between liquid and “solid” phases due to the recoverable changes in viscosity at a critical shear rate [1]. The use of STFs opens up many opportunities in developing new passive, energy-absorbing systems in applications including liquid dampers/brakes, liquid armor, etc. Over the last few decades, the shear thickening behavior of concentrated dispersions has been a major topic of interest for rheologists owing to their immense importance in industry [1-4]. Shear thickening was initially believed to be a severe problem, because it leads to such issues as failure of mixer motors due to overloading, damage mixer blade and other processing equipment, and induce dramatic changes in suspension microstructure, such as particle aggregation, which results in poor fluid and coating qualities [1]. The early investigations of shear thickening behavior were to mitigate damage on processing equipment caused by the shear thickening transition [5, 6]. Later STFs have become attractive due to their unique property that makes them ideal for energy absorption applications. When subjected to an impact, this shear rate-activated fluid converts from a low viscous to a high viscous state almost instantaneously, and it can absorb some of impact energy while helping to dissipate the remaining energy. Many studies have been done on the energy absorption applications of STFs. For the personal protection with application of STFs as ‘liquid armor’, it has attracted many efforts in research [1, 7-9], and STFs-treated fabrics showed not only