SPH fluids for viscous jet buckling

We present a novel meshfree technique for animating\ud free surface viscous liquids with jet buckling effects, such as\ud coiling and folding. Our technique is based on Smoothed Particle\ud Hydrodynamics (SPH) fluids and allows more realistic and\ud complex viscous behaviors than the preceding SPH frameworks\ud in computer animation literature. The viscous liquid is modeled\ud by a non-Newtonian fluid flow and the variable viscosity under\ud shear stress is achieved using a viscosity model known as Cross\ud model. The proposed technique is efficient and stable, and our\ud framework can animate scenarios with high resolution of SPH\ud particles in which the simulation speed is significantly accelerated\ud by using Computer Unified Device Architecture (CUDA)\ud computing platform. This work also includes several examples\ud that demonstrate the ability of our technique.FAPESP - processos nos. 2013/19760-5 e 2014/11981-5FAPES - processos no. 53600100/11CNP

Fabrication of High Content Carbon Nanotube–Polyurethane Sheets with Tailorable Properties

We have fabricated carbon nanotube (CNT)–polyurethane (TPU) sheets via a one-step filtration method that uses a TPU solvent/nonsolvent combination. This solution method allows for control of the composition and processing conditions, significantly reducing both the filtration time and the need for large volumes of solvent to debundle the CNTs. Through an appropriate selection of the solvents and tuning the solvent/nonsolvent ratio, it is possible to enhance the interaction between the CNTs and the polymer chains in solution and improve the CNT exfoliation in the nanocomposites. The composition of the nanocomposites, which defines the characteristics of the material and its mechanical properties, can be precisely controlled. The highest improvements in tensile properties were achieved at a CNT:TPU weight ratio around 35:65 with a Young’s modulus of 1270 MPa, stress at 50% strain of 35 MPa, and strength of 41 MPa, corresponding to ∼10-fold improvement in modulus and ∼7-fold improvement in stress at 50% strain, while maintaining a high failure strain. At the same composition, CNTs with higher aspect ratio produce nanocomposites with greater improvements (e.g., strength of 99 MPa). Electrical conductivity also shows a maximum near the same composition, where it can exceed the values achieved for the pristine nanotube buckypaper. The trend in mechanical and electrical properties was understood in terms of the CNT–TPU interfacial interactions and morphological changes occurring in the nanocomposite sheets as a function of increasing the TPU content. The availability of such a simple method and the understanding of the structure–property relationships are expected to be broadly applicable in the nanocomposites field

Enhanced Shear Performance of Hybrid Glass Fiber–Epoxy Laminates Modified with Boron Nitride Nanotubes

Matrix enhancement using nanotubes is one method to produce hybrid, multiscale fiber reinforced polymer (FRP) composites with improved interlaminar performance and added functional properties. Carbon nanotubes (CNTs) have been shown to be promising, and recent advances in the manufacturing of boron nitride nanotubes (BNNTs), which are largely unexplored for structural reinforcement of hybrid composites with microscale fibers, offer new opportunities to employ BNNTs in reinforced hybrid composite structures. This study investigates the shear and impact properties of BNNT hybrid composites, specifically glass fiber–epoxy/BNNT composite laminates. Two manufacturing techniques were used to fabricate the specimens: wet layup and vacuum-assisted resin transfer molding (VARTM). Shear punch, short beam shear, and modified Charpy tests were selected for their relevance to complex loading systems that involve shear, such as ballistic or other impact loading. The addition of 1 wt % BNNTs to the epoxy resin was found to improve the performance of the laminates: 8% increase in specific shear punch strength, 15% increase in the specific short beam shear strength, and an average of 22% increase in the specific fracture energy per area in modified Charpy tests. Improvements were lower in test cases approaching pure shear, which led to the conclusion that BNNT reinforcement most effectively improves laminate performance in more complex loading situations in which an element of normal stress, such as bending, is present. As such, BNNT reinforcement, which offers different functional properties than CNTs, is also promising to improve the impact performance in multiscale hybrid composites