Dissertation Defence: Characterization and Modeling of an Advanced Ultra-High Molecular Weight Polyethylene (UHMWPE) Fabric Composite System Consists of Shear Thickening Fluid and Bis–Diazirine Based Crosslinkers, at Low-To-Medium Loading Rates
December 9 at 10:00 am - 2:00 pm
Mahshid Mahbod, supervised by Dr. Abbas Milani and Dr. Reza Vaziri, will defend their dissertation titled “Characterization and Modeling of an Advanced Ultra-High Molecular Weight Polyethylene (UHMWPE) Fabric Composite System Consists of Shear Thickening Fluid and Bis–Diazirine Based Crosslinkers, at Low-To-Medium Loading Rates” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mechanical Engineering.
An abstract for Mahshid Mahbod’s dissertation is included below.
Examinations are open to all members of the campus community as well as the general public. Please email abbas.milani@ubc.ca to receive the Zoom link for this exam.
ABSTRACT
Fibre-reinforced polymer composites are today widely used in aerospace, automotive, and marine industries, among others, owing to their lightweight and superior mechanical properties. Among various composite materials, ultra-high molecular weight polyethylene (UHMWPE) woven fabrics have gained attention, particularly in the applications requiring high ballistic and/or puncture resistance, such as armours. However, achieving the desired performance often requires application of several fabric layers, making the product potentially heavy. To address this, the application of shear thickening fluids (STFs) have been explored in the past literature as modifier to enhance the mechanical properties of the base UHMWPE fabrics.
Aligned with this research trend, this study experimentally and numerically characterizes the mechanical performance of a new material system, as ‘UHMWPE-based composite enhanced with STF and cross-linkers’. Namely, a set of chemically crosslinked UHMWPE fabrics with different areal densities, and impregnated with a shear thickening fluid (STF), are evaluated under tensile, shear, bending, puncture, and drop tower/impact loadings. The crosslinkers in the new material system are based on Bis–Diazirine polymer and the STF consists of fumed silica nanoparticles suspended in polyethylene glycol. Initially, different possible crosslinkers were tested and compared through a multi-criteria decision-making (MCDM) technique, to select the most effective option for subsequent STF impregnations. The combined and individual effects of the selected chemical crosslinking and STF on the base fabric’s mechanical behaviour were analyzed for the first time. Additionally, the influence of strain rate on the tensile and shear behaviour of the material was investigated. Pertinent to armour applications at low-to-medium velocity loading regimes, the results particularly demonstrated a significant improvement in puncture resistance, with an increase up to 92%, when compared to the control fabric. Next, the finite element (FE) modelling of the MCDM-selected material system was established and validated against experimental data. During modelling, statistical analysis and an inverse optimization routine identified key material parameters that are often to characterize directly from experimental tests. These included the friction coefficient between the ply ‘in the weave form’ and the punch, and the maximum stress threshold within the material system for element deletion. The optimized parameters resulted in a very good agreement between the simulation and experimental data (with a minimal error of 5% in the absorbed energy during the puncture test), providing a comprehensive understanding of the mechanical performance enhancement potential of such UHMWPE composite fabrics for future applications.
