Date of Award
Master of Science in Mechanical Engineering and Applied Mechanics
Mechanical, Industrial and Systems Engineering
An experimental investigation was conducted to understand the fundamental physics of various dynamic events. The study seeks to understand the shock response of composite materials after long-term exposure to accelerated weathering conditions, polyurea coated composites subjected to near field underwater explosions, and the implosion behavior of brittle volumes.
First, the shock response of carbon/epoxy composites subjected to aggressive marine environments was explored. In order to simulate a prolonged submergence in oceanic conditions, an elevated temperature, salt water environment was created. The material was submerged in a 3.5%, 65°C salt solution for 0, 30 and 60 days. Tensile and four point bend experiments were performed for each case to determine quasi-static properties, while shock tube experiments were used to determine dynamic behavior of the material. After 30 days of submergence, the mechanical properties of the composite diminished. Furthermore, after an additional 30 days of submergence, the 60 day submerged specimens displayed similar quasi-static and dynamic mechanical behavior to the 30 day case.
Secondly, the transient response of polyurea coated E-Glass/Epoxy composites exposed to near field underwater explosions was investigated. The composite panels were positioned as a boundary between air and water, simulating a ship hull. Three types of panels were studied with varying thicknesses and material layups. The specimens are as follows: 0.762 mm thick with no coating, 1.524 mm with no coating and 0.762 mm composite with 0.762 mm polyurea coating. The 0.762 mm panel served as the control sample while the 1.524 mm thick panels with and without coating were compared. In all cases, fully clamped panels were subjected to an underwater explosive charge with a 5 cm standoff distance. All panels displayed deflection, however the polyurea coated composite displayed a lower maximum deflection, with an adjusted weight parameter, than the 1.524 mm thick composite. Also, shearing at the fully clamped boundaries, leading to fluid penetration, did not occur when polyurea coated the composite panels.
Lastly, the implosion behavior of brittle volumes submerged in pressurized water was studied. The implodable volumes chosen in this study were polymethylmethacrylate (PMMA) tubing. Three geometries of tubing were chosen with an outer diameter of 25.4 mm and lengths of 76.2 mm, 152.4 mm and 228.6 mm. All specimens were placed within a confined vessel equipped with a viewing window for high speed photography. In all cases, pressure was increased at a quasi-static rate until the tubes dynamically collapsed. Experiments uncovered distinct fracture patterns and high crack velocity due to a biaxial loading boundary condition.
Shillings, Christopher S., "Dynamic Behavior of Materials Subjected to Extreme Environments" (2015). Open Access Master's Theses. Paper 769.