DYNAMIC BEHAVIOR OF COMPOSITE STRUCTURES SUBJECTED TO AGGRESSIVE MARINE ENVIRONMENTS: AN EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION

Four studies were completed to investigate the dynamic behavior of composite structures after exposure to marine environments, with a fifth study which deals with the energy absoption effects of foam materials in underwater implosion. These studies evaluated the following: In-air blast response of composite plates after prolonged exposure to saline water; The in-air blast response of composite plates after prolonged exposure to ultraviolet radiation; Hydrostatic and blast initiated implosion of composite cylinders after exposure to saline water; Underwater blast response of fully submerged composite plates after exposure to saline water; Hydrostatic initiated implosion of metallic cylinders with foam fillers. Two high-speed cameras were used to record the deformation of the structures in real time, where a third camera was used to record the explosive gas bubble when applicable. For air blast experiments, three piezoelectric pressure sensors were used to record the transient pressure data, whereas for underwater applications, tourmaline pressure transducers were utilized to record the dynamic pressure. Three-dimensional Digital Image Correlation was employed to obtain full field displacements, strains, and velocities during dynamic loading. Numerical simulations were included to compliment the experiments and obtain further understanding not achievable with experimental data. The air blast response of composites was modeled using the LS-DYNA code with a material model capable of including damage in tension, tensile shear, and compression. The underwater explosives response of composite plates was a Coupled Eulerian-Lagrange model created using the DYSMAS software. The completion of these studies concluded that: Exposure to saline water decreases the blast performance of composites. Furthermore, the removal of moisture shows that there is permanent material degradation after exposure to saline water; Ultraviolet radiation exposure increases the stiffness of composite materials and decreases the failure strains in tension and shear; exposing hollow cylindrical composites to saline water decreases the critical collapse pressure in hydrostatic implosion, and the overall energy released during implosion is lower for weathered composites when compared to virgin structures; the underwater blast performance of saline water exposed plates is governed by the standoff distance of the explosive as well as the hydrostatic pressure of the fluid; and foam materials can mitigate the energy assosiated with implosion when placed inside of cylindrical structures