Date of Award
Doctor of Philosophy in Mechanical Engineering and Applied Mechanics
Mechanical, Industrial and Systems Engineering
Fiber reinforced composite materials offer a variety of advantages in marine applications. They are corrosion resistant, require minimal maintenance, and offer a high strength to weight ratio. Additionally, they can be used to create complex geometries, can be tailored for optimal mechanical performance and are often inexpensive to produce and work with. Because of these advantageous properties they have been employed in a variety of settings, both military and commercial.
When employed in harsh environments, from the battlefield to the marine oil field, structures built from composite laminates may be subjected to dynamic events such as underwater explosive loading, both close-in and far-field, as well as overwhelming hydrostatic forces which could lead to implosion. In order to protect against these dynamic events composite structures are often over designed and the weight savings that composites offer goes unrealized. The confident use of composites in harsh marine environments requires the ability to predict their response to an array of severe loading conditions. The goal of this study is a better understanding of the response of composites to extreme loadings and computational tools and methods to predict these events.
First, the effects of preload on the response of flat composite plates to underwater explosive loading were investigated via computational simulations. Three preload conditions were investigated: directly applied compression, indirectly applied compression, and directly applied tension. Preload effects were assessed through comparison of material damage, delamination evolution and center point displacement. The primary effect of the preload is seen in the time required for the plate to recover from the displaced shape. Little effect was observed on the amount of damage and delamination.
The second focus of this study was on the computational simulation of the implosion of composite cylinders composed of differing materials, Carbon/Epoxy and Eglass/ Polyester. Simulations were built using the Dynamic System Mechanics Advanced Simulation software suit developed by the Naval Surface Warfare Center, Indian Head. Predicted dynamic pressures in the surrounding fluid were compared with experimental results from previous studies. Damage evolution in the simulations was also compared with experimental observations. It was found that the material model employed was not capable of predicting the damage evolution in the cylinders, however, pressure predictions for the initial collapse phase provided a reasonable correlation with measured data.
The third phase of this study was an experimental investigation of the response of composite cylinders with and without polyurea coatings to near field underwater explosive loading. Two coating thickness were investigated (100% and 200% of composite thickness) and each cylinder configuration was subjected to explosive loading at two different charge standoffs, 2.54 cm and 5.08 cm. The responses of the non-charge side of the cylinders were compared as well as damage sustained by the cylinders. It was found that the coatings had a slight effect on the response of the cylinders but significantly reduced the sustained damage.
Gauch, Erin, "Experimental and Computational Study of the Response of Composite Structures to Extreme Loading" (2016). Open Access Dissertations. Paper 447.
Available for download on Wednesday, April 25, 2018