Date of Award

2019

Degree Type

Thesis

Degree Name

Master of Science in Civil and Environmental Engineering

Department

Civil and Environmental Engineering

First Advisor

George Tsiatas

Abstract

The dynamic response of composite materials subjected to underwater and air shock loading conditions has been studied. Additionally, the effects of low temperatures on the mechanical and fracture properties of these materials has been evaluated. The primary contribution of the author is on the computational modeling aspects of each of the dynamic loading studies conducted. The experimental work presented has been completed by the author’s collaborators from the University of Rhode Island. The low temperature effects on the materials is solely an experimental investigation and was undertaken in collaboration with researchers at the Naval Undersea Warfare Center. The objective of the project is to develop a better understanding of the response of composite materials when subjected to shock loading conditions leading to more efficiently designed structures. The work is divided into five phases as described in the following overview.

In the first phase of the research the near field underwater explosion response of E-Glass / Epoxy plates was investigated. The study also included the effects of elastomeric polyurea coatings on both the transient response and damage characteristics. The computational models developed in the study were shown to simulate the testing accurately, and using the Russell Error measure, demonstrate model correlation that can be described as excellent. The models are able to accurately simulate the detonation of the explosive charge and the resulting pressure fields and plate deflections.

The objective of the second phase of the project was to investigate the effects of material ageing on the response of Carbon-Epoxy laminates when subjected to air blast loading. The shock loading was induced through the use of an air driven shock tube and the effects of seawater exposure were quantified in terms of transient response and material failure onset. Computational models of the experiments were developed through the use of the Ls-Dyna code for both fully clamped and simply supported edge conditions. The models were shown to accurately capture both the timing and displacement magnitudes of the specimens as well as the onset of material failure.

The third phase of the project investigates the response of composite cylinders when subjected to near field underwater explosive loading, including the effects of polyurea coatings. The objective is to determine the influence of both charge standoff and coating thickness on the transient response as well as damage mechanisms / evolution during loading. Experiments with corresponding simulations were performed with good agreement between the two in terms of pressure loads and damage extents. The simulations were further utilized to examine the internal and kinetic energy levels and distributions during loading as well as the surface strain characteristics.

The effects of material ageing on the response of flat plates subjected to near field explosive loading is the focus of the fourth part of the research. In this investigation, bi-axial Carbon/Epoxy laminates with and without long term seawater immersion effects were subject to the explosive loading to determine the influence of material degradation on the panel response. A fully coupled Eulerian-Lagrangian computational approach was utilized for the modeling of the corresponding experiments. The simulations were used to demonstrate an increase of maximum strains with ageing as well as the characteristics of stress wave propagation as a function of laminate architecture.

The final aspect of the research presented is aimed at investigating the influence of temperature on the mechanical and fracture performance of composite laminates. The focus is on the low temperatures associated with seawater in the arctic regions and deep depths of the oceans. Mechanical characterization is in the form of tensile, compression, and short beam shear and fracture is evaluated in terms of Mode-I failure. The results show that for both E-Glass and Carbon Epoxy materials there is an influence of temperature on both mechanical and fracture performance of the material.

Available for download on Wednesday, April 01, 2020

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