Date of Award
1-1-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Mechanical Engineering and Applied Mechanics
Specialization
Solid Mechnics
Department
Mechanical, Industrial and Systems Engineering
First Advisor
Arun Shukla
Second Advisor
Helio Matos
Abstract
Polymeric composites have gained popularity in the marine industry, where they are at an ever-increasing risk of encountering high intensity underwater (UNDEX) or in air (AIREX) explosive loading. Furthermore, improving the collapse capacity of submerged collapsable structures like pipelines have also been of great interest to the industry. This dissertation comprises six chapters encompassing material behavior characterization, the AIREX as well as UNDEX response of the composite structures, and dynamic buckling of thin-walled aluminum tubes. Chapter 1 and 2 discusses the high-strain rate shear constitutive behavior as well as the wave propagation through closed-cell PVC foams under air shock loading. Chapter 3, 4, and 5 covers the dynamic behavior of polymeric composite monolithic plates as well as sandwich composite panels under air and underwater shock loading. Chapter 6 delineates a novel approach to improve the collapse capacity of thin-walled tubular structures.
Chapter 1 discusses the wave propagation through closed-cell foams under air shock loading. It was observed that the complex modulus of the material in place of elastic modulus of these porous polymeric materials, give better approximations of the stress wave velocities. Elastic stress wave velocity in foams increases with increasing foam density. Force amplification was recorded during the shock loading experiments where foam specimens remain in their elastic regime. However, no amplification in transmitted force was observed at higher intensity shock loading, due to crushing in the foam.
Chapter 2 describes the shear constitutive behavior and compression behavior of closed-cell PVC foams in the foam rise direction at varied strain rates. The results showed that the shear strength as well as the crushing strength of the closed-cell PVC foams increases with increase in the loading rate. However, the rate of increase in strength shows contrasting trends for the shear and crushing behavior. Also, the shear strength of the PVC closed-cell foam along the foam rise direction is less than 50% of the crushing strength, at respective loading rate.
Chapter 3 provides a comparison of the dynamic response of a polymeric composite monolithic plate to one-dimensional shock loading in air and water medium. Experimental results showed that the plates deformed in Mode 1 under both air and underwater shock loading, with the maximum deformation occurring at the center of the circular plate. For same loading pressure, the maximum deformation of the plate specimens under air shock loading was 75% higher than that measured for the underwater shock loading. The magnitude of deflection in circular plates was influenced by the rate of increase in loading pressure. In underwater shock loading, peak deflection occurred in the post-cavitation loading phase. Furthermore, the circular plates exhibited an oscillatory response under air shock loading, which was not observed for the underwater case.
Chapter 4 describes the results on dynamic response of curved sandwich panels subjected to air shock loading. The interplay of panel curvature and boundary conditions strongly influence the deformation behavior. The sandwich panels with higher density cores exhibit enhancement in threshold pressure for interfacial damage and failure for the curved sandwich structures with greater angular extent. Damage progression and postmortem observations revealed that the sandwich panels with low-density cores primarily fail from core cracking due to transverse shear stresses. However, this failure mode changes to interfacial de-bond at the core-facesheet interface towards the shock.
Chapter 5 delineates the findings on the dynamic response and the fluid-structure interaction behavior of air-backed flat sandwich composite panels submerged in water to underwater blasts. The results showed that simultaneous collapse of the gas bubble and surface cavitation bubble jetting on panel causes significantly high impulsive loading on the structure. The dynamics of the surface cavitation is governed by the panel deformation i.e. less structural stiffness and high intensity of shock loading results in greater surface cavitation. Also, the surface cavitation repels the gas bubble due to greater fluid velocity at the surface cavitation interface, consequently affecting the explosion gas bubble geometry in its proximity.
Chapter 6 discusses the effect of groove geometry on the dynamic buckling behavior of aluminum tubes under hydrostatic pressure. Experiments were conducted in a water-filled pressure vessel facility, utilizing high-speed imaging with 3D Digital Image Correlation and piezoelectric transducers to capture transient collapse behavior of cylindrical shells and associated local pressure histories. Finite element simulations complemented the experiments to analyze critical pressure sensitivity to groove wall thickness. The presence of a mid-length groove increased collapse capacity by 25% to 50% compared to non-grooved tubes and reduced peak dynamic overpressure. Groove depth significantly influenced failure mode: deeper grooves induced local buckling, while shallow grooves led to global collapse. Simulations further demonstrated collapse capacity improvements reaching up to 65% for tubes with a groove.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Recommended Citation
Pandey, Akash, "CHARACTERIZATION AND DYNAMIC RESPONSE OF COMPOSITE AND METALLIC STRUCTURES UNDER EXTREME LOADING ENVIRONMENTS" (2025). Open Access Dissertations. Paper 4465.
https://digitalcommons.uri.edu/oa_diss/4465