Experimental and numerical investigation of ballistic impacts: an introduction to novel polymer foam core sandwich structures and adaptive SPH formulation

Raviprasad, Srikanth

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Description

Title

Experimental and numerical investigation of ballistic impacts: an introduction to novel polymer foam core sandwich structures and adaptive SPH formulation

Author(s)

Raviprasad, Srikanth

Issue Date

2016-12-21

Director of Research (if dissertation) or Advisor (if thesis)

Jasiuk, Iwona M.

Committee Member(s)

Geubelle, Philippe H.

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Ballistic impacts
• Aromatic thermosetting copolyester (ATSP) polymer
• Foam core sandwich structures
• Large deformation
• Smoothed particle hydrodynamics

Abstract

The present thesis contains two different research projects on ballistic impacts. The first project describes the research on ballistic impacts of novel foam core sandwich structures. The second project involves an introduction to a novel finite element modeling approach to simulate both, large deformation as well as small deformation effects using a single formulation with significant accuracy. Project I: With the ever increasing need for a material that has a low density and yet high toughness, many researchers are working on developing hybrid structures that are primarily derivatives of either lattice core sandwiches or foam core sandwiches. Sandwich structures have been used in ballistic applications over the past several decades due to their high strength to weight ratio and high rigidity. In pursuit of achieving low density and high toughness, researches have been developing variants of PUF and PVC polymer foams, although none of these materials were comparable to the impact strength and toughness of stochastic closed cell aluminum foam core sandwich structures. This work involved qualitative and quantitative analysis of the impact resistance of Aromatic Thermosetting co-Polyester (ATSP) foam core sandwich structures as well as ATSP foam core sandwich structures infused with 3wt% graphene nano-platelets (GNP), as compared against stochastic closed cell aluminum foam core sandwich structures at velocities ranging from 240m/s to 540m/s. The ATSP foam core structures were observed to have much lower densities than the aluminum foam core structures and yet performed significantly better than the latter at impact velocities ranging between 240-300m/s due to their high toughness and impact strength. They exhibited high adhesion strength and unlike the aluminum foam core sandwich structure, they did not fail from delamination. This material can be primarily used in applications that require non-conductive materials with extremely high toughness and low density. Project II: In regard to numerical ballistics, a myriad of work has been carried out on developing constitutive relations to accurately model material behavior on finite element solvers. While one can model the low strain rate phenomenon with significant accuracy, material modeling for high strain rate and large deformation problems is extremely challenging as it is drastically influenced by the adiabatic as well as pressure-deviatoric effects. Lagrangian, Coupled- Eulerian Lagrangian, Smoothed Particle Hydrodynamics and a few other material erosion formulations have been developed to accurately model and simulate any structural problem. However, each of these methods have their own advantages and disadvantages that limit their domain of application. The Lagrangian method is superior to SPH in applications involving small deformations; however, it is much inferior to SPH in application involving large deformations. Although SPH can be used to capture large deformations with arguable accuracy, it is only effective for simulating localized damages and fails to properly simulate the material behavior in the boundary or far field regions. In order to accurately simulate both large as well as small deformations in the same model, this project introduced a novel approach (Adaptive SPH approach), wherein only those elements of Lagrangian mesh that experienced large deformation, were adaptively converted to SPH particles during the course of the simulation. In this work, aluminum 6061 plate targets were modeled using Lagrangian, SPH and Adaptive SPH approach and were impacted against aluminum projectiles moving at velocities ranging from Mach 1 to Mach 3 on ABAQUS Explicit 6.14. After qualitative and quantitative comparison against experimental data, it was observed that the Adaptive SPH model simulated the deformation in both, the localized region as well as the boundary region of targets, with high accuracy. The accuracy of damage characteristics of the projectile after impact was also validated and recorded. Furthermore, the 3 formulations were quantitatively compared against experiments over 5 different predefined damage criteria. This comparison also led to a conclusion that the results obtained from the Adaptive SPH model closely matched with the experimental results over a wide range of damage parameters, unlike the Lagrangian and SPH approach.

Graduation Semester

2017-05

Type of Resource

text

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Copyright 2017 Srikanth Raviprasad

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