Structures and Materials Commons^™

Impact Simulation And Analysis Of Sandwich Structures, Daewon Kim

Master's Theses - Daytona Beach

Impact damage on aircraft and spacecraft can be a severe problem that may cause catastrophic results. Several aerospace structures have been used to resist or absorb energy in the occasion of impact. Among these, a sandwich structure has advantages with high stiffness, strength to weight ratio, and its relatively cheap cost. However, finding the impact structural response of a sandwich structure, by performing experiments, has disadvantages. First, impact is a complex problem with a multi-parameter nature and many factors should be considered. Secondly, it is a destructive test and the test subject may be damaged during the test. On the …

Boundary Interference Assessment And Correction For Open Jet Wind Tunnels Using Panel Methods, Wael Ahmed Mokhtar

Mechanical & Aerospace Engineering Theses & Dissertations

The presence of nearby boundaries in a wind tunnel can lead to aerodynamic measurements on a model in the wind tunnel that differ from those that would be made when the boundaries of the moving fluid were infinitely far away. The differences, referred to as boundary interference or wall interference, can be quite large, such as when testing aircraft models developing high lift forces, or whose wingspan is a large fraction of the wind tunnel width, or high drag models whose frontal area is a large fraction of the tunnel cross section. Correction techniques for closed test section (solid walled) …

Structural Design Of Wing Twist For Pitch Control Of Joined Wing Sensor Craft, Fred A. Kimler Iii

Theses and Dissertations

This research investigated two aspects of the aft wing structure of a joined wing SensorCraft. First, the efficacy of a novel approach for incorporating wing twist for pitch control was analyzed. This design involved adding a spanwise sliding joint into the wing structure at the lower aft spar of the vehicle's aft wing. Second, the joint section where the forward and aft wings connect and form the outboard wing was redesigned and analyzed to improve the load transmission between the wing spars. Using MSC.NASTRAN, linear and non-linear static analyses were performed to examine the efficiency of the wing twist sliding …

Detailed Design Of The Rigidizable Inflatable Get-Away-Special Experiment, Jeremy S. Goodwin

Theses and Dissertations

The Rigidizable Inflatable Get-Away-Special Experiment is a Space Shuttle experiment that will study the effects of the zero-gravity space environment on the deployment and modal analysis of three inflatable and rigidizable tubes using a sub-Tg rigidization technique. In 2004, RIGEX was transitioned from the Space Shuttle's Get-Away-Special (GAS) canister to its Canister for All Payload Ejections (CAPE), requiring several modifications to the design. The results of these modifications, along with further refinements made to previous efforts, combine to form the detailed design of the experiment. In addition to the design modifications, analyses were conducted to determine the containment capabilities of …

Development And Testing Of An Inflatable, Rigidizable Space Structure Experiment, Sarah K. Helms

Theses and Dissertations

Many recent space technology concepts require large space structures such as solar arrays and large aperture antennas; however, tight constraints on payload mass and volume often preclude their launch. Employing inflatable, rigidizable structures can reduce mass and volume while providing sufficient packing flexibility and structural stiffness. AFIT has developed RIGEX to flight-test this type of structure. RIGEX will test the deployment and structural characteristics of three thermoplastic composite Sub-Tg tubes. Once launched on the Space Shuttle in 2007, the spaceflight results will be compared to lab data to validate on-orbit reliability and ground test methods. This paper documents three main …

Characterization Of Functionally Graded Materials, Benjamin D. Chapman

Theses and Dissertations

The purpose of this study was to characterize the behavior of a functionally graded material through experimentation and analytical modeling. Functionally graded materials are a ceramic metal composite which transitions from metal on one face to ceramic on the opposite face. Creating reliable models required verifying the material properties. This was accomplished through the use of a static modulus of elasticity test as well as a dynamic ping test. The natural frequencies from the dynamic test were compared with finite element models to determine which material properties most accurately represented the functionally graded material. It was found that the material …

Simulation Of A Moving Elastic Beam Using Hamilton's Weak Principle, Elliott J. Leigh

Theses and Dissertations

Hamilton's Law is derived in weak form for slender beams with closed cross sections. The result is discretized with mixed space-time finite elements to yield a system of nonlinear, algebraic equations. An algorithm is proposed for solving these equations using unconstrained optimization techniques, obtaining steady-state and time accurate solutions for problems of structural dynamics. This technique provides accurate solutions for nonlinear static and steady-state problems including the cantilevered elastica and flatwise rotation of beams. Modal analysis of beams and rods is investigated to accurately determine fundamental frequencies of vibration, and the simulation of simple maneuvers is demonstrated.

Adaptive Control Of A Projectile Fin Using Piezoelectric Elastic Beam, Smitha Mani, Sahjendra N. Singh, Surya Kiran Parimi, Woosoon Yim, Mohamed B. Trabia

Mechanical Engineering Faculty Research

No abstract provided.

Design And Ground-Testing Of An Inflatable-Rigidizable Structure Experiment In Preparation For Space Flight, Chad R. Moeller

Theses and Dissertations

As the demand for larger space structures increases, complications arise including physical dimensions, weight, and launch costs. These constraints have forced the space industry to look for smaller, more lightweight, and cost-effective solutions. Future antennas, solar sails, sun shields, and other structures have the potential to be exponentially larger than their launch envelopes. Current research in this area is focused on the use of inflatable, rigidizable structures to reduce payload size and mass, ultimately reducing launch costs. These structures can be used as booms, trusses, wings, or can be configured to almost any simple shape. More complex shapes can be …

Damage Assessment And Strength Predictions In S-Glass/Epoxy Laminates Subjected To Low Energy Impact, Tuan-Khoi Dang Nguyen

Master's Theses - Daytona Beach

Composite materials have become one of the leading materials for manufacturing in the aerospace industry today. Compared to "conventional" aerospace metals, composites generally have higher strength-to-weight and stiffness-to-weight ratios, good fatigue and corrosion resistance and reduced parts count. However, like any other material, they also have disadvantages. They are inherently brittle and are thus prone to impact damage. Low energy/velocity impact damage, in particular, can be dangerous because the damage oftentimes goes undetected and can subsequently grow under load. Also known as barely visible impact damage (BVID), this area of concentration focuses on the small-scale damage that may be very …

Fabrication And Compressive Yield Strength Of Open Cell Corrugated Cellular Solids, Jeong Ho Choi

Master's Theses - Daytona Beach

This thesis studied the fabrication and compressive yield strength of open cell corrugated cellular solids made from type 304 stainless steel. Test samples were made by corrugating woven wire meshes, then laminating these in a high temperature argon environment. Mesh sizes ranging from 9.5 pore/cm (24 pore/in) to 31.5 pore/cm (80 pore/in) with wire diameters ranging from 0.178 mm (0.007 in) to 0.3556 mm (0.014 in) were bonded using lithobraze 925 (Ag-7.5Cu-0.2Li) to create cellular solids having relative densities ranging from 0.0384 to 0.0920. Test samples were then quasistatically compressed to measure the stress-strain response. The stress level at 25% …

Shape Memory Alloy Applications On Control Of Thermal Buckling, Panel Flutter And Random Vibration Of Composite Panels, Xinyun Guo

Mechanical & Aerospace Engineering Theses & Dissertations

Shape Memory Alloy (SMA) has a unique ability to recover large prestrain (up to 8∼10% elongation for Nitinol, a typical SMA material) completely when the alloy is heated (e.g. aerodynamic heating) above the austenite finish temperature Af. An innovative concept is to utilize the large recovery stress by embedding the prestrained SMA in a traditional fiber-reinforced laminated composite plate, which is called SMA hybrid composite (SMAHC) plate. In this research, static thermal and aerothermal deflections, dynamic panel flutter and random response are investigated for traditional composite plates and SMAHC plates under combined aerodynamic, random and thermal loads by employing nonlinear …

Nonlinear Flutter Of Curved Panels Under Yawed Supersonic Flow Using Finite Elements, Mohamed Salim Azzouz

Mechanical & Aerospace Engineering Theses & Dissertations

In the extensive published literature on panel flutter, a large number of papers are dedicated to investigation of flat plates in the supersonic flow regime. Very few authors have extended their work to flutter of curved panels. The curved geometry generates a pre-flutter behavior, triggering a static deflection due to a static aerodynamic load (SAL) over the panel as well as dynamic characteristics unique to this geometry. The purpose of this dissertation is to provide new insights in the subject of flutter of curved panels. Finite element frequency and time domain methods are developed to predict the pre/post flutter responses …

Pilot Performance And Eye Movement Activity With Varying Levels Of Display Integration In A Synthetic Vision Cockpit, Julie Michele Stark

Psychology Theses & Dissertations

The primary goal of the present study was to investigate the effects of display integration in a simulated commercial aircraft cockpit equipped with a synthetic vision display. Combinations of display integration level (low/high), display view (synthetic vision view/traditional display), and workload (low/high) were presented to each participant. Sixteen commercial pilots flew multiple approaches under IMC conditions in a moderate fidelity fixed-base part-task simulator. Pilot performance data, visual activity, mental workload, and self-report situation awareness were measured.

Congruent with the Proximity Compatibility Principle, the more integrated display facilitated superior performance on integrative tasks (lateral and vertical path maintenance), whereas a less …

Neural Network Fatigue Life Prediction In 7075-T6 Aluminum From Acoustic Emission Data, Emeka Chigozie Ibekwe

Master's Theses - Daytona Beach

The objective of this research was to classify acoustic emission (AE) -data associated with fatigue cracks in aluminum fatigue specimens and to use early cycle life AE data to predict failure in such members. An AE data acquisition system coupled with a Kohonen self organizing map and a back propagation neural network were used to perform the analysis. AE waveforms were recorded during fatigue cycling of twenty-four notched 7075-T6 aluminum specimens using broad-band piezoelectric transducers. A Kohonen self organizing map was used to classify the AE flaw growth signals. The signals were classified into three categories based on their AE …

Ultimate Strength Prediction In Fiberglass/Epoxy Beams Subjected To Three-Point Bending Using Acoustic Emission And Neural Networks, Michele D. Dorfinan

Master's Theses - Daytona Beach

The research presented herein demonstrates the feasibility of predicting ultimate strengths in composite beams subjected to 3-point bending using a neural network analysis of acoustic emission (AE) amplitude distribution data. Fifteen unidirectional fiberglass/epoxy beams were loaded to failure in a 3-point bend test fixture in an MTS load frame. Acoustic emission data were recorded from the onset of loading until failure. After acquisition, the acoustic emission data were filtered to include only data acquired up to 80 percent of the average ultimate load.

A backpropagation neural network was constructed to predict the ultimate failure load using these AE amplitude distribution …

Structural Design And Analysis Of A Rigidizable Space Shuttle Experiment, Raymond G. Holstein Iii

Theses and Dissertations

AFIT is in the process of designing a Space Shuttle experiment designated as the Rigidized Inflatable Get-Away-Special Experiment (RIGEX) to study the effects of microgravity on the deployment of rigidizable composite structures. Once in space, the experiment will inflate and rigidize three composite structures and perform a vibration analysis on each by exciting the tubes using piezoelectric patches and collecting data via an accelerometer. This paper presents the structural and vibration analysis of the RIGEX assembly and inflatable composite tubes using ABAQUS Finite Element Analysis (FEA) software. Comparison of the analysis has been carried out with Eigenvalue/Eigenvector experimentation by means …

Experimental And Computational Analysis Of Modes In A Partially Constrained Plate, Robert M. Vandawaker

Theses and Dissertations

The field of structural health monitoring (SHM) attempts to reduce labor and cost by allowing technicians to monitor selected properties of an aircraft's structure to detect impending failure. This research examines methods to detect damage to a thermal protection system (TPS) tile using representative 2024-T3 aluminum plates. Plates are subjected to modal analysis in single and joined conditions in an attempt to provide the capability of sensing damage to a tile on the surface of a vehicle while the sensors remain on the superstructure of the airframe. Jointly, the development of a means to model the system using finite element …

Effect Of A Variable Contact Load On Fretting Fatigue Behavior Of Ti-6al-4v, Andrew J. Jutte

Theses and Dissertations

Effects of a variable contact load on the high cycle fretting fatigue behavior of Ti-6AL-4V were investigated. Experimental tests were performed using a new test setup capable of applying a contact load varying in amplitude, frequency, and phase and independently measuring shear forces on opposite sides of a specimen. Finite element analysis (FEA) of experimental and idealized loading conditions was performed and local mechanistic parameters and the Modified Shear Stress Range (MSSR) fatigue parameter were determined. Correlations between contact width, slip amplitude, fatigue life and a variable contact load were established with variable contact loading shown to have a damaging …

Computation Of Shock Induced Noise In Imperfectly Expanded Supersonic Jets, Bulent Imamoglu

Mechanical & Aerospace Engineering Theses & Dissertations

Screech noise exists only in imperfectly expanded jets. The exit pressure of imperfectly expanded jets does not match ambient pressure, so expansion or compression waves appear out of the nozzle and generate shock cell patterns. Screech is generated by the interaction of shock cells and instability waves. Many experiments and computations have been done to model screech noise, but it is not yet a very well known subject.

A numerical study is performed to understand screech generation mechanisms and to compare with latest experiments. A supersonic underexpanded jet of 25.4 mm diameter is modeled for cases of Mach numbers of …

Nonlinear Response And Fatigue Estimation Of Aerospace Curved Surface Panels To Acoustic And Thermal Loads, Adam Przekop

Mechanical & Aerospace Engineering Theses & Dissertations

This work presents a finite element modal formulation for large amplitude free vibration of arbitrary laminated composite shallow shells. The system equations of motion are formulated first in the physical structural-node degrees of freedom (DOF). Then, the system is transformed into general Duffing-type modal equations with modal amplitudes of coupled linear bending-inplane modes. The linear bending-inplane coupling is due to the shell curvature as well as unsymmetric lamination stacking. Multiple modes, inplane inertia, and the first-order transverse shear deformation for composites are considered in the formulation. A triangular shallow shell finite element is developed from an extension of the triangular …

Residual Compressive Strength Prediction Of Carbon/Epoxy Laminates Subjected To Low Velocity Impact Damage, Christopher D. Hess

Master's Theses - Daytona Beach

Low energy impact damage to a composite structure is difficult to detect and can have profound effects on compressive strengths. Low energy impact damage is sometimes termed as barely visible impact damage (BVID). Detecting BVID is only possible by implementing nondestructive testing (NDT) techniques. Depending upon the support conditions, material system, laminate thickness, lay-up orientation, and impactor geometry, velocity, and hardness, the types of damage associated with BVID include delaminations, longitudinal and transverse matrix cracks, and in some cases, fiber breaks. Material properties such as the strengths of the matrix, fibers, fiber/matrix interface, and more important for BVID, ply interface …

Implementation And Testing Of Unsteady Reynolds-Averaged Navier-Stokes And Detached Eddy Simulation Using An Implicit Unstructured Multigrid Scheme, Juan A. Palaez

Mechanical & Aerospace Engineering Theses & Dissertations

Investigation and development of the Detached Eddy Simulation (DES) technique for the computation of unsteady flows on unstructured grids are presented. The motivation of the research work is driven by the ultimate goal of predicting separated flows of aerodynamic importance, such as massive stall or flows over complex non-streamlined geometries. These cases, in which large regions of massively separated flow are present, represent a challenge for conventional Unsteady Reynolds-Averaged Navier-Stokes (URANS) models, that in many cases, cannot produce solutions accurate enough and/or fast enough for industrial design and applications. A Detached Eddy Simulation model is implemented and its performance compared …

Experimental And Computational Failure Analysis Of Graphite/Bismaleimide Laminated Composite And Carbon Foam In Sandwich Construction, Troy C. Welker

Theses and Dissertations

Sandwich beams consisting of a carbon foam core and graphite/bismaleimide face sheets were constructed and tested. Nine specimens were fabricated using three distinct cross-ply symmetric face sheet layups with a constant core thickness. Four-point bend testing controlled by a constant rate of midspan vertical displacement was used to load the specimens to failure. Displacements and strains from the experiment were compared to analytical sandwich beam theory and displacements and failure loads were compared to a layerwise finite element solution. A phenomenological failure criterion was developed that compares favorably with experimental failure data. The finite element solution gives failure within an …

Structurally Integrated Antennas On A Joined-Wing Aircraft, Ben P. Smallwood

Theses and Dissertations

This research is a foundational study of conformal, load-bearing antenna arrays embedded into the wing structure of a joined-wing aircraft. It is a multidisciplinary effort that touches on the aerodynamic structural and electromagnetic design considerations that stem from this unique type of sensor integration. The antenna performance Finite Element Model (FEM) and control surface effectiveness are investigated. The theory describing an ensemble of dipole antenna elements that conform to the shape of a section of the joined wing is developed. The far held flee space radiation pattern of the sensor is then analyzed for a wing that is deflected due …

Numerical Study Of Two-Dimensional Secondary Injection Into A Mach 3.5 Freestream, Stephen C. Coghill

Mechanical & Aerospace Engineering Theses & Dissertations

Upstream interaction within a dual-mode scramjet engine is investigated numerically. The upstream interaction is investigated by increasing the freestream-to-injector pressure ratio. The constant area duct and sudden expansion geometries are used to achieve these results. Analysis using the symmetry boundary condition is compared to the full boundary condition for the constant area duct. Numerical analysis of the Mach 3.5 freestream is conducted using normal sonic injection of nitrogen gas to create the upstream interaction. Comparisons, where applicable, are made to experimental results. Due to the high speed of the flowfield, oblique shockwaves are present causing numerical convergence difficult to achieve. …

New Approaches To Gortler And Tollmien-Schlichting Boundary-Layer Instabilities, Vijay Kalburgi

Mechanical & Aerospace Engineering Theses & Dissertations

A detailed understanding of the physical processes that lead to instability and transition in the external viscous boundary layers of airfoils has been the goal of researchers for decades. This study seeks to enhance our understanding of Gortler and Tollmien-Schlichting instabilities through a critical review of prior theoretical methodology and fundamental experiments, the development of dimensionally consistent disturbance equations, and novel interpretation of the resulting flow physics revealed by their solutions to explain the process of transition.

Gortler vortices arise in boundary layers along concave surfaces due to centrifugal effects and these vortices in combination with other instabilities play an …

Torque Limit Of A Mechanical Fastener In A Graphite/Epoxy Joint, Kristian M. Kostreva

Master's Theses - Daytona Beach

Presently there is a lack of confidence amongst engineers when specifying the preload of a mechanical fastener in a composite joint due to a lack of a fundamental knowledge base regarding the behavior of composites under fastener compressive load. As such, a novel experimental procedure was developed herein to determine the through-the-thickness compressive (TTTC) material properties. A total of 206 property tests were performed on four different graphite/epoxy material systems. The results confirmed that TTTC material properties vary with fiber orientation, laminate thickness, fiber volume fraction, and even laminate surface finish. Hence, the 'rule of mixtures' provides a poor estimate …

Electromagnetic Scattering From A Gap In A Magneto-Dielectric Coating On An Infinite Ground Plane, George R. Simpson

Theses and Dissertations

The electromagnetic scattering from a gap in a magneto-dielectric coating on an infinite ground plane is analyzed. In this context, the gap forms a break only in the magneto-dielectric slab coating while the ground plane is continuous and unbroken. Volume equivalence is used to convert the gap region to one containing unknown volumetric equivalent electric and magnetic currents. The equivalent problem then is one of these currents radiating in the presence of an unbroken grounded magneto-dielectric slab. A Green's function for this geometry is developed consisting of two terms: a direct coupling term and correction term to account for the …

Modeling Of Acoustic Emission Failure Mechanism Data From A Unidirectional Fiberglass/Epoxy Tensile Test Specimen, Daniel R. Lendzioszek

Master's Theses - Daytona Beach

The purpose of this work was to model the acoustic emission (AE) flaw growth data that resulted from the tensile test of a unidirectional fiberglass/epoxy specimen. The data collected and stored during the test were the six standard AE quantification parameters for each event. A classification neural network was used to sort the data into five failure mechanism clusters. The resulting frequency histograms of the sorted data were then mathematically modeled herein using the three types of Johnson distributions: bounded, lognormal, and unbounded. These provided a reasonably good fit for all six AE parameter distributions for each of the five …