Engineering Science and Materials Commons^™

The Effects Of Damage Arrestment Devices In Composite Plate Sandwiches With Fastener Holes, Mark Anderson, Nancy Hung Choy, Lacey Jones, Rita Kourskaya

Aerospace Engineering

Composite materials such as a carbon fiber are used in a variety of new technologies including aircraft, spacecraft, and motor vehicles. Carbon fiber has a high strength to weight ratio, a key advantage over other material options. This report discusses the use of composite damage arrestment devices (DADs) in composite sandwich panels with a foam core. There are three different curing cycles tested for the DADs: pressure only, vacuum only, and vacuum with 1000 lbs of pressure. Using a Tetrahedron Heat Press to cure the composite specimen and an Instron Machine to perform tensile testing, data was collected for each …

Review Of The Maxus 8 Sounding Rocket Experiment To Investigate Solidification In A Ti-Al-Nb Alloy, Robin Mooney, David Browne, Olga Budenkova, Yves R. Fautrelle, Ludo Froyen, Andrey Kartavykh, Stephan Rex, Burkhard Schmitz, Daniella Voss, Shaun Mcfadden

Conference Papers

A review of the MAXUS 8 sounding rocket microgravity experiment to investigate solidification structures in a Ti-Al-Nb intermetallic alloy is presented. The experiment was part of the Intermetallic Materials Processing in Relation to Earth and Space Solidification (IMPRESS) EU FP6 project. Key objectives were to investigate columnar and equiaxed solidification, and to achieve Columnar-to-Equiaxed Transition (CET) in the alloy. A microgravity experiment was designed to achieve this using a controlled power-down method. Two alloys were tested: one inoculated with a grain refiner and the other without grain refinement. Unrefined samples displayed axial and radial columnar growth. Boride inoculated samples displayed …

The Influence Of Pressure Relaxation On The Structure Of An Axial Vortex, Robert L. Ash, Irfan Zardadkhan, Allan J. Zuckerwar

Mechanical & Aerospace Engineering Faculty Publications

Governing equations including the effects of pressure relaxation have been utilized to study an incompressible, steady-state viscous axial vortex with specified far-field circulation. When sound generation is attributed to a velocity gradient tensor-pressure gradient product, the modified conservation of momentum equations that result yield an exact solution for a steady, incompressible axial vortex. The vortex velocity profile has been shown to closely approximate experimental vortex measurements in air and water over a wide range of circulation-based Reynolds numbers. The influence of temperature and humidity on the pressure relaxation coefficient in air has been examined using theoretical and empirical approaches, and …

Design, Fabrication, Structural Testing, And Numerical Analysis Of A Small Scale Composite Wing, Jacob David Gaunt, Juan Carlos Flores, Vincent Andrew Perry

Aerospace Engineering

A small scale composite wing based on a design found on an experimental aircraft was designed, constructed, and tested dynamically and statically. The wing was constructed similarly to an experimental aircraft wing. The performed static test was intended to produce pure bending. Strain gages were used to measure strains on the wing structure. The strains were converted to stresses to aid in analysis. The static test results suggested that the wing was actually under torsion. Four structural modes were found from the static test. A finite element analysis model was made to compare experimental results to numerical analytical results. The …

Multiscale Transformation Field Analysis Of Progressive Damage In Fibrous Laminates, Yehia Bahei-El-Din, Ritesh Khire, Prabhat Hajela

Centre for Advanced Materials

As part of an ongoing effort to model uncertainty propagation across multiple scales in fibrous laminates, this paper presents a deterministic transformation field analysis for modeling damage progression under membrane forces and bending moments. In this approach, equivalent eigenstresses are computed in the phases and/or plies such that their respective stress components that satisfy the underlying failure criteria are reduced to zero. Superposition of the solutions found for the undamaged laminate under applied loads and under the eigenstress field provide the entire response. Failure criteria are based on stress averages in the fiber and matrix. Damage mechanisms considered are frictional …

Modified Sandwich Structures For Improved Impact Resistance Of Wind Turbine Blades, Yehia Bahei-El-Din, Mostafa Shazly, I. El-Habbal, Y. Elbahy

Centre for Advanced Materials

Wind turbine blades are susceptible to damage due to fatigue as well as impact by flying objects and parts broken off failed blades of nearby wind towers. Localized, permanent compression of the foam core and delamination of the fibrous composite face sheets are typical damage modes and can lead to progressive structural failure. Sandwich structures modified by inclusion of flexible polyurethane (PU) layers within the cross section are examined under both impact and dynamic loads. Finite element models of sandwich structures with conventional and modified designs show that sandwich designs modified with PU interlayes exhibit reduced foam core crushing and …

Processing Of Zrb2-Zrc-Zrxsiy Ceramic By Reactive Metal Penetration, Nischel B. Maheswaraiah

Open Access Theses & Dissertations

The processing of ZrB2-ZrC-ZrxSiy composite by reactive metal penetration was investigated as a successor to the ZrB2-SiC composites for hypersonic vehicles application, which cannot be used for extended time at temperatures greater than 1600C due to formation of SiO and CO gases. Zirconium (Zr), zirconium disilicide (ZrSi2), and boron carbide (B4C) were reacted in graphite crucibles for 60, 120, 180, and 240 minutes. Microscopy and x-ray diffraction (XRD) deduced the formation of a heterogeneous microstructure of ZrB2-ZrC-ZrxSiy precipitates surrounded by a solidified Zr-Si melt. Unreacted boron carbide was observed in samples held at 1860C for 60 minutes and 120 minutes, …

Microstructure Investigation Of Al-Rich Titanium Aluminum Alloys, David Pham

Open Access Theses & Dissertations

The microstructures of Ti-Al alloys with 70-80 wt% Al were investigated. Aluminum wire (99.999%) and TiH₂ powder (99.7%) were used to produce the sample compositions inside a vertical tube furnace at 1600^oC in an Ar atmosphere. Argon is purified through a dehumidification and deoxidation system. Magnesium perchlorate Mg(ClO₄)₂ acts as a desiccant and titanium sponge pulls oxygen from the Ar in furnaces operating at 800^oC and 750^oC. X-ray diffraction and an optical microscope are used to identify phases and compositions

Studies Of Dynamic Crack Propagation And Crack Branching With Peridynamics, Youn Doh Ha, Florin Bobaru

Department of Engineering Mechanics: Faculty Publications

In this paper we discuss the peridynamic analysis of dynamic crack branching in brittle materials and show results of convergence studies under uniform grid refinement (m-convergence) and under decreasing the peridynamic horizon (δ-convergence). Comparisons with experimentally obtained values are made for the crack-tip propagation speed with three different peridynamic horizons.We also analyze the influence of the particular shape of themicro-modulus function and of different materials (Duran 50 glass and soda-lime glass) on the crack propagation behavior. We show that the peridynamic solution for this problem captures all the main features, observed experimentally, of dynamic crack propagation and branching, as well …

Application Of Systems Engineering To Rapid Prototyping For Close Air Support, John M. Colombi, Richard G. Cobb

Faculty Publications

Twenty-first century military operations have brought forth many new challenges for the Armed Forces of the United States. One such challenge is with new operating environments, where current systems are not always effective. While it is desirable to apply a systems engineering approach to best meet critical user needs, there may be a misconception that systems engineering requires a lengthy and detailed process not nimble enough for a rapid prototyping effort. This article describes how a classic systems engineering methodology was successfully tailored to the rapid development of potential material solutions to meet a critical operational need. Key observations are …

Multiscale Modeling Of Impact On Heterogeneous Viscoelastic Solids With Evolving Microcracks, Flavio V. Souza

Department of Engineering Mechanics: Dissertations, Theses, and Student Research

Multiscale computational techniques play a major role in solving problems related to viscoelastic composite materials due to the complexities inherent to these materials. In the present work, a numerical procedure for multiscale modeling of impact on heterogeneous viscoelastic solids containing evolving microcracks is proposed in which the (global scale) homogenized viscoelastic incremental constitutive equations have the same form as the local scale viscoelastic incremental constitutive equations, but the homogenized tangent constitutive tensor and the homogenized incremental history dependent stress tensor depend on the amount of damage accumulated at the local scale. Furthermore, the developed technique allows the computation of the …

Effect Of Steam Environment On Creep Behavior Of Nextel720/Alumina-Mullite Ceramic Matrix Composite At Elevated Temperature, Tolga Kutsal

Theses and Dissertations

The tensile creep behavior of an oxide-oxide ceramic matrix composite (CMC) was investigated at 1000 and 1100° C in laboratory air and steam. The oxide-oxide CMC studied in this research was Nextel™ 720/alumina-mullite (N720/AM). The composite consists of N720/fibers with 0°/90° fiber orientation and a porous alumina-mullite matrix. Tensile-strain behavior was investigated and tensile properties measured at 900, 1000 and 1100° C. The effect of loading rate on tensile properties of N720/AM ceramic matrix composite at 1100° C in steam was also examined. Creep-rupture tests were performed at 1100° C in laboratory air and steam, and at 1000° C only …

A Finite Element Evaluation Of An Experiment Related To Coating Damping Properties, Armando Deleon

Theses and Dissertations

Typically turbine engine blades gain protection from thermal damage by the use of hard coatings, such as magnesium aluminate spinel. Known as Thermal Barrier Coatings (TBC's), they have material properties that include several nonlinearities. These TBC's create damping primarily due to their nonlinear dissipation of energy. In order to effectively represent their damping properties, it is necessary to create a method which combines experimentation and analysis. Previous work has shown the need for a beam bounded and loaded in such a fashion that external support energy dissipation functions i.e. boundary conditions and aerodynamics are eliminated. Thus, a new experimental apparatus …

Effects Of Prior Aging At 316°C In Argon On Inelastic Deformation Behavior Of Pmr-15 Polymer At 316°C: Experiment And Modeling, Ozgur Ozmen

Theses and Dissertations

The inelastic deformation behavior of PMR-15 neat resin, a high-temperature polymer, was investigated at 316 deg C. The experimental program was designed to explore the influence of strain rate on tensile loading, unloading, and strain recovery behaviors. In addition, the effect of the prior strain rate on the relaxation response of the material, as well as on the creep behavior following strain controlled loading were examined. The material exhibits positive, nonlinear strain rate sensitivity in monotonic loading and unloading. Early failures occur in the inelastic regime. The recovery of strain at zero stress and creep response are strongly affected by …

Volume Viscosity In Fluids With Multiple Dissipative Processes, Allan J. Zuckerwar, Robert L. Ash

Mechanical & Aerospace Engineering Faculty Publications

The variational principle of Hamilton is applied to derive the volume viscosity coefficients of a reacting fluid with multiple dissipative processes. The procedure, as in the case of a single dissipative process, yields two dissipative terms in the Navier-Stokes equation: The first is the traditional volume viscosity term, proportional to the dilatational component of the velocity; the second term is proportional to the material time derivative of the pressure gradient. Each dissipative process is assumed to be independent of the others. In a fluid comprising a single constituent with multiple relaxation processes, the relaxation times of the multiple processes are …

Understanding Practical Limits To Heavy Truck Drag Reduction, Drew Landman, Richard Wood, Whitney Seay, John Bledsoe

Mechanical & Aerospace Engineering Faculty Publications

A heavy truck wind tunnel test program is currently underway at the Langley Full Scale Tunnel (LFST). Seven passive drag reducing device configurations have been evaluated on a heavy truck model with the objective of understanding the practical limits to drag reduction achievable on a modern tractor trailer through add-on devices. The configurations tested include side skirts of varying length, a full gap seal, and tapered rear panels. All configurations were evaluated over a nominal 15 degree yaw sweep to establish wind averaged drag coefficients over a broad speed range using SAE J1252. The tests were conducted by first quantifying …

High Temperature Oxidation Behavior Of Nb-20mo-15si-5b-20cr Alloy, Julieta Angelica Ventura

Open Access Theses & Dissertations

Materials for high temperature applications, such as jet engines, gas turbines and turbine blades, require a balanced combination of physical and chemical properties to withstand the aggressive environments in which they are utilized. Some of the properties required are high strength, low density, high melting point and good oxidation resistance at elevated temperatures [1-3]. For this reason, the microstructure and oxidation behavior of the Nb-20Mo-15Si-5B-20Cr alloy (at.%) has been studied as a potential candidate to replace Nickel-based alloys currently used in the aerospace industry.

Short term oxidation (STO) and long term oxidation (LTO) studies have been performed in air for …

Hypersonic Boundary Layer Receptivity To Acoustic Disturbances Over Cones, Kursat Kara

Mechanical & Aerospace Engineering Theses & Dissertations

The receptivity mechanisms of hypersonic boundary layers to free stream acoustic disturbances are studied using both linear stability theory (LST) and direct numerical simulations (DNS). A computational code is developed for numerical simulation of steady and unsteady hypersonic flow over cones by combining a fifth-order weighted essentially non-oscillatory (WENO) scheme with third-order total-variation-diminishing (TVD) Runge-Kutta method. Hypersonic boundary layer receptivity to free-stream acoustic disturbances in slow and fast modes over 5-degree, half-angle blunt cones and wedges are numerically investigated. The free-stream Mach number is 6.0, and the unit Reynolds number is 7.8×106/ft. Both the steady and unsteady solutions are obtained …

Cyclic Creep And Recovery Behavior Of Nextel™ 720/Alumina Ceramic Matrix Composite At 1200° C In Air And Steam Environments, Bridgett A. Whiting

Theses and Dissertations

The cyclic creep and recovery behaviors of the N720/Al₂O₃ composite were investigated in this research. The ceramic matrix composite (CMC) contains a porous alumina matrix with laminated, woven mullite/alumina (Nextel^TM 720) fibers. The composite does not have an interface between the fiber and matrix. The CMC relies on the porous nature for flaw tolerance. The objective of this study the influences of monotonic creep and cyclic creep loading histories on the creep lifetime, creep strain rate, accumulated creep strain as well as on the recovery of creep strain at near zero stress. The cyclic creep and …

The Effects Of Environment On The Interlaminar Shear Performance Of An Oxide/Oxide Ceramic Matrix Composite At Elevated Temperature, Patrick D. Laffey

Theses and Dissertations

This research investigated the interlaminar shear performance of an oxide/oxide ceramic matrix composite consisting of Nextel™ 720 fibers in a high purity, porous alumina (Al₂O₃) matrix. The interlaminar shear performance was observed in both tension and compression of double notched specimens (DNS) at 1200 °C. Interlaminar shear creep behavior was examined in both laboratory air and in steam environment at 1200 °C. In air, the creep stress was -6.5 MPa. In steam creep stresses included -4.0, -5.0, and -6.5 MPa. Primary and secondary creep regimes were observed in all air creep tests and the creep test …

Effects Of Prior Aging At 191°C On Creep Response Of Im7/Bmi 5250-4, Robert A. Salvia

Theses and Dissertations

The creep behavior of IM7/BMI 5250-4 with fiber orientations of [± 45] and [0/90] that were aged in air at 191 °C for up to 1000 hours was evaluated. The total weight loss during the aging process was also evaluated. Weight loss due to aging was 0.64% for the [0/90] fiber orientation and 0.72% for the [± 45] fiber orientation. Tensile tests to failure were conducted to establish tensile properties. The [0/90] specimens have a much higher stiffness and Ultimate Tensile Strength (UTS) values than the [± 45] specimens. The tensile tests of the aged specimens revealed that the Ultimate …

Effects Of Prior Aging On The Creep Response Of Carbon Fiber Reinforced Pmr-15 Neat Resin At 288°C In An Air Environment, Christopher A. Back

Theses and Dissertations

The mechanical response of carbon fiber reinforced PMR-15 neat resin with a ± 45 fiber orientation was investigated at 288 °C. Mechanical testing was performed on unaged specimens and specimens that were aged up to 1000 hours in an air environment. Tensile tests were performed to determine Young's modulus of elasticity and Ultimate Tensile Strength. Creep tests were performed at creep stress levels of 30 and 60 MPa. Creep periods of at least 25 h in duration were followed by recovery at zero stress. Duration of the recovery period was at least twice the time of the creep period. Oxidation …

Compressive Creep Behavior Of Nextel™ 720/Alumina Ceramic Matrix Composite At 1200°C In Air And In Steam Environment, Neil R. Szymczak

Theses and Dissertations

The aerospace community continues to push the envelope in engineering aircraft that fly higher, faster, and safer while operating with a greater degree of efficiency. To meet these operational requirements innovative aerospace components must be designed to operate in aggressive environments. This research will investigate the ultimate compressive strength and the compressive creep behavior of Nextel^TM 720/Alumina ceramic matrix composite at 1200 °C in air and 100% steam environments. The effects of creep loading history on the tensile and compressive material behavior will also be examined. The primary strengths of the N720/A composite are its oxide/oxide composition which inherently …

Tension-Compression Fatigue Behavior Of A Carbon Fiber/Epoxy (Im7/Epon 862) Composite Fabricated Using Vacuum Assisted Resin Transfer Molding Process, David W. Katwyk

Theses and Dissertations

New composite materials and processing methods are continually being developed for use in high performance aerospace systems. One of these new processing methods is the vacuum assisted resin transfer molding (VARTM) process, which shows promise in producing large structural components that have good properties at a lower cost than traditional manufacturing methods. Future widespread use of components manufactured using the VARTM process depends on understanding how these components perform under service conditions, specifically under impact and fatigue conditions. The tension-compression fatigue behavior of a four-harness satin weave carbon fiber/epoxy (IM7/EPON 862) composite manufactured using the VARTM process is investigated in …

An Evaluation Of High Velocity Wear, Gregory J. Cameron

Theses and Dissertations

The Holloman High Speed Test Track (HHSTT) is a rocket-powered sled track facility used for testing a variety of hypervelocity aerospace applications. The current speed record is 6,453 miles per hour. While this seems fast there are customers at the track that have requirements demanding even faster speeds. Significant research has been conducted in the area of rail gouging as it relates to the test track, and efforts are under way to reduce and even eliminate this phenomenon. Any steps taken in this effort may eliminate catastrophic sled failures caused by gouging, however wear is another damaging issue that needs …

Damage Detection Using Lamb Waves For Structural Health Monitoring, Jeffrey S. Crider Ii

Theses and Dissertations

Nondestructive structural health monitoring (SHM) is an evolving technology being developed for monitoring air and space systems. The information gathered on a system's structural integrity through SHM detection methods may result in reduced costly maintenance inspections, enhanced safety, and system failure predictions. This study evaluates Lamb wave approaches used to detect simulated cracks in laboratory experiments on thin plates to detect more realistic damage in a test article representing the complex geometry of an existing aircraft bulkhead. We take a "hot-spot" monitoring approach, where we monitor an area of the structure known to fail. In our experiment, we evaluated the …

Experimental Methods To Characterize Nonlinear Vibration Of Flapping Wing Micro Air Vehicles, Adam P. Tobias

Theses and Dissertations

For urban combat reconnaissance, the flapping wing micro air vehicle concept is ideal because of its low speed and miniature size, which are both conducive to indoor operations. The focus of this research is the development of experimental methods best suited for the vibration testing of the wing structure of a flapping wing micro air vehicle. This study utilizes the similarity of a beam resonating at its first bending mode to actual wing flapping motion. While computational finite element analysis based on linear vibration theory is employed for preliminary beam sizing, an emphasis is placed on experimental measurement of the …

Lamb Wave Propagation In Varying Thermal Environments, Jennifer P. Andrews

Theses and Dissertations

During flight, launch, and reentry, external surfaces on aerospace vehicles undergo extreme thermo-acoustic loads resulting in structural degradation. Structural health monitoring techniques are being devised to evaluate the health of these structures by locating and quantifying structural damage during and after flight. One such technique uses Lamb wave propagation to assess damage on the surface and through the thickness of thin materials. The objective of this study was to assess the sensitivity of piezo-generated Lamb wave propagation to isothermal and thermal gradient environments using both theoretical and experimental methods. Experimental isothermal tests were conducted over a temperature range of 0-225 …

Effects Of Prior Aging At Elevated Temperature In Air And In Argon Environments On Creep Response Of Pmr-15 Neat Resin, Joseph L. Broeckert

Theses and Dissertations

Creep behavior of PMR-15 neat resin, a polyimide thermoset polymer, aged in air or argon gaseous environments at 288 °C for up to 1000 h was evaluated. Creep tests were performed at 288 C at creep stress levels of 20 and 10 MPa. Creep periods of at least 25 h in duration were followed by recovery at zero stress. Weight loss and growth of the oxidation layer were also monitored and correlated with aging time. The aging time in both air and argon environments had a strong influence on the creep and recovery response of PMR-15 neat resin. Samples aged …

Evaluation Of Factors Contributing To Damping Of Coated And Uncoated Titanium Plates, Dustin W. Lee

Theses and Dissertations

High Cycle Fatigue (HCF) is the leading cause of component failure in gas turbine engines today, which poses great risk to aircraft, engines, and their crews. Mitigation of HCF effects has become a priority topic, and the damping benefits of hard coatings are being reevaluated for this purpose. Research was conducted to further understanding of damping measurements on these coatings. This study continues work to characterize the damping effects of a magnesium aluminate spinel (mag spinel) coating applied to a titanium plate via vibration testing. Two different plate sizes were evaluated in a clamped-free-free-free condition and a free-free-free-free condition, respectively. …