Some Boundary Value Problems of Elastic Media Containing Rigid Inclusions Under Compressive Mechanical Loads

In this work we discuss some 2D boundary-value problems related to an elastic medium containing a thin rigid inclusion with general geometrical shape located in the interface between two separate elastic half-planes and subjected to compressive loading. Assuming perfect bonding between the inclusion and elastic medium, Fourier and Henkel integral transformation techniques are used to obtain the exact solution for the problem. Explicit forms are presented for arbitrary forms of thin inclusions, demonstrating that the tangent shear stress at the end-points of the inclusion has a square-root singularity. It is also shown that the normal stress has a logarithmic singularity when the end-points of the inclusion are approached from the inside of the inclusion and a square-root singularity when the end-points of the inclusion are approached from the outside of the inclusion. For special, extreme cases the solutions for anti-cracks are also presented.

Development and Testing of a Small Scale Bladeless Turbine for Power Production Applications

Bladeless turbines were first proposed and demonstrated almost 100 years ago, but they have not found widespread application. They have the potential for converting flow energy into rotational energy at high efficiencies. This paper discusses an effort to understand the factors affecting bladeless turbine efficiency, and the related experimental program performed. A theoretical model of turbine performance was developed and used to predict the performance of a small scale test unit. The model inputs include geometric parameters and inlet conditions including pressure and flow rate. The test unit was designed and assembled. Rapid prototyping techniques were used to facilitate part fabrication. It was coupled to an experimental set up including appropriate instrumentation. A comparison of model predictions and test results is presented.

A Procedure to Evaluate the Thermal Response of a Multilayered Thermal Protection System Subjected to Aerodynamic Heating

Next generation reusable re-entry vehicles must be capable of sustaining consistent repeated aero-thermal loads without damage or deterioration. This means that such structures must tolerate the high temperatures engendered by aero-thermal re-entry fluxes due to the establishment of a hypersonic regime over the body. Thermal Protection Systems (TPS) are used to maintain a reusable launch vehicle’s structural temperature within acceptable limits during re-entry flights; that is, internal temperature should not overcome the temperature limit use of the internal structure. TPS are usually composed by several layers made of different materials. Heat transfer through a multilayer insulation during atmospheric re-entry involves combined modes of heat transfer: heat conduction through the solid, heat radiation to the outer space etc. In the frame of TPS design activities a procedure based on one dimensional analytical solutions of transient nonlinear analyses has been developed in order to estimate the temperature variation with time and space of a multilayered body subjected to aerodynamic heating inside a radiating space. Since internal temperature values of TPSs of re-entry vehicles cannot exceed certain values, that procedure allows to quickly evaluate those temperature values and to preliminary size layer thicknesses before preparing and performing Finite Element analyses.

Aerothermal and Trajectory Analysis of Small Payloads Launched to Low Earth Orbit From an Airborne Platform

In recent years there has been an ever increasing need to launch small payloads (∼1–100 kg) into low earth orbit (LEO); examples include the defense, telecommunications and other civilian industries. NASA’s stated mission of launching a manned mission to Mars requires many tons of raw materials to be economically launched into LEO and assembled there. Conventional rocket launch from earth is prohibitively expensive for small mass payloads. Estimates range from $7000–$20,000 to launch 1 kg of mass into low earth orbit. Several concepts have been proposed to economically launch small payloads from earth, including light gas guns, electromagnetic launchers and the so called “slingatron” concept. The goal of these concepts is to reduce the cost per kg (to under $1000) to achieve LEO. Each of these concepts involves launching small payloads that traverse the atmosphere and then placed into a circular low earth orbit. As the launch vehicle traverses the dense lower portion of the atmosphere it experiences thermal heating loads that must be absorbed by a thermal protection system (TPS) if the payload is to survive the transit. High launch angles are desirable from the standpoint of minimizing TPS mass. However, for ballistic trajectories, high launch angles require a large propellant mass to achieve a stable circular orbit. This effort performs aerothermal and trajectory analyses on a nominal 10 kg payload launched from 16 km altitude airborne platform into a 200 km circular orbit. The study focuses on two efforts: 1) computing ballistic trajectories of sphere cones with ablation assuming laminar and turbulent flow in order to quantify the total ablation and required propellant mass to circularize the orbit for given launch conditions and 2) study lifting trajectories without ablation by flying axisymmetric sphere-cone projectiles at small angles of attack and asymmetric projectiles (ellipsleds) that turn the velocity vector during atmospheric transit in an effort to reduce the ΔV needed to circularize the orbit. The TPS is assumed to be made of graphite. Total parasitic mass is reported for several launch angles. Even though ablation is not considered for the lifting trajectories, the study allows comparison of relative effectiveness of various lifting trajectories in reducing the ΔV required to circularize the orbit.

Electrical Characterization of Carbon Fiber Polymer Matrix Composites

This paper studies the response of carbon fiber polymer matrix composites subjected to DC electric currents. We have developed a new fully instrumented experimental setup that enables one to measure electric field characteristics (amperage, voltage, resistance) and temperature at the surface of the electrified composites in real time. The experimental procedure ensured a low contact resistance between the composite and electrodes, high uniformity in the density of the applied electric current, and low resistance heating. An extensive experimental study on the electrical characterization of carbon fiber polymer composites of different composition, ply sequence, thickness, etc. was conducted. The effect of the resistance heating was carefully analyzed through experimental analysis as well as the finite element modeling.

The Effect of Surface Over-Aging on the Strength and SCC Susceptibility of 7075 Aluminum Alloy

A novel heat treatment procedure combining the shot-peening with a two-step aging operation was proposed to improve both the strength and the stress corrosion cracking (SCC) resistance of the high-strength 7075 aluminium alloy. The heat treatment included one shot-peening stage before or between the two stages of aging at 120°C for 24 h and at 160°C for 1 h, respectively. The mechanical properties obtained during the aforementioned operations were extremely similar to those of the T6 sample owing to the unaffected bulk microstructure over such a low over-aging period. The SCC resistance of these samples was considerably improved, compared to that of the T6 sample and of the conventional shot-peened T6 sample due to the over-aging of the surface like the T7 treatment leading from the diffusion acceleration by the dislocations generated in the surface layer during shot-peening. In spite of the further depth of deformation caused by shot-peening prior to the first step of aging, the sample shot-peened after the first step of aging showed no significant decrease in the SCC resistance because of its higher generated dislocation by shot-peening.

3D Numerical Simulation of Contaminant Distribution in an Aircraft

Indoor air quality studies are very important as they allow designers to verify that a comfortable and healthy environment is being provided before it is physically constructed. It can be especially important on the closed confines such as a commercial aircraft which may carry a high density of people from various parts of the world. In this study, 3-D contaminant dispersion simulation within an aircraft is conducted by using Finite Volume Methods. Effects of two types of air distribution systems on contaminant dispersion are analyzed. The preliminary results show that the Under Floor Air Distribution system performs better in the overall air quality provided to the passengers of the aircraft than the Ceiling Air Distribution system.

Development of a “Smart” Dynamic Strain Measurement System for Turbine Engine Ground Testing

The Arnold Engineering Development Center (AEDC) testing complex includes more than 50 wind tunnels, test cells, arc heaters, and other specialized test facilities. Of these, 27 units have capabilities that are unmatched in the United States, and 14 are unmatched in the world. These unique facilities pose equally unique testing challenges, including several related to test preparation. A dynamic strain measurement system is being developed for turbine engine ground testing applications. The system is being developed to be compatible with the IEEE-1451 Smart Transducer Interface Standard in order to enable “plug and play” test set up. This will help to minimize the time between the test article installation and completion of test preparations. It will also help to minimize “manual” record keeping associated with testing. The system will also utilize the IEEE-1588 precision time protocol to maintain sampling synchronization. This paper discusses the development of the system consisting of the Smart Transducer Interface Modules (STIMs), the network interfaces (NCAPs), and the system server for control and data storage. It also discusses initial testing and evaluation of the system.

Cracked Elastic Layer Under a Compressive Mechanical Load

In the present work, the problem of an elastic layer weakened by a finite penny shaped crack parallel to a layer’s surface that is loaded in compression is considered. Assuming that the surfaces of the crack have frictional slipping contact, Henkel and Legendre integral transformation techniques are employed to formulate solutions in the form of an infinite system of linear algebraic equations. The regularity of the equations is established and closed-form solutions are obtained for stresses and strains. Assuming shear stress on the crack surfaces is linearly distributed, numerical results show both geometric and physical parameters have an essential influence on the stress distribution around the crack, with specific parameter values indicating the normal stress along the crack surface can change its sign from negative to positive. The implications of the work will be discussed.

Dynamic Optical Investigations of Hypervelocity Impact Damage

Hypervelocity impact is a rising concern in spacecraft missions where man-made debris in low-earth orbit as well as micrometeroids have the potential to damage not only the structural components, but also the optical, electrical, and thermal components of a space asset. Little has been investigated regarding damage mechanisms and dynamic fracture mechanics resulting from a hypervelocity impact in-situ. Two optical techniques, the methods of photoelasticity and caustics, in conjunction with high-speed photography are used to examine stress waves from impact of unloaded plates, as well as pre-cracked and pre-loaded plates in tension. The resulting photographs are analyzed to extract information regarding stress wave interactions, crack speeds and the dynamic stress field ahead of the moving cracks.