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No description available.

No description available.

No description available.

No description available.

Thin-ply composite laminates capable of enduring high strains are currently under investigation for compliant deployable spacecraft structures. Deployable structures such as booms fabricated from these materials can be flattened and coiled to high curvatures, achieving a compact configuration for stowage. Once in orbit, they are released with minimal actuation for deployment, allowing the operational geometry to be recovered. Previous studies have shown that the viscoelastic properties of the composite epoxy matrix can negatively impact final shape accuracy due to stress relaxation during stowage. In addition, since the strain energy stored is relied upon for deployment, considerable relaxation can potentially result in deployment stall. Stress relaxation in composites and the aforementioned effects it can have on deployment have not been analyzed sufficiently for space applications. The objective of this thesis is to investigate the moment relaxation and curvature recovery behavior of thin-ply composite laminates through a combination of analytical, numerical, and experimental approaches. The viscoelastic Kirchhoff plate model that serves as the theoretical basis of the analyses is first presented. An analytical solution for the recovery of a composite plate after stowage is derived. The numerical integration of the viscoelastic plate constitutive equations and its implementation as a user-defined subroutine in finite element programs is then described. The subroutine allows relaxation of 3D thin-shell structures to be modeled, and is applied to simulate stowage and recovery of a thin-ply composite currently of interest for solar sailing applications. The subroutine is then compared with results obtained from experiments for a thin-ply composite for bending relaxation and curvature creep recovery after being unloaded.

Propulsion systems are influenced by the efficiency of combustion systems. One approach to substantially improve combustion efficiency is through pressure gain combustion or detonation-based engines. Detonations exhibit attractive features such as increased stagnation pressure and rapid heat release; however, their highly unsteady and three-dimensional nature makes them difficult to characterize. In addition, the deflagration state prior to detonation is not well defined experimentally. Detonations can be achieved via the deflagration-to-detonation transition (DDT), where a deflagration that propagates on the order of 1 – 10 m/s is accelerated to a detonation that propagates on the order of 2000 m/s. The DDT process is highly dynamic and can occur through several mechanisms such as the Zeldovich reactivity-gradient mechanism where hot spots are created by Mach stem reflections, localized vorticial explosions, boundary layer effects, or turbulence. This work focuses on transient compressible flame regimes within the turbulent DDT (tDDT) process which causes a flame to undergo various burning modes. These burning modes can be categorized into four regimes: (1) slow deflagrations, (2) fast deflagrations, (3) shock-flame complex, and (4) detonation. To achieve each burning mode, turbulence levels and propagation velocities are tailored using perforated plates and various fuel-oxidizer compositions. The primary goal of this dissertation is to characterize the relationship between the turbulent flame speed (ST) and Chapman-Jouguet (CJ) deflagration speed (SCJ) using high-speed optical diagnostics in a turbulent shock tube facility. This work will: (1) further validate and classify the turbulence-compressibility characteristics associated with fast flames that lead to detonation onset in a highly turbulent environment, (2) quantify local ST for fast flames, and (3) investigate the flow field conditions of flame modes relating to the SCJ criteria, from slow deflagrations to shock-flame complexes.

The work presented herein consist of first studying the instantaneous properties of the detonation waves in a rotating detonation rocket engine by tracking each individual wave and recording its position, velocity, and peak intensity as it travels around the annulus. Results for a steady portion of a test performed on a rotating detonation rocket engine show that the wave properties exhibit oscillatory behavior. Results obtained from the rotating detonation rocket engine show that the properties are highly dependent on the azimuthal position. In an attempt to understanding the cause of such a behavior, similar investigations were performed on an air-breathing rotating detonation engine with a different injection design to see if the behavior persists. Results show that air-breathing rotating detonation engines do indeed exhibit this behavior in a more attenuated fashion. It is demonstrated that the pre-detonation hole might be the reason for the observed combustion instabilities. After establishing the steady state behavior of a single mode in a rotating detonation rocket engine, transient analyses of multiple tests were performed in order to capture the relative wave speeds between the modes. Wave speeds and operational frequency plots showcasing the range of operation of each mode (single and counter-propagating) were constructed. Moreover, operating maps of the engine were built and clearly demonstrate where each mode resides. The mode transition instability phenomenon observed in rotating detonation rocket engines is then studied. Each mode transition is distinguished by different mechanics and behavior requiring different diagnostic tools and research techniques to analyse. In this investigation, five possible mode transitions in rotating detonation engines have been identified and are Types AS, DS, AO, DO and SO and their behavior is discussed. Also, the counter-propagation wave behavior within an intermidiate period for Type _O mode transition have been discussed.

Increasing energy demands, and the subsequent need for cleaner energy conversion to combat climate change, creates a challenge that requires both short- and long-term solutions. To that end, new energy conversion cycles such as the Allam-Fetvedt cycle uses the combustion products (CO2) as the working fluid to increase efficiency and reduce emissions. There are several challenges regarding the implementation of these cycles, namely the extreme combustor conditions required (approximately 300 bar). The new High Pressure, Extended Range Shock Tube for Advanced Research (HiPER-STAR) was designed, built, and characterized to study combustion at these conditions to aid in the development of these sCO2 systems, among other extreme environments such as rocket chamber conditions. Further, development of chemical kinetics models used to predict combustion in these conditions typically assume reactions only in the homogeneous bulk gas region, while in these systems there are stagnation regions where hot gases are in contact with a heated wall for extended durations. Heterogeneous reactions are historically difficult to study, as typically there are coupled gas dynamic and transport-related complications that affect the reactions. A shock tube is an ideal location to mitigate and decouple these effects. The current work explores reactive and non-reactive end wall effects at high pressure, an area of interest for implementation by industry and resultantly where better efficiency can be achieved. Further designs have been completed and fabrication is underway to improve the capabilities of the facility to better decouple thermal wall effects and catalytic surface effects, as well as improve other combustion diagnostic capabilities of the facility.

Polymer thin membranes are used in a variety of deployable structures that require large areas and compact stowage. Packaging membrane structures often involves creasing the membrane along predefined fold lines to enforce the desired kinematics under folding action. Inducing permanent deformation by folding to a high curvature is a common method to create creases, particularly in the design of solar sails. The distinct mechanical characteristics at the crease regions have a profound effect on the subsequent deployment and tensioning of the membrane structures. The mechanical and geometric properties at the crease are related to the crease formation process, but the relationship is not well understood due to the presence of viscoelasticity and plasticity. This thesis seeks to investigate the relation between permanent material deformation and creasing behavior. In particular, creasing experiments are performed on polyimide thin films to identify the conditions for creasing onset. Uniaxial tension yield tests are conducted to relate material yielding with creasing onset.