This study will present the Experimental, numerical and analytical characterizations of composite sandwich structures needed to optimize structure design. In this study, the effects of varying honeycomb core ribbon orientation and varying face sheet thickness’s have on the flexural behavior of honeycomb sandwich structures was investigated. Honeycomb sandwich panels were constructed using Hexcel 6367 A250-5H carbon fiber face sheets and Hexcel Nomex HRH-10-1/8-5 honeycomb cores. The mechanical properties of the constituent materials were discovered experimentally using ASTM standards and theoretical models using honeycomb mechanics and classical beam and plate theory are described. A failure mode map for loading under three point bending is developed from previous works by Triantafillou and Gibson26, showing the dependence of failure mode on face sheet to core thickness and honeycomb core ribbon orientation. Beam specimens are tested with the effects of Honeycomb core ribbon orientation and unequal face sheet thickness’s examined. Experimental data sufficiently agrees with theoretical predictions. A finite element model was developed in ABAQUS/CAE to validate experimental and analytical analysis and produced agreeable results. Optimal bending stiffness and strength with respect to minimum weight was analyzed. The results reveal an important role core ribbon orientation has in a sandwich beam’s bending behavior, and design of unequal ply count face sheets can produce higher stiffness to weight ratios than conventional symmetric sandwich structures of similar weight when subjected to a single static load.

Although fiberglass reinforced polyester manholes and wetwalls have been proven by the American Society for Testing Materials (ASTM) and are currently being used in some parts of the world, there still exists a lack of investigation for testing manhole covers made with different inorganic fillers under static and dynamic behavior. The filler would not only improve the mechanical properties of fiber-reinforced polymer matrix composite not otherwise achieved by the resin ingredients alone but also lower the overall manufacturing costs by decreasing the amount of fiber content without adversely affecting the composite’s mechanical properties. The main objective involved the development of fiberglass laminated manhole covers with different inorganic fillers and to study the static and dynamic behavior of the material by performing experimental and numerical analysis. The materials used for the composite laminated test specimens consisted of E-glass woven roving fabric, epoxy, and filler. Two types of inorganic fillers were used for this study, calcium carbonate and high-density adhesive fillers. The static/dynamic test results showed that the laminates made with fiberglass and filler experienced lower performance in tensile strength but higher improvement in flexural strength. The modal analysis results showed that laminates with less filler experienced higher modes within the specified frequency range. This was expected since the material property of filler increased the stiffness and damping behavior in the composite material.

The structure and payload of a CubeSat flight experiment that investigates the performance of particle dampers in a micro-gravity environment was designed, built, and tested, and will provide on orbit data for model validation and improved performance predictions for space applications of particle damping. A 3-D solid model of the integrated CubeSat structure and payload was created satisfying all constraints from CubeSat and the System Dynamics Department at Northrop Grumman Aerospace Systems. The model was verified using commercially available Finite Element Analysis software (FEA), and a prototype structure part was fabricated. The prototype was tested and verified the FEA. A complete subassembly ready for flight was manufactured as an engineering unit and tested to space qualification loads of both launch vibration and thermal vacuum. Two additional units were contracted out for manufactured to serve as the flight unit and backup, and are currently ready for launch.

This paper focused on two significant space forces that can affect the success of a spacecraft: the radiation and micrometeoroid environments. Both are looked at in the context of the region of space between Earth and Mars. The goal was create reference environments, to provide context to results of environmental modeling, and to provide recommendations to assist in early design decisions of interplanetary spacecraft. The radiation section of this report used NASA's OLTARIS program to generate data for analysis. The area of focus was on the radiation effects for crewed missions, therefore effective dose equivalent was the metric used to compare different models of radiation and shielding. Test spheres with one, two, or three different materials layers were compared, along with modifiers such as alloys or weight vs. thickness emphasis. Results were compared to limits set by the European and Russian Space Agencies to provide context. The results hinged heavily on the intensity of the Solar Particle Events (SPEs), with testing using additional temporary radiation shielding proving to be a requirement for feasible shielding masses. Differences in shield material effectiveness were found to be negligible for thin Galactic Cosmic Rays (GCRs) and thick SPEs. Thick shields were found to perform better when the more efficient shield was on the outside of the test sphere. The micrometeoroid section used equations and programs from multiple sources to generate state vectors, flux, and finally impact models for four different case studies. Impacts v were generated with mass, velocity, and impact angle/location statistics. The mass and velocity results were run through statistical software to generate information such as mean and standard deviation with confidence intervals. Also looked at were higher mass impacts, limited to above 10-3 grams as opposed to above 10-6 for the regular case. The results of this show that very thin monolithic shields (0.1 cm-0.25 cm) could protect against the average 10-6 impact. The Ram, Nadir, and Anti-sun faces received the highest quantity of impacts and Wake received the least. When looking at the worst cases average mass and velocity for the high mass impacts significantly higher shielding was required to prevent penetration (up to 5 cm for some cases). However, the test cases had probabilities of no high mass impacts greater than 46% of the time, with shorter mission having greater chances of no high mass impacts.

Recent advancements in corrosion-resistance coating technology has reduce the use of environmentally harmful compounds such as Hexavalent Chromium by replacing Hexavalent Chromium in primers and topcoat. However, marking inks were neglected in the process. Products such as Enthone 50 series are still widely used, which contain compounds such as lead, hexavalent chromium, bisphenol A (BPA), Cadmium Sulfide, and more. Excluding catalyst compositions in Enthone, the chemicals in the ink alone contained three reproductive toxicant and numerous carcinogens. Therefore, it was essential to search and validate the performance of potential marking ink that would meet the standards in military applications. Eleven products were tested, and two products were recommended for use: Sherwin Williams MIL-PRF-22750 Type I and Union Ink Uniglaze. Both products contain at most one carcinogen ingredient and no reproductive toxicant. Both products passed MIL-STD 202G Method 215K solvent test, MIL-STD 202G Method 107G thermal shock test, MIL-STD-810G, Method 507.5 humidity test, cleaning system test, ASTM D3359, measure adhesion by tape test.

An important consideration for spacecraft material selection is the space environment that the spacecraft will be operating in. Two features of the space environment that drive material selection are material outgassing and the presence of atomic oxygen in low Earth orbit (LEO). Materials that are considered for use in space are tested to be able to understand how they’ll outgas on orbit and how they’ll respond to interactions with atomic oxygen. However, testing to understand how atomic oxygen interaction with a material will affect how the material will outgas is rare and not standardized. This thesis used a vacuum chamber intended to determine the outgassing properties of materials using ASTM E595 and another vacuum chamber intended to determine how materials are affected by atomic oxygen using ASTM E2089 to determine how atomic oxygen affects outgassing of silicones, which are of interest as atomic oxygen can alter the chemical composition of the surface of silicones. CV-2500, CV2-2289- 1, and SCV2-2590, three silicone elastomers that are products of NuSil Technology LLC, were tested. Significant trends in atomic oxygen reducing the amount of matter outgassed from these three materials were observed. This can be explained by the conversion of the surface of silicone to silica, which was confirmed using Fourier Transform Infrared (FTIR) spectroscopy. Retesting of these three materials in a chamber designed for ASTM E595 with a temperature measurement system capable of adhering to ASTM E595 to confirm the results of this thesis with more confidence in uniform temperature exposure is recommended.

Al 7050-T7451 alloy with good combinations of strength, stress corrosion cracking resistance and toughness, is used broadly in the aerospace/aviation industry for fatigue-critical airframe structural components. However, it is also considered as a highly anisotropic alloy as the crack growth behavior along the short transverse direction is very different from the one in the long transverse direction, due to the inhomogeneous microstructure with the elongated grains distributed in the work material used in the sheet/plate applications. Further processes on these materials are needed to improve its mechanical and material properties and broaden its applications. The material with ultra-fine or nano grains exhibits improved wear and corrosion resistance, higher hardness and better fatigue life, compared to the one with coarse grains. In recent times, the development of novel processing technologies has gained great attention in the research community to enhance the properties of the materials employed in the aerospace, biomedical, precision instrument, automotive, nuclear/power industries. These novel processing technologies modify the microstructure of this alloy and improve the properties. The aim of this dissertation is to investigate the effects of cryogenic processes, including friction stir processing (FSP), machining and burnishing, on Al 7050-T7451 alloy to solve the inhomogeneity issue and improve its surface integrity. FSP is applied to modify the microstructure of Al 7050-T7451 alloy for achieving more homogeneous structure with near ultra-fine grains (UFG) which were less than 2 µm, particularly in cryogenic FSP with liquid nitrogen as the coolant. Approximately 10% increase could be observed from the hardness measurement from the samples processed by cryogenic FSP, in contrast to dry FSP. Also, the texture change from Al (200) to Al (111) could be achieved in all the samples processed by dry and cryogenic FSP. Cryogenic machining and burnishing processes were also applied to enhance the surface integrity of the manufactured components with near-UFG structure. The highest cutting temperature was reduced by up to 44.7% due to the rapid cooling effect of liquid nitrogen in cryogenic machining, compared with dry machining. Nano grains were produced in the refined layers induced by cryogenic burnishing. And, up to 35.4% hardness increase was obtained within the layer depth of 200 µm in the cryogenically-burnished surface. A numerical finite element method (FEM) model was developed for predicting the process performance in burnishing. Less than 10% difference between the experimental and predicted burnishing forces was achieved in the simulation of cryogenic burnishing, and reasonable predictions were also achieved for temperatures, severe plastic deformation (SPD) layers.

Hui and Chen (1986) were the first to show that the well-known Koiter’s General Theory of Elastic Stability of 1945 can be significantly improved by evaluating the postbuckling b coefficient at the actual applied load, rather than at the classical buckling load. Such improvement method was demonstrated to be (1) very simple to apply with no tedious algebra, (2) significant reduction in imperfection sensitivity and (3) although it is still asymptotically valid, there exists a significant extension of the range of validity involving larger imperfection amplitudes. Strictly speaking, Koiter’s theory of 1945 is valid only for vanishingly small imperfection amplitudes. Hence such improved method is termed Hui’s Postbuckling method. This study deals with the postbuckling and imperfection sensitivity of different kinds of cylinders, using the Hui’s postbuckling method. For unstiffened cylinder and laminate cylinder the results are compared with ABAQUS simulation results, and a parameter variation of stringer/ring stiffened cylinder is also evaluated. A significant positive shift of the postbuckling b coefficient is found which indicates that Koiter's general stability theory of 1945 has significantly overestimated the imperfection sensitivity of the structure. Also, compared with the Koiter's general stability theory, the valid region is significantly increased by using Hui's postbuckling method.

This study describes a method for conducting the structural dynamic analysis of a crane fly (family Tipulidae) forewing under different airflow conditions. Wing geometry is captured via micro-computed tomography scanning. A finite element model of the forewing is developed from the reconstructed model of the scan. The finite element model is validated by comparing the natural frequencies of an elliptical membrane with similar dimensions of the crane fly forewing to its analytical solution. Furthermore, a simulation of the fluid-structure interaction of the forewing under different airflows is performed by coupling the finite element model of the wing with a computation fluid dynamics model. From the finite element model, the mode shapes and natural frequencies are investigated; similarly, from the fluid-structure interaction, the time-varying out-of-plane deformation, and the coefficients of drag and lift are determined.

In order to investigate the thermal stress and expansion as well as the associated strain effect on material properties caused by high temperature and large temperature gradient, a two-way thermo-mechanical coupling solver is developed. This solver integrates a new structural response module to the Kentucky Aerothermodynamics and Thermal response System (KATS) framework. The structural solver uses a finite volume approach to solve either hyperbolic equations for transient solid mechanics, or elliptic equations for static solid mechanics. Then, based on the same framework, a quasi-static approach is used to couple the structural response and thermal response to estimate the thermal expansion and stress within Thermal Protection System (TPS) materials. To better capture the thermal expansion and study its impacts on material properties such as conductivity and porosity, a moving mesh scheme is also developed and incorporated into the solver. Grid deformation is transferred among different modules in the form of variations of geometric parameters and strain effects. By doing so, a bi-direction information loop is formed to accomplish the two-way strong thermo-mechanical coupling. Results revealed that the thermal stress experienced during atmospheric re-entry concentrates in a banded area at the edge of the pyrolysis zone and its magnitude can be large enough to cause the failure of the TPS. In addition, thermal expansion causes the whole structure to deform and the changes in material properties. Results also indicated that the impacts coming from structural response should not be ignored in thermal response.