Journal of Aerospace Engineering

The mechanical response of E-862 and PR-520 resins is investigated in tensile and shear loadings. At both types of loading the resins are tested at strain rates of about $5\times {10}^{-5}$ , 2, and $450–700{\mathrm{s}}^{-1}$ . In addition, dynamic shear modulus tests are carried out at various frequencies and temperatures, and tensile stress relaxation tests are conducted at room temperature. The results show that the toughened PR-520 resin can carry higher stresses than the untoughened E-862 resin. Strain rate has a significant effect on the response of both resins. In shear, both resins show a ductile response with maximum stress that is increasing with strain rate. In tension, a ductile response is observed at low strain rate $(\sim 5\times {10}^{-5}{\mathrm{s}}^{-1})$ , and brittle response is observed at the medium and high strain rates (2 and $700{\mathrm{s}}^{-1}$ ). The hydrostatic component of the stress in the tensile tests causes premature failure in the E-862 resin. Localized deformation develops in the PR-520 resin when loaded in shear. An internal state variable constitutive model is proposed for modeling the response of the resins. The model includes a state variable that accounts for the effect of the hydrostatic component of the stress on the deformation.

The need for aircraft, both military and civilian, to serve longer and cost less to operate is ever present. The ability to potentially extend service life and reduce operating and maintenance costs are key factors in the many choices with aircraft programs. The field of structural health monitoring 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 tile using representative 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 whereas the sensors remain on the substructure of the airframe. Jointly, the development of a means to model the system using finite-element techniques is explored. It is found that the finite-element modeling technique produces correlating modal frequencies within a 7.19% worst case average when compared to the physical tests. This leads to the ability to compare mode shapes and frequencies to detect damage in such a system.

In this paper a modification of the classical Weibull statistics is applied to nanostructures. A comparison is presented of “nanoscale” versus classical Weibull statistics in treating recent experimental results on the fracture strength of C nanofibers and nanotubes, and ${\mathrm{WS}}_2$ nanotubes. “Nanoscale” Weibull moduli of 3.8 for electrospun and then heat-treated carbon nanofibers, 2.7 for arc-discharge synthesized multiwalled carbon nanotubes, 1.8 for chemical vapor deposited multiwalled carbon nanotubes, and 3.0 for multiwalled ${\mathrm{WS}}_2$ nanotubes, are deduced.

Tape springs, defined as thin metallic strips with an initially curved cross section, are an attractive structural solution and hinge mechanism for small satellite deployable structures due to their low mass, low cost, and general simplicity. When mounted at skewed angles to the hinge line, the tapes can be subjected to complex folds involving both bending and twisting of the tape. These folds have been experimentally investigated and theories have been developed to model the resulting opening moment. However, the opening moments of these theories are not equivalent to the opening moment about the hinge line, which is the parameter required in satellite deployment applications. This paper derives a method to determine the hinge moment from the previous theories and compares the theoretical predictions with experimental and finite element results. It uses this model to investigate the predicted hinge moment trends for full deployments of 180°. The model is then applied to a practical spacecraft hinge application.

Velocities of primary $\left(P\right)$ and shear $\left(S\right)$ waves in granular materials are highly dependent on confining stress. These wave velocities are related to mechanical properties of the materials such as stiffness, density, and stress history. Measurements of the wave velocities using piezoelectric sensors provide scientists and engineers a technique for nonintrusive characterization of those mechanical properties. For aerospace engineering, measuring the wave velocities under microgravity, which simulates low loading and stress conditions, has a number of potential applications. It can help the understanding of the soil mechanics and the development of appropriate materials handling technologies in extraterrestrial environments, which will be crucial to meeting NASA’s future space exploration goals. This paper presents the technique and results of experiments conducted at NASA Glenn Research Center using the $2.2\mathrm{s}$ drop tower. Velocities of $P$ and $S$ waves in three sizes of glass beads and one size of alumina beads were measured under initially dense or loose compaction states. It was found that under microgravity, the wave signals were significantly weaker and the velocities were much slower. The material that makes up the beads has a strong influence on the wave velocities as well. The initial compaction state also has some influence on the wave velocities.

Results investigating the processes—of generation and collection of monodisperse droplets flowing in microgravity and high vacuum—are presented. We applied these results to droplet radiators for systems of thermal stabilization and low-potential heat rejection from spacecraft power systems. The experiments were conducted on the “Mir” orbital station. Main constituents of the working process were reproduced: Generation of the droplets and collection of droplets flow on the moving fluid film at the collector surface. The developed model—with systems of measurement, thermal stabilization, and control—allowed us to obtain and record information about the process in the model in real time and (by telemetry, video recording, etc.). As a result of this space experiment, and for the first time in microgravitation and high vacuum, we demonstrated the feasibility to realize forced capillary breakdown of jets into monodisperse droplets, under the action of acoustic oscillations. A stable ancillary film of working fluid, moving over the collector inner surface and providing collection of the droplet flow, was produced.

Among the time-integration methods used in solid mechanics, Newmark family of algorithms (along with Galerkin finite element) has been most popular and has gathered much attention over the years. Recently, the time discontinuous Galerkin method (TDG) and discontinuous Galerkin method (DGM) are being investigated by the researchers due to their advantages in wave propagation problems. In this study, TDG and DGM are combined to have space-time discontinuous Galerkin formulation for the first time for solid mechanics problems. The basic formulations are presented and some examples are studied.