Journal of Aerospace Engineering

The paper deals with the effect of moisture and temperature on the postbuckling response of a laminated composite plate subjected to hygrothermomechanical loadings. Mechanical loading consists of uniaxial, biaxial, shear, and their combinations. The distribution of temperature and moisture on the surface is considered to be uniform. The degradation in material properties due to moisture and temperature is taken into account using a micromechanical model. The mathematical formulation is based on higher order shear deformation theory and von Karman’s nonlinear kinematics. The quadratic extrapolation technique and fast converging finite double Chebyshev series are used for linearization and spatial discretization of the governing nonlinear equations of equilibrium, respectively. The effects of temperature rise, moisture concentration, fiber-volume fraction, and plate parameters on buckling and postbuckling response of the plate are presented.

In this paper, an improved higher-order zigzag theory for vibration of soft core sandwich plates with random material properties is proposed. The theory satisfies the condition of continuity in transverse shear stresses at all the layer interfaces and transverse shear stress free condition at the top and bottom of the plate, including the transverse flexibility effect of the core. The variation of in-plane displacements through thickness is assumed to be cubic while transverse displacement varies quadratically within the core and constant throughout the faces. The core is modeled as a 3D elastic continuum. An efficient $C^0$ finite element in conjunction with a first-order perturbation approach is developed for the implementation of the proposed plate theory in a random environment and is employed to evaluate the second-order statistics of the eigensolutions by modeling lamina material properties as basic random variables. The mean and standard deviations of natural frequencies and their mode shapes are computed and validated with Monte Carlo simulation.

Scale model approach in thermal testing of aircraft components has been proposed in this study. The idea of thermal scaling has been validated experimentally. Quite often, it may not be possible to carry out experimental validation of design analysis at high temperatures on prototype structures at the design stage since exact simulation of thermal environments may not be possible. Under such conditions, the designer may resort to study the structural behavior using scale model testing at a different temperature where the material does not change phase at the scaled temperature.

Numerical studies of the free vibration analysis of open skewed circular cylindrical shells supported only on selected segments of the straight edges are presented in this paper. The uniform thickness shell geometry is defined by the radius, subtended angle and the length, all with reference to the middle surface. The open skewed circular cylindrical shell is modeled by dividing the reference surface into few patches and introducing upon them displacement nodal points and also five degrees of freedom in accordance with the first order shear deformable shell theory are assigned to each of these nodal points. The free vibration analysis of the shell structure is performed using two types of interpolating polynomials, viz. simple high order algebraic and Bezier, respectively. The number of nodal points per patch determines the order of the displacement polynomials. As a consequence considerably high-order polynomials are used in computations for the accurately converged results. Convergence studies are carried out to validate the method for cases in which the skewed cylindrical shell is supported only on the third of each of the two straight edges. Additionally, the performance of the present method is assessed and discussed by comparing frequency results with those from standard finite element methods using linear and parabolic quadrilateral elements.

The proper orthogonal decomposition (POD) method is used and assessed as a fast technique for estimation of aerodynamics data with variation of some aerodynamics parameters. In this way, four extensions to the POD method are considered for steady viscous/inviscid compressible aerodynamic applications. The first extension is a coupling between the POD method with a cubic spline interpolation, as introduced for inviscid flows. The second and the third ones are essentially new techniques which are introduced here for the first time. In these methods, some additional calibrations (including a kind of filtering and reprojection) are needed to achieving more accurate estimations. The so-called gappy POD, is considered as the fourth extension, which is a known method in reconstruction and repairing the missed aerodynamics data. The methods are applied on the steady viscous and inviscid flows and for subsonic, transonic, and supersonic flow regimes. The results show good agreements between the new proposed methods and the other methods.

Force measurement and surface oil flow visualization were carried out in wind tunnel to investigate the effects of wing’s planform and flexibility on aerodynamics for flow over low-aspect ratio wings. It is found that the empirical formulas proposed by Polhamus can present remarkably accurate predictions before stall for both rigid and flexible wings. The spiral vortex is responsible for rigid and flexible wing abrupt drop of lift coefficient after stall when the sweep angle is below 35°. The maximum lift coefficient and the stall angle for flexible wings are smaller than those for rigid ones when the sweep angle is below 40°, and the wing flexibility nearly does not influence the aerodynamics as the sweep angle is beyond 40°. Moreover, lift coefficient curves exist hysteresis loop in the following range of sweep angle: 10°–35° for the flexible wings and 5°–50° for the rigid wings. It can be deduced from oil visualization experiment that the sudden disappearance of spiral vortex flow structure may be responsible for the hysteresis.

Glass fiber-reinforced polymer (GFRP) materials possess inherently high strength-to-weight ratios, but their effective elastic moduli are low relative to civil engineering (CE) construction materials. While elastic modulus may be comparable to that of some CE materials, the lower shear modulus adversely affects stiffness. As a result, serviceability issues are what govern GFRP deck design in the CE bridge industry. An innovative solution to increase the stiffness of a commercial GFRP reinforced-sinusoidal honeycomb sandwich panel was proposed; this solution would completely replace the GFRP honeycomb core with a hexagonal honeycomb core constructed from commercial steel roof decking. The purpose of this study was to perform small-scale tests to characterize the steel hexagonal honeycomb core equivalent elastic moduli in an effort to simplify the modeling of the core. The steel core equivalent moduli experimental results were compared with theoretical hexagonal honeycomb elastic modulus equations from the literature, demonstrating the applicability of the theoretical equations to the steel honeycomb core. Core equivalent elastic modulus equations were then proposed to model and characterize the steel hexagonal honeycomb as applicable to sandwich panel design. The equivalent honeycomb core will enable an efficient sandwich panel stiffness design technique, both for structural analysis methods (i.e., hand calculations) and finite-element analysis procedures.

This study was carried out to assess the tensile and shear strength in lunar soil, and to examine the variation as a function of density and confinement. Geotechnical engineering properties of the lunar soil simulant designated Johnson Space Center Number One-A lunar soil simulant (JSC-1A) have been investigated experimentally. To better understand these soil properties, a variety of conventional and unconventional experiments were conducted on JSC-1A to determine its grain-size distribution, cohesion, friction angle, dilatancy angle, tensile strength, and appropriate low strain elastic constants. These experiments were conducted on JSC-1A at a variety of densities prepared through tamping densification to quantify the response of the soil over a range of conditions. To simulate lunar conditions, the samples were prepared at medium to very high relative densities. Grain-size distribution, shear strength, tensile strength, dilatancy angles, and elasticity modulus of the JSC-1A were compared with lunar soil and other simulants.

This article looks at the wire coating analysis by withdrawal from a bath of magnetohydrodynamic Johnson-Segalman fluid. An analytic technique, the homotopy analysis method, is employed to obtain the series solution of the resulting nonlinear problem. The convergence of the obtained solution is studied. The effects of various emerging parameters are graphed and discussed.

The establishment of human habitats on the Moon and on Mars will require protecting them from the hazards of near-Earth and interplanetary space. In addition to solar radiation, another hazard to be faced by these habitats is the damage that can result from the high speed impact of a meteoroid on a critical structural component. Therefore, lunar habitats and their accompanying support facilities need to be designed with adequate levels of protection that will allow them to also withstand the damage that can result from a meteoroid impact. In this paper we discuss some approaches to shielding for lunar habitats, focusing on shielding that is intended primarily to provide protection against meteoroid impacts and on shielding approaches that use resources mined or extracted from the Moon. The Moon’s mineralogy is discussed and suggestions are presented for materials and material combinations that can be used to develop shielding for lunar habitats and which are comprised primarily or entirely of lunar materials. Several shielding mechanisms are also presented that could be effective against impacts by meteoroid particles having diameters on the order of that which are likely to strike a fairly large lunar habitat at least one or two times per year. The paper concludes with recommendations for continuing work in optimizing the design of meteoroid shielding for lunar habitats.