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An investigation of heuristic failure theories based on the Shanley-Ryder (S-R) stress ratio formulations and their extensions to ratios of stress invariants is undertaken. The deterministic structural margin (MS) and factor of safety (FoS) are re-examined and their multiple valued relevances to probabilistic analyses based on statistical loads as well as statistical material failure properties are discussed. MS's have no unique meaning in stochastic analyses while factors of safety effectively increase allowable loads thereby decreasing failure probabilities. [ABSTRACT FROM AUTHOR]

The application of chaos theory to forces inducing rolling maneuvers by acting on linear or nonlinear temperature dependent viscoelastic wings with actual widely scattered random material properties is investigated in detail. Published experimental data shows widely scattered 1-D viscoelastic moduli and small excursions from average or beginning values - the basis for chaos theory - is realistically inapplicable and would simply constitute a purely academic exercise excursion. While conventional approaches have been associated with applied forces, such as probability theory, to characterize these deterministic and stochastic properties, chaos theory is offered as an additional alternate generalized protocol to characterize viscoelastic responses to chaotic flight loads. At this time unfortunately no deterministic, stochastic or chaotic experimental data seems to be available, nor experimental data on aero-viscoelastic structural responses to flight vehicle maneuvers at any temperature. [ABSTRACT FROM AUTHOR]

The present paper is a continuation and expansion of a previous Part I [1] emphasizing material failure modeling and visualization protocols in conjunction with aero - elastic/viscoelastic phenomena. Failure is defined in terms of the Shanley-Ryder stress ratio relations and through the generalization based on the first three stress invariant ratios. Both deterministic and stochastic stress and strain as well as failure analyses are carried out. Visualization examples of multi-dimensional failure surfaces depending on possibly more than 35 elastic and 47 viscoelastic parallel coordinates is formulated, presented and discussed. Separate analyses are formulated for elastic and viscoelastic combined unsymmetrical bendingtorsion during level flight and for vehicle rolling motion. The overall bending degrees of freedom considered are plunging, in plane and chord-wise motions. Bending-torsion effects on and changes in angles of attack due the rolling velocity as well as the infiuence of moving shear centers and neutral axes and of material failures are considered during simultaneous occurrences. The final goal is to establish conditions for bending and torsional flutter, torsional divergence, control effectiveness and ultimate survival time of the wing due to material failures and structural instabilities (buckling) with future extensions to the entire vehicle under the rubric of system of systems approach, leading to a single pair of critical velocities and frequencies including material failure effects. The original Shanley-Ryder stress ratio failure criterion as well as its successor three stress invariant formulations are utilized. The latter has the advantage of having an unlimited number of arbitrary coefficients to be used to in fitting analytical expressions to stochastic experimental data. The multi-D numerical example results are displayed as a single figure of multiple 2-D parallel coordinates (1 1-cor(is) as opposed to numerous simultaneous, but separate, 2-D trace plots of a multi-D aeroelastic/aero-viscoelastic combined stability, buckling and material failure surface. In the present analyses, the use of Inselberg's parallel coordinates protocols clearly demonstrates in a single graph the individual and collective influences of many parameters on critical velocities without recourse to multiple 3-D critical surface representations. The critical velocities are also displayed as separate 2-D traces for each of the divers parameters, as well as in H-coords renderings. A small sample of randomly chosen subsonic wing parametric variation calculations show that compared to the free standing bending-torsion configuration, combinations involving plunging and in-plane bending, control effectiveness and reversal, with or without positive or negative roll velocities, and absent or present Timoshenko effects, produce substantially altered fiutter velocities and their paired frequencies. Finally, it noteworthy to mention that failure conditions can be improved by introducing morphing to the structure. Morphing [2], 13] airfoil shapes, although not treated here in detail, can produces significant improvements in aerodynamic, aeroelastic, aero-viscoelastic and structural performances, and delay as well as reduce their failure probabilities - all with relatively little energy expenditures. Additionally, the optimizing process that leads to the design of high performance Liebeck airfoils [4] contributes in equal measures. [ABSTRACT FROM AUTHOR]

The hereditary and/or convolution integrals associated with linear viscoelastic material constitutive relations based on Prony series [1] characterization are recast into ordinary nonconvolution time integrals, which can be more efficiently evaluated analytically and numerically. Application of this protocol greatly reduces computational time, CPU usage and memory requirements used to solve linear temperature dependent and/or independent viscoelastic problems involving integral-differential equations with variable coefficients. The formulation includes temperature dependent materials with time and space dependent temperatures as well as stresses due to thermal expansions. Approximate approaches for dealing with time dependent temperatures are derived and solutions to non-convolution integral equations as well as to differential equations with variable coefficients are formulated. Relaxation time consistent relations are derived for isotropic viscoelastic materials. Applications of Galerkin and Runge-Kutta methods to viscoelastic solutions are discussed and evaluated. These protocols include solutions to IODEs and IPDEs with variable coefficients. An illustrative algorithm to be used in conjunction with differential equation solvers such as MATLAB's™ ODE45 has been developed which allows for numerical solutions simultaneously in both real and reduced time spaces without approximations of linear and nonlinear integral differential equations with variable or without coefficients. Similar protocols could be readily extended to other software such as MATHEMATICA™, MAPLE™, etc. [ABSTRACT FROM AUTHOR]

Large deflection analyses of nonhomogeneous nonlinear elastic or viscoelastic columns (elastica and viscoelastica) with initial curvature and with deflection dependent cross sectional areas subjected to follower loads are formulated. Column end shortening due to both curvature and compressive loads is taken into account and the governing coupled nonlinear differential equations are solved by successive approximation methods (SAM) and numerically by a double Runge-Kutta iterative shooting approach. Various solution protocols are analyzed and evaluated. The effects of end shortening and follower load angle on elastic and viscoelastic columns are discussed. The hierarchal setting between column instability and material failures is examined. [ABSTRACT FROM AUTHOR]

The permissible forms and nature of linear viscoelastic functionally graded inhomogeneous material (VFGM) functions are formulated and examined in terms of consistency principles. It is shown that no separable temporal and spatial VFGM isotropic or anisotropic inhomogeneous modulus or compliance function is admissible nor can the VFGM solutions be cast into similarly separable constructions. However, finite or infinite sums of individual separable functions are admissible combinations provided each series term in its own form satisfies boundary and initial conditions, and provided one considers such an expressions as a mathematical model without necessarily any affinity to generalized Kelvin or Maxwell models. [ABSTRACT FROM AUTHOR]

The details on technological developments in aircraft design structures, which are developed by companies such as Boeing Co., are presented.

NASA Langley and Northrop Grumman conducted the first successful combined-loads structural tests. It was conducted on a 5-ft x 6ft integrated, toughened graphite-epoxy composite cryotank shell segment section at the NASA Langley Cryo-Pressure Box Facility under the Next Generation Launch Technology Program.

Various structure projects investigated and developed during 2003 at Universities and Institutes in the United States are focused. NASA is working on hot structures technology to reduce maintenance of reusable launch vehicle (RLV) structures and to improve performance.

Comparison analyses are conducted for straight and curved viscoelastic beams based on da Vinci-Euler-Bernoulli-Winkler strength of materials prescriptions and on rigorous formulations in terms of 3-D field equations. The concepts of elastic straight and curved beam analyses are well established. In the present paper, these geometric principles are extended to linear viscoelastic materials. The beams are considered subjected to un-symmetric bending as well as to thermal expansions. The distinct conditions leading to shear center and neutral axis motions in time, previously observed in straight beams are investigated. The applicability of the elastic-viscoelastic correspondence principle (analogy) in terms of integral transforms is demonstrated by application to several simulations. Comparison studies are based on pure bending loading configurations as these offer the least distinct geometric deformation patterns and focus primarily on the influence of constitutive relations. [ABSTRACT FROM AUTHOR]

Following the unified approach to viscoelastic Timoshenko beams (spars) formulated in [1], similar inclusive analyses are formulated for elastic and viscoelastic combined unsymmetrical bending-torsion during level flight and for vehicle rolling motion. The overall bending degrees of freedom considered are plunging, in plane and chord-wise motions. Bending-torsion effects on and changes in angles of attack due the rolling velocity as well as the influence of moving shear centers and neutral axes and of material failures are considered during simultaneous occurrences. The final goal is to establish conditions for bending and torsional flutter, torsional divergence, control effectiveness and ultimate survival time of the wing due to material failures and structural instabilities (buckling) with future extensions to the entire vehicle under the rubric of system of systems (SoS) approach, leading to a single pair of critical velocities and frequencies including material failure effects. A new stress invariant stochastic generalization to the original Shanley-Ryder stress ratio failure criterion is derived and utilized. The latter has the advantage of having an unlimited number of arbitrary coefficients to be used to in fitting analytical expressions to stochastic experimental data. The multi-D numerical example results are displayed as a single figure of multiple 2-D parallel coordinates (ǁ-coords), as opposed to numerous simultaneous, but separate, 2-D traces of a multi-D aeroelastic/aero-viscoelastic combined stability, buckling and material failure surface. In the present analyses, the use of ǁ-coords clearly graphically demonstrates the individual and collective influences of many parameters on critical velocities without recourse to a multidimensional critical surface representation. The critical velocities are also displayed as separate 2-D traces for each of the divers parameters, as well as in ǁ-coords renderings. A small sample of randomly chosen subsonic wing parametric variation calculations show that compared to the free standing bending-torsion configuration, combinations involving plunging and inplane bending, control effectiveness and reversal, with or without positive or negative roll velocities, and absent or present Timoshenko effects, produce substantially altered flutter velocities and their paired frequencies. [ABSTRACT FROM AUTHOR]