Development of Rene' 41 honeycomb structure as an integral cryogenic tankage/fuselage concept for future space transportation systems

The status of the structural development of an integral cryogenic-tankage/hot-fuselage concept for future space transportation systems (STS) is discussed. The concept consists of a honeycomb sandwich structure which serves the combined functions of containment of cryogenic fuel, support of vehicle loads, and thermal protection from an entry heating environment. The inner face sheet is exposed to a cryogenic (LH2) temperature of -423 F during boost; and the outer face sheet, which is slotted to reduce thermal stress, is exposed to a maximum temperature of 1400 F during a high altitude, gliding entry. A fabrication process for a Rene' 41 honeycomb sandwich panel with a core density less than 1 percent was developed which is consistent with desirable heat treatment processes for high strength

Design data for brazed Rene 41 honeycomb sandwich

Strength data, creep data and residual strength data after cyclic thermal exposure were obtained at temperatures from 78 K to 1144 K (-320 F to 1600 F). The influences of face thickness, core depth, core gage, cell size and thermal/stress exposure conditions on the mechanical design properties were investigated. A braze alloy and process was developed that is adequate to fully develop the strength of the honeycomb core while simultaneously solution treating and aging the Rene 41 fact sheets. New test procedures and test specimen configurations were developed to avoid excessive thermal stresses during cyclic thermal exposure

A numerical and analytical investigation of Rayleigh-Taylor instability in a solid tungsten plate

The Rayleigh-Taylor instability response of an elastic-plastic tungsten plate is investigated by numerical experiments and an approximate modal analysis. The so-called ''minimum amplitude'' instability criteria derived from plasticity analyses is shown to be incomplete as a general indicator of instability or stability at very large driving pressures. Model equations are derived which are able to reproduce the basic qualitative features of the observed instability response given by the numerical calculations. 11 refs., 29 figs

REDUCTIONS WITHOUT REGRET: DETAILS - AVOIDING BOX CANYONS, ROACH MOTELS, AND WRONG TURNS

The United States is concurrently pursuing the goals of reducing the size of its nuclear weapons force – strategic and non-strategic, deployed and non-deployed – and of modernizing the weapons it continues to possess. Many of the existing systems were deployed 30 to 50 years ago, and the modernization process can be expected to extend over the next decade or more. Given the impossibility of predicting the future over the lifetime of systems that could extend to the end of this century, it is essential that dead ends in force development be avoided, and the flexibility and availability of options be retained that allow for • Scalability downward in the event that further reductions are agreed upon; • Reposturing to respond to changes in threat levels and to new nuclear actors; and • Breakout response in the event that a competitor significantly increases its force size or force capability, In this paper, we examine the current motivations for reductions and modernization; review a number of historical systems and the attendant capabilities that have been eliminated in recent decades; discuss the current path forward for the U.S. nuclear force; provide a view of the evolving deterrence situation and our assessment of the uncertainties involved; and present examples of possibly problematic directions in force development. We close with our thoughts on how to maintain flexibility and the availability of options for which a need might recur in the future

Parallel algorithm for transient solid dynamics simulations using finite elements and smoothed particle hydrodynamics

An efficient, scalable, parallel algorithm for treating contacts in solid mechanics has been applied to interactions between particles in smooth particle hydrodynamics (SPH). The algorithm uses three different decompositions within a single timestep: (1) a static FE-decomposition of mesh elements; (2) a dynamic SPH-decomposition of SPH particles; (3) and a dynamic contact-decomposition of contact nodes and SPH particles. The overhead cost of such a scheme is the cost of moving mesh and particle data between the decompositions. This cost turns out to be small in practice, leading to a highly load-balanced decomposition in which to perform each of the three major computational states within a timestep

A parameter-free total Lagrangian smooth particle hydrodynamics algorithm applied to problems with free surfaces

This paper presents a new Smooth Particle Hydrodynamics computational framework for the solution of inviscid free surface flow problems. The formulation is based on the Total Lagrangian description of a system of first-order conservation laws written in terms of the linear momentum and the Jacobian of the deformation. One of the aims of this paper is to explore the use of Total Lagrangian description in the case of large deformations but without topological changes. In this case, the evaluation of spatial integrals is carried out with respect to the initial undeformed configuration, yielding an extremely efficient formulation where the need for continuous particle neighbouring search is completely circumvented. To guarantee stability from the SPH discretisation point of view, consistently derived Riemann-based numerical dissipation is suitably introduced where global numerical entropy production is demonstrated via a novel technique in terms of the time rate of the Hamiltonian of the system. Since the kernel derivatives presented in this work are fixed in the reference configuration, the non-physical clumping mechanism is completely removed. To fulfil conservation of the global angular momentum, a posteriori (least-squares) projection procedure is introduced. Finally, a wide spectrum of dedicated prototype problems is thoroughly examined. Through these tests, the SPH methodology overcomes by construction a number of persistent numerical drawbacks (e.g. hour-glassing, pressure instability, global conservation and/or completeness issues) commonly found in SPH literature, without resorting to the use of any ad-hoc user-defined artificial stabilisation parameters. Crucially, the overall SPH algorithm yields equal second order of convergence for both velocities and pressure

Electromagnetic simulation of electronic packaging designs (95-ERP-003). 1995 LDRD final report

The primary focus of the project summarized in this report has been to evaluate the performance of the 3D, time-domain electromagnetic code DS13D in the simulation of structures used in microwave microelectronics circuits. We`ve adopted two test cases, coaxial and stripline transmission lines, for which well-known results are available so that results obtained with DS13D could be easily and accurately checked. Our goals have been three-fold: (1) To develop specialized mode-launching capabilities for single-mode signals typically found in test geometries and the diagnostics necessary to evaluate the performance of the code in modeling the propagation of those signals. (2) To analyze the effect of different zoning schemes on the accuracy with which the code models the propagation of signals through the geometries by checking against known analytic results and calculations performed with other codes. (3) To examine the effect of code modifications aimed at enhancing the accuracy of the simulations. The calculated transmission line impedance was chosen as the primary means of evaluating code performance. Since the lowest-order propagating modes for the test cases were transverse electromagnetic (TEM) modes, the computation of impedance was reasonably straightforward. Both time- and frequency-domain values (the latter obtained from the code output by post-processing with a discrete Fourier transform) were obtained and compared