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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 343 records · Page 19

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NASA NTRS1984

On dynamics of laminated anisotropic plates using a refined mixed plate element

An analysis of the free vibration and transient response of laminates using a mixed shear flexible element is presented. The element is based on a refined theory that accounts for a parabolic distribution of the transverse shear stresses through each lamina and requires no shear correction coefficients. The mixed formulation of the theory treats the five displacement functions and six stress resultants independently so that they are nodal degrees of freedom in the finite element model. Sample problems using the element are analyzed and the results of free vibration and transient response are presented. Compared to the existing shear deformation plate theory the present refined theory gives more accurate results for frequencies, displacements and stresses.

Putcha, N. S.↗

NASA NTRS2003

Effects Of Environmental And Operational Stresses On RF MEMS Switch Technologies For Space Applications

Micro Electro Mechanical Systems (MEMS) have been heralded for their ability to provide tremendous advantages in electronic systems through increased electrical performance, reduced power consumption, and higher levels of device integration with a reduction of board real estate. RF MEMS switch technology offers advantages such as low insertion loss (0.1- 0.5 dB), wide bandwidth (1 GHz-100 GHz), and compatibility with many different process technologies (quartz, high resistivity Si, GaAs) which can replace the use of traditional electronic switches, such as GaAs FETS and PIN Diodes, in microwave systems for low signal power (x < 500 mW) applications. Although the electrical characteristics of RF MEMS switches far surpass any existing technologies, the unknown reliability, due to the lack of information concerning failure modes and mechanisms inherent to MEMS devices, create an obstacle to insertion of MEMS technology into high reliability applications. All MEMS devices are sensitive to moisture and contaminants, issues easily resolved by hermetic or near-hermetic packaging. Two well-known failure modes of RF MEMS switches are charging in the dielectric layer of capacitive membrane switches and contact interface stiction of metal-metal switches. Determining the integrity of MEMS devices when subjected to the shock, vibration, temperature extremes, and radiation of the space environment is necessary to facilitate integration into space systems. This paper will explore the effects of different environmental stresses, operational life cycling, temperature, mechanical shock, and vibration on the first commercially available RF MEMS switches to identify relevant failure modes and mechanisms inherent to these device and packaging schemes for space applications. This paper will also describe RF MEMS Switch technology under development at NASA GSFC.

Jah, Muzar↗

NASA NTRS1988

Structural tailoring of high-speed turbine blades (SSME/STAEBL)

Space shuttle main engine (SSME) blades are subject to severe thermal, pressure, and forced vibration environments. Structural optimization provides an automated alternative to time consuming iterations. Any number of analyses, design variables, and constraints can be incorporated in a structural optimization computer code. This idea was applied to develop the code SSME/STAEBL, which is a stand alone code suitable for automated design of SSME turbopump blades. Additions and modifications of STAEBL included in SSME/STAEBL include the following: (1) thermal stress analysis, (2) gas dynamic (pressure) loads, (3) temperature-dependent material and thermal properties, (4) forced vibrations, (5) tip displacement constraints, (6) single crystal material analysis, (7) blade cross-section stacking offsets, and (8) direct time integration algorithm for transient dynamic response.

Rubinstein, Robert↗

NASA NTRS2002

Advanced Vibration Analysis Tools and New Strategies for Robust Design of Turbine Engine Rotors

The adverse effects of small, random structural irregularities among the blades, called mistuning, can result in blade forced-response amplitudes and stresses that are much larger than those predicted for a perfectly tuned rotor. Manufacturing tolerances, deviations in material properties, or nonuniform operational wear causes mistuning; therefore, mistuning is unavoidable. Furthermore, even a small mistuning can have a dramatic effect on the vibratory behavior of a rotor because it can lead to spatial localization of the vibration energy (see the following photographs). As a result, certain blades may experience forced response amplitudes and stresses that are substantially larger than those predicted by an analysis of the nominal (tuned) design. Unfortunately, these random uncertainties in blade properties, and the immense computational effort involved in obtaining statistically reliable design data, combine to make this aspect of rotor design cumbersome.

Min, James B.↗

NASA NTRS2002

Advanced Vibration Analysis Tools and New Strategies for Robust Design of Turbine Engine Rotors

Min, James B.↗

NASA NTRS1991

Computational aspects of sensitivity calculations in linear transient structural analysis

The calculation of sensitivities of displacements, velocities, accelerations, and stresses in linear, structural, and transient response problems is studied. Several existing sensitivity calculation methods and two new methods are compared for three example problems. Approximation vectors such as vibration mode shapes are used to reduce the dimensionality of the finite model. To be computationally practical in large-order problems, the overall finite difference methods must use the approximation vectors from the original design in the analyses of the perturbed models. This was found to result in poor convergence of stress sensitivities in several cases. Two semianalytical techniques are developed to overcome this poor convergence. Both new methods result in very good convergence of the stress sensitivities; the computational cost is much less than would result if the vibration modes were recalculated and then used in an overall finite difference method.

Greene, W. H.↗

NASA NTRS1989

Space Shuttle Main Engine structural analysis and data reduction/evaluation. Volume 7: High pressure fuel turbo-pump third stage impeller analysis

This volume summarizes the analysis used to assess the structural life of the Space Shuttle Main Engine (SSME) High Pressure Fuel Turbo-Pump (HPFTP) Third Stage Impeller. This analysis was performed in three phases, all using the DIAL finite element code. The first phase was a static stress analysis to determine the mean (non-varying) stress and static margin of safety for the part. The loads involved were steady state pressure and centrifugal force due to spinning. The second phase of the analysis was a modal survey to determine the vibrational modes and natural frequencies of the impeller. The third phase was a dynamic response analysis to determine the alternating component of the stress due to time varying pressure impulses at the outlet (diffuser) side of the impeller. The results of the three phases of the analysis show that the Third Stage Impeller operates very near the upper limits of its capability at full power level (FPL) loading. The static loading alone creates stresses in some areas of the shroud which exceed the yield point of the material. Additional cyclic loading due to the dynamic force could lead to a significant reduction in the life of this part. The cyclic stresses determined in the dynamic response phase of this study are based on an assumption regarding the magnitude of the forcing function.

Pool, Kirby V.↗

NASA NTRS1974

Digital vibration control techniques

Analog vibration control techniques are reviewed and are compared with digital techniques. The advantages of the digital methods over the analog methods are demonstrated. The following topics are covered: (1) methods of computer-controlled random vibration and reverberation acoustic testing; (2) methods of computer-controlled sinewave vibration testing; and (3) methods of computer-controlled shock testing. Basic concepts are stressed rather than specific techniques or equipment. General algorithms are described in the form of block diagrams and flow diagrams. Specific problems and potential problems are discussed. The material is computer sciences oriented but is kept at a level that facilitates an understanding of the basic concepts of computer-controlled induced environmental test systems.

Chapman, P.↗

NASA NTRS1976

Higher-order effects of initial deformation on the vibrations of crystal plates

A system of plate equations for the thickness-shear and flexural vibrations superposed on large initial deflection due to bending is derived; in the stress-strain relations, the terms associated with the fourth-order elastic stiffness coefficients are retained. An explicit formula for the change in the fundamental cut-off thickness shear frequency is obtained, and the effects of the terms associated with the fourth-order constants appear to be significant for large gradients of the rotation angles.

Markenscoff, X.↗

NASA NTRS1991

Transient motion of thick anisotropic plates

Analyses are developed for the response of anisotropic plate strips to a transient load. The load is taken in the form of a line load of normal stress on the surface or within the body of the strip. The characteristic free vibrational modes of the strip are derived and used to derive the secular equation for this case in closed form and to isolate the mathematical conditions for symmetric and antisymmetric wave mode propagation in completely separate terms. The applied loads are expanded in terms of these normal modes and the response of the plate is obtained by superposition of the appropriate components. Material systems of higher symmetry are contained implicitly in the analysis.

Nayfeh, Adnan H.↗

NASA NTRS1987

Self Locking Fasteners

Detroit Tool Industries' Spiralock threading tool solves a major industrial problem, fasteners coming loose under vibration. Loosening is caused between the flanks of the bolt and nut threads. This lateral movement releases the locking friction that holds the joint together. Spiralock is a uniquely designed female thread form which used with male fasteners of standard thread form provides a self locking action that prevents the lateral movement, and thus makes the threaded joint highly resistant to the effects of vibration. Additionally, a thread contract runs the entire length of the nut, offering greater stress resistance than earlier fasteners.

Source record↗

NASA NTRS1990

Optimization of rotor blades for combined structural, dynamic, and aerodynamic properties

Optimal helicopter blade design with computer-based mathematical programming has received more and more attention in recent years. Most of the research has focused on optimum dynamic characteristics of rotor blades to reduce vehicle vibration. There is also work on optimization of aerodynamic performance and on composite structural design. This research has greatly increased our understanding of helicopter optimum design in each of these aspects. Helicopter design is an inherently multidisciplinary process involving strong interactions among various disciplines which can appropriately include aerodynamics; dynamics, both flight dynamics and structural dynamics; aeroelasticity: vibrations and stability; and even acoustics. Therefore, the helicopter design process must satisfy manifold requirements related to the aforementioned diverse disciplines. In our present work, we attempt to combine several of these important effects in a unified manner. First, we design a blade with optimum aerodynamic performance by proper layout of blade planform and spanwise twist. Second, the blade is designed to have natural frequencies that are placed away from integer multiples of the rotor speed for a good dynamic characteristics. Third, the structure is made as light as possible with sufficient rotational inertia to allow for autorotational landing, with safe stress margins and flight fatigue life at each cross-section, and with aeroelastical stability and low vibrations. Finally, a unified optimization refines the solution.

He, Cheng-Jian↗

NASA NTRS1989

Dynamics of articulated structures

An articulated structure is defined as an assembly of flexible bodies that may be coupled by kinematic connections and force elements that permit large relative displacement and rotation. Kinematics of such systems is defined using one reference frame for each body in the system and deformation modal coordinates that define displacement fields within flexible bodies. Deformation kinematics are defined by both elastic vibration and static correction deformation modes. Linear elastic deformation is presumed; i.e., a linear stress-strain relation is valid and relative displacements within each elastic component are small enough so that the theory of linear elasticity applies. Coupling of reference and modal coordinates leads to a system of nonlinear equations of motion. Methods of automatically generating and solving these equations of motion are outlined.

Haug, Edward J.↗

NASA NTRS1990

Space Cryogenic Workshop, 8th, California Institute of Technology, Pasadena, July 31, Aug. 1, 1989, Proceedings

Recent advances in cryogenic technology for space applications are examined in reviews and reports. Topics addressed include very-low-force cooling contacts for the ISO cryostat cover, convective heat flow in space cryogenics plugs, liquid-acquisition devices for superfluid He transfer, and pressure drop in the SHOOT superfluid-He acquisition system. Consideration is given to a liquid-He vibration cryostat for space qualification tests, closed-cycle coolers for temperatures below 30 K, stress analysis down to liquid-He temperature, a cryogenic valve actuator, and a spaceborne He-3 refrigerator. Also discussed are an adiabatic-demagnetization refrigerator for SIRTF, rejection of waste heat from O liquefaction operations at a lunar O production plant, SHOOT flowmeter and pressure transducers, and space qualification of the ISO cryogenic rupture disks.

Source record↗

NASA NTRS1940

New Equipment for Testing the Fatigue Strength of Riveted and Welded Joints

The mechanical and electrical construction of a new experimental instrument for fatigue testing riveted and welded joints is described. This experimental device has the advantage of being able to stress, even with comparatively low magnetic exciter force, structural components in alternate bending by resonance vibrations up to incipient fatigue failure.

Muller, W↗

NASA NTRS2014

Development Status of a CVD System to Deposit Tungsten onto UO2 Powder via the WCI6 Process

Nuclear Thermal Propulsion (NTP) is under development for deep space exploration. NTP's high specific impulse (> 850 second) enables a large range of destinations, shorter trip durations, and improved reliability. W-60vol%UO2 CERMET fuel development efforts emphasize fabrication, performance testing and process optimization to meet service life requirements. Fuel elements must be able to survive operation in excess of 2850 K, exposure to flowing hydrogen (H2), vibration, acoustic, and radiation conditions. CTE mismatch between W and UO2 result in high thermal stresses and lead to mechanical failure as a result UO2 reduction by hot hydrogen (H2) [1]. Improved powder metallurgy fabrication process control and mitigated fuel loss can be attained by coating UO2 starting powders within a layer of high density tungsten [2]. This paper discusses the advances of a fluidized bed chemical vapor deposition (CVD) system that utilizes the H2-WCl6 reduction process.

Mireles, O. R.↗

NASA NTRS2016

Mechanical Testing of MLCCs

Cracking of multilayer ceramic capacitors, MLCCs, remains a serious problem for space systems. This problem increases substantially for large size capacitors and in cases when manual soldering is involved or the system experiences mechanical shock or vibration. In any case, a fracture occurs when the sum of external and internal mechanical stresses exceeds the strength of the part. To reduce the probability of cracking, the level of stress should be reduced, e.g. by optimizing the assembly workmanship and rules for board design, and the strength of the parts increased by selecting the most mechanically robust capacitors. The latter might possibly be achieved by selecting MLCCs based on the in-situ measurements of mechanical characteristics using four types of tests: flexural strength, hardness, fracture toughness, and flex bend testing. Note that military specifications MIL-PRF-123 and MIL-PRF-55681 do not have requirements for mechanical testing of the parts. However, specifications for automotive industry components employ two types of mechanical tests: beam load (break strength) test per AEC-Q200-003 and board flex test per AEC-Q200-005. A recent military specification for thin dielectric capacitors, MIL-PRF-32535, has one mechanical test, board flex testing, that is similar to AEC-Q200-005. The purpose of this report was assessment of the efficiency of different mechanical tests for selection robust capacitors and comparison of mechanical characteristics of Base Metal Electrode (BME) and Precious Metal Electrode (PME) capacitors. The report has three parts related to the first three mechanical tests mentioned above.

Precious Metal Electrode (PME) capacitors↗

NASA NTRS1973

Measurement of vibration rate of manually operated percussion machines

A special apparatus for measurement of accelerations of between 1 and 5000 g and shock stress pulses from 20 kg/cu cm up, with durations of 50.1 million sec and higher was designed and built. The amplitudes and shapes of the peak vibroshock pulses, arising during operation of a hammer, are obtained; the recording time of the continuous process is determined by the time of one revolution of the drum of a specially made mechanical photo attachment.

Aleksandrov, Y. V.↗