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At least 55 records · Page 3

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NASA NTRS1975

Design study of structural concepts for an arrow-wing supersonic-cruise aircraft

An analytical study was performed to determine the best structural approach for design of primary wing and fuselage structure of a Mach number 2.7 arrow-wing supersonic cruise aircraft. Concepts were evaluated considering near-term start-of-design. Emphasis was placed on the complex interactions between thermal stress, static aeroelasticity, flutter, fatigue and fail-safe design, static and dynamic loads, and the effects of variations in structural arrangements, concepts and materials on these interactions. Results indicate that a hybrid wing structure incorporating low-profile convex-beaded and honeycomb sandwich surface panels of titanium alloy 6Al-4V were the most efficient. The substructure includes titanium alloy spar caps reinforced with Boron-polyimide composites. The fuselage shell is a closed-hat stiffened skin and frame construction of titanium alloy 6Al-4V. This paper presents an executive summary of the study effort, and includes a discussion of the overall study logic, design philosophy and interaction between the analytical methods for supersonic cruise aircraft design.

Sakata, I. F.↗

NASA NTRSDate not supplied

Method Development for Experimental Characterization of Dynamic Strength of Aluminum Structures

Space Flight Hardware (SFH) experiences intense vibratory loading during flight, which only lasts a few minutes. When determining the appropriate size of these components to withstand such loading without becoming damaged (plastically deforming or breaking), standard design practice is to assume that the peak dynamic loads are applied statically. In doing so, the resulting stress is compared against a material strength parameter obtained from a quasi-static experiment. Since the near-peak stresses are only experienced over a small fraction of time in reality, this approach leads to design conservatism that unnecessarily increases structural mass as well as the associated inefficiency and financial cost. In an effort to modernize engineering design standards to appropriately consider the higher practical strength of dynamically loaded structures, this overarching research project seeks to develop an experimental test procedure for quantifying the dynamic strength of metallic alloys as a function of excitation frequency. In the ideal case, the characterization test would include an in-situ method for monitoring the onset and progression of plastic deformation of the test specimen undergoing vibratory loading. These new tests are designed to be high intensity (forcing amplitude), short term (60 seconds at full amplitude), and cyclic in nature (sinusoidal excitation via attached stinger to an otherwise cantilevered beam). In addition, the initial metallic alloy under investigation is 6061 aluminum, due to its wide use and applicability for SFH. Thus far, the most promising monitoring method under development with live-capacity is to track hysteresis behavior of the beam from power dissipation trends, calculated via force (from transducer on excitation stinger) and velocity (measurements from Laser Doppler Vibrometer) data and work to distinguish between elastic and plastic features. As a key component of this ongoing method development, any pseudo-live indication of plasticity can be corroborated against the outcome of a pre-post assessment of damage via macroscopic evaluation of beam geometry (i.e. assessing any permanent change in the beam’s tip deflection). Support for experimental design decisions as well as dynamic strength data from tests with excitation frequencies of 10, 40, and 55 Hz will be discussed. This work contributes to the foundation for a new type of vibration-based characterization experiments and generates initial data on the functional strength of 6061 aluminum under the conditions considered. Keywords: vibrations, plastic deformation, aluminum

vibrations↗

NASA NTRS2000

Thermoelastic Analysis of Hyper-X Camera Windows Suddenly Exposed to Mach 7 Stagnation Aerothermal Shock

To visually record the initial free flight event of the Hyper-X research flight vehicle immediately after separation from the Pegasus(registered) booster rocket, a video camera was mounted on the bulkhead of the adapter through which Hyper-X rides on Pegasus. The video camera was shielded by a protecting camera window made of heat-resistant quartz material. When Hyper-X separates from Pegasus, this camera window will be suddenly exposed to Mach 7 stagnation thermal shock and dynamic pressure loading (aerothermal loading). To examine the structural integrity, thermoelastic analysis was performed, and the stress distributions in the camera windows were calculated. The critical stress point where the tensile stress reaches a maximum value for each camera window was identified, and the maximum tensile stress level at that critical point was found to be considerably lower than the tensile failure stress of the camera window material.

Ko, William L.↗

NASA NTRS1971

High-impact dynamic-response analysis of nonlinear structures

Program predicts expected deformations and stresses in nonlinear simple geometric structures subjected to high-impact loading. Technique is based on node-wise predictor-corrector approach and requires moderate computer storage and run time for most problems. Program extends to include physical and geometrical nonlinearities.

Gupta, K. K.↗

NASA NTRS1987

Initial dynamic load estimates during configuration design

This analysis includes the structural response to shock and vibration and evaluates the maximum deflections and material stresses and the potential for the occurrence of elastic instability, fatigue and fracture. The required computations are often performed by means of finite element analysis (FEA) computer programs in which the structure is simulated by a finite element model which may contain thousands of elements. The formulation of a finite element model can be time consuming, and substantial additional modeling effort may be necessary if the structure requires significant changes after initial analysis. Rapid methods for obtaining rough estimates of the structural response to shock and vibration are presented for the purpose of providing guidance during the initial mechanical design configuration stage.

Schiff, Daniel↗

NASA NTRS1985

SSME lifetime prediction and verification, integrating environments, structures, materials: The challenge

The planned missions for the space shuttle dictated a unique and technology-extending rocket engine. The high specific impulse requirements in conjunction with a 55-mission lifetime, plus volume and weight constraints, produced unique structural design, manufacturing, and verification requirements. Operations from Earth to orbit produce severe dynamic environments, which couple with the extreme pressure and thermal environments associated with the high performance, creating large low cycle loads and high alternating stresses above endurance limit which result in high sensitivity to alternating stresses. Combining all of these effects resulted in the requirements for exotic materials, which are more susceptible to manufacturing problems, and the use of an all-welded structure. The challenge of integrating environments, dynamics, structures, and materials into a verified SSME structure is discussed. The verification program and developmental flight results are included. The first six shuttle flights had engine performance as predicted with no failures. The engine system has met the basic design challenges.

Ryan, R. S.↗

NASA NTRS2010

Ares Launch Vehicle Transonic Buffet Testing and Analysis Techniques

It is necessary to define the launch vehicle buffet loads to ensure that structural components and vehicle subsystems possess adequate strength, stress, and fatigue margins when the vehicle structural dynamic response to buffet forcing functions are considered. In order to obtain these forcing functions, the accepted method is to perform wind-tunnel testing of a rigid model instrumented with hundreds of unsteady pressure transducers designed to measure the buffet environment across the desired frequency range. The buffet wind-tunnel test program for the Ares Crew Launch Vehicle employed 3.5 percent scale rigid models of the Ares I and Ares I-X launch vehicles instrumented with 256 unsteady pressure transducers each. These models were tested at transonic conditions at the Transonic Dynamics Tunnel at NASA Langley Research Center. The ultimate deliverable of the Ares buffet test program are buffet forcing functions (BFFs) derived from integrating the measured fluctuating pressures on the rigid wind-tunnel models. These BFFs are then used as input to a multi-mode structural analysis to determine the vehicle response to buffet and the resulting buffet loads and accelerations. This paper discusses the development of the Ares I and I-X rigid buffet model test programs from the standpoint of model design, instrumentation system design, test implementation, data analysis techniques to yield final products, and presents normalized sectional buffet forcing function root-mean-squared levels.

Piatak, David J.↗

NASA NTRS2011

Comparison of Ares I-X Wind-Tunnel Derived Buffet Environment with Flight Data

The Ares I-X Flight Test Vehicle (FTV), launched in October 2009, carried with it over 243 buffet verification pressure sensors and was one of the most heavily instrumented launch vehicle flight tests. This flight test represented a unique opportunity for NASA and its partners to compare the wind-tunnel derived buffet environment with that measured during the flight of Ares I-X. It is necessary to define the launch vehicle buffet loads to ensure that structural components and vehicle subsystems possess adequate strength, stress, and fatigue margins when the vehicle structural dynamic response to buffet forcing functions are considered. Ares I-X buffet forcing functions were obtained via wind-tunnel testing of a rigid buffet model (RBM) instrumented with hundreds of unsteady pressure transducers designed to measure the buffet environment across the desired frequency range. This paper discusses the comparison of RBM and FTV buffet environments, including fluctuating pressure coefficient and normalized sectional buffet forcing function root-mean-square magnitudes, frequency content of power-spectral density functions, and force magnitudes of an alternating flow phenomena. Comparison of wind-tunnel model and flight test vehicle buffet environments show very good agreement with root-mean-square magnitudes of buffet forcing functions at the majority of vehicle stations. Spectra proved a challenge to compare because of different wind-tunnel and flight test conditions and data acquisition rates. However, meaningful and promising comparisons of buffet spectra are presented. Lastly, the buffet loads resulting from the transition of subsonic separated flow to supersonic attached flow were significantly over-predicted by wind-tunnel results.

Piatak, David J.↗

NASA NTRS1992

Ultrasonic Dynamic Vector Stress Sensor

Stress inferred from measurements in specimens rather than in bonded gauges. Ultrasonic dynamic vector stress sensor (UDVSS) measures changes in dynamic directional stress occurring in material or structure at location touched by device when material or structure put under cyclic load. Includes phase-locked loop, synchronous amplifier, and contact probe. Useful among manufacturers of aerospace and automotive structures for stress testing and evaluation of designs.

Heyman, Joseph S.↗

NASA NTRS1987

Structural dynamics system model reduction

Loads analysis for structural dynamic systems is usually performed by finite element models. Because of the complexity of the structural system, the model contains large number of degree-of-freedom. The large model is necessary since details of the stress, loads and responses due to mission environments are computed. However, a simplified model is needed for other tasks such as pre-test analysis for modal testing, and control-structural interaction studies. A systematic method of model reduction for modal test analysis is presented. Perhaps it will be of some help in developing a simplified model for the control studies.

Chen, J. C.↗

NASA NTRS1933

Dynamic Breaking Tests of Airplane Parts

The static stresses of airplane parts, the magnitude of which can be determined with the aid of static load assumptions, are mostly superposed by dynamic stresses, the magnitude of which has been but little explored. The object of the present investigation is to show how the strength of airplane parts can best be tested with respect to dynamic stresses with and without superposed static loading, and to what extent the dynamic strength of the parts depends on their structural design. Experimental apparatus and evaluation methods were developed and tried for the execution of vibration-strength tests with entire structural parts both with and without superposed static loading. Altogether ten metal spars and spar pieces and two wooden spars were subjected to vibration breaking tests.

Hertel, Heinrich↗

NASA NTRS1990

A superelement methodology for coupled loads analysis of Space Station Freedom

A technique for calculating the effects of on-orbit loads on the structural dynamics of the International Space Station is developed on the basis of MSC/NASTRAN superelement solution sequences. The complexity of the Space Station program with its multiple configurations, international partners, and contractors is stressed, and the impact of this complexity on the dynamic-load analysis process is indicated. The MSC/NASTRAN-based approach is outlined, and its application to two versions of the Permanent Manned Capability configuration is described in detail, including component mode synthesis, GFSC/FLAME coupled-loads analysis (with components from the system FEM model or from the Work Package), and ISI/MATRIX-X generation of closed-loop forcing functions. The results of these sample analyses are presented in extensive tables and graphs and briefly characterized.

Del Basso, Steve↗

NASA NTRS2015

Overview of the Space Launch System Transonic Buffet Environment Test Program

Fluctuating aerodynamic loads are a significant concern for the structural design of a launch vehicle, particularly while traversing the transonic flight environment. At these trajectory conditions, unsteady aerodynamic pressures can excite the vehicle dynamic modes of vibration and result in high structural bending moments and vibratory environments. To ensure that vehicle structural components and subsystems possess adequate strength, stress, and fatigue margins in the presence of buffet and other environments, buffet forcing functions are required to conduct the coupled load analysis of the launch vehicle. The accepted method to obtain these buffet forcing functions is to perform wind-tunnel testing of a rigid model that is heavily instrumented with unsteady pressure transducers designed to measure the buffet environment within the desired frequency range. Two wind-tunnel tests of a 3 percent scale rigid buffet model have been conducted at the Langley Research Center Transonic Dynamics Tunnel (TDT) as part of the Space Launch System (SLS) buffet test program. The SLS buffet models have been instrumented with as many as 472 unsteady pressure transducers to resolve the buffet forcing functions of this multi-body configuration through integration of the individual pressure time histories. This paper will discuss test program development, instrumentation, data acquisition, test implementation, data analysis techniques, and several methods explored to mitigate high buffet environment encountered during the test program. Preliminary buffet environments will be presented and compared using normalized sectional buffet forcing function root-meansquared levels along the vehicle centerline.

Piatak, David J.↗

NASA NTRS1973

Study of an experimental technique for application to structural dynamic problems

An experimental program was conducted to determine the feasibility of using subscale plastic models to determine the response of full-scale aerospace structural components to impulsive, pyrotechnic loadings. A monocoque cylinder was impulsively loaded around the circumference of one end, causing a compressive stress wave to propagate in the axial direction. The resulting structural responses of two configurations of the cylinder (with and without a cutout) were recorded by photoelasticity, strain gages, and accelerometers. A maximum dynamic stress concentration was photoelastically determined and the accelerations calculated from strain-gage data were in good agreement with those recorded by accelerometers. It is concluded that reliable, quantitative structural response data can be obtained by the experimental techniques described in this report.

Snell, R. F.↗

NASA NTRS1978

Considerations in STS payload environmental verification

Considerations regarding the Space Transportation System (STS) payload environmental verification are reviewed. It is noted that emphasis is placed on testing at the subassembly level and that the basic objective of structural dynamic payload verification is to ensure reliability in a cost-effective manner. Structural analyses consist of: (1) stress analysis for critical loading conditions, (2) model analysis for launch and orbital configurations, (3) flight loads analysis, (4) test simulation analysis to verify models, (5) kinematic analysis of deployment/retraction sequences, and (6) structural-thermal-optical program analysis. In addition to these approaches, payload verification programs are being developed in the thermal-vacuum area. These include the exposure to extreme temperatures, temperature cycling, thermal-balance testing and thermal-vacuum testing.

Keegan, W. B.↗

NASA NTRS1990

SIRTF high earth orbit mission conceptual structural design and analysis

The Space Infrared Telescope Facility (SIRTF) is a cryogenically cooled, space based, one meter class telescope for infrared astronomy. A recent mission option study has moved SIRTF from a previous low earth orbit (900 km) shuttle launched design to a high earth orbit (100,000 km) Titan IV/Centaur launched design. The mission option study requirements and trades relating to the structural configuration and the chosen SIRTF design are described. Also discussed is a dynamic stress analysis of the new SIRTF baseline structural design which has been performed using finite element modeling and simulated launch interface loads.

Chang, LI↗

NASA NTRS2003

Interface Finite Elements for the Analysis of Fracture Initiation and Progression

Progressive failure analyses (PFA) are important for the prediction of residual strength and damage tolerance of vehicle structures, and to predict the energy absorbing capability of vehicle structures under crash-type loads. Typically continuum damage mechanics (CDM) and fracture mechanics (FM) are the methods used for PFA. The method of interfacial damage mechanics (IDM) is used for PFA in this research. IDM has capabilities intermediate between CDM and FM, and is used to numerically model the initiation, growth, and arrest of cracks. IDM smooths the stress singularity at the crack tip, and is easily adaptable with other nonlinearties such as plasticity and material damage. IDM is implemented by user-defined interface elements in the ABAQUS/ Standard structural analysis software package. The structural components selected to demonstrate the effectiveness PFA using interface elements are, for the most part, those with published test data. These structural components were subjected to quasi-static loading in the tests. Thus, the ABAQUS analyses are used to predict geometrically and materially nonlinear equilibrium states. Impact loading, dynamic fracture, reflected stress waves, inertia, and time dependent material behavior are not considered.

Ambur, Damodar R.↗

NASA NTRS1989

Space Shuttle Main Engine structural analysis and data reduction/evaluation. Volume 6: Primary nozzle diffuser analysis

The primary nozzle diffuser routes fuel from the main fuel valve on the Space Shuttle Main Engine (SSME) to the nozzle coolant inlet mainfold, main combustion chamber coolant inlet mainfold, chamber coolant valve, and the augmented spark igniters. The diffuser also includes the fuel system purge check valve connection. A static stress analysis was performed on the diffuser because no detailed analysis was done on this part in the past. Structural concerns were in the area of the welds because approximately 10 percent are in areas inaccessible by X-ray testing devices. Flow dynamics and thermodynamics were not included in the analysis load case. Constant internal pressure at maximum SSME power was used instead. A three-dimensional, finite element method was generated using ANSYS version 4.3A on the Lockheed VAX 11/785 computer to perform the stress computations. IDEAS Supertab on a Sun 3/60 computer was used to create the finite element model. Rocketdyne drawing number RS009156 was used for the model interpretation. The flight diffuser is denoted as -101. A description of the model, boundary conditions/load case, material properties, structural analysis/results, and a summary are included for documentation.

Foley, Michael J.↗