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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 91 records · Page 5
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NASA NTRS2018

NASA ACC High Energy Dynamic Impact Methodology and Outcomes

For High Energy Dynamic Impact (HEDI) events, testing to evaluate the structural response of primary aircraft structure for design and certification is both expensive and time consuming. This paper discusses current work seeking to assess, develop, and validate appropriate analytical models that accurately predict physical response, damage, and failure modes for large scale composite structures in HEDI events. Four state-of-the-art Progressive Damage Analysis (PDA) methods were employed for this phased project: LS-DYNA MAT162, LS-DYNA MAT261, Smoothed Particle Galerkin (SPG), and EMU Peridynamics. Multiple material systems were considered, namely T700/5208 textile-infusion triaxial braid, T800/AMD-825 textile-infusion triaxial braid, IM7/8552 uni-directional tape, and SPG 196-PW/8552 plain-weave fabric. Extensive ballistic impact testing was performed to support this activity and measured results were compared to predictive models for assessment using panel delamination, panel displacement, force at the load cells, and threshold velocity as measures. Ultimately, the work under this activity provided significant progress in advancing the state-of-the-art in the use of PDA for HEDI events. Each material model had favorable performance comparing to test in some parameters and needed improvement in others. With the lessons learned from this activity, significant progress was made in the ability to predict panel behavior for a more general case beyond the flat panel in a ballistic impact event. Subsequent Phase II of the NASA ACC HEDI effort will continue to build on the coupon testing, flat panel ballistic impact testing, and analysis performed to-date with application of the PDA methods for intended material selections to test articles with greater complexity of configuration, curvature, and scale. It is not the intention of this paper to present a full set of data, but rather to give an overview of the NASA HEDI effort and show a small representative subset of the test and analysis results.

Hunziker, Kenneth J.↗
NASA NTRS1977

Dynamical implications of the petrology and distribution of impact melt rocks

Petrographic and structural relations of rocks resulting from melting of target materials during impact indicate constraints that can be applied to theoretical models and experimental production of craters. Topics discussed in this context include the motion of shock melted material, the mixing of melts, the energies required for heating and melting the necessary volumes of target rocks, diameter to depth ratios, and the formation of structural modifications. The motion of shock melted material involves ejection of some of the lowermost parts of the target, incorporation of distant fragmental material, outward flow, settling into cracks after breccia formation, and completion in a short time span. Melts must be completed within tens of seconds to a couple of minutes after impact.

Phinney, W. C.↗
NASA NTRS1984

Crashworthiness of light aircraft fuselage structures: A numerical and experimental investigation

The dynamic behavior of aircraft fuselage structures subject to various impact conditions was investigated. An analytical model was developed based on a self-consistent finite element (CFE) formulation utilizing shell, curved beam, and stringer type elements. Equations of motion were formulated and linearized (i.e., for small displacements), although material nonlinearity was retained to treat local plastic deformation. The equations were solved using the implicit Newmark-Beta method with a frontal solver routine. Stiffened aluminum fuselage models were also tested in free flight using the UTIAS pendulum crash test facility. Data were obtained on dynamic strains, g-loads, and transient deformations (using high speed photography in the latter case) during the impact process. Correlations between tests and predicted results are presented, together with computer graphics, based on the CFE model. These results include level and oblique angle impacts as well as the free-flight crash test. Comparisons with a hybrid, lumped mass finite element computer model demonstrate that the CFE formulation provides the test overall agreement with impact test data for comparable computing costs.

Nanyaro, A. P.↗
NASA NTRS1992

Static and dynamic strain energy release rates in toughened thermosetting composite laminates

In this work, the static and dynamic fracture properties of several thermosetting resin based composite laminates are presented. Two classes of materials are explored. These are homogeneous, thermosetting resins and toughened, multi-phase, thermosetting resin systems. Multi-phase resin materials have shown enhancement over homogenous materials with respect to damage resistance. The development of new dynamic tests are presented for composite laminates based on Width Tapered Double Cantilevered Beam (WTDCB) for Mode 1 fracture and the End Notched Flexure (ENF) specimen. The WTDCB sample was loaded via a low inertia, pneumatic cylinder to produce rapid cross-head displacements. A high rate, piezo-electric load cell and an accelerometer were mounted on the specimen. A digital oscilloscope was used for data acquisition. Typical static and dynamic load versus displacement plots are presented. The ENF specimen was impacted in three point bending with an instrumented impact tower. Fracture initiation and propagation energies under static and dynamic conditions were determined analytically and experimentally. The test results for Mode 1 fracture are relatively insensitive to strain rate effects for the laminates tested in this study. The test results from Mode 2 fracture indicate that the toughened systems provide superior fracture initiation and higher resistance to propagation under dynamic conditions. While the static fracture properties of the homogeneous systems may be relatively high, the apparent Mode 2 dynamic critical strain energy release rate drops significantly. The results indicate that static Mode 2 fracture testing is inadequate for determining the fracture performance of composite structures subjected to conditions such as low velocity impact. A good correlation between the basic Mode 2 dynamic fracture properties and the performance is a combined material/structural Compression After Impact (CAI) test is found. These results underscore the importance of examining rate-dependent behavior for determining the longevity of structures manufactured from composite materials.

Cairns, Douglas S.↗
NASA NTRSDate not supplied

Wind Tunnel to Full Scale Mapping of Winds and Loads for Launch-Vehicle Ground Wind Loads

A launch vehicle ground-wind-loads program was conducted at the NASA Langley Transonic Dynamics Tunnel. The objectives were to quantify key aerodynamic and structural characteristics that impact the occurrence of large wind-induced oscillations of a launch vehicle when exposed to ground winds prior to launch. Of particular interest is the dynamic response of a launch vehicle when a von Kármán vortex street forms in the wake of the vehicle resulting in quasiperiodic lift and drag forces.Vehicle response to these quasiperiodic forces can become quite large when the frequency of vortex shedding nears that of a lowly-damped structural mode thereby exciting a resonant response. The study of ground-wind-loads presents unique challenges to quantify significant characteristics of the approaching wind and to relate the wind-tunnel acquired static, dynamic, and gravitational loads to full-scale vehicles. This paper will explain the correlation process between model-scale and full-scale wind characteristics and resulting structural loads. Characterization of the wind at a launch site requires knowledge of the vehicle dynamics and the anemometer performance. Vehicle dynamics dictate the frequency range of interest in characterization of the atmospheric turbulence, and in defining the required data window-length to model dynamic oscillation build-up during wind-gust analysis. Knowledge of the anemometer performance is required to infer peak wind magnitudes since most anemometers cannot directly measure instantaneous peak values. Following proper wind-speed correlation, static and dynamic wind-tunnel loads must be converted to full-scale equivalent values to derive design and operational guidance. In addition to the direct computation of full-scale equivalent loads using relevant scaling parameters, the corrections applied to dynamic loads accounting for differences in structural damping will also be discussed. Furthermore, a phenomenon that manifests in many slender and flexible launch vehicles is a load magnification due to gravity resulting from mass offset under deflection. A method for scaling this contribution from model-scale to full-scale is presented. Finally, a comparison of wind-tunnel derived loads using the described methodologies to launch vehicle measured loads is presented.

ground wind loads↗
NASA NTRSDate not supplied

Wind-Tunnel to Full-Scale Mapping of Winds and Loads for Launch-Vehicle Ground Wind Loads

A launch vehicle ground-wind-loads program was conducted at the NASA Langley Transonic Dynamics Tunnel. The objectives were to quantify key aerodynamic and structural characteristics that impact the occurrence of large wind-induced oscillations of a launch vehicle when exposed to ground winds prior to launch. Of particular interest is the dynamic response of a launch vehicle when a von Kármán vortex street forms in the wake of the vehicle resulting in quasiperiodic lift and drag forces. Vehicle response to these quasiperiodic forces can become quite large when the frequency of vortex shedding nears that of a lowly-damped structural mode thereby exciting a resonant response. The study of ground-wind-loads presents unique challenges to quantify significant characteristics of the approaching wind and to relate the wind-tunnel acquired static, dynamic, and gravitational loads to full-scale vehicles. This paper will explain the correlation process between model-scale and full-scale wind characteristics and resulting structural loads. Characterization of the wind at a launch site requires knowledge of the vehicle dynamics and the anemometer performance. Vehicle dynamics dictate the frequency range of interest in characterization of the atmospheric turbulence, and in defining the required data window-length to model dynamic oscillation build-up during wind-gust analysis. Knowledge of the anemometer performance is required to infer peak wind magnitudes since most anemometers cannot directly measure instantaneous peak values. Following proper wind-speed correlation, static and dynamic wind-tunnel loads must be converted to full-scale equivalent values to derive design and operational guidance. In addition to the direct computation of full-scale equivalent loads using relevant scaling parameters, the corrections applied to dynamic loads accounting for differences in structural damping will also be discussed. Furthermore, a phenomenon that manifests in many slender and flexible launch vehicles is a load magnification due to gravity resulting from mass offset under deflection. A method for scaling this contribution from model-scale to full-scale is presented. Finally, a comparison of wind-tunnel derived loads using the described methodologies to launch vehicle measured loads is presented.

Ground wind loads↗
NASA NTRS2022

Firefly: The Case for a Holistic Understanding of the Global Structure and Dynamics of the Sun and the Heliosphere

This white paper presents the current knowledge gaps in understanding how magnetic fields control solar (and by extension, stellar) activity in timescales from minutes to years and discusses a transformative observational approach to fill those gaps. The solar activity drives space weather as the result of dynamic magnetic fields forming in the solar interior and evolving continuously until reaching levels of complexity in the atmosphere that trigger eruptions. However, we do not fully understand how solar and, more generally, stellar magnetic fields are generated and how they evolve through the eruptive states. The major obstacle is our reliance on observations from a single viewpoint, particularly in the ecliptic plane. This vantage point can only provide limited information for (i) understanding the generation of solar magnetic fields deep in the convection zone; (ii) determining the origin of the solar cycle and predicting its timing and strength; (iii) explaining the causes of solar activity and their triggers; (iv) reliably predicting when and how CMEs will impact Earth and other planets; (v) fathoming the structure and dynamics of the corona as it creates the heliosphere; (vi) understanding the energization and transport of energetic particles; etc.

Nour E. Raouafi↗
NASA NTRS1994

Design of orbital debris shields for oblique hypervelocity impact

A new impact debris propagation code was written to link CTH simulations of space debris shield perforation to the Lagrangian finite element code DYNA3D, for space structure wall impact simulations. This software (DC3D) simulates debris cloud evolution using a nonlinear elastic-plastic deformable particle dynamics model, and renders computationally tractable the supercomputer simulation of oblique impacts on Whipple shield protected structures. Comparison of three dimensional, oblique impact simulations with experimental data shows good agreement over a range of velocities of interest in the design of orbital debris shielding. Source code developed during this research is provided on the enclosed floppy disk. An abstract based on the work described was submitted to the 1994 Hypervelocity Impact Symposium.

Fahrenthold, Eric P.↗
NASA NTRS1992

Gallery of fluid motion

Winning photographs from the ninth Annual Fluid Mechanics Photo Contest held by the Division of Fluid Dynamics of the American Physical Society in November 1991 are displayed. Pictures are presented of vortex flows, a periodic axisymmetric vortex breakdown in a cylinder with a rotating end wall, impacting water drops, a vortex structure behind a disk started from rest, dynamic stall, blue waves, isotherms in turbulent Rayleigh-Benard convection, a square jet, 'vapor lines' emanating from water droplets, viscosity effects on the directional solidification of NH4Cl solution in a Hele-Shaw cell, and stationary cross-flow vortices.

Reed, Helen L.↗
NASA NTRS1989

Transient analysis techniques in performing impact and crash dynamic studies

Because of the emphasis being placed on crashworthiness as a design requirement, increasing demands are being made by various organizations to analyze a wide range of complex structures that must perform safely when subjected to severe impact loads, such as those generated in a crash event. The ultimate goal of crashworthiness design and analysis is to produce vehicles with the ability to reduce the dynamic forces experienced by the occupants to specified levels, while maintaining a survivable envelope around them during a specified crash event. DYCAST is a nonlinear structural dynamic finite element computer code that started from the plans systems of a finite element program for static nonlinear structural analysis. The essential features of DYCAST are outlined.

Pifko, A. B.↗
NASA NTRS1985

NASA experiments onboard the controlled impact demonstration

The structural crashworthiness tests conducted by NASA on the December 1, 1984 controlled impact demonstration are discussed. The components and locations of the data acquisition and photographic systems developed by NASA to evaluate impact loads throughout the aircraft structure and the transmission of loads into the dummies are described. The effectiveness of the NASA designed absorbing seats and the vertical, longitudinal, and transverse impact loads are measured. Data that is extremely applicable to crash dynamics structural research was obtained by the data acquisition system and very low load levels were measured for the NASA energy absorbing seats.

Hayduk, R. J.↗
NASA NTRSDate not supplied

Impact Of Rotation on the Sun’s Subsurface Structure

It is well known that the dynamical evolution of subsurface flows of the Sun and magnetic fields is strongly linked to rotation. Observational investigation of sub surface structuring and dynamics can be performed only with relatively low resolution using helioseismic inversion techniques. To confidently model the coupling of turbulent convection, magnetic fields, and rotation in the solar interior, we perform advanced radiative hydrodynamic and MHD modeling of local scales. To explore the coupling effects in the upper layers of the convection zone, we present results of analysis from a series of hydrodynamic simulations performed for a 25-Mm-deep computational domain at different latitudes obtained for 1) the Carrington rotation rate at all latitudes and 2) the realistic rotation rate from the global helioseismic inversions during the solar minimum. Using additional 3D radiative hydrodynamic models, we reveal how physical properties of the solar convection are affected by rotation.

Heliophysics↗
NASA NTRS1968

Excerpts from Test Films: Langley Impacting Structures Facility, Lunar Module

The film includes excerpts from three studies: (1) Landing characteristics of a dynamic model of the HL-10 manned lifting entry vehicle, conducted by Sandy M. Stubbs, in which the vehicle landed on water at horizontal velocities of 240- and 250-feet per second (ft/sec). (2) Dynamic model investigation of water pressures and accelerations encountered during landings of the Apollo spacecraft conducted by Sandy M. Stubbs, in which horizontal velocity was 50 ft/sec. and pitch attitude was -12 and -28 degrees. (3) Comparative landing impact tests of a 1/6-scale model as a free body under earth gravity and a tethered full-scale lunar module on the Lunar Gravity Simulator. Landing 8 is shown, with a vertical velocity of 10 ft/sec. and a horizontal velocity of 8 ft/sec. Motion pictures were taken at 400 and 64 pps.

Source record↗
NASA NTRS1997

Health Monitoring of Composite Material Structures using a Vibrometry Technique

Large composite material structures such as aircraft and Reusable Launch Vehicles (RLVS) operate in severe environments comprised of vehicle dynamic loads, aerodynamic loads, engine vibration, foreign object impact, lightning strikes, corrosion, and moisture absorption. These structures are susceptible to damage such as delamination, fiber breaking/pullout, matrix cracking, and hygrothermal strain. To ensure human safety and load-bearing integrity, these structures must be inspected to detect and locate often invisible damage and faults before becoming catastrophic. Moreover, nearly all future structures will need some type of in-service inspection technique to increase their useful life and reduce maintenance and overall costs. Possible techniques for monitoring the health and indicating damage on composite structures include: c-scan, thermography, acoustic emissions using piezoceramic actuators or fiber-optic wires with gratings, laser ultrasound, shearography, holography, x-ray, and others. These techniques have limitations in detecting damage that is beneath the surface of the structure, far away from a sensor location, or during operation of the vehicle. The objective of this project is to develop a more global method for damage detection that is based on structural dynamics principles, and can inspect for damage when the structure is subjected to vibratory loads to expose faults that may not be evident by static inspection. A Transmittance Function Monitoring (TFM) method is being developed in this project for ground-based inspection and operational health monitoring of large composite structures as a RLV. A comparison of the features of existing health monitoring approaches and the proposed TFM method is given.

Schulz, Mark J.↗
NASA NTRS1986

Impact dynamics instrumentation

One of the tasks specified in the NASA Langley controlled impact demonstration (CID) work package was to furnish dynamic instrumentation sensors. The types of instrumentation sensors required were accelerometers for aircraft structural loads measurements, seat belt load cells to measure anthropomorphic dummy responses to the aircraft impact, and strain gage bending bridges to measure the aircraft fuselage and wing bending during impact. The objective in the selection of dynamic instrumentation for the CID was to provide 352 of the highest quality transducers and remain within budget allocation. The transducers that were selected for the CID evaluation process were each subjected to rigorous laboratory acceptance tests and to aircraft fuselage section drop tests at the LaRC Impact Dynamics Research Facility. Data compiled from this series of tests showed the selected transducers to be best suited for the CID mission requirement. The transducers installation technique on the airframe proved successful. The transducer quality assurance was guaranteed through rigorous acceptance testing. Data acquired was 97.0%.

Mccormck, R. F.↗
NASA NTRS1984

Full-scale crash-test evaluation of two load-limiting subfloors for general aviation airframes

Three six place, low wing, twin engine general aviation airplane test specimens were crash tested at the Langley Impact Dynamics Research Facility under controlled free flight conditions. One structurally unmodified airplane was the base line specimen for the test series. The other two airplanes were structurally modified to incorporate load limiting (energy absorbing) subfloor concepts into the structure for full scale crash test evaluation and for comparison with the unmodified airplane test results. Typically, the lowest floor accelerations, the lowest anthropomorphic dummy responses, and the least seat crushing of standard and load limiting seats occurred in the airplanes modified with load limiting subfloors, wherein the greatest structural crushing of the subfloor took place. The better performing of the two load limiting subfloor concepts reduced the peak airplane floor accelerations to -25g to -30g as compared with approximately -40g to -55g for the unmodified airplane structure.

Carden, H. D.↗