SEARCH · Search NASA

Results for “structural failure”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11

All sources NASA NTRS DOE OSTI

NASA NTRS2003

A New Modular Approach for Tightly Coupled Fluid/Structure Analysis

Static aeroelastic computations are made using a C++ executive suitable for closely coupled fluid/structure interaction studies. The fluid flow is modeled using the Euler/Navier Stokes equations and the structure is modeled using finite elements. FORTRAN based fluids and structures codes are integrated under C++ environment. The flow and structural solvers are treated as separate object files. The data flow between fluids and structures is accomplished using I/O. Results are demonstrated for transonic flow over partially flexible surface that is important for aerospace vehicles. Use of this development to accurately predict flow induced structural failure will be demonstrated.

Guruswamy, Guru↗

NASA NTRS2004

Foreign Object Damage Behavior of a SiC/SiC Composite at Ambient and Elevated Temperatures

Foreign object damage (FOD) behavior of a gas-turbine grade SiC/SiC ceramic matrix composite (CMC) was determined at 25 and 1316 C, employing impact velocities from 115 to 440 meters per second by 1.59-mm diameter stell-ball projectiles. Two different types of specimen support were used at each temperature: fully supported and partially supported. For a given temperature, the degree of post-impact strength degradation increased with increasing impact velocity, and was greater in a partially supported configuration than in a fully supported one. The elevated-temperature FOD resistance of the composite, particularly under partially supported loading at higher impact velocities greater than or equal to 350 meters per second, was significantly less than the ambient-temperature counterpart, attributed to a weakening effect of the composite. For fully supported loading, frontal contact stress played a major role in generating composite damage; whereas, for partially supported loading, both frontal contact and backside bending stresses were combined sources of damage generation. The SiC/SiC composite was able to survive higher energy impacts without complete structural failure but suffered more strength affecting damage from low energy impacts than AS800 and SN282 silicon nitrides.

Bhatt, Ramakrishna T.↗

NASA NTRS1999

Is skeletal muscle ready for long-term spaceflight and return to gravity?

It is now clear that prevention of muscle debilitation during spaceflight will require a broader approach than simple exercise aimed at strengthening of the muscle fibers. The levels of several hormones and receptors are altered by unloading and must be returned to homeostasis. Pharmacotherapy and gene transfer strategies to raise the relative level of structural proteins may minimize the problems faced by astronauts in readapting to Earth-gravity. Up to now, we have only minimally exploited microgravity for advancing our understanding of muscle biology. A research laboratory in the space station with a centrifuge facility (gravity control) is essential for conducting basic research in this field. Microgravity has proven an excellent tool for noninvasively perturbing the synthesis of muscle proteins in the search for molecular signals and gene regulatory factors influencing differentiation, growth, maintenance and atrophy of muscle. Understanding the relation between blood flow and interstitial edema and between workload and subsequent structural failure are but two important problems that require serious attention. The roles of hormones and growth factors in regulating gene expression and their microgravity-induced altered production are other urgent issues to pursue. These types of studies will yield information that advances basic knowledge of muscle biology and offers insights into countermeasure design. This knowledge is likely to assist rehabilitation of diseased or injured muscles in humans on Earth, especially individuals in the more vulnerable aging population and persons participating in strenuous sports. Will the skeletal muscle system be prepared for the increased exposure to microgravity and the return to gravity loading without injury when space station is operational? The answer depends in large part on continued access to space and funding of ground-based models and flight experiments. The previous two decades of spaceflight research have described the effects of microgravity on multiple systems. The next generation of experiments promises to be even more exciting as we are challenged to define the cellular and molecular mechanisms of microgravity-induced changes.

manned↗

NASA NTRS1948

Ditching Tests of Two Models of the Army B-36 Airplane

The ditching characteristics of the Army B-36 airplane were determined by testing 1/20- and 1/30-scale dynamic models in calm water in Langley tank no. 2 and at the outdoor catapult. The scope of the tests consisted of ditching the models at various conditions of simulated damage, landing attitudes, and speeds, with various flap settings using several degrees of restraint of the flap hinges. The ditching behavior was evaluated from recordings of deceleration, length of run, and motions of the models. The results showed that the airplane should be ditched at an attitude of about 9 deg with flaps full down. The probable ditching behavior will be a smooth run with a maximum longitudinal deceleration of 3g to 4g and a landing run of 4 to 5 fuselage lengths. Structural failure of the underside of the fuselage will not seriously affect the behavior of the airplane.

Fisher, Lloyd J.↗

NASA NTRS1995

Spatial and Temporal Distribution of Ion Engine Accelerator Grid Erosion

Structural failure of the accelerator grid in two-grid ion optics due to charge exchange ion erosion is considered one of the dominant failure modes for ion engines. A detailed examination of three accelerator grids used in long duration tests of inert gas ion thrusters was undertaken to characterize the radial mass loss distribution, the local distribution of mass loss in the erosion pattern and how it varies as the pattern evolves. The results show significant broadening of the radial profile compared to what is expected in space with significant variations from grid to grid. The local distribution of mass loss and how it varies with increasing total mass loss in the erosion pattern was also found to differ considerably among the three grids. The results indicate that the details of the erosion geometry cannot be ignored when generalizing test results or modeling grid failure to calculate useful engine service life.

Ion Engine↗

NASA NTRS2008

NASA Experience with Pogo in Human Spaceflight Vehicles

An overview of more than 45 years of NASA human spaceflight experience is presented with respect to the thrust axis vibration response of liquid fueled rockets known as pogo. A coupled structure and propulsion system instability, pogo can result in the impairment of the astronaut crew, an unplanned engine shutdown, loss of mission, or structural failure. The NASA history begins with the Gemini Program and adaptation of the USAF Titan II ballistic missile as a spacecraft launch vehicle. It continues with the pogo experienced on several Apollo-Saturn flights in both the first and second stages of flight. The defining moment for NASA s subsequent treatment of pogo occurred with the near failure of the second stage on the ascent of the Apollo 13 mission. Since that time NASA has had a strict "no pogo" philosophy that was applied to the development of the Space Shuttle. The "no pogo" philosophy lead to the first vehicle designed to be pogo-free from the beginning and the first development of an engine with an integral pogo suppression system. Now, more than 30 years later, NASA is developing two new launch vehicles, the Ares I crew launch vehicle propelling the Orion crew excursion vehicle, and the Ares V cargo launch vehicle. A new generation of engineers must again exercise NASA s system engineering method for pogo mitigation during design, development and verification.

Larsen, Curtis E.↗

NASA NTRS2007

Did Vertigo Kill America's Forgotten Astronaut?

On November 15, 1967, U.S. Air Force test pilot Major Michael J. Adams was killed while flying the X-15 rocket-propelled research vehicle in a parabolic spaceflight profile. This flight was part of a joint effort with NASA. An electrical short in one of the experiments aboard the vehicle caused electrical transients, resulting in excessive workload by the pilot. At altitude Major Adams inappropriately initiated a flat spin that led to a series of unusual aircraft attitudes upon atmospheric re-entry, ultimately causing structural failure of the airframe. Major Adams was known to experience vertigo (i.e. spatial disorientation) while flying the X-15, but all X-15 pilots most likely experienced vertigo (i.e. somatogravic, or "Pitch-Up", illusion) as a normal physiologic response to the accelerative forces involved. Major Adams probably experienced vertigo to a greater degree than did others, since prior aeromedical testing for astronaut selection at Brooks AFB revealed that he had an unusually high degree of labyrinthine sensitivity. Subsequent analysis reveals that after engine burnout, and through the zenith of the flight profile, he likely experienced the oculoagravic ("Elevator") illusion. Nonetheless, painstaking investigation after the mishap revealed that spatial disorientation (Type II, Recognized) was NOT the cause, but rather, a contributing factor. The cause was in fact the misinterpretation of a dual-use flight instrument (i.e. Loss of Mode Awareness), resulting in confusion between yaw and roll indications, with subsequent flight control input that was inappropriate. Because of the altitude achieved on this flight, Major Adams was awarded Astronaut wings posthumously. Understanding the potential for spatial disorientation, particularly the oculoagravic illusion, associated with parabolic spaceflight profiles, and understanding the importance of maintaining mode awareness in the context of automated cockpit design, are two lessons that have direct application to the commercial space industry today.

Bendrick, Gregg A.↗

NASA NTRS2008

An Alternative Method Of Specifying Shock Test Criteria

Shock testing of aerospace vehicle hardware has presented many challenges over the years due to the high magnitude and short duration of the specifications. Recently, component structural failures have occurred during testing that have not manifested themselves on over 200 Space Shuttle solid rocket booster (SRB) flights (two boosters per flight). It is suspected that the method of specifying shock test criteria may be leaving important information out of the test process. The traditional test criteria specification, the shock response spectrum, can be duplicated by any number of waveforms that may not resemble the actual flight test recorded time history. One method of overcoming this limitation is described herein, which may prove useful for qualifying hardware for the upcoming Constellation Program.

Ferebee, R. C.↗

NASA NTRS2008

Aircraft Loss-of-Control Accident Prevention: Switching Control of the GTM Aircraft with Elevator Jam Failures

Switching control, servomechanism, and H2 control theory are used to provide a practical and easy-to-implement solution for the actuator jam problem. A jammed actuator not only causes a reduction of control authority, but also creates a persistent disturbance with uncertain amplitude. The longitudinal dynamics model of the NASA GTM UAV is employed to demonstrate that a single fixed reconfigured controller design based on the proposed approach is capable of accommodating an elevator jam failure with arbitrary jam position as long as the thrust control has enough control authority. This paper is a first step towards solving a more comprehensive in-flight loss-of-control accident prevention problem that involves multiple actuator failures, structure damages, unanticipated faults, and nonlinear upset regime recovery, etc.

Chang, Bor-Chin↗

NASA NTRS1957

Experimental Investigation of Vibratory Stresses in a Concentric-Ring Direct-Air-Cycle Nuclear Fuel Element

Preliminary tests made by the General Electric Company indicated that aerodynamic loads might cause large enough distortions in the thin sheet-metal rings of a nuclear fuel element to result in structural failure. The magnitude of the distortions in a test fuel element was determined from strains measured with airflow conditions simulating those expected during engine operation. The measured vibratory strains were low enough to indicate the improbability of failure by fatigue. A conservative estimate of the radial deflection that accompanied peak strains in the outer ring was +0.0006 inch.

Chiarito, Patrick T.↗

NASA NTRS2009

Structural Dynamic Behavior of Wind Turbines

The structural dynamicist s areas of responsibility require interaction with most other members of the wind turbine project team. These responsibilities are to predict structural loads and deflections that will occur over the lifetime of the machine, ensure favorable dynamic responses through appropriate design and operational procedures, evaluate potential design improvements for their impact on dynamic loads and stability, and correlate load and control test data with design predictions. Load prediction has been a major concern in wind turbine designs to date, and it is perhaps the single most important task faced by the structural dynamics engineer. However, even if we were able to predict all loads perfectly, this in itself would not lead to an economic system. Reduction of dynamic loads, not merely a "design to loads" policy, is required to achieve a cost-effective design. The two processes of load prediction and structural design are highly interactive: loads and deflections must be known before designers and stress analysts can perform structural sizing, which in turn influences the loads through changes in stiffness and mass. Structural design identifies "hot spots" (local areas of high stress) that would benefit most from dynamic load alleviation. Convergence of this cycle leads to a turbine structure that is neither under-designed (which may result in structural failure), nor over-designed (which will lead to excessive weight and cost).

Thresher, Robert W.↗

NASA NTRS2008

Qualification Testing of Engineering Camera and Platinum Resistance Thermometer (PRT) Sensors for Mars Science Laboratory (MSL) Project under Extreme Temperatures to Assess Reliability and to Enhance Mission Assurance

Package Qualification and Verification (PQV) of advanced electronic packaging and interconnect technologies and various other types of qualification hardware for the Mars Exploration Rover/Mars Science Laboratory flight projects has been performed to enhance the mission assurance. The qualification of hardware (Engineering Camera and Platinum Resistance Thermometer, PRT) under extreme cold temperatures has been performed with reference to various project requirements. The flight-like packages, sensors, and subassemblies have been selected for the study to survive three times (3x) the total number of expected temperature cycles resulting from all environmental and operational exposures occurring over the life of the flight hardware including all relevant manufacturing, ground operations and mission phases. Qualification has been performed by subjecting above flight-like qual hardware to the environmental temperature extremes and assessing any structural failures or degradation in electrical performance due to either overstress or thermal cycle fatigue. Experiments of flight like hardware qualification test results have been described in this paper.

package reliability↗

NASA NTRS2009

Probabilistic Estimation of Critical Flaw Sizes in the Primary Structure Welds of the Ares I-X Launch Vehicle

The primary structure of the Ares I-X Upper Stage Simulator (USS) launch vehicle is constructed of welded mild steel plates. There is some concern over the possibility of structural failure due to welding flaws. It was considered critical to quantify the impact of uncertainties in residual stress, material porosity, applied loads, and material and crack growth properties on the reliability of the welds during its pre-flight and flight. A criterion--an existing maximum size crack at the weld toe must be smaller than the maximum allowable flaw size--was established to estimate the reliability of the welds. A spectrum of maximum allowable flaw sizes was developed for different possible combinations of all of the above listed variables by performing probabilistic crack growth analyses using the ANSYS finite element analysis code in conjunction with the NASGRO crack growth code. Two alternative methods were used to account for residual stresses: (1) The mean residual stress was assumed to be 41 ksi and a limit was set on the net section flow stress during crack propagation. The critical flaw size was determined by parametrically increasing the initial flaw size and detecting if this limit was exceeded during four complete flight cycles, and (2) The mean residual stress was assumed to be 49.6 ksi (the parent material s yield strength) and the net section flow stress limit was ignored. The critical flaw size was determined by parametrically increasing the initial flaw size and detecting if catastrophic crack growth occurred during four complete flight cycles. Both surface-crack models and through-crack models were utilized to characterize cracks in the weld toe.

Pai, Shantaram S.↗

NASA NTRS2011

Comparison of Adhesion and Retention Forces for Two Candidate Docking Seal Elastomers

To successfully mate two pressurized vehicles or structures in space, advanced seals are required at the interface to prevent the loss of breathable air to the vacuum of space. A critical part of the development testing of candidate seal designs was a verification of the integrity of the retaining mechanism that holds the silicone seal component to the structure. Failure to retain the elastomer seal during flight could liberate seal material in the event of high adhesive loads during undocking. This work presents an investigation of the force required to separate the elastomer from its metal counter-face surface during simulated undocking as well as a comparison to that force which was necessary to destructively remove the elastomer from its retaining device. Two silicone elastomers, Wacker 007-49524 and Esterline ELASA-401, were evaluated. During the course of the investigation, modifications were made to the retaining devices to determine if the modifications improved the force needed to destructively remove the seal. The tests were completed at the expected operating temperatures of -50, +23, and +75 C. Under the conditions investigated, the comparison indicated that the adhesion between the elastomer and the metal counter-face was significantly less than the force needed to forcibly remove the elastomer seal from its retainer, and no failure would be expected.

Hartzler, Brad D.↗

NASA NTRS2011

Measurements of Ground Acoustic Environments for Small Solid Rocket Motor Firings

Mobile launcher deck and tower are exposed to severe acoustic environments during launch. These environments, if not properly managed, can weaken ground support equipment and result in structure failure. The objectives of this study were: (1) Characterize the acoustic ground environment with and without water suppression systems. (2) Validate the ground acoustic prediction based on scaling of Saturn V data. and (3) Validate a semi-empirical acoustic analysis.

Vu, Bruce↗

NASA NTRS2003

Explicit Pore Pressure Material Model in Carbon-Cloth Phenolic

An explicit material model that uses predicted pressure in the pores of a carbon-cloth phenolic (CCP) composite has been developed. This model is intended to be used within a finite-element model to predict phenomena specific to CCP components of solid-fuel-rocket nozzles subjected to high operating temperatures and to mechanical stresses that can be great enough to cause structural failures. Phenomena that can be predicted with the help of this model include failures of specimens in restrained-thermal-growth (RTG) tests, pocketing erosion, and ply lifting

Gutierrez-Lemini, Danton↗

NASA NTRS2012

Fiber Bragg Grating Sensor System for Monitoring Smart Composite Aerospace Structures

Lightweight, electromagnetic interference (EMI) immune, fiber-optic, sensor- based structural health monitoring (SHM) will play an increasing role in aerospace structures ranging from aircraft wings to jet engine vanes. Fiber Bragg Grating (FBG) sensors for SHM include advanced signal processing, system and damage identification, and location and quantification algorithms. Potentially, the solution could be developed into an autonomous onboard system to inspect and perform non-destructive evaluation and SHM. A novel method has been developed to massively multiplex FBG sensors, supported by a parallel processing interrogator, which enables high sampling rates combined with highly distributed sensing (up to 96 sensors per system). The interrogation system comprises several subsystems. A broadband optical source subsystem (BOSS) and routing and interface module (RIM) send light from the interrogation system to a composite embedded FBG sensor matrix, which returns measurand-dependent wavelengths back to the interrogation system for measurement with subpicometer resolution. In particular, the returned wavelengths are channeled by the RIM to a photonic signal processing subsystem based on powerful optical chips, then passed through an optoelectronic interface to an analog post-detection electronics subsystem, digital post-detection electronics subsystem, and finally via a data interface to a computer. A range of composite structures has been fabricated with FBGs embedded. Stress tensile, bending, and dynamic strain tests were performed. The experimental work proved that the FBG sensors have a good level of accuracy in measuring the static response of the tested composite coupons (down to submicrostrain levels), the capability to detect and monitor dynamic loads, and the ability to detect defects in composites by a variety of methods including monitoring the decay time under different dynamic loading conditions. In addition to quasi-static and dynamic load monitoring, the system can capture acoustic emission events that can be a prelude to structural failure, as well as piezoactuator-induced ultrasonic Lamb-waves-based techniques as a basis for damage detection.

Moslehi, Behzad↗

NASA NTRS2012

Qualification of Engineering Camera for Long-Duration Deep Space Missions

Qualification and verification of advanced electronic packaging and interconnect technologies, and various other types of hardware elements for the Mars Exploration Rover s Spirit and Opportunity (MER)/Mars Science Laboratory (MSL) flight projects, has been performed to enhance the mission assurance. The qualification of hardware (engineering camera) under extreme cold temperatures has been performed with reference to various Mars-related project requirements. The flight-like packages, sensors, and subassemblies have been selected for the study to survive three times the total number of expected diurnal temperature cycles resulting from all environmental and operational exposures occurring over the life of the flight hardware, including all relevant manufacturing, ground operations, and mission phases. Qualification has been performed by subjecting above flight-like hardware to the environmental temperature extremes, and assessing any structural failures or degradation in electrical performance due to either overstress or thermal cycle fatigue. Engineering camera packaging designs, charge-coupled devices (CCDs), and temperature sensors were successfully qualified for MER and MSL per JPL design principles. Package failures were observed during qualification processes and the package redesigns were then made to enhance the reliability and subsequent mission assurance. These results show the technology certainly is promising for MSL, and especially for longterm extreme temperature missions to the extreme temperature conditions. The engineering camera has been completely qualified for the MSL project, with the proven ability to survive on Mars for 2010 sols, or 670 sols times three. Finally, the camera continued to be functional, even after 2010 thermal cycles.

Ramesham, Rajeshuni↗