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NASA NTRS2009

Defining the Physiological Factors that Contribute to Postflight Changes in Functional Performance

Astronauts experience alterations in multiple physiological systems due to exposure to the microgravity conditions of space flight. These physiological changes include sensorimotor disturbances, cardiovascular deconditioning and loss of muscle mass and strength. These changes might affect the ability of crewmembers to perform critical mission tasks immediately after landing on lunar and Martian surfaces. To date, changes in functional performance have not been systematically studied or correlated with physiological changes. To understand how changes in physiological function impact functional performance an interdisciplinary pre/postflight testing regimen (Functional Task Test, FTT) has been developed that systematically evaluates both astronaut postflight functional performance and related physiological changes. The overall objective of the FTT is to identify the key underlying physiological factors that contribute to performance of functional tests that are representative of critical mission tasks. This study will identify which physiological systems contribute the most to impaired performance on each functional test. This will allow us to identify the physiological systems that play the largest role in decrement in functional performance. Using this information we can then design and implement countermeasures that specifically target the physiological systems most responsible for the altered functional performance associated with space flight. The functional test battery was designed to address high priority tasks identified by the Constellation program as critical for mission success. The set of functional tests making up the FTT include the: 1) Seat Egress and Walk Test, 2) Ladder Climb Test, 3) Recovery from Fall/Stand Test, 4) Rock Translation Test, 5) Jump Down Test, 6) Torque Generation Test, and 7) Construction Activity Board Test. Corresponding physiological measures include assessments of postural and gait control, dynamic visual acuity, fine motor control, plasma volume, orthostatic intolerance, upper and lower body muscle strength, power, fatigue, control and neuromuscular drive. Crewmembers perform both functional and physiological tests before and after short (Shuttle) and long-duration (ISS) space flight. Data are collected on R+0 (Shuttle only), R+1, R+6 and R+30.

Bloomberg, J. J.↗
NASA NTRS1996

Evaluating Fatigue in Operational Settings: The NASA Ames Fatigue Countermeasures Program

In response to a 1980 Congressional request, NASA Ames initiated a program to examine fatigue in flight operations. The Program objectives are to examine fatigue, sleep loss, and circadian disruption in flight operations, determine the effects of these factors on flight crew performance, and the development of fatigue countermeasures. The NASA Ames Fatigue Countermeasures Program conducts controlled laboratory experiments, full-mission flight simulations, and field studies. A range of subjective, behavioral, performance, physiological, and environmental measures are used depending on study objectives. The Program has developed substantial expertise in gathering data during actual flight operations and in other work settings. This has required the development of ambulatory and other measures that can be carried throughout the world and used at 41,000 feet in aircraft cockpits. The NASA Ames Fatigue Countermeasures Program has examined fatigue in shorthaul, longhaul, overnight cargo, and helicopter operations. A recent study of planned cockpit rest periods demonstrated the effectiveness of a brief inflight nap to improve pilot performance and alertness. This study involved inflight reaction time/vigilance performance testing and EEG/EOG measures of physiological alertness. The NASA Ames Fatigue Countermeasures Program has applied scientific findings to the development of education and training materials on fatigue countermeasures, input to federal regulatory activities on pilot flight, duty, and rest requirements, and support of National Transportation Safety Board accident investigations. Current activities are examining fatigue in nonaugmented longhaul flights, regional/commuter flight operations, corporate/business aviation, and psychophysiological variables related to performance.

Rosekind, Mark R.↗
NASA NTRS2007

Capabilities and History of NASA Marshall Space Flight Center's Hydrogen Test Facility

The Hydrogen Test Facility (HTF) has conducted mechanical testing for aerospace materials at NASA's Marshall Space Flight Center for many years. One of the first facilities of its kind to run high-pressure cryogenic permeability tests in liquid hydrogen, HTF is now characterized as a unique national resource capable of overcoming hazardous conditions to perform tests directly in various hydrogen environments. At HTF, custom test systems are operated in eight structurally reinforced test cells from 0 to 68,948 kPa (0 to 10,000 psi) at -253 to 982 C (--423 to 1800 F) in hydrogen, air, helium, and nitrogen, with other environments available upon request. Standard mechanical procedures include compression, fatigue crack growth rate, four-point bend, high/low cycle fatigue, fracture toughness, shear, strain-to-crack, and tensile testing. Cryogenic permeability and thermal conductivity and gaseous creep testing are offered, as well as simulated service under different combinations of operating environment(s), stress, pressure, and ambient-to-extreme temperatures. Advanced tests are routinely developed upon demand, and special component testing is also available. Current efforts include the renovation of two high-pressure gaseous test cells to generate data for a J-2X engine designed for Constellation's Ares I and V vehicles. In the past, HTF has supported other critical NASA programs, such as Apollo, Space Shuttle, and Next Generation Launch Technologies. During the 1990's, hundreds of tests were conducted in liquid hydrogen and liquid nitrogen during development of the Space Shuttle's super lightweight tank, which provided the thrust required to achieve low Earth orbit for the International Space Station. This facility was designed and built in 1963. Originally called the Low Temperature Test Facility, it became known as the Cryogenic Test Facility in the late 1980's and HTF in the early 1990's.

Malone, T. W.↗
NASA NTRS1972

Space shuttle orbiter windshield system design and test

The development and testing of primary structural elements that are necessary to design a windshield system for the space shuttle orbiter are summarized. The elements include the outer (heat shield) panes, the inner pressure panes, the seals for both panes, and components of both window frames. One test article representing a pressure pane, including frames and seals, was tested under two sets of conditions. One set represented 100 mission cycles with temperature and pressure typical of those exerted on the innermost pane of the three-pane window system, and the second set represented 100 mission cycles with temperature and pressure typical of those exerted on a middle pane. A second test article representing an outer (heat sheild) pane was tested to conditions of 120 entry cycles, which equates to 100 entry cycles plus sufficient fatigue on the pane to account for 100 boost cycles. All elements of the design survived the test conditions in good condition. Window system for the shuttle orbiter vehicle.

Hayashida, K.↗
NASA NTRS1972

Reevaluation of the stress-life relation in rolling-element bearings

Four groups of 12.7 millimeter diameter vacuum-degassed AISI 52100 balls were tested, each at a maximum Hertz stress in the range of 4.5 times 10 to 9th power to 6.0 times 10 to 9th power N/m2. Tests were run in the five-ball fatigue tester at a contact angle of 30 deg and a shaft speed of 10,000 rpm. The 10 percent fatigue lives at the four stress levels indicated that fatigue life is inversely proportional to maximum Hertz stress raised to the power of 12. This result agrees with a survey of the literature which suggests that a stress-life exponent of approximately 12 is typical of vacuum-processed bearing steels rather than the exponent of 9 which has been generally accepted by the bearing industry.

Parker, R. J.↗
NASA NTRS1976

Program definition and preliminary results of a long-term evaluation program of advanced composites for supersonic cruise aircraft applications

Advanced composites will play a key role in the development of the technology required for the design and fabrication of future supersonic vehicles. A program is in progress to determine the time-temperature-stress capabilities of several high-temperature composite materials. Tests included in this study are thermal aging, ambient aging, fatigue, creep, fracture, tensile, and real-time flight-simulation exposure. The program has two parts. The first includes all the material-property determinations and aging and simulation exposures up through 10,000 h. The second continues these tests up to 50,000 cumulative h. The program is currently in the midst of the 10,000-h phase. Some of the results obtained to date and the status of the various tests are discussed.

Kerr, J. R.↗
NASA NTRS1977

Fatigue criterion for the design of rotating shafts under combined stress

A revised approach to the design of transmission shafting which considers the flexure fatigue characteristics of the shaft material under combined cyclic bending and static torsion stress is presented. A fatigue failure relation, corroborated by published combined stress test data, is presented which shows an elliptical variation of reversed bending endurance strength with static torsional stress. From this elliptical failure relations, a design formula for computing the diameter of rotating solid shafts under the most common condition of loading is developed.

Loewenthal, S. H.↗
NASA NTRS1977

Manufacture and engine test of advanced oxide dispersion strengthened alloy turbine vanes

Oxide-Dispersion-strengthened (ODS) Ni-Cr-Al alloy systems were exploited for turbine engine vanes which would be used for the space shuttle thermal protection system. Available commercial and developmental advanced ODS alloys were evaluated, and three were selected based on established vane property goals and manufacturing criteria. The selected alloys were evaluated in an engine test. Candidate alloys were screened by strength, thermal fatigue resistance, oxidation and sulfidation resistance. The Ni-16Cr (3 to 5)Al-ThO2 system was identified as having attractive high temperature oxidation resistance. Subsequent work also indicated exceptional sulfidation resistance for these alloys.

Bailey, P. G.↗
NASA NTRS1980

Multi-Parameter Yield Zone Model for Predicting Spectrum Crack Growth

A systematic technique is presented for modeling crack growth load interaction effects due to spectrum loading. The Multi-Parameter Yield Zone (MPYZ) model accounts for crack growth retardation, acceleration, and underload effects. The load interactions are attributed to the residual stress intensity due to the plastic deformation at the crack tip. Fatigue crack growth was predicted and compared with test data for a variety of spectrum loadings.

Johnson, W. S.↗
NASA NTRS1983

Stress-corrosion behavior of aluminum-lithium alloys in aqueous environments

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

Pizzo, P. P.↗
NASA NTRS1984

Stress-corrosion behavior of aluminum-lithium alloys in aqueous salt environments

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg; two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

Pizzo, P. P.↗
NASA NTRS1984

Methods for assessing the structural reliability of brittle materials

Failure from contact-induced surface flaws is considered along with controlled indentation flaws for construction of toughness and fatigue master maps, fatigue properties of ceramics with natural and controlled flaws, and a statistical analysis of size and stress state effects on the strength of an alumina ceramic. Attention is also given to dynamic and static fatigue of a machinable glass ceramic, the effect of multiregion crack growth on proof testing, and a fracture mechanics analysis of defect sizes. Other topics explored are related to the effect of temperature and humidity on delayed failure of optical glass fibers, subthreshold indentation flaws in the study of fatigue properties of ultrahigh-strength glass, the lifetime prediction for hot-pressed silicon nitride at high temperatures, static fatigue in high-performance ceramics, and requirements for flexure testing of brittle materials.

Freiman, S. W.↗
NASA NTRS1985

Wide-range displacement expressions for standard fracture mechanics specimens

Wide-range algebraic expressions for the displacement of cracked fracture mechanics specimens are developed. For each specimen two equations are given: one for the displacement as a function of crack length, the other for crack length as a function of displacement. All the specimens that appear in ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399) are represented in addition to the crack mouth displacement for a pure bending specimen. For the compact tension sample and the disk-shaped compact tension sample, the displacement at the crack mouth and at the load line are both considered. Only the crack mouth displacements for the arc-shaped tension samples are presented. The agreement between the displacements or crack lengths predicted by the various equations and the corresponding numerical data from which they were developed are nominally about 3 percent or better. These expressions should be useful in all types of fracture testing including fracture toughness, K-resistance, and fatigue crack growth.

Kapp, J. A.↗
NASA NTRS1988

Constitutive response of Rene 80 under thermal mechanical loads

The applicability of a classical constitutive model for stress-strain analysis of a nickel base superalloy, Rene' 80, in the gas turbine thermomechanical fatigue (TMF) environment is examined. A variety of tests were conducted to generate basic material data and to investigate the material response under cyclic thermomechanical loading. Isothermal stress-strain data were acquired at a variety of strain rates over the TMF temperature range. Creep curves were examined at 2 temperature ranges, 871 to 982 C and 760 to 871 C. The results provide optimism on the ability of the classical constitutive model for high temperature applications.

Kim, K. S.↗
NASA NTRS1992

Delivery of cardiopulmonary resuscitation in the microgravity environment

The microgravity environment presents several challenges for delivering effective cardiopulmonary resuscitation (CPR). Chest compressions must be driven by muscular force rather than by the weight of the rescuer's upper torso. Airway stabilization is influenced by the neutral body posture. Rescuers will consist of crew members of varying sizes and degrees of physical deconditioning from space flight. Several methods of CPR designed to accommodate these factors were tested in the one G environment, in parabolic flight, and on a recent shuttle flight. Methods: Utilizing study participants of varying sizes, different techniques of CPR delivery were evaluated using a recording CPR manikin to assess adequacy of compressive force and frequency. Under conditions of parabolic flight, methods tested included conventional positioning of rescuer and victim, free floating 'Heimlich type' compressions, straddling the patient with active and passive restraints, and utilizing a mechanical cardiac compression assist device (CCAD). Multiple restrain systems and ventilation methods were also assessed. Results: Delivery of effective CPR was possible in all configurations tested. Reliance on muscular force alone was quickly fatiguing to the rescuer. Effectiveness of CPR was dependent on technique, adequate restraint of the rescuer and patient, and rescuer size and preference. Free floating CPR was adequate but rapidly fatiguing. The CCAD was able to provide adequate compressive force but positioning was problematic. Conclusions: Delivery of effective CPR in microgravity will be dependent on adequate resuer and patient restraint, technique, and rescuer size and preference. Free floating CPR may be employed as a stop gap method until patient restraint is available. Development of an adequate CCAD would be desirable to compensate for the effects of deconditioning.

Barratt, M. R.↗
NASA NTRS1997

Fatigue-Life Prediction Methodology Using Small-Crack Theory

This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using 'small-crack theory' for various materials and loading conditions. Crack-tip constraint factors, to account for three-dimensional state-of-stress effects, were selected to correlate large-crack growth rate data as a function of the effective-stress-intensity factor range (delta K(eff)) under constant-amplitude loading. Some modifications to the delta k(eff)-rate relations were needed in the near-threshold regime to fit measured small-crack growth rate behavior and fatigue endurance limits. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens made of two aluminum alloys and a steel under constant-amplitude and spectrum loading. Fatigue lives were calculated using the crack-growth relations and microstructural features like those that initiated cracks for the aluminum alloys and steel for edge-notched specimens. An equivalent-initial-flaw-size concept was used to calculate fatigue lives in other cases. Results from the tests and analyses agreed well.

Newmann, James C., Jr.↗