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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Topic Modeling Tool for PeTaL (Periodic Table of Life)

A topic modeling tool is constructed for the purpose of providing insights from biology to the engineer within the framework of PeTaL (Periodic Table of Life). The machine learning text mining tools–latent Dirichlet allocation (LDA) and nonnegative matrix factorization (NMF) with Kullback-Leibler (KL) divergence—are used to provide topic clusters to the user. Topic clusters are the underlying themes of a paper. For the text modeling problem, NMF-KL is the equivalent of probabilistic latent semantic analysis. Both LDA and NMF-KL are top-performing modeling tools. These tools are used to identify biological specimens relevant to the user. Various organisms solve a particular survival problem in nature differently. The topic clusters allow people without domain expertise to find these cross-topic themes in the body of documents and then branch out and examine papers whose target organisms solve the engineer’s problem. Abstracts from the Journal of Experimental Biology were used as input for the clustering tool in addition to a curated set of articles for validation. The tool is able to accept alternate input sources.

Machine learning↗
NASA NTRS2017

Getting to the Heart of Cardiovascular Risk Assessment in Astronauts for Exploration Class Missions

Since the beginning of manned spaceflight, NASA has recognized the potential risk of cardiovascular decrements due to stressors in the space environment. Of particular concern is the effect of space radiation on cardiovascular disease since astronauts will be exposed to higher levels of galactic cosmic rays outside the Earth's protective magnetosphere. To date, only a few studies have examined the effects of heavy ion radiation on cardiovascular disease, and at lower, space-relevant doses, the association between radiation exposure and cardiovascular pathology is more varied and unclear. Furthermore, other spaceflight conditions such as microgravity, circadian shifts, and confinement stress pose unique challenges in estimating the health risks that can be attributed to exposure to ionizing radiations. In this work, we review age, cause of mortality, and radiation exposure amongst early NASA astronauts in selection groups and discuss the limitations of assessing such a cohort when attempting to characterize the risk of space flight, including stressors such as space radiation and microgravity exposure, on cardiovascular health. METHODS: NASA astronauts in selection groups 1-7 were chosen and the comparison population was white men of the same birth cohort as drawn from data from the CDC Wonder Database and CDC National Center for Health Statistics Life Tables. Cause of death information was obtained from the Lifetime Surveillance of Astronaut Health program and deceased astronauts were classified based on ICD-10 codes: ischemic heart disease (IHD), stroke, cancer, acute occupational events, non-NASA accidents, and other/unknown. Expected years of life left and expected age at death were calculated for the cohort. RESULTS AND CONCLUSIONS: There were 32 deaths in this early astronaut population, 12 of which were due to accidents or acute occupational events that impacted lifespan considerably. The average age at death from these causes is 30 years lower than the average expected ~70 years of age in the general population. Remarkably, all 41 living early astronauts outlived our calculated expected age at death for members of their birth cohort; furthermore, 13 of the 20 deceased astronauts who did not die in NASA/non-NASA accidents exceeded this age. There was no difference in IHD between the astronaut cohort and the comparison population; therefore, it is not possible to associate IHD mortality with radiation in that astronaut cohort. As NASA looks toward future exploration-class missions, early astronaut cohorts provide a convenient option for assessing these risks and for developing mitigation strategies. However, many challenges still exist when assessing such limited evidence, including small cohort size, health and lifestyle confounders (such as smoking and drinking), the high accident mortality rate, and the fact that many of these astronauts are still alive, outliving many of their birth-cohort peers. Future analysis should include a longitudinal study, monitoring cases as they occur in the cohort. As this cohort is currently followed-up over time, and as more IHD cases are anticipated in a population of this age, this type of study is not as resource-intensive as would normally be the case.

Elgart, S. R.↗
NASA NTRS2010

Space Radiation Heart Disease Risk Estimates for Lunar and Mars Missions

The NASA Space Radiation Program performs research on the risks of late effects from space radiation for cancer, neurological disorders, cataracts, and heart disease. For mortality risks, an aggregate over all risks should be considered as well as projection of the life loss per radiation induced death. We report on a triple detriment life-table approach to combine cancer and heart disease risks. Epidemiology results show extensive heterogeneity between populations for distinct components of the overall heart disease risks including hypertension, ischaemic heart disease, stroke, and cerebrovascular diseases. We report on an update to our previous heart disease estimates for Heart disease (ICD9 390-429) and Stroke (ICD9 430-438), and other sub-groups using recent meta-analysis results for various exposed radiation cohorts to low LET radiation. Results for multiplicative and additive risk transfer models are considered using baseline rates for US males and female. Uncertainty analysis indicated heart mortality risks as low as zero, assuming a threshold dose for deterministic effects, and projections approaching one-third of the overall cancer risk. Medan life-loss per death estimates were significantly less than that of solid cancer and leukemias. Critical research questions to improve risks estimates for heart disease are distinctions in mechanisms at high doses (>2 Gy) and low to moderate doses (<2 Gy), and data and basic understanding of radiation doserate and quality effects, and individual sensitivity.

Cucinotta, Francis A.↗
DOE OSTI2025

The Impact of Demographic Lifecycle States on Time to Vehicle Purchase: Insights from the Panel Study of Income Dynamics

This study examines the impact of demographic lifecycle stages on the timing of vehicle purchases, using data from the Panel Study of Income Dynamics from 1999 to 2021. Survival analysis was employed to model the duration until households purchase vehicles, incorporating key lifecycle variables such as age, employment status, marital status, childbirth, home ownership, and the presence of school-going children. The life table results indicate that early adulthood (ages 20–35) is the prime period for vehicle acquisition, with significant peaks around ages 25 to 30. Additionally, the instantaneous hazard of purchasing a vehicle is highest in the late 40s and early 50s. According to the Cox proportional hazards model, employment, marital status, and home ownership significantly increase the likelihood of purchasing a vehicle, while living in multi-unit dwellings decreases it. Interaction effects reveal that married individuals with employed spouses are substantially more likely to purchase vehicles. In conclusion, this study serves as a steppingstone toward integrating demographic lifecycle analysis into car ownership modeling that better reflects real-world scenarios and increases the accuracy of policy and strategic planning.

Car ownership↗
NASA NTRS2007

Finding Uncertainties that Cause the Age Dependence of Dose Limits to Be Immature

Space radiation permissible exposure limits (PEL) are intended to set acceptable levels of cancer risks, and avoid any clinical significant non-cancer effects. The 1989 recommendation of the National Council of Radiation Protection and Measurements (NCRP) recommended a strong age dependence of dose limits that departed drastically from the then mature 1970 dose limits recommendations from the National Academy of Science, which were independent of age. In 2000, the NCRP recommended revised limits that showed a similar trend of risk with age to the 1989 report. In this model, the cancer risk per Sv varies by more than 2-fold for ages between 30- and 50-yr. Therefore for galactic cosmic rays exposure, astronaut age has a larger influence on risk then radiation shielding mass or material composition, vehicle propulsion method, or position in the solar cycle. For considering the control of mission costs and resources, the possibility of using astronaut age as a trade variable in mission design could be considered. However, the uncertainties in describing the age dependence on risk have not been fully explored. We discuss biological factors that influence the age dependence of radiation risks, including susceptibility, expression and latency, and radiation quality. These factors depend not only on the individual s age, but also their genetic sensitivity and interaction with other environmental factors. Epidemiological data is limited in describing the age dependence on risk. The 2005, BEIR VII report recommends an age dependence for cancer risk attributable solely to the life-table disagreeing strongly with the NCRP model. However, BEIR VII also noted the limited power of human data for concomitantly describing both age and age after exposure dependences of cancer risks. Many experimental studies have shown that high LET radiation (e.g., high charge and energy (HZE) nuclei and neutrons) display reduced latency compared to low LET radiation, suggesting distinct biological factors are important. We discuss potential molecular mechanisms that would influence the age dependence of radiation risks. A probability distribution function for the uncertainties in age-dependence of risk models is described and predictions for Mars missions discussed. Our report suggests that theoretical considerations based on new experimental studies are needed to ensure the correct age dependence in space radiation risk models and the resulting Astronaut PEL.

Cucinotta, Francis A.↗
NASA NTRS2011

Sensitivity Analysis of Median Lifetime on Radiation Risks Estimates for Cancer and Circulatory Disease amongst Never-Smokers

Radiation risks are estimated in a competing risk formalism where age or time after exposure estimates of increased risks for cancer and circulatory diseases are folded with a probability to survive to a given age. The survival function, also called the life-table, changes with calendar year, gender, smoking status and other demographic variables. An outstanding problem in risk estimation is the method of risk transfer between exposed populations and a second population where risks are to be estimated. Approaches used to transfer risks are based on: 1) Multiplicative risk transfer models -proportional to background disease rates. 2) Additive risk transfer model -risks independent of background rates. In addition, a Mixture model is often considered where the multiplicative and additive transfer assumptions are given weighted contributions. We studied the influence of the survival probability on the risk of exposure induced cancer and circulatory disease morbidity and mortality in the Multiplicative transfer model and the Mixture model. Risks for never-smokers (NS) compared to the average U.S. population are estimated to be reduced between 30% and 60% dependent on model assumptions. Lung cancer is the major contributor to the reduction for NS, with additional contributions from circulatory diseases and cancers of the stomach, liver, bladder, oral cavity, esophagus, colon, a portion of the solid cancer remainder, and leukemia. Greater improvements in risk estimates for NS s are possible, and would be dependent on improved understanding of risk transfer models, and elucidating the role of space radiation on the various stages of disease formation (e.g. initiation, promotion, and progression).

Chappell, Lori J.↗
NASA NTRS2018

Biocene 2018 - Welcome to the Period of New Life

Biocene is the period of new life. When our descendants look back at this period in time, they will see evidence, in the geologic and electronic record, of anthropic climate change, growing population, and scarcity of resources. But they will also see the rebirth of human ingenuity as we overcame the challenges that faced us through nature-inspired exploration. The Periodic Table of Life (PeTaL) is a proposed tool and open source framework that uses artificial intelligence to aid in the systematic inquiry of biology for its application to human systems. This presentation defines the PeTaL concept and workflow. Biomimicry, biophysics, biomimetics, bionics and numerous other terms refer to the use of biology and biological principles to inform practices in other disciplines. For the most part, the domain of inquiry in these fields have been confined to extant biological models with the proponents of biomimicry often citing the evolutionary success of extant organisms relative to extinct ones. The primary objective of this paper is to expand the domain of inquiry for human processes that seek to model those that are, were or could be found in nature with examples that relate to the field of aerospace and to spur development of tools that can work together to accelerate the use of artificial intelligence in problem solving. Specifically specialized fields such as paleomimesis, anthropomimesis and physioteleology are proposed in conjunction with artificial evolution. Blockchain technology may be vital in allowing open source design tools such as PeTaL to democratize design and yet protect intellectual property. The overarching philosophy outlined here can be thought of as physiomimetics, a holistic and systematic way of learning from natural history. The backbone of PeTaL integrates an unstructured database with an ontological model consisting of function, morphology, environment, state of matter and ecosystem. Tools include text classification, thesaurus, data visualization, and analysis. Applications of PeTaL include guiding human space exploration, understanding human and geological history, and discovering new or extinct life.

Biocene↗
NASA NTRS2018

Characterization and Analysis of Phoca Vitulina, Zalophus Californianus and Mirounga Angustirostris Vibrissae

Vibrissae of Phoca Vitulina (harbor seal) and Mirounga Angustirostris (elephant seal) possess undulations along their length. Harbor seal vibrissae have shown potential to reduce vortex induced vibrations and reduce drag compared to cylinders and ellipses. The exact geometry of the whiskers has not been well documented and the parameters that are responsible for the reduction in drag and vortex induced vibrations have not been characterized. Samples of six harbor seal vibrissae, six elephant seal vibrissae and six California sea lion (Zalophus californianus) vibrissae were collected from the Marine Mammal Center in California. The objectives of this study were to (1) Compare measurement techniques for digitizing and extracting parameters of the seal whiskers for the PeTaL (Periodic Table of Life) database. CT scanning, microscopy and 3D scanning techniques were compared. (2) Compare aerodynamic characteristics of a representative harbor seal whisker, elephant seal whisker, California sea lion whisker and ellipse at Re = 12000 and Re = 23000 based on major axis and free stream velocity. The data (in appendices) is available to compare CFD models or for further experimental validation, (3) Show close up images of whiskers and look for surface roughness effects. Variations in the seven parameters of the seal whisker were observed that may either be a feature of the vibration reduction mechanism or a result of natural variation. It is hypothesized that six parameters are sufficient to characterize seal whiskers based on analytic fitting. The drag coefficient of harbor seal whiskers examined in this study were found to be 25 percent lower than that of an ellipse with comparable major and minor axis lengths at Reynolds number of 12000. The dissipation length scale was found to be larger for seal whiskers. Potential applications of seal whisker morphology for aerospace are discussed. Roughness is not thought to play a factor in seal hydrodynamics.

Shyam, Vikram↗
NASA NTRS2008

Interference Fit Life Factors for Roller Bearings

The effect of hoop stresses in reducing cylindrical roller bearing fatigue life was determined for various classes of inner ring interference fit. Calculations were performed for up to seven interference fit classes for each of ten bearing sizes. Each fit was taken at tightest, average and loosest values within the fit class for RBEC-5 tolerance, thus requiring 486 separate analyses. The hoop stresses were superimposed on the Hertzian principal stresses created by the applied radial load to calculate roller bearing fatigue life. The method was developed through a series of equations to calculate the life reduction for cylindrical roller bearings based on interference fit. All calculated lives are for zero initial bearing internal clearance. Any reduction in bearing clearance due to interference fit was compensated by increasing the initial (unmounted) clearance. Results are presented as tables and charts of life factors for bearings with light, moderate and heavy loads and interference fits ranging from extremely light to extremely heavy and for bearing accuracy class RBEC 5 (ISO class 5). Interference fits on the inner bearing ring of a cylindrical roller bearing can significantly reduce bearing fatigue life. In general, life factors are smaller (lower life) for bearings running under light load where the unfactored life is highest. The various bearing series within a particular bore size had almost identical interference fit life factors for a particular fit. The tightest fit at the high end of the RBEC-5 tolerance band defined in ANSI/ABMA shaft fit tables produces a life factor of approximately 0.40 for an inner-race maximum Hertz stress of 1200 MPa (175 ksi) and a life factor of 0.60 for an inner-race maximum Hertz stress of 2200 MPa (320 ksi). Interference fits also impact the maximum Hertz stress-life relation.

Oswald, Fred B.↗
NASA NTRS2022

Mars 2020 Perseverance Rover SHERLOC Instrument Isolation System

The NASA Jet Propulsion Laboratory (JPL) successfully landed the Mars 2020 Perseverance Rover at Jezero Crater on the Martian surface. Perseverance’s main mission objective is to cache Martian rock and regolith samples in hermetically sealed tubes to be brought back to Earth by future missions. To achieve this goal the rover is equipped with a 2-meter-long Robotic Arm (RA) which manipulates the Turret to interact with the surface. The Turret is comprised of science instruments and tools that enable surface sampling and science. The backbone of the Turret hardware is the Rotary Percussive Coring Drill. The science instruments, which are directly mounted to the structural housing of this drill, must be able to withstand not only the launch and entry, descent and landing (EDL) loads of the vehicle but also the dynamic percussive environment, induced by the drill throughout surface operations. This paper discusses the technical hardware design, development and testing of a vibration isolation system to protect the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Instrument from these dynamic environments. The hardware design aspect of this problem was limited by both size and mass constraints. The Turret is tightly configured and the physical space in which hardware can reside is restricted due to multiple axes of surface interaction points. Another driving requirement is the extreme range of thermal non-operational environment from -135C to +90C. This, in addition to SHERLOC being a heavier instrument than previously integrated on a turret, made the use of isolation systems employed on previous rover missions problematic. The final design incorporates custom wire mesh springs preloaded within titanium hexapod struts equipped with flexure ends. Custom versions of commercially available wire mesh springs were designed and tested. These custom springs differed in dimension, density and stiffness from the off the shelf options. The newly designed springs went through various stages of flight acceptance testing. Detailed physics-based modeling to understand what loads the isolation system would experience was used to define the test conditions for the springs and entire isolation subsystem. The testing program developed around this was extensive to fully characterize the isolation performance over cleanliness levels, temperature and life. Another major aspect of this work was developing a method of replicating the drill’s percussive environment for performance and life testing of Turret mounted hardware. Attaching the instrument to an operating drill for testing was not a viable option. A method of using a Highly Accelerated Life Test (HALT) table was developed and applied across the project as the most representative and tunable option to physically simulate this new environment. This method, along with launch environment random vibration testing, was used to build an entire dynamic qualification and flight hardware test program. The results of the design, modeling, testing and analysis of the SHERLOC Isolation System is described throughout the following paper.

Krafchak, Todd↗
NASA NTRS2010

Interference-Fit Life Factors for Ball Bearings

The effect of hoop stresses on the rolling-element fatigue life of angular-contact and deep-groove ball bearings was determined for common inner-ring interference fits at the ABEC-5 tolerance level. The analysis was applied to over 1150 bearing configurations and load cases. Hoop stresses were superimposed on the Hertzian principal stresses created by the applied bearing load to calculate the inner-race maximum shearing stress. The resulting fatigue life of the bearing was recalculated through a series of equations. The reduction in the fatigue life is presented as life factors that are applied to the unfactored bearing life. The life factors found in this study ranged from 1.00 (no life reduction)--where there was no net interface pressure--to a worst case of 0.38 (a 62-percent life reduction). For a given interference fit, the reduction in life is different for angular-contact and deep-groove ball bearings. Interference fits also affect the maximum Hertz stress-life relation. Experimental data of Czyzewski, showing the effect of interference fit on rolling-element fatigue life, were reanalyzed to determine the shear stress-life exponent. The Czyzewski data shear stress-life exponent c equals 8.77, compared with the assumed value of 9. Results are presented as tables and charts of life factors for angular-contact and deep-groove ball bearings with light, normal, and heavy loads and interference fits ranging from extremely light to extremely heavy.

Oswald, Fred B.↗
NASA NTRS2009

Interference-Fit Life Factors for Roller Bearings

The effect of hoop stresses in reducing cylindrical roller bearing fatigue life was determined for various classes of inner-ring interference fit. Calculations were performed for up to 7 fit classes for each of 10 bearing sizes. The hoop stresses were superimposed on the Hertzian principal stresses created by the applied radial load to calculate roller bearing fatigue life. A method was developed through a series of equations to calculate the life reduction for cylindrical roller bearings. All calculated lives are for zero initial internal clearance. Any reduction in bearing clearance due to interference fit would be compensated by increasing the initial (unmounted) clearance. Results are presented as tables and charts of life factors for bearings with light, moderate, and heavy loads and interference fits ranging from extremely light to extremely heavy for bearing accuracy class RBEC-5 (ISO class 5). Interference fits on the inner ring of a cylindrical roller bearing can significantly reduce bearing fatigue life. In general, life factors are smaller (lower life) for bearings running under light load where the unfactored life is highest. The various bearing series within a particular bore size had almost identical interference-fit life factors for a particular fit. The tightest fit at the high end of the tolerance band produces a life factor of approximately 0.40 for an inner-race maximum Hertz stress of 1200 MPa (175 ksi) and a life factor of 0.60 for an inner-race maximum Hertz stress of 2200 MPa (320 ksi). Interference fits also impact the maximum Hertz stress-life relation.

Oswald, Fred B.↗
NASA NTRS1988

Organic matter in carbonaceous chondrites, planetary satellites, asteroids and comets

A detailed review is given of the organic compounds found in carbonaceous chondrite meteorites, especially the Murchison meteorite, and detected spectroscopically in other solar-system objects. The chemical processes by which the organic compounds could have formed in the early solar system and the conditions required for these processes are discussed, taking into account the possible alteration of the compounds during the lifetime of the meteoroid. Also considered are the implications for prebiotic evolution and the origin of life. Diagrams, graphs, and tables of numerical data are provided.

Cronin, John R.↗
NASA NTRS2000

Environmental Exposure Conditions for Teflon FEP on the Hubble Space Telescope Investigated

The Hubble Space Telescope (HST) was launched into low Earth orbit on April 24,1990. During the first servicing mission in December 1993 (3.6 years after launch), multilayer insulation (MLI) blankets were retrieved from the two magnetic sensing systems located on the light shield. Retrieval of one of the solar arrays during this mission also provided MLI blanket material from the solar array drive arm. These MLI materials were analyzed in ground-based facilities, and results indicate that the space-facing outer layer of the MLI, aluminized Teflon FEP (DuPont; fluorinated ethylene propylene), was beginning to degrade. Close inspection of the FEP revealed through-the-thickness cracks in areas with the highest solar exposure and stress concentration. During the second servicing mission in February 1997 (6.8 years after launch), astronauts observed and documented severe cracking in the outer layer of the MLI blankets on both the solar-facing and anti-solar-facing surfaces. During this second mission, some material from the outer layer of the light shield MLI was retrieved and subsequently analyzed in ground-based facilities. After the second servicing mission, a Failure Review Board was convened by NASA Goddard Space Flight Center to address the MLI degradation problem on HST. Members of the Electro-Physics Branch of the NASA Glenn Research Center at Lewis Field participated on this board. To determine possible degradation mechanisms, board researchers needed to consider all environmental constituents to which the FEP MLI surfaces were exposed. On the basis of measurements, models, and predictions, environmental exposure conditions for FEP surfaces on HST were estimated for various time periods from launch in 1990 through 2010, the planned end-of-life for HST. The table summarizes these data including the number and temperature ranges of thermal cycles; equivalent Sun hours; fluence and absorbed radiation dose from solar event x rays; fluence and absorbed dose from solar wind protons and electrons trapped in Earth s magnetic field; fluence of plasma electrons and protons; and atomic oxygen fluence.

Dever, Joyce A.↗
NASA NTRS2004

Subsystem Details for the Fiscal Year 2004 Advanced Life Support Research and Technology Development Metric

This document provides values at the assembly level for the subsystems described in the Fiscal Year 2004 Advanced Life Support Research and Technology Development Metric (Hanford, 2004). Hanford (2004) summarizes the subordinate computational values for the Advanced Life Support Research and Technology Development (ALS R&TD) Metric at the subsystem level, while this manuscript provides a summary at the assembly level. Hanford (2004) lists mass, volume, power, cooling, and crewtime for each mission examined by the ALS R&TD Metric according to the nominal organization for the Advanced Life Support (ALS) elements. The values in the tables below, Table 2.1 through Table 2.8, list the assemblies, using the organization and names within the Advanced Life Support Sizing Analysis Tool (ALSSAT) for each ALS element. These tables specifically detail mass, volume, power, cooling, and crewtime. Additionally, mass and volume are designated in terms of values associated with initial hardware and resupplied hardware just as they are within ALSSAT. The overall subsystem values are listed on the line following each subsystem entry. These values are consistent with those reported in Hanford (2004) for each listed mission. Any deviations between these values and those in Hanford (2004) arise from differences in when individual numerical values are rounded within each report, and therefore the resulting minor differences should not concern even a careful reader. Hanford (2004) u es the uni ts kW(sub e) and kW(sub th) for power and cooling, respectively, while the nomenclature below uses W(sub e) and W(sub th), which is consistent with the native units within ALSSAT. The assemblies, as specified within ALSSAT, are listed in bold below their respective subsystems. When recognizable assembly components are not listed within ALSSAT, a summary of the assembly is provided on the same line as the entry for the assembly. Assemblies with one or more recognizable components are further described by the indented entries below them. See Yeh, et al. (2002), Yeh, et al. (2003), and Yeh, et al. (2004) for details about ALSSAT organization. Except for the dry food mass listed within the Food Processing, Packaging, and Storage within the Food Subsystem, total values for assemblies would be the sum of their components. The Dry Food Mass, however, is that portion of the food system that was neglected during the computation of the Fiscal Year 2004 ALS R&TD Metric. It is listed here to provide a reference, but it is otherwise ignored in the overall totals. See Hanford (2004) for details of this process and supporting rationale. When applicable, the technology label from ALSSAT is listed in the second column, and the associated abbreviations are listed below in Section 4. For more details of the technologies assumed for each mission, please see Hanford (2004) for descriptions of each subsystem and an overall life support system schematic.

Hanford, Anthony J.↗
NASA NTRS1975

High-Temperature, Low-Cycle Fatigue of Copper-Base Alloys for Rocket Nozzles. Part 1: Data Summary for Materials Tested in Prior Programs

A more detailed analysis of the results obtained in 188 previously reported low-cycle fatigue tests of various candidate materials for regeneratively-cooled, reusable rocket nozzle liners was reported. Plots of load range versus cycles were reported for each test along with a stress-strain hysteresis loop near half-life. In addition, a summary table was provided to compare N5 (cycles to a five percent load range drop) and Nf (cycles to complete specimen separation) values for each test.

Conway, J. B.↗