SEARCH · Search NASA

Results for “STRESS”

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 667 records · Page 37

All sources NASA NTRS DOE OSTI

DOE OSTI2024

Chloride-Induced Stress Corrosion Cracking of Friction Stir-Welded 304L Stainless Steel: Effect of Microstructure and Temperature

Dry storage canisters of used nuclear fuels are fabricated using SUS 304L stainless steel. Chloride-induced stress corrosion cracking (CISCC) is one of the major failure modes of dry storage canisters. The cracked canisters can be repaired by friction stir welding (FSW), a low-heat input ‘solid-phase’ welding process. It is important to evaluate the ClSCC resistance of the friction stir welded material. Stress corrosion cracking (SCC) studies were carried out on mill-annealed base materials and friction stir welded 304L stainless U-bend specimens in 3.5% NaCl + 5 N H2SO4 solution at room temperature and boiling MgCl2 solution at 155 °C. The engineering stress on the outer fiber of the FSW U-bend specimen was ~60% higher than that of the base metal (BM). In spite of the higher stress level of the FSW, both materials (FSW and BM) showed almost similar SCC failure times in the two different test solutions. The SCC occurred in the thermo-mechanically affected zone (TMAZ) of the FSW specimens in the 3.5% NaCl + 5 N H2SO4 solution at room temperature, while the stirred zone (SZ) was relatively crack-free. The failure occurred at the stirred zone when tested in the boiling MgCl2 solution. Hydrogen reduction was the cathodic reaction in the boiling MgCl2 solution, which promoted hydrogen-assisted cracking of the heavily deformed stirred zone. The emergence of the slip step followed by passive film rupture and dissolution of the slip step could be the SCC events in the 3.5% NaCl + 5 N H2SO4 solution at room temperature. However, the slip step height was not sufficient to cause passivity breakdown in the fine-grained SZ. Therefore, the SCC occurred in the partially recrystallized softer TMAZ. Overall, the friction-stirred 304L showed higher tolerance to ClSCC than the 304L base metal.

304L austenitic stainless steel↗

NASA NTRS1967

Crack propagation at stresses below the fatigue limit.

Crack propagation for stainless steel and Ti alloy at stresses below fatigue limit, noting of alternating stress cycles crack propagation for stainless steel and Ti alloy at stresses below fatigue limit, noting role of alternating stress cycles

STAINLESS STEEL↗

NASA NTRS1981

Analysis of Barkhausen noise to assess shrink fit stresses

The possible application of Barkhausen Noise Analysis to assess shrink fit stresses in steel bushings was investigated. Ten specimens of four different size NAS steel bushings were used in experiments to determine the relationship between the Barkhausen signal amplitude and the hoop-stress in the bushings. This relationship was investigated for specimens which were loaded by a simple clamping fixture and specimens subjected to actual thermal interference fits. The results show that while the relationship of Barkhausen signal amplitude to hoop stress is predictable for specimens loaded by the simple clamping fixture, the relationship was less predictable for actual thermal fit bushings. The variation in results could possibly be due to variable levels of axial stress produced by the differential thermal expansion of the steel and aluminum.

Nondestructive testing↗

NASA NTRS1951

Relation of Engine Turbine-blade Life to Stress-rupture Properties of the Alloys, Stellite 21, Hastelloy B, Cast S-816, Forged S-816, X-40, Nimonic 80, Refractaloy 26, N-155, and Inconel X

An investigation was conducted to relate the engine performance of the heat-resistant alloys, Stellite 21, Hastelloy B, cast S-816, forged S-816, X-40, Nimonic 80, Refractory 26, N-155, and Iconel X to their stress-rupture properties. The engine test consisted of the repetition of a 20-minute cycle, 15 minutes at rated speed and approximately 5 minutes at idle. The results of the investigation indicated a direct correlation between stress-rupture life and blade life for the relatively low-strength alloys. The stress-rupture life and blade life for the relatively high-strength alloys did not correlate because of the effects of the vibratory stresses and the corrosive-gas atmosphere.

ALLOYS, HEAT-RESISTING↗

NASA NTRS1950

Instrument for measuring the wall shearing stress of turbulent boundary layers

It is shown that at a smooth wall in a turbulent boundary layer the velocity profile next to the wall is dependent, aside from the material constants of the flowing medium, only on the shearing stress transmitted to the wall, even with pressure rise or with pressure drop. Consequently, the heat transfer of a small element that is built into the wall and has a higher temperature than that of the flowing medium is a measure of the wall shearing stress. Theoretical considerations indicate that the wall shearing stress of the boundary layer can be defined by means of a heat-transfer measurement with an instrument mounted in the wall. Such an instrument is described. The calibration curve and its directional sensitivity curve are indicated. It permits the determination of the wall shearing stress in magnitude and direction.

BOUNDARY LAYER, TURBULENT↗

NASA NTRS2003

Hindlimb unloading increases oxidative stress and disrupts antioxidant capacity in skeletal muscle

Skeletal muscle disuse with space-flight and ground-based models (e.g., hindlimb unloading) results in dramatic skeletal muscle atrophy and weakness. Pathological conditions that cause muscle wasting (i.e., heart failure, muscular dystrophy, sepsis, COPD, cancer) are characterized by elevated "oxidative stress," where antioxidant defenses are overwhelmed by oxidant production. However, the existence, cellular mechanisms, and ramifications of oxidative stress in skeletal muscle subjected to hindlimb unloading are poorly understood. Thus we examined the effects of hindlimb unloading on hindlimb muscle antioxidant enzymes (e.g., superoxide dismutase, catalase, glutathione peroxidase), nonenzymatic antioxidant scavenging capacity (ASC), total hydroperoxides, and dichlorohydrofluorescein diacetate (DCFH-DA) oxidation, a direct indicator of oxidative stress. Twelve 6 month old Sprague Dawley rats were divided into two groups: 28 d of hindlimb unloading (n = 6) and controls (n = 6). Hindlimb unloading resulted in a small decrease in Mn-superoxide dismutase activity (10.1%) in the soleus muscle, while Cu,Zn-superoxide dismutase increased 71.2%. In contrast, catalase and glutathione peroxidase, antioxidant enzymes that remove hydroperoxides, were significantly reduced in the soleus with hindlimb unloading by 54.5 and 16.1%, respectively. Hindlimb unloading also significantly reduced ASC. Hindlimb unloading increased soleus lipid hydroperoxide levels by 21.6% and hindlimb muscle DCFH-DA oxidation by 162.1%. These results indicate that hindlimb unloading results in a disruption of antioxidant status, elevation of hydroperoxides, and an increase in oxidative stress.

NASA Discipline Musculoskeletal↗

NASA NTRS2002

Phenylephrine-induced elevations in arterial blood pressure are attenuated in heat-stressed humans

To test the hypothesis that phenylephrine-induced elevations in blood pressure are attenuated in heat-stressed humans, blood pressure was elevated via steady-state infusion of three doses of phenylephrine HCl in 10 healthy subjects in both normothermic and heat stress conditions. Whole body heating significantly increased sublingual temperature by ~0.5 degrees C, muscle sympathetic nerve activity (MSNA), heart rate, and cardiac output and decreased total peripheral vascular resistance (TPR; all P < 0.005) but did not change mean arterial blood pressure (MAP; P > 0.05). At the highest dose of phenylephrine, the increase in MAP and TPR from predrug baselines was significantly attenuated during the heat stress [DeltaMAP 8.4 +/- 1.2 mmHg; DeltaTPR 0.96 +/- 0.85 peripheral resistance units (PRU)] compared with normothermia (DeltaMAP 15.4 +/- 1.4 mmHg, DeltaTPR 7.13 +/- 1.18 PRU; all P < 0.001). The sensitivity of baroreflex control of MSNA and heart rate, expressed as the slope of the relationship between MSNA and diastolic blood pressure, as well as the slope of the relationship between heart rate and systolic blood pressure, respectively, was similar between thermal conditions (each P > 0.05). These data suggest that phenylephrine-induced elevations in MAP are attenuated in heat-stressed humans without affecting baroreflex control of MSNA or heart rate.

Non-NASA Center↗

NASA NTRS2001

Elevated stress hormone levels relate to Epstein-Barr virus reactivation in astronauts

OBJECTIVE: The objective of this study was to determine the effects of stress and spaceflight on levels of neuroendocrine hormones and Epstein-Barr virus (EBV)-specific antibodies in astronauts. METHODS: Antiviral antibody titers and stress hormones were measured in plasma samples collected from 28 astronauts at their annual medical exam (baseline), 10 days before launch (L-10), landing day (R+0), and 3 days after landing (R+3). Urinary stress hormones were also measured at L-10 and R+0. RESULTS: Significant increases (p <.01) in EBV virus capsid antigen antibodies were found at all three time points (L-10, R+0, and R+3) as compared with baseline samples. Anti-EBV nuclear antigen antibodies were significantly decreased at L-10 (p <.05) and continued to decrease after spaceflight (R+0 and R+3, p <.01). No changes were found in antibodies to the nonlatent measles virus. The 11 astronauts who showed evidence of EBV reactivation had significant increases in urinary epinephrine and norepinephrine as compared with astronauts without EBV reactivation. CONCLUSION: These findings indicate that physical and psychological stresses associated with spaceflight resulted in decreased virus-specific T-cell immunity and reactivation of EBV.

NASA Center JSC↗

NASA NTRS1997

Intracellular pH changes in human aortic smooth muscle cells in response to fluid shear stress

The smooth muscle cell (SMC) layers of human arteries may be exposed to blood flow after endothelium denudation, for example, following balloon angioplasty treatment. These SMCs are also constantly subjected to pressure driven transmural fluid flow. Flow-induced shear stress can alter SMC growth and metabolism. Signal transduction mechanisms involved in these flow effects on SMCs are still poorly understood. In this work, the hypothesis that shear stress alters the intracellular pH (pHi) of SMC is examined. When exposed to venous and arterial levels of shear stress, human aortic smooth muscle cells (hASMC) undergo alkalinization. The alkalinization plateau persisted even after 20 min of cell exposure to flow. Addition of amiloride (10 micromoles) or its 5-(N-ethyl-N-isopropyl) analog (EIPA, 10 micromoles), both Na+/H+ exchanger inhibitors, attenuated intracellular alkalinization, suggesting the involvement of the Na+/H+ exchanger in this response. The same concentrations of these inhibitors did not show an effect on pHi of hASMCs in static culture. 4-Acetamido-4'-isothio-cyanatostilbene-2,2'-disulfonic acid (SITS, 1 mM), a Cl-/HCO3- exchange inhibitor, affected the pHi of hASMCs both in static and flow conditions. Our results suggest that flow may perturb the Na+/H+ exchanger leading to an alkalinization of hASMCs, a different response from the flow-induced acidification seen with endothelial cells at the same levels of shear stress. Understanding the flow-induced signal transduction pathways in the vascular cells is of great importance in the tissue engineering of vascular grafts. In the case of SMCs, the involvement of pHi changes in nitric oxide production and proliferation regulation highlights further the significance of such studies.

NASA Discipline Cell Biology↗

NASA NTRS1995

Mechanical stress regulation of plant growth and development

The authors introduce the chapter with a discussion of lessons from nature, agriculture, and landscapes; terms and definitions; and an historical perspective of mechanical stress regulation of plant growth and development. Topics include developmental responses to mechanical stress; mechanical stress-environment interactions; metabolic, productivity, and compositional changes; hormonal involvement; mechanoperception and early transduction mechanisms; applications in agriculture; and research implications. The discussion of hormonal involvement in mechanical stress physiology includes ethylene, auxin, gibberellins, and other phytohormones. The discussion of applications in agriculture examines windbreaks, nursery practices, height control and conditioning, and enhancement of growth and productivity. Implications for research are related to handling plant materials, space biology, and future research needs.

NASA Discipline Plant Biology↗

NASA NTRS2004

Stress-induced subclinical reactivation of varicella zoster virus in astronauts

Varicella zoster virus (VZV) becomes latent in human ganglia after primary infection. VZV reactivation occurs primarily in elderly individuals, organ transplant recipients, and patients with cancer and AIDS, correlating with a specific decline in cell-mediated immunity to the virus. VZV can also reactivate after surgical stress. The unexpected occurrence of thoracic zoster 2 days before space flight in a 47-year-old healthy astronaut from a pool of 81 physically fit astronauts prompted our search for VZV reactivation during times of stress to determine whether VZV can also reactivate after non-surgical stress. We examined total DNA extracted from 312 saliva samples of eight astronauts before, during, and after space flight for VZV DNA by polymerase chain reaction: 112 samples were obtained 234-265 days before flight, 84 samples on days 2 through 13 of space flight, and 116 samples on days 1 through 15 after flight. Before space flight, only one of the 112 saliva samples from a single astronaut was positive for VZV DNA. In contrast, during and after space flight, 61 of 200 (30%) saliva samples were positive in all eight astronauts. No VZV DNA was detected in any of 88 saliva samples from 10 healthy control subjects. These results indicate that VZV can reactivate subclinically in healthy individuals after non-surgical stress. Copyright 2004 Wiley-Liss, Inc.

Astronauts↗

NASA NTRS2004

Stress, Cognition, and Human Performance: A Literature Review and Conceptual Framework

The following literature review addresses the effects of various stressors on cognition. While attempting to be as inclusive as possible, the review focuses its examination on the relationships between cognitive appraisal, attention, memory, and stress as they relate to information processing and human performance. The review begins with an overview of constructs and theoretical perspectives followed by an examination of effects across attention, memory, perceptual-motor functions, judgment and decision making, putative stressors such as workload, thermals, noise, and fatigue and closes with a discussion of moderating variables and related topics. In summation of the review, a conceptual framework for cognitive process under stress has been assembled. As one might imagine, the research literature that addresses stress, theories governing its effects on human performance, and experimental evidence that supports these notions is large and diverse. In attempting to organize and synthesize this body of work, I was guided by several earlier efforts (Bourne & Yaroush, 2003; Driskell, Mullen, Johnson, Hughes, & Batchelor, 1992; Driskell & Salas, 1996; Haridcock & Desmond, 2001; Stokes & Kite, 1994). These authors should be credited with accomplishing the monumental task of providing focused reviews in this area and their collective efforts laid the foundation for this present review. Similarly, the format of this review has been designed in accordance with these previous exemplars. However, each of these previous efforts either simply reported general findings, without sufficient experimental illustration, or narrowed their scope of investigation to the extent that the breadth of such findings remained hidden from the reader. Moreover, none of these examinations yielded an architecture that adequately describes or explains the inter-relations between information processing elements under stress conditions.

Stress↗

NASA NTRS2006

Maximum von Mises Stress in the Loading Environment of Mass Acceleration Curve

Method for calculating stress due to acceleration loading: 1) Part has been designed by FEA and hand calculation in one critical loading direction judged by the analyst; 2) Maximum stress can be due to loading in another direction; 3) Analysis procedure to be presented determines: a) The maximum Mises stress at any point; and b) The direction of maximum loading associated with the "stress". Concept of Mass Acceleration Curves (MAC): 1) Developed by JPL to perform preliminary structural sizing (i.e. Mariners, Voyager, Galileo, Pathfinder, MER,...MSL); 2) Acceleration of physical masses are bounded by a curve; 3) G-levels of vibro-acoustic and transient environments; 4) Convergent process before the couple loads cycle; and 5) Semi-empirical method to effectively bound the loads, not a simulation of the actual response.

von Mises stress↗

NASA NTRS2015

The Effect of Stochastically Varying Creep Parameters on Residual Stresses in Ceramic Matrix Composites

Constituent properties, along with volume fraction, have a first order effect on the microscale fields within a composite material and influence the macroscopic response. Therefore, there is a need to assess the significance of stochastic variation in the constituent properties of composites at the higher scales. The effect of variability in the parameters controlling the time-dependent behavior, in a unidirectional SCS-6 SiC fiber-reinforced RBSN matrix composite lamina, on the residual stresses induced during processing is investigated numerically. The generalized method of cells micromechanics theory is utilized to model the ceramic matrix composite lamina using a repeating unit cell. The primary creep phases of the constituents are approximated using a Norton-Bailey, steady state, power law creep model. The effect of residual stresses on the proportional limit stress and strain to failure of the composite is demonstrated. Monte Carlo simulations were conducted using a normal distribution for the power law parameters and the resulting residual stress distributions were predicted.

residual stress↗

NASA NTRS2016

Time-Dependent Stress Rupture Strength Degradation of Hi-Nicalon Fiber-Reinforced Silicon Carbide Composites at Intermediate Temperatures

The stress rupture strength of silicon carbide fiber-reinforced silicon carbide composites with a boron nitride fiber coating decreases with time within the intermediate temperature range of 700 to 950 degree Celsius. Various theories have been proposed to explain the cause of the time-dependent stress rupture strength. The objective of this paper is to investigate the relative significance of the various theories for the time-dependent strength of silicon carbide fiber-reinforced silicon carbide composites. This is achieved through the development of a numerically based progressive failure analysis routine and through the application of the routine to simulate the composite stress rupture tests. The progressive failure routine is a time-marching routine with an iterative loop between a probability of fiber survival equation and a force equilibrium equation within each time step. Failure of the composite is assumed to initiate near a matrix crack and the progression of fiber failures occurs by global load sharing. The probability of survival equation is derived from consideration of the strength of ceramic fibers with randomly occurring and slow growing flaws as well as the mechanical interaction between the fibers and matrix near a matrix crack. The force equilibrium equation follows from the global load sharing presumption. The results of progressive failure analyses of the composite tests suggest that the relationship between time and stress-rupture strength is attributed almost entirely to the slow flaw growth within the fibers. Although other mechanisms may be present, they appear to have only a minor influence on the observed time-dependent behavior.

Progressive Failure Analysis↗

NASA NTRS2015

The Effect of Stochastically Varying Creep Parameters on Residual Stresses in Ceramic Matrix Composites

processing↗

NASA NTRS2016

Unpredictable Variable Prenatal Stress Programs Expression of Genes Involved in Appetite Control and Energy Expenditure

Exposure to stress in the womb shapes neurobiological and physiological outcomes of offspring in later life, including body weight regulation and metabolic profiles. Our previous work utilizing a centrifugation-induced hyper-gravity demonstrated significantly increased (8-15%) body mass in male, but not female, rats exposed throughout gestation to chronic 2-g from conception to birth. We reported a similar outcome in adult offspring exposed throughout gestation to Unpredictable Variable Prenatal Stress (UVPS). Here we examine gene expression changes and the plasma of animals treated with our UVPS model to identify a potential role for prenatal stress in this hypergravity programming effect. Specifically we focused on appetite control and energy expenditure pathways in prenatally stressed adult (90-day-old) male Sprague-Dawley rats.

Prenatal Stress↗

NASA NTRS2017

Non-Classical Stress Concentration Behavior in a Radically Stretched Hyperelastic Sheet Containing a Circular Hole

Non-classical stress concentration behavior in a stretched circular hyperelastic sheet (outer radius b = 10 in., thickness t = 0.0625 in.) containing a central hole (radius a = 0.5 in.) was analyzed. The hyperelastic sheet was subjected to different levels of remote radial stretchings. Nastran large-strain large-deformation analysis and the Blatz-Ko large deformation theory were used to calculate the equal-biaxial stress concentration factors K. The results show that the values of K calculated from the Blatz-Ko theory and Nastran are extremely close. Unlike the classical linear elasticity theory, which gives the constant K = 2 for the equal-biaxial stress field, the hyperelastic K values were found to increase with increased stretching and can exceed the value K = 6 at a remote radial extension ratio of 2.35. The present K-values compare fairly well with the K-values obtained by previous works. The effect of the hole-size on K-values was investigated. The values of K start to decrease from a hole radius a = 0.125 in. down to K = 1 (no stress concentration) as a shrinks to a = 0 in. (no hole). Also, the newly introduced stretch and strain magnification factors {K(sub λ),K(sub ε) } are also material- and deformation-dependent, and can increase from linear levels of {1.0, 4.0} and reaching {3.07, 4.61}, respectively at a remote radial extension ratio of 2.35.

stress concentration↗