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All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Concept for Determining the Life of Ceramic Matrix Composites Using Nondestructive Characterization Techniques

Damping measurements have been taken on ceramic matrix composite (CMC) turbopump blisks in the as fabricated, post proof testing, and post turbopump testing conditions. These results indicate that damping is able to quantify fatigue of the CMC blisk. This gives hope for the potential of determining the actual and residual life of CMC materials using a combination of nondestructive techniques. If successful, then this new paradigm for life prediction of CMCs could revolutionize the approach for designing and servicing CMC components, thereby significantly reducing costs for design, development, health monitoring, and maintenance of CMC components and systems. The Nondestructive Characterization (NDC) life prediction approach would complement life prediction using micromechanics and continuum finite element models. This paper reports on the initial concept of NDC life prediction and how changes in damping and ultrasonic elastic modulus data have established the concept as a possibility.

Effinger, Michael↗
NASA NTRS1999

Analyses of Fatigue and Fatigue-Crack Growth under Constant- and Variable-Amplitude Loading

Studies on the growth of small cracks have led to the observation that fatigue life of many engineering materials is primarily crack growth from micro-structural features, such as inclusion particles, voids, slip-bands or from manufacturing defects. This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using small-crack theory under various loading conditions. Constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (delta K(sub eff)) under constant-amplitude loading. Modifications to the delta K(sub eff)-rate relations in the near-threshold regime were needed to fit measured small-crack growth rate behavior. 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 under constant-amplitude and spectrum loading. Fatigue lives were predicted using crack-growth relations and micro-structural features like those that initiated cracks in the fatigue specimens for most of the materials analyzed. Results from the tests and analyses agreed well.

Newman, J. C., Jr.↗
NASA NTRS2010

Failure Analysis of Space Shuttle Orbiter Valve Poppet

The poppet failed during STS-126 due to fatigue cracking that most likely was initiated during MDC ground-testing. This failure ultimately led to the discovery that the cracking problem was a generic issue effecting numerous poppets throughout the Shuttle program's history. This presentation has focused on the laboratory analysis of the failed hardware, but this analysis was only one aspect of a comprehensive failure investigation. One critical aspect of the overall investigation was modeling of the fluid flow through this valve to determine the possible sources of cyclic loading. This work has led to the conclusion that the poppets are failing due to flow-induced vibration.

Russell, Rick↗
DOE OSTI2025

DROP DURABILITY ASSESSMENT OF ELECTRONIC ASSEMBLIES UNDER OFF-AXIS LOADING WITH SKEWED FIXTURES

This thesis studies drop durability of electronic assemblies when the acceleration vector is oriented at 45° to the out-of-plane direction of the circuit card. The off-axis drop tests are accomplished with a skewed fixture and are conducted as a proxy for multiaxial drop testing. Advanced shock testing and vibration test methods have been developed over the last few decades to better represent real-world field environments during ground-based laboratory testing. However, many of these test methods require expensive and specialized equipment not available in most laboratories. An alternative approach for approximating simultaneous loading along multiple axes on conventional equipment utilizes skewed fixtures which have seen use in off-axis random vibration and drop impact testing. These methods generally rely on the conversion of a uniaxial input load from the test equipment (using a uniaxial drop tower or shaker) into a multiaxial load when resolved in the reference frame of the test article (mounted on a skewed fixture). Skewed fixture design is presented and recommendations for conducting skewed angle drop testing are introduced based on local measurements along the skewed face of the fixture to accurately monitor the impact event. Characterization tests were performed with a skewed fixture, at simultaneous acceleration loads from 500 to 3,000 g in two (in-plane and out-of-plane) directions, while meeting standard time domain tolerances. Upon experimental characterization, drop shock durability tests were conducted on a printed circuit assembly (PCA). Mean drops-to-failure were measured and quantified with Weibull statistics. Dominant solder joint failure modes were identified via failure analysis. Prior work on inclined angle impact testing is limited, and the majority of solder joint interconnect level fatigue studies are conducted considering perpendicular loading normal the circuit card. Low-cycle fatigue curves are generated based on plastic strain and plastic work density within the solder joint. A multiscale nonlinear finite element model is used to relate board-level flexure to solder joint interconnect level plastic strain. A high strain rate solder constitutive model allows for accurate modeling of solder plasticity resulting from high-impact drop shock. Fatigue parameters are computed from the Coffin-Manson relation and Palmgren-Miner damage accumulation. This work serves to apply established low-cycle fatigue methods for conventional drop shock loading (impact normal to circuit card) to non-perpendicular loading with a skewed fixture.

Hower, Jonathan [Kansas City National Security Cam↗
NASA NTRS1960

A Study of Some Factors Affecting Rolling-Contact Fatigue Life

A series of investigations using the fatigue spin rig to study the effect of several factors contributing to rolling contact fatigue life is summarized. Ball specimens of 1/2 and 9/16 inch diameter were tested at maximum theoretical Hertz compressive stresses in the range of 600,000 to 750,000 psi. Life was found to vary inversely with the tenth power of stress. In forging fiber studies, a greater concentration of failures and poorer life were observed where the greatest angle of intersection between the fiber flow lines and the surface occurred. This effect was independent of alloy composition. Higher lubricant viscosity was found to increase fatigue life, Lubricants having the same viscosity but of different base stock produced wide differences in life that correlated with the pressure viscosity coefficient of the lubricant. Higher temperature produced lower fatigue life. Dry powder lubricants produced poor fatigue life at 450 F; failure appearance indicated that the lubricant particles probably acted as minute stress raisers. In metallographic studies, nonmetallic inclusions were found to have a deleterious effect on fatigue life the inclusion size, location, composition, and condition of the matrix being contributing factors; failures were by shear cracking in the subsurface zone of maximum shear stress and eventual propagation into a shallow surface spall. Vacuum melting improved fatigue life, although a general correlation between cleanliness and fatigue life was not found. Life results for ten different bearing materials are presented.

Carter, Thomas L.↗
NASA NTRS2000

Fatigue Damage Mechanisms in Advanced Hybrid Titanium Composite Laminates

Hybrid Titanium Composite Laminates (HTCL) are a type of hybrid composite laminate with promise for high-speed aerospace applications, specifically designed for improved damage tolerance and strength at high-temperature (350 F, 177 C). However, in previous testing, HTCL demonstrated a propensity to excessive delamination at the titanium/PMC interface following titanium cracking. An advanced HTCL has been constructed with an emphasis on strengthening this interface, combining a PETI-5/IM7 PMC with Ti-15-3 foils prepared with an alkaline-perborate surface treatment. This paper discusses how the fatigue capabilities of the "advanced" HTCL compare to the first generation HTCL which was not modified for interface optimization, in both tension-tension (R = 0.1) and tension-compression (R=-0.2). The advanced HTCL under did not demonstrate a significant improvement in fatigue life, in either tension-tension or tension-compression loading. However, the advanced HTCL proved much more damage tolerant. The R = 0.1 tests revealed the advanced HTCL to increase the fatigue life following initial titanium ply damage up to 10X that of the initial HTCL at certain stress levels. The damage progression following the initial ply damage demonstrated the effect of the strengthened PMC/titanium interface. Acetate film replication of the advanced HTCL edges showed a propensity for some fibers in the adjacent PMC layers to fail at the point of titanium crack formation, suppressing delamination at the Ti/PMC interface. The inspection of failure surfaces validated these findings, revealing PMC fibers bonded to the majority of the titanium surfaces. Tension compression fatigue (R = -0.2) demonstrated the same trends in cycles between initial damage and failure, damage progression, and failure surfaces. Moreover, in possessing a higher resistance to delamination, the advanced HTCL did not exhibit buckling following initial titanium ply cracking under compression unlike the initial HTCL.

Johnson, W. Steven↗
NASA NTRS1980

Influence of Microstructure on the Fatigue Crack Growth of A516 in Hydrogen

Some day hydrogen may be used as a viable energy storage and transport medium within the United States. Hydrogen gas may be used to dilute and extend our present methane supply as a blend or may even be used in its pure elemental form as a primary fuel. Independent of the methods of production, storage, and distribution, the interaction of hydrogen with its containment material will play an integral role in the success of a hydrogen energy program. Presently, the selection of hydrogen containment materials can be made such that the material will remain reasonably free from environmental degradation; however, costly alloying additions are required. Unfortunately, high alloy steels are economically prohibitive when large-scale hydrogen energy storage, transmission, and conversion systems are desired. Therefore, in order to implement such hydrogen energy systems in the future, existing low-cost materials must be improved via mechanical, thermal, or thermo-mechanical processing methods or new low-cost materials which are compatible with hydrogen must be developed. Originally, low strength, low alloy steels at room temperature were thought to be immune to hydrogen gas embrittlement, since no sustained load crack growth is observed. However, results of Clark in HY8O and Nelson in SAE 1020 have shown that the fatigue crack growth rate can be greatly accelerated in the presence of hydrogen gas. In recent results reported by Louthan and Mucci, the smooth bar fatigue life of an A1068 pipeline steel was reduced up to a factor of ten when the tests were performed in a 13.8 MPa hydrogen environment. These results suggest that the selection of material for structures designed to operate in hydrogen under cyclic loads must include consideration of hydrogen/metal fatigue interaction. Although the hydrogen/metal fatigue interaction can be severe in low strength low alloy steels, the degree of degradation may be altered by the underlying ferrous microstructure. At present, no correlation between microstructure and degree of hydrogen susceptibility exists for low strength steels. However, in high strength steels, susceptibility to hydrogen embrittlement has been shown to be strongly sensitive to the metallurgical microstructure. In addition, compositional effects and grain size can 703 Some day hydrogen may be used as a viable energy storage and transport medium within the United States. Hydrogen gas may be used to dilute and extend our present methane supply as a blend or may even be used in its pure elemental form as a primary fuel. Independent of the methods of production, storage, and distribution, the interaction of hydrogen with its containment material will play an integral role in the success of a hydrogen energy program. Presently, the selection of hydrogen containment materials can be made such that the material will remain reasonably free from environmental degradation; however, costly alloying additions are required. Unfortunately, high alloy steels are economically prohibitive when large-scale hydrogen energy storage, transmission, and conversion systems are desired. Therefore, in order to implement such hydrogen energy systems in the future, existing low-cost materials must be improved via mechanical, thermal, or thermo-mechanical processing methods or new low-cost materials which are compatible with hydrogen must be developed.

Wachob, Harry F.↗
NASA NTRS1976

Moessbauer effect measurement in single crystal iron subjected to cyclic stress

Backscattered Moessbauer spectra were recorded at different fatigue levels in cyclically fatigued high-purity single-crystal iron specimens in the form of rectangular strips with appropriate concentrators in the midplane. The Moessbauer spectra were submitted to a least-squares analysis to determine the isomer shift, quadrupole shift, hyperfine field, and peak spectral widths in each spectrum. It is shown that the quadrupole shift and the isomer shift changed little with fatigue, whereas the effective internal field and the associate line widths exhibit significant variation as a function of fatigue level. It is concluded that the impurity concentration builds up slowly with increasing fatigue level in the region of stress concentration. Since there is a direct correlation between crack initiation and defect concentration level, it is expected that Moessbauer measurements in the test specimen can provide a means of monitoring the impurity buildup presumed to be the eventual cause of fatigue crack initiation and failure.

Singh, J. J.↗
NASA NTRS1995

Fatigue-Arrestor Bolts

Bolts that arrest (or, more precisely, retard) onset of fatigue cracking caused by inelastic strains developed. Specifically developed to be installed in flange holes of unrestrained rocket engine nozzle. Fanges sometimes used to bolt nozzle to test stand; however, when rocket engine operated without this restraint, region around bolt holes experience severe inelastic strains causing fatigue cracking. Interference fits introduce compressive preloads that retard fatigue by reducing ranges of strains. Principle of these fatigue-arrestor bolts also applicable to holes in plates made of other materials and/or used for different purposes.

Onstott, Joseph W.↗
NASA NTRS1978

High Velocity Burner Rig Oxidation and Thermal Fatigue Behavior of Si3N4- and SiC Base Ceramics to 1370 Deg C

One SiC material and three Si3N4 materials including hot-pressed Si3N4 as a baseline were exposed in a Mach-1-gas-velocity burner rig simulating a turbine engine environment. Criteria for the materials selection were: potential for gas-turbine usage, near-net-shape fabricability and commercial/domestic availability. Cyclic exposures of test vanes up to 250 cycles (50 hr at temperature) were at leading-edge temperatures to 1370 C. Materials and batches were compared as to weight change, surface change, fluorescent penetrant inspection, and thermal fatigue behavior. Hot-pressed Si3N4 survived the test to 1370 C with slight weight losses. Two types of reaction-sintered Si3N4 displayed high weight gains and considerable weight-change variability, with one material exhibiting superior thermal fatigue behavior. A siliconized SiC showed slight weight gains, but considerable batch variability in thermal fatigue.

Sanders, W. A.↗
NASA NTRS1988

Calibration of a Mode II test specimen

Mode II and Mode I calibrations of the NASA Lewis Research Center Mode II fatigue specimen were performed experimentally over crack length to specimen width ratios (a/W) of 0.5 to 0.9. Mode II displacements were measured both at the specimen notch mouth and at the intersection of the notch with the centerline of the loading pin holes. Mode I displacements were measured across the span of the specimen at the loading pins' centerline. Analytical stress intensity factor coefficients for both Mode II and Mode I are also presented.

Buzzard, Robert J.↗
DOE OSTI2024

Environmentally Assisted Fatigue in Light Water Reactor Environment

This report summarizes the Environmentally Assisted Fatigue (EAF) research conducted at ANL under the US DOE Light Water Reactor Sustainability (LWRS) program. Starting from a rich background in theoretical and experimental EAF, ANL previously developed an approach to evaluate fatigue performance of reactor materials in light water reactor environments with the correction factor F en . The approach was based on a large body of experimental work performed at ANL and elsewhere, and was consistent with American Society of Mechanical Engineers (ASME)’s methodology governing the design and construction of reactor components. In recent years, the program was focused on component fatigue prediction and made several major and fundamental contributions in this area. These accomplishments help meet the needs identified by the industry concerning component level fatigue predictions in complex, transient conditions. The main contribution of the ANL program involved the development of a system-level model for estimating residual strain and life of nuclear reactor coolant system components under connected-system-thermal-mechanical boundary conditions. The goal was to predict the stress hotspots, strain residuals, strain amplitudes and the resulting fatigue lives. Thermal-mechanical stress analysis was performed considering thermal stratification and a design-basis reactor loading cycle. Based on the finite element (FE) model results, the strain residuals, strain amplitudes and resulting fatigue lives of reactor coolant system (RCS) components were predicted. The results show that some of the RCS components can have significantly different strain amplitudes, residual strain, and fatigue lives, despite having similar geometry and material. In addition, the simulated component-level strain profile can guide the selection of appropriate test inputs for conducting laboratory-scale EAF tests. Building upon the system-level model, ANL developed a digital twin (DT) framework to predict the structural states and associated fatigue life of components in real-time. This framework is a comprehensive system designed to predict the structural states and fatigue lives of reactor components. It includes multiple models and integrates artificial intelligence (AI), machine learning (ML), and FE based modeling tools to evaluate the structural states and fatigue lives.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRSDate not supplied

Analysis of Crack Propagation Transients in Accelerated Fatigue Characterization of Adhesives

The characterization of the rates of crack propagation by means of a Paris law is intended for steady-state fatigue conditions. While rates of crack propagation are primarily driven by 𝐽𝐽𝑚𝑚𝑚𝑚𝑚𝑚, in the presence of evolving process zones and fiber bridging they also depend on the crack propagation length: cracks with fully formed process zones propagate more slowly. Analyses of the rates of crack propagation in laminates secondarily bonded with AF163-2K film adhesive were conducted to identify the rate transients that occur during the formation of the process zone in the adhesive and during the evolution of bridging of the adhesive’s carrier knit across the crack faces. Dávila's CF22 cohesive fatigue damage model was used in finite element analyses of the double cantilever beam test to explain discrepancies in experimental rates of propagation obtained from tests conducted with either increasing or decreasing 𝐽max. The results indicate that the analyses accurately reproduce transient and steady-state rates of propagation observed in the experimental results, as well as the threshold of propagation. Transient rates of propagation always exceed those in steady state, which underscores the need to understand transients and account for them in fatigue characterization. The results also highlight that a Paris curve for steady-state propagation can be obtained most quickly using a decreasing load function, but that this curve consists of an unconservative bound to the rates of propagation. A lateral shift in the Paris curve is proposed for a conservative characterization that removes the effect of bridging and other R-curve effects.

fracture mechanics; delamination; J-integral↗
NASA NTRSDate not supplied

Analysis of Crack Propagation Transients in Accelerated Fatigue Characterization of Adhesives

The characterization of the rates of crack propagation by means of a Paris law is intended for steady-state fatigue conditions. While rates of crack propagation are primarily driven by 𝐽𝐽𝑚𝑚𝑚𝑚𝑚𝑚, in the presence of evolving process zones and fiber bridging they also depend on the crack propagation length: cracks with fully formed process zones propagate more slowly. Analyses of the rates of crack propagation in laminates secondarily bonded with AF163-2K film adhesive were conducted to identify the rate transients that occur during the formation of the process zone in the adhesive and during the evolution of bridging of the adhesive’s carrier knit across the crack faces. Dávila's CF22 cohesive fatigue damage model was used in finite element analyses of the double cantilever beam test to explain discrepancies in experimental rates of propagation obtained from tests conducted with either increasing or decreasing 𝐽max. The results indicate that the analyses accurately reproduce transient and steady-state rates of propagation observed in the experimental results, as well as the threshold of propagation. Transient rates of propagation always exceed those in steady state, which underscores the need to understand transients and account for them in fatigue characterization. The results also highlight that a Paris curve for steady-state propagation can be obtained most quickly using a decreasing load function, but that this curve consists of an unconservative bound to the rates of propagation. A lateral shift in the Paris curve is proposed for a conservative characterization that removes the effect of bridging and other R-curve effects.

fracture mechanics; delamination; J-integral↗
NASA NTRS1981

Test methods and design allowables for fibrous composites; Proceedings of the Symposium, Dearborn, MI, October 2, 3, 1979

Papers are presented on special test methods for fibrous composites for quantifying design material properties. Studies are divided into four major areas: (1) new and special test methods, including those for transverse tensile strength, shear modulus, longitudinal compression, and impact resistance; (2) special test methods and analysis, including off-axes and angle-plied tension and compression, fracture and fatigue, and biaxial stress states; (3) design allowables, describing procedures for setting and selecting design allowables in general, and also for composite aircraft structures, graphite/polyimide bolted joints, cost-effective mechanical property characterization, statistical considerations, intraply hybrids, and compression and fatigue; (4) design allowables for special applications, describing procedures for buckling of cylindrical components, proof load of pressure vessels, strength of composite joints, and environmental effects and creep. The papers provide considerable information for test methods and for composite analysis of these methods, as well as tests and procedures for establishing design allowables.

Chamis, C. C.↗
NASA NTRS1999

Blood flow dynamics in heart failure

BACKGROUND: Exercise intolerance in heart failure (HF) may be due to inadequate vasodilation, augmented vasoconstriction, and/or altered muscle metabolic responses that lead to fatigue. METHODS AND RESULTS: Vascular and metabolic responses to rhythmic forearm exercise were tested in 9 HF patients and 9 control subjects (CTL) during 2 protocols designed to examine the effect of HF on the time course of oxygen delivery versus uptake (protocol 1) and on vasoconstriction during exercise with 50 mm Hg pressure about the forearm to evoke a metaboreflex (protocol 2). In protocol 1, venous lactate and H+ were greater at 4 minutes of exercise in HF versus CTL (P<0.05) despite similar blood flow and oxygen uptake responses. In protocol 2, mean arterial pressure increased similarly in each group during ischemic exercise. In CTL, forearm blood flow and vascular conductance were similar at the end of ischemic and ambient exercise. In HF, forearm blood flow and vascular conductance were reduced during ischemic exercise compared with the ambient trial. CONCLUSIONS: Intrinsic differences in skeletal muscle metabolism, not vasodilatory dynamics, must account for the augmented glycolytic metabolic responses to moderate-intensity exercise in class II and III HF. The inability to increase forearm vascular conductance during ischemic handgrip exercise, despite a normal pressor response, suggests that enhanced vasoconstriction of strenuously exercising skeletal muscle contributes to exertional fatigue in HF.

NASA Discipline Cardiopulmonary↗
NASA NTRS1992

Behavior of surface and corner cracks subjected to tensile and bending loads in a Ti-6Al-4V alloy

The behavior of part-through flaws with regard to failure under monotonic loading and their growth under fatigue loading was investigated experimentally and analytically. The objective of this paper is to present comparisons of experimental values of toughness obtained using surface- and corner-cracked specimens with those obtained using standard test specimens, and also to compare experimental growth cycles with numerical predictions using the NASA/FLAGRO computer program. Tests were conducted on various types of surface and corner cracks under tensile and bending loads. Room temperature laboratory air provided the test environment. The material used in this investigation was the Ti-6Al-4V alloy in the solution treated and aged (STA) and stress-relieved condition. Detailed tabulation of the fracture toughness data and results of life prediction using the NASA/FLAGRO program are presented. Fatigue crack growth rates for the part-through-cracked specimens are compared with a base curve fitted from the data obtained using standard specimens. The fatigue loading used in the crack growth testing was of constant-amplitude sinusoidal type.

Forman, Royce G.↗

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