SEARCH · Search NASA

Results for “STRAIN FATIGUE”

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 217 records · Page 12

All sources NASA NTRS DOE OSTI

NASA NTRS1984

Effects of processing and microstructure on the fatigue behaviour of the nickel-base superalloy Rene95

Forms of the nickel-base superalloy Rene95 produced by three processing methods were evaluated in tensile, low cycle fatigue and fatigue crack propagation tests at 540 and 650 C. Two powder-metallurgy (PM) forms, hot-isostatically-pressed and extruded-and-forged, and a conventionally cast-and-wrought form were all given the same heat treatment. The extruded-and-forged form showed superior fatigue life in low strain range tests though the two PM forms exhibited nearly identical mechanical behavior in all other respects. Further, this life difference could not be explained by significant differences in the types, sizes or shapes of the defects initiating failure. The cast-and-wrought Rene95, however, had lower strength, ductility and fatigue life, but higher fatigue crack propagation resistance because of a larger grain size. It did not exhibit the environmentally-assisted intergranular mode of propagation which occurs in PM Rene95 and other fine-grained superalloys at these test temperatures and frequencies.

Miner, R. V.↗

NASA NTRS2013

Multiaxial and Thermomechanical Fatigue of Materials: A Historical Perspective and Some Future Challenges

Structural materials used in engineering applications routinely subjected to repetitive mechanical loads in multiple directions under non-isothermal conditions. Over past few decades, several multiaxial fatigue life estimation models (stress- and strain-based) developed for isothermal conditions. Historically, numerous fatigue life prediction models also developed for thermomechanical fatigue (TMF) life prediction, predominantly for uniaxial mechanical loading conditions. Realistic structural components encounter multiaxial loads and non-isothermal loading conditions, which increase potential for interaction of damage modes. A need exists for mechanical testing and development verification of life prediction models under such conditions.

Kalluri, Sreeramesh↗

NASA NTRS1972

Temperature effects on the strainrange partitioning approach for creep-fatigue analysis.

Examination is made of the influence of temperature on the strain-range partitioning approach to creep-fatigue. Results for 2.5Cr-1Mo steel and Type 316 stainless steel show the four partitioned strain range-life relationships to be temperature insensitive to within a factor of two on cyclic life. Monotonic creep and tensile ductilities were also found to be temperature insensitive to within a factor of two. The approach provides bounds on cyclic life that can be readily established for any type of inelastic strain cycle.

Halford, G. R.↗

NASA NTRS1985

Creep-fatigue interaction of titanium alloy Ti-6Al-2Cb-1Ta-0.8Mo at room temperature

The present investigation is concerned with the mutual influence of creep and fatigue in the case of Ti-6211, which represents a new weldable, stress-corrosion resistant alloy. Attention is given to the effect of creep on fatigue, the effect of fatigue on creep, and microstructural studies. It is found that prior creep in the amounts investigated, from 0.2 percent to 2.7 percent, is beneficial to low-cycle fatigue life. Hold time at peak strain is found to be beneficial to low-cycle fatigue life. Hold time at constant stress has no effect on low-cycle fatigue when specimens are cycled only once between hold times; but increasing fatigue loading for 50 or more cycles between hold times can prolong the fatigue life. There is an acceleration of creep by cyclic loading when comparison of cyclic and static creep is based on mean stress.

Chu, H. P.↗

NASA NTRS1988

A model for life predictions of nickel-base superalloys in high-temperature low cycle fatigue

Extensive characterization of low-cycle fatigue damage mechanisms was performed on polycrystalline Rene 80 and IN100 tested in the temperature range from 871 to 1000 C. Low-cycle fatigue life was found to be dominated by propagation of microcracks to a critical size governed by the maximum tensile stress. A model was developed which incorporates a threshold stress for crack extension, a stress-based crack growth expression, and a failure criterion. The mathematical equivalence between this mechanistically based model and the strain-life low-cycle fatigue law was demonstrated using cyclic stress-strain relationships. The model was shown to correlate the high-temperature low-cycle fatigue data of the different nickel-base superalloys considered in this study.

Romanoski, Glenn R.↗

NASA NTRS2016

Fatigue Analysis of Notched Laminates: A Time-Efficient Macro-Mechanical Approach

A coupled transversely isotropic deformation and damage fatigue model is implemented within the finite element method and was utilized along with a static progressive damage model to predict the fatigue life, stiffness degradation as a function of number of cycles, and post-fatigue tension and compression response of notched, multidirectional laminates. Initially, the material parameters for the fatigue model were obtained utilizing micromechanics simulations and the provided [0], [90] and [plus or minus 45] experimental composite laminate S-N (stress-cycle) data. Within the fatigue damage model, the transverse and shear properties of the plies were degraded with an isotropic scalar damage variable. The damage in the longitudinal (fiber) ply direction was suppressed, and only the strength of the fiber was degraded as a function of fatigue cycles. A maximum strain criterion was used to capture the failure in each element, and once this criterion was satisfied, the longitudinal stiffness of the element was decreased by a factor of 10 (sup 4). The resulting, degraded properties were then used to calculate the new stress state. This procedure was repeated until final failure of the composite laminate was achieved or a specified number of cycles reached. For post-fatigue tension and compression behavior, four internal state variables were used to control the damage and failure. The predictive capability of the above-mentioned approach was assessed by performing blind predictions of the notched multidirectional IM7/977-3 composite laminates response under fatigue and post-fatigue tensile and compressive loading, followed by a recalibration phase. Although three different multidirectional laminates were analyzed in the course of this study, only detailed results (i.e., stiffness degradation and post-fatigue stress-train curves as well as damage evolution states for a single laminate ([30/60/90/minus 30/minus 60] (sub 2s)) are discussed in detail here.

Composite Fatigue analysis↗

NASA NTRS1993

Effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates

The effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates with ply orientation of (0(2),90(2))2S and (90(2),0(2))2S are examined. The relative importance of shear and tensile stresses is examined by varying the span-to-depth ratios of flexural test specimens from 8 to 45. Acoustic emission signals are measured during the flexural tests in order to monitor the initiation and growth of damage. Optical microscopy is used to examine specimens for resin cracking, delamination, and fiber breaks after testing. Transverse matrix cracks and delaminations occur in all specimens, regardless of ply orientation, span-to-depth ratio, or previous exposure of specimens to thermal and mechanical fatigue. A small amount of fiber tensile fracture occurs in the outer 0 deg ply of specimens with high span-to-depth ratios. Because of the complex failure modes, the flexural test results represent the 'apparent' strengths rather than the true flexural or shear strengths for these cross-ply laminates. Thermal cycling of specimens prior to flexural testing does not reduce the apparent flexural strength or change the mode of failure. However, fewer acoustic events are recorded at all strains during flexural testing of specimens exposed to prior thermal cycling. High temperature thermal cycling (32 to 260 C, 100 cycles) causes a greater reduction in acoustic events than low temperature thermal cycling (-85 to +85 C, 500 cycles). Mechanical cycling (0 to 50 percent of the flexural strength, 100 cycles) has a similar effect, except that acoustic events are reduced only at strains less than the maximum strain applied during flexural fatigue.

Roberts, Gary D.↗

NASA NTRS1988

Bithermal fatigue of a nickel-base superalloy single crystal

The thermomechanical fatigue behavior of a nickel-base superalloy single crystal was investigated using a bithermal test technique. The bithermal fatigue test was used as a simple alternative to the more complex thermomechanical fatigue test. Both in-phase and out-of-phase bithermal tests were performed on (100)-oriented coated and bare Rene N4 single crystals. In out-of-plane bithermal tests, the tensile and compressive halves of the cycle were applied isothermally at 760 and 982 C, respectively, while for the in-phase bithermal tests the temperature-loading sequence was reversed. The bithermal fatigue lives of bare specimens were shorter than the isothermal fatigue lives at either temperature extreme when compared on an inelastic strain basis. Both in-phase and out-of-phase bithermal fatigue life curves converged in the large strain regime and diverged in the small strain regime, out-of-phase resulting in the shortest lives. The coating had no effect on life for specimens cycled in-phase; however, the coating was detrimental for isothermal fatigue at 760 C and for out-of-phase fatigue under large strains.

Verrilli, Michael J.↗

NASA NTRS1995

Assessment of microalloying effects on the high temperature fatigue behavior of NiAl

Binary NiAl suffers from a lack of strength and poor creep properties at and above 1000 K. Poor creep resistance in turn affects low cycle fatigue (LCF) lives at low strain ranges due to the additional interactions of creep damage. One approach for improving these properties involved microalloying with either Zr or N. As an integral part of a much larger alloying program the low cycle fatigue behavior of Zr and N doped nickel aluminides produced by extrusion of prealloyed powders has been investigated. Strain controlled LCF tests were performed in air at 1000 K. The influence of these microalloying additions on the fatigue life and cyclic stress response of polycrystalline NiAl are discussed.

Noebe, R. D.↗

NASA NTRS1986

Fatigue delamination behavior of PEEK thermoplastic composite laminates

The delamination resistance of graphite-reinforced PEEK composites was quantified by conducting static and cyclic edge delamination tests on (35n/-35n/0n/90n)s AS4/PEEK laminates, where n = 1, 2. The experimentally determined mechanical delamination onset strains were used to calculate the critical strain-energy release rate for delamination onset as a function of fatigue cycle. The delamination onset strains decreased dramatically with fatigue cycles and then began to level off to an endurance limit at 1 million cycles. Although the static interlaminar fracture toughness of the AS4/PEEK composite is much greater than the toughness of graphite epoxy composites, the delamination fatigue threshold, calculated from the cyclic strain endurance limit at 1 million cycles, was only slightly greater than the threshold for graphite epoxy composites. The contribution of residual thermal stresses to delamination in the AS4/PEEK is substantial due to the large temperature range between the manufacture and the room temperatures.

O'Brien, T. K.↗

NASA NTRS1990

Observations of fatigue crack initiation and damage growth in notched titanium matrix composites

The purpose was to characterize damage initiation and growth in notched titanium matrix composites at room temperature. Double edge notched or center open hole SCS-6/Ti-15-3 specimens containing 0 deg plies or containing both 0 and 90 deg plies were fatigued. The specimens were tested in the as-fabricated (ASF) and in heat-treated conditions. A local strain criterion using unnotched specimen fatigue data was successful in predicting fatigue damage initiation. The initiation stress level was accurately predicted for both a double edge notched unidirectional specimen and a cross-plied center hole specimen. The fatigue produced long multiple cracks growing from the notches. These fatigue cracks were only in the matrix material and did not break the fibers in their path. The combination of matrix cracking and fiber/matrix debonding appears to greatly reduce the stress concentration around the notches. The laminates that were heat treated showed a different crack growth pattern. In the ASF specimens, matrix cracks had a more tortuous path and showed considerable more crack branching. For the same specimen geometry and cyclic stress, the (0/90/0) laminate with a hole had far superior fatigue resistance than the matrix only specimen with a hole.

Naik, R. A.↗

NASA NTRS1991

Observations of fatigue crack initiation and damage growth in notched titanium matrix composites

Naik, Rajiv A.↗

NASA NTRS1969

Crack initiation at notches in low cycle fatigue Final report, 1 Aug. 1968 - 15 Mar. 1969

Crack initiation at notches in low cycle fatigue determined by plastic strain distribution

Adachi, M.↗

NASA NTRS1973

High modulus filament wound vessels for cryogenic containers in spacecraft.

Compared to metallic vessels, filament-wound vessels for containment of cryogens and high pressure gases offer high potential weight savings for NASA spacecraft applications. Since carbon fiber/epoxy resin composites exhibit high strength-to-density ratios, high-cycle fatigue life, and excellent strain compatibility with internal metallic liners, filament-wound carbon fiber/epoxy resin composites were evaluated for application to cryogenic internal pressure vessels. Compared to room temperature values, the cryogenic strengths of the composites were reduced by about 15% at -423 F (with the exception of one composite) while moduli increased as much as 25%. Filament-wound carbon fiber/epoxy resin vessel specimens, made by three fabricators, defined and solved problems in the processing of these friable high-modulus fibers into structurally efficient vessel specimens.

Simon, R. A.↗

NASA NTRS1987

Cyclic hardening mechanisms in Nimonic 80A

A nickel base superalloy was fatigued under constant plastic strain range control. The hardening response was investigated as a function of plastic strain range and particle size of the gamma prime phase. Hardening was found to be a function of the slip band spacing. Numerous measurements of the slip band spacing and other statistical data on the slip band structures were obtained. Interactions between intersecting slip systems were shown to influence hardening. A Petch-Hall model was found to describe best this relationship between the response stress and the slip band spacing.

Lerch, B. A.↗

NASA NTRS2010

Temperature-Dependent Electrical and Micromechanical Properties of Lanthanum Titanate with Additions of Yttria

Temperature-dependent elastic properties were determined by establishing continuous flexural vibrations in the material at its lowest resonance frequency of 31tHz. The imaginary part of the complex impedance plotted as a function of frequency and temperature reveals a thermally activated peak, which decreases in magnitude as the temperature increases. Additions of yttria do not degrade the electromechanical in particularly the elastic and anelastic properties of lanthanum titanate. Y2O3/La2Ti2O7 exhibits extremely low internal friction and hence may be more mechanical fatigue-resistant at low strains.

Goldsby, Jon C.↗

NASA NTRS2008

Performance Evaluation and Modeling of Erosion Resistant Turbine Engine Thermal Barrier Coatings

The erosion resistant turbine thermal barrier coating system is critical to the rotorcraft engine performance and durability. The objective of this work was to determine erosion resistance of advanced thermal barrier coating systems under simulated engine erosion and thermal gradient environments, thus validating a new thermal barrier coating turbine blade technology for future rotorcraft applications. A high velocity burner rig based erosion test approach was established and a new series of rare earth oxide- and TiO2/Ta2O5- alloyed, ZrO2-based low conductivity thermal barrier coatings were designed and processed. The low conductivity thermal barrier coating systems demonstrated significant improvements in the erosion resistance. A comprehensive model based on accumulated strain damage low cycle fatigue is formulated for blade erosion life prediction. The work is currently aiming at the simulated engine erosion testing of advanced thermal barrier coated turbine blades to establish and validate the coating life prediction models.

Miller, Robert A.↗

NASA NTRS1988

Fatigue life prediction modeling for turbine hot section materials

A major objective of the fatigue and fracture efforts under the Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.

Halford, G. R.↗