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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Support of the Development of EPP Plus SMT Design Method (FY2020 Test Results)

Experiments in support of the development of the integrated Elastic–Perfectly Plastic (EPP) analysis and Simplified Model Test (SMT) design methodology continued in FY 2020. The previously developed single-bar SMT (SBSMT) technique was successfully extended to tubular shaped Alloy 617 specimens for evaluation of the effect of primary pressure load on SMT creep-fatigue (CF) properties at 950°C. A series of pressurized SMT tests were performed with various elastic follow-up factors and strain ranges. The results show that the primary pressure load reduces the SMT CF cycles. The reduction of SMT CF life due to primary load was found to be dependent on strain ranges, elastic follow up and test temperatures. These results are crucial for verification of the EPP strain range analysis in the EPP+SMT evaluation procedure. Additionally, hold time effect on the SMT CF life cycles is a determining factor for generating the EPP+SMT CF design curves. Lack of test data in the high cycle and low strain range region results in major uncertainty in developing the design curves. In FY2020, experiments were designed, and testing started on Alloy 617 at 950°C to fill the gap in experimental data. The on-going CF and additional SMT CF with elastic follow-up at low strain ranges will generate the information needed to verify the methods for extrapolation to long hold time and finalize the EPP+SMT design method.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Subcomponent Validation of Composite Joints for Marine Energy Structures

The Marine Energy Advanced Materials project addresses the barriers and uncertainties facing marine renewable energy developers in using composite materials for load-bearing structures. Sponsored by the U.S. Department of Energy's Water Power Technologies Office, the multiyear project comprises of collaborators from the National Renewable Energy Laboratory (NREL), Sandia National Laboratories, Pacific Northwest National Laboratory (PNNL), Montana State University (MSU), Florida Atlantic University (FAU), and industry stakeholders. As part of the Marine Energy Advanced Materials project, marine renewable energy industry surveys and assessments were conducted to identify key materials and knowledge gaps that hinder the adoption of composite materials in marine renewable energy structures. Specific knowledge gaps highlighted for composite materials were environmental effects, fatigue strengths, and bonded and bolted interconnects (composite/composite and composite/metal). It was concluded that many of these gaps could be addressed through subcomponent validation; consequently, a program was developed at NREL with the goals of developing subcomponent validation methods for appropriate marine energy materials, which would improve the understanding of design allowables for full-scale structural components and joints. Ultimately, the aim is to reduce timelines and costs associated with full-scale structural validation efforts while also providing near-net-scale static and fatigue data of composite/metal subcomponents for marine renewable energy systems. To approach these goals, a testing program was developed at NREL to investigate a variety of materials and structural design details at the subcomponent scale to understand (a) the effects of harsh and corrosive marine energy environments and (b) the static and fatigue strengths of the complex geometries. The recent study from this testing program is perhaps the largest that has ever been conducted with respect to specimen scale and geographic diversity of underwater environmental conditions that the specimens were subjected to. A variety of specimen geometries were designed by NREL to highlight key features of multimaterial (composite/composite or metal/composite) interconnects that may be used in marine renewable energy structural designs. The designs used several different composite matrices, adhesives, and marine-grade steels, which were highlighted in the surveys as being the most appropriate for harsh marine environments. Composite panels were then manufactured at MSU, and were subsequently manufactured into test specimens by NREL. The specimens were shipped to FAU and PNNL for conditioning in ocean water tanks at various temperatures for an extended period. The specimens were then returned to NREL for structural validation. This presentation will provide an overview of recent advances within the testing program in terms of specimen design and test methods, and will discuss results and key findings of the subcomponent testing program to date at NREL.

adhesives↗
NASA NTRS1990

Automation software for a materials testing laboratory

The software environment in use at the NASA-Lewis Research Center's High Temperature Fatigue and Structures Laboratory is reviewed. This software environment is aimed at supporting the tasks involved in performing materials behavior research. The features and capabilities of the approach to specifying a materials test include static and dynamic control mode switching, enabling multimode test control; dynamic alteration of the control waveform based upon events occurring in the response variables; precise control over the nature of both command waveform generation and data acquisition; and the nesting of waveform/data acquisition strategies so that material history dependencies may be explored. To eliminate repetitive tasks in the coventional research process, a communications network software system is established which provides file interchange and remote console capabilities.

Mcgaw, Michael A.↗
NASA NTRS1973

Evaluation of load-life relation with ball bearings at 500 deg F

A survey of the literature suggests that a stress-life exponent of approximately 12 is typical of vacuum-processed steels for ball bearings rather than the exponent of 9 which has been generally accepted by the bearing industry and bearing users. Tests run with vacuum-degassed AISI 52100 balls in the five-ball fatigue tester at four maximum Hertz stress levels in the range from 650000 to 875000 psi showed good agreement with the literature. However, tests run with consumable-electrode vacuum melted AISI M-50 steel angular-contact ball bearings at 500 deg F at three thrust loads did not show significant deviation from the accepted ninth power stress-life relation.

Parker, R. J.↗
NASA NTRS1998

Simulated Bladed MMC Disk LCF Validation

The goal of this program was to evaluate the low cycle fatigue behavior of an SCS-6/Ti-6Al-4V sub-component under bi-axial loading conditions at 316 C(600 F). A simulated bladed TMC disk was designed having thirty four blades representing the number that would be used in Allied Signal's JTAGG II impeller. The outer diameter of the bladed ring was 254 mm (10.0 inch) and the inner diameter 114.3 mm (4.50 inch). The outer and inner diameter of the composite zone was 177.8 mm (7.00 inch) and 127.O mm(5.00 inch) respectively. Stress analysis showed that the fatigue life of the bladed composite ring would be about 12000 cycles for the test conditions applied. A modal analysis was conducted which showed that the blades would have sufficient life margin from dynamic excitation. The arbor design was the same as that employed in the spin-to burst test of NAS3-27027. A systematic stress analysis of each part making up the arbor was undertaken to assure the design would meet the low cycle fatigue requirements of the program. The Textron Systems grooved foil-fiber process was chosen to make the SCS-6/Ti-6Al-4V core ring based on the success they had in contract NAS3-27027. Fiber buckling, however, was observed at several locations in the first ring made which rendered it unsuitable for spin testing. The fiber buckling was attributed to cracking of the graphite tooling during the consolidation process. On this basis a second ring was made but it too contained fiber buckling defects. Analysis by Textron indicated that the fiber buckling was most likely due to poor placement of the SCS-6 fiber in the etched grooves of the Ti-6Al-4V foil. This was also a contributor to the defects in the first ring. Since there was little indication of control in the process to manufacture a quality ring a third attempt at making a ring was not undertaken.

Merrick, H. F.↗
NASA NTRS1984

Low cycle fatigue behavior of conventionally cast MAR-M 200 AT 1000 deg C

The low cycle fatigue behavior of the nickel-based superalloy MAR-M 200 in conventionally cast form was studied at 1000 C. Continuous cycling tests, without hold times, were conducted with inelastic strain ranges of from 0.04 to 0.33 percent. Tests were also conducted which included a hold time at peak strain in either tension or compression. For the conditions studied, it was determined that imposition of hold times did not significantly affect the fatigue life. Also, for continuous cycling tests, increasing or decreasing the cycle frequency did not affect life. Metallographic analysis revealed that the most significant damage mechanism involved environmentally assisted intergranular crack initiation and propagation, regardless of the cycle type. Changes in the gamma morphology (rafting and rod formation) were observed, but did not significantly affect the failure.

Milligan, W. W.↗
NASA NTRS2008

Post Test Evaluation of HSCT Nozzle Acoustic Liner Subcomponents Subjected to a Hot Acoustic Durability Test

The acoustic liner system designed for use in the High Speed Civil Transport (HSCT) was tested in a thermal-acoustic environment. Five ceramic matrix composite (CMC) acoustic tile configurations, five bulk acoustic absorbers, and one thermal protection system design were tested. The CMC acoustic tiles were subjected to two 2 3/4 hr ambient temperature acoustic exposures to measure their dynamic response. One exposure was conducted on the tiles alone and the second exposure included the tiles and the T-foam bulk absorber. The measured tile RMS strains were small. With or without the T-foam absorber, the dynamic strains were below strain levels that would cause damage during fatigue loading. After the ambient exposure, a 75-hr durability test of the entire acoustic liner system was conducted using a thermal-acoustic cycle that approximated the anticipated service cycle. Acoustic loads up to 139 dB/Hz and temperatures up to 1670 F (910 C) were employed during this 60 cycle test. During the durability test, the CMC tiles were exposed to temperatures up to 1780 F and a transient through thickness gradient up to 490 F. The TPS peak temperatures on the hot side of the panels ranged from 750 to 1000 F during the 60 cycles. The through thickness delta T ranged from 450 to 650 F, varying with TPS location and cycle number. No damage, such as cracks or chipping, was observed in the CMC tiles after completion of the testing. However, on tile warped during the durability test and was replaced after 43 or 60 cycles. No externally observed damage was found in this tile. No failure of the CMC fasteners occurred, but damage was observed. Cracks and missing material occurred, only in the fastener head region. No indication of damage was observed in the T-foam acoustic absorbers. The SiC foam acoustic absorber experienced damage after about 43 cycles. Cracking in the TPS occurred around the attachment holes and under a vent. In spite of the development of damage, the TPS maintained its insulative capability throughout the durability test. The durability test results demonstrate damage-tolerant CMC tile, CMC fastener, TPS, and T-foam absorber designs for the combined thermal and acoustic engine nozzle environment.

Verrilli, Michael J.↗
NASA NTRS1997

The Characteristics of Fatigue Damage in the Fuselage Riveted Lap Splice Joint

An extensive data base has been developed to form the physical basis for new analytical methodology to predict the onset of widespread fatigue damage in the fuselage lap splice joint. The results of detailed destructive examinations have been cataloged to describe the physical nature of MSD in the lap splice joint. ne catalog includes a detailed description, e.g., crack initiation, growth rates, size, location, and fracture morphology, of fatigue damage in the fuselage lap splice joint structure. Detailed examinations were conducted on a lap splice joint panel removed from a full scale fuselage test article after completing a 60,000 cycle pressure test. The panel contained a four bay region that exhibited visible outer skin cracks and regions of crack link-up along the upper rivet row. Destructive examinations revealed undetected fatigue damage in the outer skin, inner skin, and tear strap regions. Outer skin fatigue cracks were found to initiate by fretting damage along the faying surface. The cracks grew along the faying surface to a length equivalent to two to three skin thicknesses before penetrating the outboard surface of the outer skin. Analysis of fracture surface marker bands produced during full scale testing revealed that all upper rivet row fatigue cracks contained in a dim bay region grow at similar rates; this important result suggests that fracture mechanics based methods can be used to predict the growth of outer skin fatigue cracks in lap splice structure. Results are presented showing the affects of MSD and out-of-plane pressure loads on outer skin crack link-up.

Piascik, Robert S.↗
NASA NTRS2020

Experimental Setup and Parameters for Testing Uncoated and EBC-Coated CMCs under Thermal Gradients Induced by Laser Heating and Backside Air Cooling

An experimental setup to induce through thickness thermal gradients in ceramic matrix composite (CMC) specimens without and with an applied environmental barrier coating (EBC) is described in detail. Components of the experimental set up include a laser for the heat source on the front of the specimen, a cooling air nozzle on the back of the specimen with pyrometers to measure temperatures on both sides, and a full-field thermal image camera to ensure uniformity of the temperature distribution in the gage section of the specimen. Test specimen is loaded in a servohydraulic system, which can superimpose either static or dynamic loads on the specimen to investigate creep and fatigue behaviors of CMCs under through thickness thermal gradient conditions. Mechanical strains on the front and backsides of the test specimen were measured during the thermal gradient tests with superimposed mechanical loading using two contact extensometers. Selected through thickness thermal gradient test results generated with the experimental setup under different nominal front side temperatures and multiple constant laser power levels on uncoated and EBC coated CMCs and procedures used to generate those results are described in this report. Two examples of tests conducted using the test system on uncoated CMCs under creep and sustained-peak, low-cycle fatigue with through thickness thermal gradient conditions are provided.

ceramic matrix composite, environmental barrier co↗
NASA NTRS2014

Use of Slow Strain Rate Tensile Testing to Assess the Ability of Several Superalloys to Resist Environmentally-Assisted Intergranular Cracking

Intergranular fatigue crack initiation and growth due to environmental degradation, especially at notched features, can often limit the fatigue life of disk superalloys at high temperatures. For clear comparisons, the effects of alloy composition on cracking in air needs to be understood and compared separately from variables associated with notches and cracks such as effective stress concentration, plastic flow, stress relaxation, and stress redistribution. The objective of this study was to attempt using simple tensile tests of specimens with uniform gage sections to compare the effects of varied alloy composition on environment-assisted cracking of several powder metal and cast and wrought superalloys including ME3, LSHR, Udimet 720(TradeMark) ATI 718Plus(Registered TradeMark) alloy, Haynes 282(Trademark), and Inconel 740(TradeMark) Slow and fast strain-rate tensile tests were found to be a useful tool to compare propensities for intergranular surface crack initiation and growth. The effects of composition and heat treatment on tensile fracture strain and associated failure modes were compared. Environment interactions were determined to often limit ductility, by promoting intergranular surface cracking. The response of various superalloys and heat treatments to slow strain rate tensile testing varied substantially, showing that composition and microstructure can significantly influence environmental resistance to cracking.

fatigue(materials)↗
NASA NTRS1994

Thermomechanical Fatigue Damage/Failure Mechanisms in SCS-6/Timetal 21S [0/90](Sub S) Composite

The thermomechanical fatigue (TMF) deformation, damage, and life behaviors of SCS6/Timetal 21S (0/90)s were investigated under zero-tension conditions. In-phase (IP) and out-of-phase (OP) loadings were investigated with a temperature cycle from 150 to 650 deg C. An advanced TMF test technique was used to quantify mechanically damage progression. The technique incorporated explicit measurements of the macroscopic (1) isothermal static moduli at the temperature extremes of the TMF cycle and (2) coefficient of thermal expansion (CTE) as functions of the TMF cycles. The importance of thermal property degradation and its relevance to accurate post-test data analysis and interpretation is briefly addressed. Extensive fractography and metallography were conducted on specimens from failed and interrupted tests to characterize the extent of damage at the microstructure level. Fatigue life results indicated trends analogous to those established for similar unidirectional(0) reinforced titanium matrix composite systems. High stress IP and mid to low stress OP loading conditions were life-limiting in comparison to maximum temperature isothermal conditions. Dominant damage mechanisms changed with cycle type. Damage resulting from IP TMF conditions produced measurable decreases in static moduli but only minimal changes in the CTE. Metallography on interrupted and failed specimens revealed extensive (0) fiber cracking with sparse matrix damage. No surface initiated matrix cracks were present. Comparable OP TMF conditions initiated environment enhanced surface cracking and matrix cracking initiated at (90) fiber/matrix (F/M) interfaces. Notable static moduli and CTE degradations were measured. Fractography and metallography revealed that the transverse cracks originating from the surface and (90) F/M interfaces tended to converge and coalesce at the (0) fibers.

Castelli, Michael G.↗
NASA NTRS1980

Composite structural materials

The use of filamentary composite materials in the design and construction of primary aircraft structures is considered with emphasis on efforts to develop advanced technology in the areas of physical properties, structural concepts and analysis, manufacturing, and reliability and life prediction. The redesign of a main spar/rib region on the Boeing 727 elevator near its actuator attachment point is discussed. A composite fabrication and test facility is described as well as the use of minicomputers for computer aided design. Other topics covered include (1) advanced structural analysis methids for composites; (2) ultrasonic nondestructive testing of composite structures; (3) optimum combination of hardeners in the cure of epoxy; (4) fatigue in composite materials; (5) resin matrix characterization and properties; (6) postbuckling analysis of curved laminate composite panels; and (7) acoustic emission testing of composite tensile specimens.

Ansell, G. S.↗
NASA NTRS1979

A temperature dependent fatigue failure criterion for graphite/epoxy laminates

A fatigue failure criterion applicable to composite materials is developed and applied to predict the fatigue behavior of graphite/epoxy laminates with particular emphasis on the influence of temperature. Tensile stress-strain curves and tension-tension fatigue curves for various unidirectional, angle-ply and symmetrically balanced laminates were developed at test temperatures of 25 C, 74 C and 114 C. In general for most laminates a reduction in both static strength and fatigue strength is observed with increasing temperature. This reduction appeared more severe in fatigue loading than in static tensile loading and most severe where the shear stress in the lamina is the dominant failure mode. Through an analytical formulation of shifting functions for the influences of temperature, all fatigue data are shown to be capable of being reduced to a single reference curve at some temperature. Additionally, examples are given which demonstrate the capability of the fatigue failure criterion to predict failure of complex symmetrically balanced laminates from relevant parameters obtained from the observed behavior of unidirectional and angle-ply laminates.

Rotem, A.↗
NASA NTRS1980

Effects of temperature, thermal exposure, and fatigue on an alumina/aluminum composite

An experimental investigation of the mechanical properties and microstructure of an aluminum matrix/polycrystalline alumina fiber composite material is discussed. The effects of fabrication, isothermal exposure (up to 10,000 hours at 590 K), thermal cycling (6000 cycles between 200 K and 590 K), fatigue (1,000,000 tension-tension cycles) were determined by mechanical testing and metallurgical analysis. The fabrication process severely degraded the fiber strength by reducing the alumina to a nonstoichiometric form and quenching in the resultant vacancies and stress fields. However, isothermal exposure, thermal cycling, and fatigue cycling all restored the fiber strength by enhancing vacancy annihilation. Comparison of the as-fabricated material with other aerospace materials shows that it is an attractive candidate for select applications. Long duration isothermal exposure weakened the matrix by overaging and through the diffusional loss of lithium to a surface reaction forming lithium carbonate. Thermal cycling initiated cracks in the matrix and fibers. Tension-tension fatigue cycling caused no apparent damage to the as-fabricated material but in fact, strengthened it to the rule-of-mixtures value. Fatigue cycling after thermal exposure did have a cumulative damage effect.

Olsen, G. C.↗
NASA NTRS1973

Evaluation of load-life relation with ball bearings at 500 F

A survey of the literature suggests that a stress-life exponent of approximately 12 is typical of vacuum-processed steels for ball bearings rather than the exponent of 9 which has been generally accepted by the bearing industry and bearing users. Tests run with vacuum-degassed AISI 52100 balls in the five-ball fatigue tester at four maximum Hertz stress levels in the range from 650,000 to 875,000 psi showed good agreement with the literature. However, tests run with consumable-electrode vacuum melted AISI M-50 steel angular-contact ball bearings at 500 F at three thrust loads did not show significant deviation from the accepted ninth power stress-life relation.

Parker, R. J.↗
NASA NTRS1990

Thermal-Transient Testing Of Turbine Blades

Testing apparatus applies pulses of heat to turbine blade to determine resistance to thermal fatigue. Uses nonintrusive inductive heating and records distribution of temperature on blade with infrared video camera. Allows precise control of heating and cooling. Designed for testing blades used in advanced high-pressure, high-temperature turbines.

Wagner, William R.↗
NASA NTRS1973

Final analysis and design of a thermal protection system for 8-foot HTST combustor

The cylindrical shell combustor with T-bar supports in the 8-foot HTST at the NASA-Langley Research Center encountered vibratory fatigue cracking over a period of 50-250 tunnel tests within a limited range of the required operating envelope. A preliminary design study provided several suitable thermal protection system designs for the combustor, one of which was a two-pass regenerative type air-cooled omega-shaped segment liner. A final design layout of the omega segment liner was prepared and analyzed for steady-state and transient conditions. The design of a support system for the fuel spray bar assembly was also included. Detail drawings suitable for fabrication purposes were also prepared. Liner design problems defined during the preliminary study included (1) the ingress of gas into the attachment bulb section of the omega segment, (2) the large thermal gradient along the leg of the omega bulb attachment section and, (3) the local peak metal temperature at the radius between the liner ID and the leg of the bulb attachment. These were resolved during the final design task. Analyses of the final design of the omega segment liner indicated that all design goals were met and the design provided the capability of operating over the required test envelope with a life expectancy substantially above the goal of 1500 cycles.

Moskowitz, S.↗