Creep deformation behavior of metals under repeated stress reversals Final report
Reversed creep tests on chemical lead, aluminum, and copper and creep deformation behavior under repeated stress reversals
Kitagawa, M.↗
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Parameter identification using a creeping-random-search algorithm
A creeping-random-search algorithm is applied to different types of problems in the field of parameter identification. The studies are intended to demonstrate that a random-search algorithm can be applied successfully to these various problems, which often cannot be handled by conventional deterministic methods, and, also, to introduce methods that speed convergence to an extremal of the problem under investigation. Six two-parameter identification problems with analytic solutions are solved, and two application problems are discussed in some detail. Results of the study show that a modified version of the basic creeping-random-search algorithm chosen does speed convergence in comparison with the unmodified version. The results also show that the algorithm can successfully solve problems that contain limits on state or control variables, inequality constraints (both independent and dependent, and linear and nonlinear), or stochastic models.
Parrish, R. V.↗
Cyclic creep and fatigue of TD-NiCr (thoria-dispersion-strengthened nickel-chromium), TD-Ni, and NiCr sheet at 1200 C
The resistance of thin TD-NiCr sheet to cyclic deformation was compared with that of TD-Ni and a conventional nickel-chromium alloy. Strains were determined by a calibration technique which combines room-temperature strain gage and deflection measurements with high-temperature deflection measurements. Analyses of the cyclic tests using measured tensile and creep-rupture data indicated that the TD-NiCr and NiCr alloy specimens failed by a cyclic creep mechanism. The TD-Ni specimens, on the other hand, failed by a fatigue mechanism.
Hirschberg, M. H.↗
Temperature effects on the strainrange partitioning approach for creep-fatigue analysis
Examination is made of the influence of temperature on the strainrange partitioning approach to creep-fatigue. Results for Cr-Mo steel and Type 316 stainless steel show the four partitioned strainrange-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. Continuous strain cycling results obtained over a broad range of high temperatures and frequencies are in excellent agreement with bounds provided by the approach. The observed transition from one bound to the other is also in good agreement with the approach.
Halford, G. R.↗
Effect of temperature on the tensile and creep characteristics of PRD49 fiber/epoxy composites
Tensile and creep data of PRD49-1 and -3 fiber/epoxy resin composites are presented. Tensile data were obtained from 20 K (-423 F) to 477 K (400 F). Tensile strengths and moduli were determined at selected temperatures. Creep data up to 1000 hours are presented of fiber composites at 279 K (75 F), 422 K (300 F), and 450 K (350 F) at stress levels of approximately 50 and 80 percent of the ultimate tensile strength at 297 K (75 F). Details are presented of tensile specimens and test procedures used in the investigation.
Hanson, M. P.↗
Sensitivity of the creep-rupture properties of Waspaloy sheet to sharp-edged notches in the temperature range 1000-1400 deg F.
Time-dependent notch sensitivity of Waspaloy was observed at test temperatures from 1000 to 1300 deg F. Its occurrence in this range was dependent on the heat treatment. ?Overaging' eliminated the notch sensitivity. Optimum combination of smooth and notched specimen strengths for material solution treated at 1975 deg F were obtained by aging 24 hr at 1550 deg F. Necessary conditions for time-dependent notch sensitivity were (1) the notch specimen loads had to be below the approximate 0.2 percent offset yield strength; and (2 ) test data from smooth specimens had to indicate that small amounts of creep used up large fractions of creep-rupture life. No reasons were evident why these criteria will not prove applicable to other alloys.
Wilson, D. J.↗
Effect of temperature on the tensile and creep characteristics of PRD49 fiber/epoxy composites.
Tensile and creep data of PRD49-I and -II fiber/epoxy-resin composites are presented. Tensile data were obtained from 20 to 477 K. Tensile strengths and moduli were determined at selected temperatures. Creep data up to 1000 hours are presented for fiber composites at 279, 422, and 450 K at stress levels of approximately 50 and 80 per cent of the ultimate tensile strength at 297 K. Details are presented of tensile specimens and test procedures used in the investigation.
Hanson, M. P.↗
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.↗
Effect of temperature on tensile and creep characteristics of PRD49 fiber/epoxy composites
Tensile and creep data of PRD49-1 and 3 fiber/epoxy-resin composites are presented. Tensile data were obtained from 20 to 477 K (-423 to 400 F). Tensile strengths and moduli were determined at selected temperatures. Creep data are presented for fiber composites at 297, 422 and 450 K (75, 300, and 350 F) for as long as 1000 hours at stress levels of approximately 50 and 80 percent of the ultimate tensile strength at 297 K (75 F). Details of tensile specimens and test procedures used in the investigation are presented.
Hanson, M. P.↗
Out-of-pile creep behavior of uranium carbide
Compression creep tests were investigated on various UC-based fuel materials having a variation in both density and composition. Specimens were prepared by casting and by hot pressing. Steady-state creep rates were measured under vacuum at 1400 to 1800 C in the stress range 500-4000 psi.
Wright, T. R.↗
Hot vacuum creep forming of scale shuttle external tank dome caps
The feasibility of forming shuttle external tank dome caps by hot vacuum creep was investigated for a sub-scale configuration. Aluminum 2219-T37 at an elevated temperature equivalent to the artificial aging time and temperature was used to produce the T87 condition while achieving MIL-HBK -5 properties of 2219-T87 aluminum alloy material. A feasibility analysis was conducted in two phases: the design and build of a sub-scale hot vacuum creep forming (HVCF) die and the forming evaluation of various cap configurations. The contour was constant in all evaluations. This configuration was found to be too severe for the limited forming force available by HVCF.
Thomas, A. O.↗
Treatment of multiaxial creep-fatigue by strainrange partitioning
Strainrange partitioning is a recently developed method for treating creep-fatigue interaction at elevated temperature. Most of the work to date has been on uniaxially loaded specimens, where as practical applications often involve load multiaxiality. It is shown how the method can be extended to treat multiaxiality through a set of rules for combining the strain components in the three principal directions. Closed hysteresis loops, as well as plastic and creep strain ratcheting are included. An application to hold-time tests in torsion will be used to illustrate the approach.
S S Manson↗
Tensile and creep rupture properties of (16) uncoated and (2) coated engineering alloys at elevated temperatures
Sixteen test materials were supplied by NASA-Lewis Research Center as wrought bar or cast remelt stock. The cast remelt stock was cast into test blanks with two such materials being also evaluated after Jocoat coating was applied. Mechanical properties evaluated included tensile, modulus of elasticity, Poisson's Ratio, creep properties and creep rupture strength. Tests were conducted at temperatures applicable to the service temperature of the various alloys. This range extended from room temperature to 1000 C.
Fritz, L. J.↗
Fractographic evaluation of creep effects on strain-controlled fatigue-cracking of AISI 304LC and 316 stainless steel
Analysis of high temperature low cycle fatigue of AISI 304LC and 316 stainless steels by the method of strainrange partitioning results in four separate strainrange versus life relationships, depending upon the way in which creep-strain and plastic strain are combined within a cycle. Fractography is used in this investigation of the creep-fatigue interaction associated with these cycles. The PP and PC-cycle fractures were transgranular. The PC-cycle resulted in fewer cycles of initiation and shorter total cyclic life for the same applied inelastic strainrange. The CC-cycle had mixed transgranular and intergranular fracture, fewer cycles of initiation and shorter cycle life than PP or PC. The CP-cycle had fully integranular cracking, and failed in fewer cycles than were required for cracks to initate for PP,PC, and CC.
Oldrieve, R. E.↗
Ductility normalized-strain-range partitioning life relations for creep-fatigue life predictions
Techniques utilizing strainrange partitioning may be used to estimate the effects of the environment on the high-temperature, low-cycle, creep-fatigue resistance of alloys. Three levels of ductility-normalized strainrange-partitioning life relations are discussed: (1) strainrange partitioning relations from ductility data, (2) strainrange partitioning relations scaled by ductility ratios, and (3) strainrange partitioning life relations with measured PP lines. The procedures have demonstrated good agreement with available creep-fatigue data.
Halford, G. R.↗
Interpolation and extrapolation of creep rupture data by the Minimum Commitment Method. I - Focal-point convergence. II - Oblique translation. III - Analysis of multiheats
The framework in which minimum-commitment analyses of creep-rupture data can be implemented is outlined. The approach is termed the focal point convergence method (FPCM) because the basic parameter A, also known as stability factor, is geometrically the (imaginary) focal point of convergence of all isothermals when extended to the very long or very short times necessary for such convergence to occur. The method can be implemented either by manual-graphical analysis or by computer code. The method is illustrated in detail for the nickel-base alloy Astroloy, as well as for steels, other nickel-base alloys, and aluminum alloys. The minimum-commitment concept is extended to the analysis of creep-rupture data where each isothermal is generated by an oblique translation of the 'master curve' when plotted on log rupture time and log stress axes. The oblique translation method uses the same types of functions in the FPCM. Approaches for treating multiheats on the basis of the FPCM are discussed in detail.
Manson, S. S.↗
A quarter-century of progress in the development of correlation and extrapolation methods for creep rupture data
Developments in the analysis of creep-rupture data are reviewed with particular reference to time temperature relations for the correlation and extrapolation of creep and stress rupture data, the minimum commitment method, and successive regression methods. Some contributions to the development of time-temperature parameters are noted.
Manson, S. S.↗
The fracture morphology of nickel-base superalloys tested in fatigue and creep-fatigue at 650 C
The fracture surfaces of compact tension specimens from seven nickel-base superalloys fatigue tested at 650 C were studied by scanning electron microscopy and optical metallography to determine the nature and morphology of the crack surface in the region of stable growth. Crack propagation testing was performed as part of an earlier study at 650 C in air using a 0.33 Hz fatigue cycle and a creep-fatigue cycle incorporating a 900 second dwell at maximum load. In fatigue, alloys with a grain size greater than 20 micrometers, HIP Astroloy, Waspaloy, and MERL 76, exhibited transgranular fracture. MERL 76 also displayed numerous fracture sites which were associated with boundaries of prior powder particles. The two high strength, fine grain alloys, IN 100 and NASA IIB-7, exhibited intergranular fracture. Rene 95 and HIP plus forged Astroloy displayed a mixed failure mode that was transgranular in the coarse grains and intergranular in the fine grains. Under creep-fatigue conditions, fracture was found to be predominantly intergranular in all seven alloys.
Gayda, J.↗