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Monday, July 27, 2020 | History

2 edition of Fatigue crack initiation and small crack growth in several airframe alloys found in the catalog.

Fatigue crack initiation and small crack growth in several airframe alloys

Fatigue crack initiation and small crack growth in several airframe alloys

  • 156 Want to read
  • 21 Currently reading

Published by National Aeronautics and Space Administration, Langley Research Center in Hampton, Va .
Written in English

    Subjects:
  • Airframes -- Fatigue.,
  • Airframes.,
  • Crack initiation.,
  • Crack propagation.,
  • Morphology.,
  • Stress intensity factors.

  • Edition Notes

    StatementM.H. Swain ... [et al.].
    SeriesNASA technical memorandum -- 102598., AVSCOM technical memorandum -- 90-B-001.
    ContributionsSwain, M. H., Langley Research Center.
    The Physical Object
    FormatMicroform
    Pagination6 p.
    ID Numbers
    Open LibraryOL16138043M

    Although the general utility of a large-crack-ΔK th approach is questionable due to the potentially rapid growth of small fatigue cracks, the low allowable stresses involved in turbine engine high cycle fatigue appear to limit and simplify the small-crack problem. An examination is also presented of the potential effects of high-cycle fatigue. The present study highlights the attempts to detect crack initiation and measure crack growth in the heavily deformed surface layers, using several measurement techniques of the following aluminum alloys: T & T

      Also at VHCF-1, the author considered the life-controlling microstructural fatigue mechanisms in homogeneous ductile metals and alloys in the UHCF regime and concluded: ‘ the initiation and slow growth of stage I fatigue cracks, including the preceding processes of bulk cyclic deformation and cyclic strain localization, will be life. @article{osti_, title = {Effect of corrosion pitting on fatigue crack initiation and fatigue life}, author = {Rokhlin, S I and Nagy, H and Zoofan, B}, abstractNote = {Fatigue crack initiation and growth from artificial pits of different depths has been studied. The experimental results were analyzed using fracture-mechanical models including those for small cracks.

    cracks at comparable growth rates. The nature of multi-site crack initiation and growth of small cracks at notches was investigated and the effort extended to lug joints that are widely used in airframe applications. Results from this work suggest the possibility of modelling crack growth from a size. Some modifications to the ΔK eff-rate relations were needed in the near-threshold regime to fit small-crack growth rate behavior and endurance limits. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched specimens made of several aluminum alloys and a titanium alloy under.


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Fatigue crack initiation and small crack growth in several airframe alloys Download PDF EPUB FB2

In materials science, fatigue is the weakening of a material caused by cyclic loading that results in progressive and localized structural damage and the growth of cracks.

Once a fatigue crack has initiated, each loading cycle will grow the crack a small amount, typically producing striations on some parts of the fracture surface. The crack will continue to grow until it reaches a critical. Get this from a library. Fatigue crack initiation and small crack growth in several airframe alloys.

[M H Swain; Langley Research Center.;]. Fatigue crack growth (FCG) in aluminum–lithium (Al–Li) and other high strength aerospace aluminum alloys may be discussed in the context of several crack growth regimes that relate to the practical aspects of cracks in components and structures.

Figure is a schematic of these FCG regimes. In the first regime, short/small (i.e., short and small) fatigue cracks nucleate at a variety of. When the fissure produced by crack initiation reaches the size at which the stress intensity range in the cycle is sufficient the crack propagates in a direction normal to the tensile stress.

The characteristics of fatigue crack propagation are summarized in Figure This shows three regions of fatigue crack growth. The former is dominated by fatigue crack growth, while the latter is dominated by fatigue crack initiation.

The similar phenomenon is also often observed in Nickel-based alloys. Abstract. The growth of naturally-initiated small cracks under a variety of constant amplitude and variable amplitude load sequences is examined for several airframe materials: the conventional aluminum alloys, T3 and T6, the aluminum-lithium alloy, T8E41, and steel.

Application of the Unified Approach requires a data reduction scheme that is illustrated schematically in Fig. fatigue crack growth tests can be performed either at constant R-ratio (minimum load/maximum load) or at constant K se, crack growth rates can be represented in terms of ΔK or K max (Fig.

1a and b), and both representations are complementary since the crack growth. In addition to the small crack growth effects, FCG response of aluminum alloys can also be significantly affected by the presence of bulk residual stresses introduced during manufacturing and post-manufacturing processes such as heat treatment.

There is a qualitative understanding of the effects of residual stress on the FCG behavior, but the effects need to be comprehensively quantified and. nucleating and growing a fatigue crack to a length at which it can be detected.

The range of effective stress intensity factor, that is, the idea of crack closure allows the growth of fatigue cracks to be rationalized. The behavior of small cracks is in many respects quite different from long cracks. A fatigue lifing framework using a lead crack concept has been developed by the DSTO for metallic primary airframe components.

The framework is based on years of detailed inspection and analysis of fatigue cracks in many specimens and airframe components, and is an important additional tool for determining aircraft component fatigue lives in the Royal Australian Air Force (RAAF) fleet.

Fatigue crack initiation and small crack growth in several airframe alloys. Article. Feb ; The initiation and growth of small cracks ( microns m) from edge notches in T3 aluminum. fatigue crack orientation in a pressurised fuselage is a longitudinal crack along the direction of maximum hoop stress.

Damage tolerant designs use fracture mechanics data and analysis to predict crack growth rates and critical crack lengths [1]. Cabin pressure results in radial growth of the skin and this radial growth is resisted by.

FATIGUE CRACK INITIATION AND SMALL CRACK GROWTH IN SEVERAL AIRFRAME ALLOYS. Swain, J. Newman, Jr., E. Phillips, and R. Everett, Jr. January National Aeronautics and Space Administration Langley Research Center Hampton, Virginia (NASA-TM-] 02 5q¢i) AND SMALL CRACK ALLOYS (NASA) FATIGUE GROWTH TN 8 p CRACK INITIATION.

good success in predicting small crack growth rates and total fatigue lives for several different mate- dais, including airframe alloys. These practical successes are encouraging, but it should be. An assessment has been made of the potential reduction in calculated fatigue-crack-growth lives when the small-crack effect is considered.

The assessment was based on small-crack and large-crack grwoth-rate data of T3 aluminum alloy forR=−1 andR=0 constant-amplitude loading and for a fighter-wing spectrum loading (FALSTAFF). The potential impact of the small-crack effect was. The growth of naturally-initiated small cracks under a variety of constant amplitude and variable amplitude load sequences is examined for several airframe materials: the conventional aluminum.

Fatigue Crack Initiation in Austenitic Stainless Steels in LWR Environments Crack growth rates plotted as a function of crack length for austenitic stainless strain–controlled fatigue tests of small polished specimens at room temperature in air.

Best–fit. of fatigue crack growth at Klevels below K c. The process of fatigue failure itself consists of several distinct processes involving initial cyclic damage (cyclic hardening or softening), formation of an initial ‘fatal’ flaw (crack initiation), macroscopic propagation of this flaw (crack growth), and final catastrophic failure or.

Understanding the fatigue crack initiation and growth in titanium alloys, however, is complicated due to the changes in their microstructure with a small change in the heat treatment process [   Fatigue test data came from a high-cycle-fatigue study by the U.S.

Air Force and a metallic materials properties handbook. A crack-closure model with a cyclic-plastic-zone-corrected effective stress-intensity factor range and equivalent-initial-flaw-sizes (EIFS) were used to calculate fatigue lives using only crack-growth-rate data. Fatigue Crack Initiation.

While on the subject of dislocations, it is appropriate to briefly discuss fatigue. Fatigue is one of the primary reasons for the failure of structural components. The life of a fatigue crack has two parts, initiation and propagation. Dislocations play a major role in the fatigue crack initiation.

Abstract. As is well known, there is considerable evidence that short/small fatigue cracks in metals grow at faster rates and lower nominal ΔK values than those characteristic of long/large cracks (Ritchie and Suresh ; Suresh and Ritchie ).In particular, short/small cracks can grow at ΔK values well below the long/large crack growth threshold, ΔK th.Attention is given to the interpretation of test data by fatigue crack growth rate using two empirical parameters in consistent with the fracture control methodology currently used by industry.

Micrograph and crack growth rate data are presented for a host of metals used by the aerospace and nuclear industry.