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  • Other Sources  (9)
  • 1
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    The Growth of Small Corrosion Fatigue Cracks in Alloy 7075 (2001)
    In:  CASI
    Details
    Publication Date: 2018-06-02
    Description: The corrosion fatigue crack growth characteristics of small (less than 35 microns) surface and corner cracks in aluminum alloy 7075 is established. The early stage of crack growth is studied by performing in situ long focal length microscope (500X) crack length measurements in laboratory air and 1% NaCl environments. To quantify the "small crack effect" in the corrosive environment, the corrosion fatigue crack propagation behavior of small cracks is compared to long through-the-thickness cracks grown under identical experimental conditions. In salt water, long crack constant K(sub max) growth rates are similar to small crack da/dN.
    Keywords: Metals and Metallic Materials
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  • 2
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    Fatigue crack propagation in aerospace aluminum alloys (1990)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: This paper reviews fracture mechanics based, damage tolerant characterizations and predictions of fatigue crack growth in aerospace aluminum alloys. The results of laboratory experimentation and modeling are summarized in the areas of: (1) fatigue crack closure, (2) the wide range crack growth rate response of conventional aluminum alloys, (3) the fatigue behavior of advanced monolithic aluminum alloys and metal matrix composites, (4) the short crack problem, (5) environmental fatigue, and (6) variable amplitude loading. Remaining uncertainties and necessary research are identified. This work provides a foundation for the development of fatigue resistant alloys and composites, next generation life prediction codes for new structural designs and extreme environments, and to counter the problem of aging components.
    Keywords: STRUCTURAL MECHANICS
    Type: ICAS Congress; Sept. 9-14, 1990; Stockholm; Sweden
    Format: text
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  • 3
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    Accelerated Threshold Fatigue Crack Growth Effect-Powder Metallurgy Aluminum Alloy (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Fatigue crack growth (FCG) research conducted in the near threshold regime has identified a room temperature creep crack growth damage mechanism for a fine grain powder metallurgy (PM) aluminum alloy (8009). At very low (Delta) K, an abrupt acceleration in room temperature FCG rate occurs at high stress ratio (R = K(sub min)/K(sub max)). The near threshold accelerated FCG rates are exacerbated by increased levels of K(sub max) (K(sub max) = 0.4 K(sub IC)). Detailed fractographic analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near threshold and K(sub max) influenced accelerated crack growth is time and temperature dependent.
    Keywords: Structural Mechanics
    Type: Fatigue 2002: 8th International Fatigue Congress; Jun 02, 2002 - Jun 07, 2002; Stockholm; Sweden
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  • 4
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    Micromechanics Modeling of Fracture in Nanocrystalline Metals (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Nanocrystalline metals have very high theoretical strength, but suffer from a lack of ductility and toughness. Therefore, it is critical to understand the mechanisms of deformation and fracture of these materials before their full potential can be achieved. Because classical fracture mechanics is based on the comparison of computed fracture parameters, such as stress intlmsity factors, to their empirically determined critical values, it does not adequately describe the fundamental physics of fracture required to predict the behavior of nanocrystalline metals. Thus, micromechanics-based techniques must be considered to quanti@ the physical processes of deformation and fracture within nanocrystalline metals. This paper discusses hndamental physicsbased modeling strategies that may be useful for the prediction Iof deformation, crack formation and crack growth within nanocrystalline metals.
    Keywords: Metals and Metallic Materials
    Type: AIAA Paper 2002-1315 , 43rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference; Apr 22, 2002 - Apr 25, 2002; Denver, CO; United States
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  • 5
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    Replica-based Crack Inspection (2007)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A surface replica-based crack inspection method has recently been developed for use in Space Shuttle main engine (SSME) hydrogen feedline flowliners. These flowliners exist to ensure favorable flow of liquid hydrogen over gimble joint bellows, and consist of two rings each containing 38 elongated slots. In the summer of 2002, multiple cracks ranging from 0.1 inches to 0.6 inches long were discovered; each orbiter contained at least one cracked flowliner. These long cracks were repaired and eddy current inspections ensured that no cracks longer than 0.075 inches were present. However, subsequent fracture-mechanics review of flight rationale required detection of smaller cracks, and was the driving force for development of higher-resolution inspection method. Acetate tape surface replicas have been used for decades to detect and monitor small cracks. However, acetate tape replicas have primarily been limited to laboratory specimens because complexities involved in making these replicas - requiring acetate tape to be dissolved with acetone - are not well suited for a crack inspection tool. More recently developed silicon-based replicas are better suited for use as a crack detection tool. A commercially available silicon-based replica product has been determined to be acceptable for use in SSME hydrogen feedlines. A method has been developed using this product and a scanning electron microscope for analysis, which can find cracks as small as 0.005 inches and other features (e.g., pits, scratches, tool marks, etc.) as small as 0.001 inches. The resolution of this method has been validated with dozens of cracks generated in a laboratory setting and this method has been used to locate 55 cracks (ranging in size from 0.040 inches to 0.004 inches) on space flight hardware. These cracks were removed by polishing away the cracked material and a second round of replicas confirmed the repair.
    Keywords: Structural Mechanics
    Type: 18th AeroMat Conference and Exposition (AeroMat 2007); Jun 25, 2007 - Jun 28, 2007; Baltimore, MD; United States
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  • 6
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    Fatigue crack propagation in aluminum-lithium alloys (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The principal mechanisms which govern the fatigue crack propagation resistance of aluminum-lithium alloys are investigated, with emphasis on their behavior in controlled gaseous and aqueous environments. Extensive data describe the growth kinetics of fatigue cracks in ingot metallurgy Al-Li alloys 2090, 2091, 8090, and 8091 and in powder metallurgy alloys exposed to moist air. Results are compared with data for traditional aluminum alloys 2024, 2124, 2618, 7075, and 7150. Crack growth is found to be dominated by shielding from tortuous crack paths and resultant asperity wedging. Beneficial shielding is minimized for small cracks, for high stress ratios, and for certain loading spectra. While water vapor and aqueous chloride environments enhance crack propagation, Al-Li-Cu alloys behave similarly to 2000-series aluminum alloys. Cracking in water vapor is controlled by hydrogen embrittlement, with surface films having little influence on cyclic plasticity.
    Keywords: METALLIC MATERIALS
    Type: International Aluminum-Lithium Conference; Mar 27, 1989 - Mar 31, 1989; Williamsburg, VA; United States
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  • 7
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    A Practical Engineering Approach to Predicting Fatigue Crack Growth in Riveted Lap Joints (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: An extensive experimental database has been assembled from very detailed teardown examinations of fatigue cracks found in rivet holes of fuselage structural components. Based on this experimental database, a comprehensive analysis methodology was developed to predict the onset of widespread fatigue damage in lap joints of fuselage structure. Several computer codes were developed with specialized capabilities to conduct the various analyses that make up the comprehensive methodology. Over the past several years, the authors have interrogated various aspects of the analysis methods to determine the degree of computational rigor required to produce numerical predictions with acceptable engineering accuracy. This study led to the formulation of a practical engineering approach to predicting fatigue crack growth in riveted lap joints. This paper describes the practical engineering approach and compares predictions with the results from several experimental studies.
    Keywords: Metals and Metallic Materials
    Type: NASA/TM-2000-210106 , NAS 1.15:210106 , L-17956
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  • 8
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    Methodology for Predicting the Onset of Widespread Fatigue Damage in Lap-Splice Joints (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: NASA has conducted an Airframe Structural Integrity Program to develop the methodology to predict the onset of widespread fatigue damage to lap-splice joints of fuselage structures. Several stress analysis codes have been developed or enhanced to analyze the lap-splice-joint configuration. Fatigue lives in lap-splice-joint specimens and fatigue-crack growth in a structural fatigue test article agreed well with calculations from small-crack theory and fatigue-crack growth analyses with the FASTRAN code. Residual-strength analyses of laboratory specimens and wide stiffened panels were predicted quite well from the critical crack-tip-opening angle (CTOA) fracture criterion and elastic-plastic finite-element analyses (two- or three-dimensional codes and the STAGS shell code).
    Keywords: Composite Materials
    Type: NASA/TM-1998-208975 , NAS 1.15:208975 , L-17799
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  • 9
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    An Extended Compact Tension Specimen for Fatigue Crack Propagation and Fracture (1996)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: An extended compact tension specimen, EC(T) has been developed for fatigue and fracture testing. Documented herein are stress-intensity factor and compliance expressions for the EC(T) specimen.
    Keywords: Composite Materials
    Type: NASA-TM-110243 , NAS 1.15:110243
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