Article

Fatigue crack growth behavior of Al7050-T7451 attachment lugs under flight spectrum variation

Force Measurement and Evaluation Lab., Korea Research Institute of Standards and Science (KRISS), Daejeon 305-701, South Korea
Theoretical and Applied Fracture Mechanics (Impact Factor: 1.14). 09/2003; DOI: 10.1016/S0167-8442(03)00041-7

ABSTRACT This paper discusses an analytical and experimental investigations of the fatigue crack growth behavior in attachment lugs subjected to a randomized flight-by-flight spectrum. In the analysis, the stress intensity factors for through-the-thickness cracks initiating from lug holes were compared by weight function method, boundary element method (BEM), the interpolation of Brussat’s solution. The stress intensity factors of a corner crack at a transition region were obtained using two parameter weight function method and correction factors. Fatigue life under a load spectrum was predicted using stress intensity factors and Willenborg retardation model considering the effects of a tensile overload. Experiments were performed under a load spectrum and compared with the fatigue life prediction using the stress intensity factors by different methods. Changes of fatigue life and aspect ratio according to the clipping level of the spectrum were discussed through experiment and prediction. Effect of the spectrum clipping level on the fatigue life was experimentally evaluated by using beach marks of fractured surface.

Download full-text

Full-text

Available from: Soon-Bok Lee, Jun 23, 2015
2 Followers
 · 
368 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Tests with middle-crack tension (M(T)) specimens made of Al 2324-T39 and Al 7050-T7451 are conducted to investigate the influence of low load truncation level on fatigue crack growth. The six different truncated spectra are obtained by removing the small cycles of which amplitudes are less than the specified percentages of the maximum amplitude in the basic flight-by-flight loading spectrum and the remainder of the spectrum is untouched. The tests indicate that the mean level of fatigue crack growth life (FCGL) increases as the load truncation level is enhanced. Considering both the time saving and the influence on FCGL, there is an applicable choice (i.e. spectrum S2 or spectrum S3 in this investigation) for full scale fatigue test. The scatter of FCGL becomes much larger than that under the basic spectrum when the load truncation level is increased to a specified high level, mainly due to the occurrence of crack slanting and branching under the high level truncated loading spectra.
    Chinese Journal of Aeronautics 08/2009; 22(4):401-406. DOI:10.1016/S1000-9361(08)60117-X · 0.69 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The finite element model of a straight attachment lug subjected to an oblique loading less than 45 degrees is built by using the finite element software ANSYS, a cosine pin-bearing pressure distribution is applied on the hole of lug as a boundary condition. The stress intensity factor (SIF) expression for the straight attachment lug with a single through-the-thickness crack, which is subjected an oblique pin-load less than 45 degrees, is determined by studying on the influence law of dimensionless crack length (a/R1),ratio of outer radius to inside radius (R2/R1), inside radius (R1) and pin-load angle (β) on the SIFs values. The expression is validated by contrasting with the ANSYS results and the data of residual strength test. The stress intensity factor’s amplitude (ΔK) are calculated by the SIF equation to get the values of the Paris constants. The fatigue crack growth model of attachment lug subjected to oblique pin-load is established, offering an analytical as well as experimental method for assessing and designing damage tolerant attachment lugs.
    07/2011; 291-294:1043-1050. DOI:10.4028/www.scientific.net/AMR.291-294.1043
  • [Show abstract] [Hide abstract]
    ABSTRACT: According to standard test method for fatigue crack growth rates of metallic materials, the crack growth rate of 30NCD16 at three stress ratio (R=0.1, 0.3 and 0.5) were measured. Based on linear elasticity fracture mechanics theory, the fatigue crack growth rate was studied through the nonlinear least squares fitting method. The Paris model parameters at steady growth region and near threshold growth region and NASGRO model parameters were obtained. The effective stress intensity factors versus curves at three stress ratios were determined by crack closure effect. The results show that the Paris equation can preferably describe relations at steady growth region. At this region the model parameter m lies 2.5-4. This result is consistent with the known statistical facts of most metallic materials. NASGRO equation can preferably describe relations from near threshold growth region to high values region. all the test data at three stress ratio was able to correlate and . Crack closure was the major factor in correlating stress ratio and crack growth rate, the degree of crack closure weaken with increasing stress ratio.
    08/2011; 311-313:822-825. DOI:10.4028/www.scientific.net/AMR.311-313.822