FATIGUE CRACK GROWTH PREDICTION UNDER FALSTAFF LOAD SEQUENCE BY K*-RMS APPROACH
Keywords:
Fatigue crack growth, FALSTAFF, Root mean square, Aluminum alloyAbstract
Fatigue crack growth behavior in a single edge notched tension specimen of an airframe grade D16 aluminum alloy under the standard FALSTAFF aircraft load sequence was predicted. Considering K* as the crack driving force parameter, the crack growth law was obtained from the constant amplitude fatigue crack growth rate (FCGR) test data. The FALSTAFF spectrum load sequence was approximated as equivalent constant amplitude (CA) load sequence with maximum and minimum stresses as root-mean square (RMS) maximum and minimum stresses of the spectrum, respectively. The crack growth behavior was then predicted under this apparent CA load sequence through cycle-by-cycle estimation. The analysis was performed for various reference stress levels. For comparison, conventional crack closure approach where the crack growth law in terms of effective stress intensity factor, ∆Keff along with constant crack opening level, Kop concept for the spectrum was used to predict the growth behavior. In general, fatigue crack growth life predicted by the proposed K*-RMS approach was comparable to that predicted by conventional crack closure approach within the allowable scatter limits. The simplicity of the K * -RMS approach is quite encouraging. Comparison of predicted results with experiments and the applicability of this approach to other types of spectrum loads need to be investigated further.
Downloads
References
Manjunatha, C.M. and Parida, B.K., 2004,“Prediction of fatigue crack growth after single overload in an aluminum alloy”, AIAA Journal, Vol. 42 No. 8, pp. 1536-1542
Elber, W., 1971, “The significance of fatigue crack closure”, In: Damage Tolerance in Aircraft Structures”,ASTM STP 486, Philadelphia, PA, pp. 230-242.
Vasudevan, A.K., Sadananda, K., and Louat, N., 1994,“A review of crack closure, fatigue crack threshold and related phenomena”, Mat. Sci. Engg., Vol. A188, pp. 1-22
Donald K, and Paris, P.C., 1999,“An evaluation of ∆Keff estimation procedures on 6061-T6 and 2024-T3 aluminum alloys”, Int. J Fatigue, Vol. 21, pp. S47-S57
Hertzberg, R.W., Newton, C.H., Jaccard, R., 1988,“Crack closure: correlation and confusion”, Int. Mechanics of Fatigue Crack Closure, ASTM STP 982. Philadelphia,PA:, pp. 139-148
Paris, P.C., Tada, H. and Donald, J.K., 1999, “Service load fatigue damage - a historical perspective”, Int. J Fatigue 1999, Vol. 21, pp. S35-S46
Meggiolaro, M.A. and Pinho de Castro, J.T., 2003, “On the dominant role of crack closure on fatigue crack growth modeling”, Int. J Fatigue, Vol. 25 pp. 843-854.
Johnson, W.S., 1981, “Multi-parameter yield zone model for predicting spectrum crack growth”, In: Methods and Models for Predicting Fatigue Crack Growth Under Random Loading, Chang J.B., Hudson C.M, Eds., ASTM STP 748, Philadelphia, PA,1981, pp. 85-102.
Kujawski, D., 2001, “A fatigue crack driving force parameter with load ratio effects”, Int. J Fatigue Vol. 23, pp. S239-S246.
Dinda, S. and Kujawski, D., 2004, “Correlation and prediction of fatigue crack growth for different Rratios using Kmax and ∆K+ parameters”, Engg. Fract. Mech., Vol. 71, No. 12, pp. 1779-1790
Van Dijk, G.M. and de Jonge, J.B., 1975 “Introduction to a fighter aircraft loading standard for fatigue evaluation-FALSTAFF”, Proceedings of 8th ICAF Symposium, International Committee on Aeronautical Fatigue, Lausanne, Switzerland, 1975, pp. 3.61/1- 3.61/39
Marchand N, Parks DM, Pelloux RM, 1986, “KI solutions for single edge notch specimens under fixed end displacements”. Int J Fracture, Vol31, pp 53-65
Hudson, C. M., 1981, “A root-mean-square approach for predicting fatigue crack growth under random loading, In: In: Methods and Models for Predicting Fatigue Crack Growth Under Random Loading, Chang J.B., Hudson C.M, Eds., ASTM STP 748, American Society for Testing and Materials, Philadelphia, PA, pp. 41-52
Newman, J.C. Jr., 1981, “A crack-closure model for predicting fatigue crack growth under aircraft spectrum loading”. In: Methods and Models for Predicting Fatigue Crack Growth under Random Loading.ASTM STP 748, Philadelphia, PA, 1981, pp. 53-84
Khalil, M. and Topper, T.H.,, 2003 “Prediction of crack opening stress levels for 1045 as-received steel under service loading spectra”, Int. J Fatigue, Vol. 25, pp. 149-157
Schijve, J., 2003, “Some formulas for the crack opening stress level”, Engg. Fract. Mech., 1981, Vol. 14, pp. 461-465.
Schijve J., 1973, “Effect of load sequences on crack propagation under random and program loading”, Engg Fract Mech., 1973, Vol. 5, No. 3, pp. 269-280.
Kim, S.T., Tadjiev, D. and Yang H.T., 2006, “Fatigue life prediction under random loading conditions in 7475-T7351 aluminum alloy using the RMS model”, Int. J Damage Mechanics, Vol. 15, pp. 89-102
