Authors: Yi Sun, Rui Zhang, Jun Ma

205

Authors: Tomáš Denk, Vladislav Oliva, Aleš Materna

Abstract: A two-parameter constraint-based fracture mechanics approach is used to explain the effect of the constraint on the apparently anomalous behavior of short fatigue cracks. The different levels of stress constraint are quantified by the T-stress, and microstructurally as well as mechanically short cracks are discussed. Short cracks generally behave more sensitively to the constraint than the long ones. It is shown that in most cases, the existence of short cracks goes hand in hand with an intrinsic loss of the constraint, which contributes to a decrease of their fatigue
threshold values and accelerates their growth. In this paper, the above effect is quantified and conclusions concerning the applicability of the fracture mechanics parameters and approaches to the estimation of the residual fatigue life of structures are discussed.

307

Authors: Jun Si, Fu Zhen Xuan, Shan Tung Tu

Abstract: The interaction behavior of two non-aligned through-wall cracks in flat plates is
investigated by the finite element method (FEM) under extensive creep condition. The
time-dependent fracture parameter C*-integral along the crack tips are calculated and compared to
the results of a single crack of the same size. For comparison purpose, the interaction of stress
intensity factors (SIFs) is also examined in the study. The results indicated that interaction of
multiple cracks is different between the time- dependent fracture characterized by C*-integral and
linear elastic fracture noted by SIF. The magnifying factors of time-dependent fracture are obviously
larger than that of the linear elastic fracture cases. Therefore, the current re-characterization rule for
multiple cracks developed from linear elastic fracture analysis may lead to a non-conservative result
and should be modified when it is used in the assessment of time dependent failure.

105

Authors: Jin San Ju, Xiu Gen Jiang, Xiang Rong Fu

Abstract: This paper primarily presents the development and application of automation
computational analysis techniques to determine the dynamic stress intensity factor for the damaged
aircraft fuselage subjected to triangle blast load. A program based on automated procedure to
simulate cracked fuselage is developed. It may create 3-dimention panel model using
parameterization. The stress around the crack tips will be captured and the dynamic stress intensity
factor can be obtained at every moment of the blast automatically. A typical curved panel model
which consists of 7 frames and 8 stringers is calculated. The calculation results shown that the form
of the dynamic SIF curve is similar to that of the triangle load curve while the peak point of
dynamic SIF curve occurs a little later than that of the load curve due to the inertia effect. The
longer the crack is, the more obvious the effect is. The peak SIF value of the crack under blast load
is bigger than that under the static load for certain crack length. The longer the crack is, the bigger
the difference between the dynamic peak SIF value and static SIF is. At the same time, the load
time has effect on the dynamic SIF curve and its peak value. These results show good agreements
with theoretical principles.

705

Authors: Li Hong Gao, Ge Ning Xu, Ping Yang

Abstract: The random formula on fatigue crack growth is deduced by the fatigue crack data and the improved Taguchi method, and the sample estimates of random variables are received by the least square method in the random formula. Fatigue fracture life and reliability of structure are analyzed by the random model. The result show the model is correct and practical, and get the same result with Monte Carlo simulation, moreover its calculation is very simple.

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