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: R.H.C. Wong, Y.S.H. Guo, K.T. Chau, Wei Shen Zhu, Shu Cai Li

Abstract: This paper presents the crack growth mechanism from a 3-D surface flaw on gabbro
specimens using strain measurement and acoustic emission (AE) technique. Based on the results of
strain and AE measurement, microcracks initiated inside the rock and extend to the surface of the
specimen. With the observation from the measurements, four types of crack patterns initiate wing
crack, anti-wing crack (opposite direction of wing crack), petal crack and compressive crack. The
strain values of anti-wing cracks are larger 1 to 2 times than that of wing crack. The AE energy
release from anti-wing crack is higher 2.5 times than that of wing crack, while the energy release
form wing crack is the least but the compressive crack is the highest. Thus, the appearance of
initiation and propagation of the anti-wing crack and compressive crack are very actively than that
of the wing crack. The strain and AE measurement is not only to provide a clear concept on the
mechanisms of crack growth form a 3-D surface flaw but also to provide useful knowledge on the
AE property of the crack patterns.

2357

Authors: Jun Ru Yang, Zhao Qian Li, Chuan Zhen Huang, Quan Wei Wang

Abstract: Basing on the theoretical study on the stress intensity factor (SIF) of the crack inclined across the interface of the cermet cladding part, the finite element analysis (FEA) of the crack’s SIF is made. The change laws of the SIF with the load action angle , the load Q, the clad thickness ratio h1/h, the elastic modulus ratio E1/E2, the inclined angle of the crack β1, and the crack length ratio a1/a2 are obtained. The research results have theoretical and steering significance on the wide application of the cermet cladding part.

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