This paper numerically discusses stress intensity factor (SIE) calculations for surface cracks in round bars subjected to single and combined loadings. Different crack aspect ratios, a/b, ranging from 0.0 to 1.2 and the relative crack depth, a j D , in the range of 0.1 to 0.6 are considered. Since the torsion loading is non-symmetrical, the whole finite element model has been constructed, and the loadings have been remotely applied to the model. The equivalent SIE F& is then used to cnmbiue the individual SIF from the bending or tension with torsion loadings. Then, it is compared with the combined SIF, FgE obtained numerically using the finite element analysis under similar loadings. It is found that the equivalent SIF method successfully predicts the combined S E F i Q for Mode I when compared with F;E. However, some discrepancies between the results, determined from the two different a~c h e s ,~ it is also noted that the F$E is higher than the FgQ A.E. Ismail (€3)
ABSTRACT-An assessment was carried out herein to study the eccentricity of cracks subjected to mixed-mode loadings. Several loading locations relative to a central line were selected to induce mixed-mode loadings, which were comvuted us in^ a fmte element method. An adaptive meshing technique was adopted during the simulation of'crackpropagation to ensure the singularity of stress at the tip of the crack. The stress intensity failure criterion was nsed and progammed, and the node splitting technique was nsed when the stress intensity factor reached the fracture toughness of the material to simulate crack propagations. It was found that large variations m the stress intensity factor were observed when off-set cracks were used, and that K,, decreased when loading distance inmeased, hut increased when the off-set crack distance was increased. Both crack eccentricity and loading distance played important roles in producing mixed-mode loading, compared to the influence of central cracks. Correction factors were introduced to m o w the calculation of stress intensity factors under mixed-mode loadings. Sunulations of nack propagation were also conducted to study the effects of crack eccentricities and loading distances. It was found that the crack length, the loading distance relative to the central crack and the mck eccentricity dominated calculations of the integrity of cracked structures.KEY WORDS : Mixed-mode loading, Crack eccentxicity, Stress intensity factor, Crack propagationThe complexity of modem engineaing designs demands reliable structural integrity, even in the presence of man-made defects such as holes or cross-sectional changes (Jun et al., Baek et al, 2008). These defects are capable of inducing for a concentration of stress that may lead to crack initiations and potentially fail catastrophically. According to the present design practice guidelines available in (Mumlami, 1987), the calculation of s e s s intensity factors for any cracked strucbx~ is based on the symmetrical loading of a crack, which is (2005) experimentally tested ceramic materials under mired-mode loadings using asymmetric fon-point flexure, and stated that the empirical mixed-mode fracture criterion was best described as the hechue behavior under mixed-mode loading, and that the minimum strain energy density criterion was an appropriate approach to desaibe & p r o p a g J u n e t n f o n n a t i o n on the ability of the frachue criteria to predict material fractures, and proposed a general fracture criterion based on the concept of maximum potential energy release rate. The developed criterion was found to be in agreement with experimental results. Yongming and Sankaran (2007) also developed a criterion to predict failure, and showed that their model was in excellent agreement with the experimental data They also extended the criterion to predict the crack propagation rate when the crack is subjected to mixed-mode loading. To determine the accuracy of their mixed-mode predictions, comection factors were introduced to compensate f...
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