Papers by Keyword: Multiple Cracks

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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.
Authors: Fei Wang, Xue Zeng Zhao, Jia Ying Chen
Abstract: Triangular cantilevers are used as small force sensors. Prediction of location and size of multiple cracks from experimental results will be of value to users and designers of cantilever deflection force sensors. We extend a method for prediction of location and size of multiple cracks in rectangular cantilevers to deal with triangular cantilevers in this paper. The cracks are assumed to introduce local flexibility change and are modeled as rotational springs. The beam is divided into a number of segments, and each segment is associated with a damage index, which can be calculated through the relationship between the damage index and strain energy of each segment and the changes in the frequencies caused by the cracks. The location of cracks can be obtained with high accuracy with sufficient segment numbers. The size of a crack can be calculated through the relationship between the crack size and its stiffness, which can be obtained from the damage index related to the crack. The maximum error in prediction of the crack position in the case of double cracks is less than 15%, and it is less than 25% in prediction of the crack size.
Authors: Wen Liu, Shi Lang Xu, Qing Hua Li
Abstract: Fatigue flexural fracture test is taken out in this paper, to study the fatigue crack propagation rate of ultra-high toughness cementitious composites (UHTCC), as well as the effect of fiber volume fraction on fatigue crack propagation rate. Three fiber volume fractions are adopted: 1.5%, 2.0% and 2.5%. Similar to Paris law, a fatigue crack propagation equation of UHTCC is introduced, as dA/dN=C(△J)m, with the two parameters A and △J are defined as the covering area of multiple fatigue cracks and the fatigue amplitude of J integral. Through experiment and analysis, the fatigue crack propagation rate slows down with the increase of PVA fiber fraction. Furthermore, the influence of PVA fiber on the propagation rate was found to become obvious with the increase of J integral.
Authors: Marko Katinic, Drazan Kozak, Ivan Samardzic, Antun Stoic, Zeljko Ivandic, Zlatko Tonkovic
Abstract: The interaction behavior of twin collinear through-wall cracks in tension loaded plate under elastic-plastic condition is investigated by the finite element method (FEM). The fracture parameter J integral for interacting cracks is calculated and compared to the J integral for a single crack the same size. In this way, the interaction factor of cracks under elastic-plastic condition is defined. This interaction factor is compared to the results of analytical solution of the interaction factor under linear elastic condition. The results show that interaction factor of cracks under elastic-plastic condition is higher than interaction factor of same cracks under linear elastic condition. Also the interaction effect of cracks under elastic-plastic condition is influenced not only by the crack configurations but also by the material properties, especially the strain hardening exponent n.
Authors: Masayuki Kamaya
Abstract: Since mechanical interaction between multiple cracks affects the rate of crack growth due to fatigue and stress corrosion cracking, it is important to consider its influence when predicting growth. In this study, a procedure predicting the growth of interacting surface cracks was developed. First, using the results of fatigue crack growth tests performed in a previous study, the transient growth behavior during coalescence and growth under interaction was evaluated based on area of crack face. It was shown that the area is a representative parameter of the growth of interacting surface cracks as well as independent cracks. The growth in area showed good correlation with the crack driving force defined using size of area. Then, in order to investigate the relationship between growth of interacting cracks and their relative spacing, crack growth simulations were carried out. The body force method was used to evaluate the change in stress intensity factors (SIF) during crack growth under interaction, and the simulation could reproduce the crack configurations obtained in the fatigue crack growth test. SIF of an interacting crack tip converges to that of a coalesced crack as the distance between cracks decreases. It was concluded that when the distance between cracks is small enough, the cracks can be replaced with a semi-elliptical crack of the same area of crack face for a growth evaluation. The threshold offset distance for the replacement was suggested to be less than 0.1Rx, where Rx is the span length of two cracks on the surface.
Authors: Željko Božić, Siegfried Schmauder, Marijo Mlikota
Abstract: This paper presents the implementation of fatigue crack growth power law equations based on ΔK, ΔJ-integral and ΔCTOD fracture mechanics parameters determined in an FE analysis, to plates with multiple site damage (MSD). Results of fatigue tests with constant amplitude tensile loading carried out on mild steel plate specimens damaged with a single central crack and with three collinear cracks are presented. A relatively larger plastic zone occurred in the crack tip region at higher fatigue crack growth rate (FCGR), from 10-7 to 10-6 m/cycle. The crack growth models based on the elastic-plastic fracture mechanics (EPFM) parameters describe better fatigue crack growth in this range as compared to the liner elastic models.
Authors: Zi Hai Shi, Yukari Nakamura, Masaaki Nakano
Abstract: Under cyclic loading, the material weakening processes in structural members inevitably involve multiple cracking originating from some of the spatially-distributed initial flaws and imperfections, and hence diverse cracking behaviors can be expected. It is known from previous studies on multiple cracks that, the cracking behavior in a structural member can abruptly change as a crack or a number of cracks reach a critical value of crack propagation, causing sudden strength degradation. In this study, by applying sequential loads at different locations of the same FE model of a notched beam, it is shown that this unique strength degradation mechanism can repeatedly occur as cracks propagate under sequential loads, leading to multistage strength degradation of the member. This result is in line with early experimental findings that the load-carrying capacity of a notched concrete beam under bending decreases in a similar fashion as the sizes of multiple initial notches are arbitrarily increased. This study has important implications for understanding the fundamental fatigue mechanisms of various engineering materials.
Authors: Masayuki Kamaya, Toshihisa Nishioka
Abstract: The finite element alternating method (FEAM), in conjunction with the finite element analysis (FEA) and the analytical solution for an elliptical crack in an infinite solid subject to arbitrary crack-face traction, can derive the stress intensity factor (SIF) of surface cracks by using the FEA results for an uncracked body. In the present study, the FEAM was applied to evaluations of SIF for noncoplanar multiple surface cracks. The SIF was evaluated for two surface cracks of dissimilar size, and three crack of the same size. The results suggested that the interaction is greatly affected by the relative crack size and negligible when the difference in the crack size is large enough, and the interaction can be evaluated by taking into account the adjacent cracks even if there are many cracks around them. Finally, the crack growth simulations were conducted and a possibility of the direct evaluation of influence of interaction between adjacent crack without using the combination rules was revealed.
Authors: X.L. Han, Tzu Chiang Wang
Authors: Zai Lin Yang, Hua Nan Xu, Bao Ping Hei, Yong Yang
Abstract: The methods of Green's function, complex function and multi-polar coordinates are applied here to report interaction of an elliptical inclusion and a crack in half-space under incident SH-waves. Based on the symmetry of SH-waves scattering, the "conformal mapping" technology was developed to construct a suitable Green's function, a fundamental solution to the displacement field for the elastic half space containing elliptical inclusion while bearing out-plane line source load at arbitrary point, for creating a beeline crack with arbitrary length at any position combined with crack-division technology. The displacement field and stress field were then deduced while the inclusion coexists with the crack Lastly, numerical examples are presented to discuss the dependence of dynamic stress concentration factor (DSCF) around the elastic inclusion on different parameters.
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