Papers by Keyword: Crack Model

Abstract: Damage detection using vibration-based methods make use of empirically derived relations to characterize the crack severity. The applicability of these relations is limited to structures with similar cross-section shape and having the same crack type. The use of these relations for composite materials is even more difficult, due to the directional dependency of the materials mechanical properties. We propose in this paper a new method to evaluate the damage severity, which is based on the global stiffness reduction. It is known that the amount of energy stored in a structure depends on its global stiffness, i.e. the value of the structure deflection under a given load. Consequently, the stiffness decrease due to a damage is signalized by an increased deflection. We defined a damage severity indicator based on the evaluation of deflection changes, which is simple to be found by a simple finite element analysis. This indicator is valid for all structures having similar cross-section shape; we used it successfully in vibration-based damage assessment.

Abstract: We research the influence of reinforced concrete beams crack on size effect by using the fracture Mechanics analysis method and Fracture toughness. First, the weight of three spot curved beam ,the load ,the steel bar, and the cohesive strength of breaking-down process area were superimposed of the stress intensity factor which has in the crack tip, in order to examine whether it has surpassed the fracture toughness, and judge the crack whether will be to expand. Then we went to iterative computation through increasing the load and the crack length which obtained the carrying capacity of corresponding size component, we used the Matlab programming in the entire computational process. The result shows that although the steel bar limited crack expansion of concretes beams and caused “the plasticity” characteristic, the reinforced concrete beams had the size effect phenomenon still, it did not obvious compare with the plain concrete.

Abstract: Crack detection of critical beam structures such as bridges and aircraft wings by vibration monitoring is based on understanding how a crack affects the vibration characteristics of a beam structure. Transfer matrix method is a convenient, effective, and hence widely used approach to beam vibration analysis, but a crack in the beam makes this method ineffective. This paper proposes an open crack model that simulates the local stiffness reduction effect of a transverse crack by a rectangular slot to make the transfer matrix method able to analyze vibrations of a cracked beam. The depth of the slot is identical to the depth of the crack, and the equivalent width of the slot is obtained by comparison of stiffness reductions of finite element analysis results and the counterpart transfer matrix method results. Different dimensions of rectangular beams, different crack positions and loading conditions are considered and statistic method is used to improve the generality and accuracy of the model. A calculation example of a cracked cantilever beam is given and the validity of the proposed model is verified with available results of existing models.

Abstract: Understanding dynamic behavior of a rotor system with a transverse crack is of great significance for operation reliability of rotating machinery. The transfer matrix method is widely used for rotor dynamic analysis, but it encounters difficulties modeling a crack. This study proposes a finite-width crack model that simulates the local stiffness reduction effect of a gaping crack in transfer matrix method. This model is obtained by comparing finite element analysis results of a shaft with a zero-width crack and its counterpart transfer matrix calculation results with a trial equivalent finite-width slot. Different shaft geometry and loading modes are considered to improve the generality of the model. An application example is given that uses the proposed model to calculate critical speeds of a multi-disk rotor system with a transverse crack at different positions.