Papers by Keyword: Crack

Abstract: In this paper free vibration analysis of cracked composite beams subjected to coupled bending-torsion loads are presented. The composite beam is assumed to have an open edge crack. A first order theory is applied to count for the effect of the shear deformations on natural frequencies as well as the effect of coupling in torsion and bending modes of vibration. Local flexibility matrix is used to obtain the additional boundary conditions of the beam in the crack area. After obtaining the governing equations and boundary conditions, GDQ method is applied to solve the obtained eigenvalue problem. Finally, some numerical results are given to show the efficacy of the method. In addition, to count for the effect of coupling on natural frequencies of the cracked beams, different fiber orientations are assumed and studied.

Abstract: The emergence of cracks of structures is the initial omen of the structural damage. From the initial stage, structural cracks which are undistinguishable by naked eyes exist gradually and then contribute to the member damage, structural deformation and systematic instability as well. This paper made a detection and analysis for cracks of cement flooring by utilizing the digital picture technology, converting a color Image into a gray-scale image. Then ,an appropriate threshold was determined to distinguish between cracks and the background in a gray-scale image. Then, an edge-detection method and morphological techniques of dilation and erosion were used respectively to eliminate noise in the corresponding binary images and obtain crack boundaries.The graphic process program developed can be used to process the gained digital pictures .

Abstract: A numerical implement to simulate the crack propagating process in arch dam and rock base has been put forward. A new remeshing strategy of FEM meshing grid was presented for improving the calculation accuracy and efficiency. In the period of dividing the dam structure and the foundation rock into an appropriate number of discrete subregion (finite elements), the adaptive element was used to divide the original 3-D element into 8 son-elements analogical to its father-elements entirely. Of course the 2-D element was divided into 4 son-elements analogical to its father-elements entirely using the same method. The element shape function was used to solve suspend nodal point. The arithmetic and shape function’s formulation also were put forward. To satisfy the engineering accurate result, the adaptive element was used to divide the son-element or the grandson-element again. In the calculating processor, the arithmetic of adaptive load step was presented. Only one element failures in a load step. So the cracking processor can be found with automatic mesh generation. An arch dam has been as example to validate the method is right and stability. The arithmetic has important theory and utility value.

Abstract: The expressions of crack spacing and width were deduced from the aspect of force-balance. The concept of maximum spacing and width of crack were put forward accordingly and they were verified and consistent with the site test results. Their relationships with soil parameters were discussed in detail. The new cracks do not appear until the spacing of adjacent cracks is greater than the maximum spacing, and the width of cracks will not be greater than the maximum width. The maximum spacing and width are judgments for describing and represent the final characteristic of cracks due to evaporation.

Abstract: In-situ synthesized two kinds of Fe-Cr-C and Fe-Cr-C-Ti layers were fabricated on the base of Q235 steel by reactive plasma cladding process using composite powder prepared by precursor carbonization-composition process as raw materials. The composite powder is composed of ferrotitanium, chromium, iron and precursor sucrose. Microstructure of the layer was observed by scanning electron microscope (SEM). The phases in the layer were determined by X-ray diffraction (XRD). Results indicate that the Fe-Cr-C layer consists of primary (Cr,Fe)₇C₃ carbide, chrysanthemum-shaped eutectic (Cr,Fe)₇C₃ carbide and eutectic austenite. The cracks in Fe-Cr-C layer might originate at the interface of the layer and the base material as well as at the pores or edges of the layer. These cracks expand along primary (Cr,Fe)₇C₃ grain boundaries in a crystalline form. Because the grains of primary (Cr,Fe)₇C₃ are fiber-shaped and the fiber direction are perpendicular to the surface of the layer, so the cracks expand perpendicularly throughout of the Fe-Cr-C layer. The Ti addition into Fe-Cr-C plays an important role in synthesizing TiC and austenite, reducing primary (Cr,Fe)₇C₃ and improving the microstructure of eutectic (Cr,Fe)₇C₃. Therefore, Fe-Cr-C-Ti has good performance in toughness and crack-resistance.

Abstract: In order to evaluate the flexural behavior of fiber-reinforced polymer cement mortar, three-point bending test is used. Compared with different test modes and different test rates of loading, 0.1 mm/min in displacement mode is the most suitable, under which the obtained data are stable and sensitive to the micro-crack formation. Besides, tests show that mixing fiber-reinforced polymer cement mortar at slow speed and curing specimens in dry condition benefit the behavior under flexural load of the mortar.

Abstract: Influence of load and rotation speed on life of PPS radial bearings under water lubricant condition was investigated. RCF tests were carried out at different loads and rotation speeds until 1.0×106 cycles. After testing, rolling contact surfaces were observed by using a laser confocal microscope. From the observation, it was concluded that the life of PPS radial bearings under water lubricant condition was dominated by cracks and flaking failures. The failure of PPS bearings was caused by the flaking failures. The cracks were observed prior to the flaking failures. The life when flaking failure occur depends on the load and the rotation speed.

Abstract: In this paper, the single disk rotor system with a transverse open crack has been taken as an example; the vibration properties on the system have been discussed theoretically. First, the equations of the motion of this kind of system are established. Then, the conditions, positions and areas of the stable vibrations and the unstable vibrations on the system are studied by applying the Floquet Theory. Finally the influence of several parameters on stability has been discussed.

Abstract: This paper evaluated the restrain effect to cracks in the concrete members containing expansive admixture addition. An experimental study modeling the slab of the field bridge is performed. The free strain, the actual strain of specimens with or without expansive admixture and steel bars is measured. Based on the experimental results, the internal restrain effect and steel restrain effect to cracks are calculated as approximately 0.35 and 0.2~0.3 respectively.

Abstract: The control of concrete crack is a complicated and difficult problem for civil engineering. It is more difficult to control the crack of the concrete poured in winter. Thorough the analysis of the construction of Shenyang subway in winter, a combination of methods are applied. Frost proof and decreasing the temperature stress of concrete are considered together. The combination of antifreezing measures and decreasing the temperature stress of concrete make the construction quality arrive a satisfying level.