Papers by Keyword: Surface Crack

Abstract: Surface cracks arising during rolling sliding contact of a wheel and a rail are investigated. A two-dimensional crack model is proposed which calculates the crack driving force using the configurational force concept. The numerical applicability of the configurational force concept for surface shear cracks under cyclic contact loading is discussed and compared to the J-integral concept. A single inclined crack in a rail loaded by an accelerated wheel is investigated. The material of the rail is described by a cyclic plastic kinematic hardening model. The evolution of the crack driving force during several cycles is investigated.

Abstract: In this paper, the experimental research on crack of four recycled aggregate concrete simple beams under a concentrated load was presented. Through the analysis of evolution and distribution characteristics of cracks with different amount of recycled brick, it is verified that the surface cracks on the recycled aggregate concrete beams have a very good fractal behavior. The research shows that the content of the recycled brick has obvious influence on the fractal dimension of the surface cracks of the beams. The more the content of the recycled brick is, the bigger the fractal dimension is. So the fractal dimension can be regarded as an index to evaluate damage degree of the recycled aggregate concrete beam. This research provides a novel idea and a method for studying the damage of the concrete structures.

Abstract: In the present work, three-dimensional finite element analyses have been conducted to calculate the-stress for semi-elliptical surface cracks in finite thickness plates under remote tension. The-stress solutions are presented along the crack front for cracks with values of 0.2, 0.4, 0.6 or 0.8 and values of 0.2, 0.4, 0.6 or 1.0. The current-stress solutions are suitable to be used as the constraint parameter for the fracture analysis.

Abstract: Recently it was shown that the temperature plays very important role in coupling with the impact of shock wave caused by explosion in a free space. The deterioration of fiber reinforced concrete structures, FRC, at the face to which the main impact of the coupled load is directed is not easy to describe. In couple of previous papers of the author the problem was solved under condition that the structure behaves elastically. It appeared that a numerical tool known as free hexagon method, which is based on soft contact problem in combination with boundary elements, seems a powerful approach solving any disconnecting media. The soft contact is identified by nonlinear spring rules. Similar idea is used in the suggested paper for solving the coupled problem envisaged, but the mesh of free hexagons is split into the air and the structure. If the impact of explosion and the subsequent shock wave cause is viewed separately from the changes in material due to temperature a very fast changes in stresses and movements in material are observed in the first case while the changes due to temperature develop much slower. On the other hand in combination of both influences the temperature increase the activity inside of structures considerably. In the paper the theory is briefly described and selected examples illustrate the mobility of the application of the method to a problem of FRC plate.

Abstract: An online slab quality diagnosis & analysis system named CISDI_SQDS ONLINE R2011 has been presented in this paper. The system is based on mechanism of defects, which mainly refer to surface crack & internal crack, heat-transfer & solidification simulation, stress & strain calculation and metallurgical process analysis about continuous casting. Combining with BP neural network, several kinds of quality loss factors are used to describe the possibility of inducement. Meanwhile, the respective crack formation indexes are introduced to be the theoretical reference data for slab quality level evaluation and guiding production. The CISDI_SQDS ONLINE R2011 system was firstly applied on the No.1 Slab Continuous Caster of Bayi Steel in China. It is preliminary proved that the model is reliable and reasonable. It can be widely used as an important theoretical tool for prediction & control for slab quality in continuous casting process.

Abstract: In order to improve the surface quality of titanium alloy in electric discharge machining (EDM) milling, presents electrode ultrasonic vibration assisted EDM milling in the kerosene fluid which fills with 12g/L SiC abrasive particles. By the comparison test of surface roughness between EDM milling and abrasive particle ultrasonic vibration assisted EDM milling in short pulse(pulse width less than 1μs), it is found that ultrasonic vibration role of SiC particle could effectively improve surface roughness from Ra 0.5μm to 0.2μm. The recast layer and surface crack are analyzed by scanning electron microscope (SEM).Results show the thickness of recast layer reduced 20-30μm and surface crack decreased obviously under the role of abrasive particle ultrasonic vibration. It shows that the combined action of ultrasonic vibration and abrasive particle can dramatically improve the surface quality of titanium alloy in EDM milling.

Abstract: The paper chose a three-span continuous steel box girder bridge with horizontal semicircular surface cracks as research object, and the cracks are non-through and unsymmetrical. Solving strain modal parameters of beams with cracks by means of the three-dimensional finite element theory, and applying continuous wavelet transform (CWT) to analyze the strain mode by Haar wavelet, then the position of the cracks could be identified by the maximum of wavelet coefficients. The validity of the method has been proved by numerical calculation and analysis. Some useful conclusions for continuous steel girders bridge have been drawn and it has been useful in surface flaw identification and diagnosis in structures.

Abstract: The great effort for reducing emissions of CO2 to atmosphere will inevitably involve the carry-out process of Carbon Capture and Storage(CCS), a novel plan which intends to capture and store anthropogenic CO2 produced at many existing industrial sources, such as power stations and petrochemical works. In particular, anthropogenic CO2 pipeline transportation from the energy plant to the remote sequestration area(both onshore and offshore) is a fundamental issue regarding the feasibility of applying the CCS technology. CO2 pipelines have been in operation in USA, Europe and North Africa for almost three decades. However, the technical challenges for pipelines transporting CO2 due to the relevant effects of different impurities coming from flue gases, are still needed to get people to take up, especially for China which is focusing on the roll-out of CCS. This paper will address a FE-based method which can assess residual life of a supercritical CO2 transmission pipeline containing an inner defect induced crack. Specifically, a portion of welded round steel pipeline is selected as the object of our analysis and an ANSYS finite element procedure is generated to simulate the stress state of an element volume along the radial direction and hence to calculate the effective stress due to the effects of crack closure. Afterwards, combining the effective stress we get in the above numeric analysis, the Paris equation is modified to build an integral analysis method for the residual life evaluation of CO2 pipeline. Lastly, in order to verify the validity of the proposed method, a pipeline example in a published paper is used as the benchmark model, the full-scale test results of which are compared with those from our method. Based on this, a section of CO2 pipeline, with an initial defect (assumed as a crack source), is analyzed and its residual life is evaluated by using the presented method. The analysis of numerical results indicates that the method presented in this paper can give us a valuable reference to life-evaluation for CO2 pipeline in CCS.

Abstract: Surface cracks are the most common defects in structures. Ultrasonic has been widely used as a non-destructive evaluation technology in the case of crack characterization. In this investigation, surface waves are applied to a steel block with artificial slots to characterize the crack depth. A series of test specimen with different depths of surface crack ranging from 4mm to 10mm was fabricated. The depth of the surface crack was evaluated using the pitch-catch ultrasonic technology. In this work, 2.25 MHz, 5 MHz and 10 MHz of incident waves were employed to investigate the effect of frequency on the crack depth detection. Experimental test results show that the accuracy of crack depth detection is increasing with the increase of frequency.

Abstract: For the structure failure of pressurized cylindrical shell under laser irradiation, studied with axial semi-elliptical surface crack of cylindrical shell under the combined action of laser radiation and pressure, analysis of its thermal force coupling of stress and material for the 30CrMnSiA steel. According to of static fracture toughness and based on theof estimated impact dynamic fracture toughness, the application of finite element method to study the fracture problem under dynamic load. Analyzing the crack initiation propagation and static dynamic initiation based on fracture criterion and dynamic fracture criterion for crack initiation propagation, provides a useful research of the analysis to a certain extent on the structure in thermal force coupling failure mechanism.