Study On Method Of Crack Diagnosing, Controlling And Maintaining And Its Application For Mechanical Load-carrying Structures

To study actions of crack is a subject, which is full of attraction and challenge. The attraction represents the extensity and destruction of existence of the crack, it has giant economical and social value to study; the challenge represents the complexity of its actions. To this day, many problems about crack actions in engineering are still studied except for a few materials with high strength and high brittleness or some structures with simple in load. With the severity of crack problems increasingly of structures, which are made up of soft steel, to study diagnosis, control, and maintain of the crack, is a new hotspot in fault diagnosis areas. This dissertation studies a new theory, and a new mean to diagnose, control, and maintain the crack of the soft steel structures based on fracture mechanics and the background of the application. It applies to build foundation of maths mode of crack maintain in theory, find fracture toughness and parameters of crack propagation of Q235 steel in experiment, develop a practicality technique to guide diagnosis, control, and maintain of the crack in application. The main research contents and results of the dissertation are as following:1) To investigate extensively the crack problems about the structures of gantry cranes in ports, analyze the investigation, and summarize the distribution and ratio of the cracks on the structures, and point out that the cracks are the serious fault in the crane.2) To measure the fracture toughness and crack propagation parameters of Q235 steel by fatigue experiment from the point of energy, J integral and the other method are used in measuring. These build a massiness foundation.3) To put forward a mean, which can be used in engineering, to diagnose and control the cracks of the structures based on composite FEM. The mean contents creating FEM mode, determination of crack sensitive areas, calculation of threshold length of crack and observing periodicity. This mean is easier, more reliable than that of other means.4) To study a method of maintaining crack from the point of improving the stress concentration at crack tip, the method make curvature radius change to infinite at the crack tip, this change the state of stress distribution at the area. Experiment has proved that the method has merit.