Study On Estimation Method For The Fracture Toughness Of Ship Steel Plate

In recent years, the ship industry is undergoing a rapid development. Many giant ships were built. However, a lot of serious accidents have also become more and more common. It is found that, the brittle fracture of giant welded structure under low temperature is one of the main reasons for these accidents. Therefore, founding the index appraisal system to evaluate the fracture toughness has become the key point of the research on fracture prevention of shipbuilding steels. Besides, the assessment of the fracture toughness of welded joints and ship steels has also become a more and more important task.Generally speaking, the assessment of the fracture toughness of welded joints and ship hull steel plate is always based on the tensile test or the COD experiment. However, the results of these two methods are not quite accurate because of the high request for the geometry size to the specimens, especially for those steel plates with thickness. Accordingly, V-Shaped Charpy Impact Experiment was put forward to assess the fracture toughness. The classification society of many countries divided steels into different levels according to the absorbing energy from the Charpy Experiment of the material, therefore, when the ship hull is built, different levels of steels could be chosen according to the intensity and toughness demands of different parts.The thesis continues the previous research on the evaluation of the fracture toughness using V-Shaped Charpy Impact Experiment, and expects to improve the method by using modern calculating methods. The main contacts of the thesis include:Firstly, based on the brief review of the previous research, the researching meaning of the thesis is introduced. Secondly, a brief introduction to the related parameters of the Sharp Experiment was made, including vE_T, vTrs, vTre andσ,etc. The key part of the thesis is the 3^rd and 4^th chapter. In chapter 3, based on the previous researches, neural networks is used to fit the relationship between the absorbing energy of Charpy Experiment and the toughness of materials, then mathematical statistics is also used to turn the relationship from single mapping into probability, based on which the calculating procedure is founded. In the 4th chapter, the BP neural networks is used to study the sample data, thus realize the mapping from absorbing energy of Charpy Experiment to fracture toughness on the basis of probability.. At last, the calculating method of the fracture toughness of ship hull steel plate based on probability is founded and the related software interface is developed as well.