Fatigue Performance Analysis Of Titanium Alloy Welded Joints Based On Rough Set

Welding is the main connection method in the engineering and the fatigue damage of welded structure has obvious local characteristics, it often show that the welded joints are the main reason of fatigue failure for welding structure. Nowadays, titanium alloy welded structure has been more widely used in the equipment manufacturing sector; the fatigue analysis of tluminum alloy welded joints is one of the important basic content of welded structure fatigue design. This topic is supported by the national natural science fund project:"based on welded structure fatigue design and basic research of Mesh-Insensitive Structural Stress", analysing tluminum alloy welded joints fatigue performance by rough set method based on106pieces of fatigue date of tlumimum alloy welded joint.This paper focused on the following research:Firstly, the paper discussse the principle of fatigue fracture for metal fatigue.the reason of fatigue failure for welding structure and analyses the fatigue characters of the welded joints. Furthermore, the basic theory of fatigue including the fatigue calculation criteria and evaluation standards is described, the main methods applied to the analysis of the welded structures are introduced, sush as the nominal stress method, the hot stress method.the Mesh-insensitive structural stress method which is introduced in detail.Secondly, the rough set theory is summarized including some related concepts, the principle of knowledge acquisition, the process of rough set knowledge modeling. The dynamic model which can be used to analyzed fatigue performance of titanium alloy welded joints is established though the steps of data acquisition, data preprocessing, model reduction and model inference based on fatigue data of titanium alloy welded joints.The main influence factors are got though the step of property reduction and the precise rules which can predict fatigue life of welded joints of aluminum are got though the step of model inference.Finally, the S-N curves based on nominal stress, structure stress and Mesh-insensitive structural stress and the rough set dynamic model are established from the fatigue data of titanium alloy welded joints. The influences of welding factors to fatigue life are analyzed and the S-N distribution of fatigue data under the condition of three different kinds of stress is analyzed and compared though the rule model. The results show that, the equivalent structural stress affected by the factors of Material-name and Joint-type etc is less than nominal stress and structural stress, the S-N data distribution based on equivalent structural stress more concentrated and uniform under the same condition. So it can be concluded that this method has a higher accuracy in fatigue life prediction of welding joint.