Lifetime prediction in creep-fatigue environment
The creep-fatigue interaction has been studied and innovative mathematical models are proposed to predict the operating life of aircraft components, specifically gas turbine blades subject to creep-fatigue at high temperatures. The historical evolution of the creep-fatigue lifetime prediction is given in order to place the present study in the context. A literature review of the life estimation under creep-fatigue environment is presented.
Application of rough set method to the weightings of high temperature creep factors of boiler water wall
At the high temperature state or the applied stress is less than the yield strength, general metal itself will generate slow plastic deformation until fracture, which is called creep rupture. Under room temperature, general alloy will have creep phenomenon, but it is not obvious. However, under high temperature environment, the creep rupture becomes very important. It is not only very important to predict the components' life, but to assess the remaining life of the equipment components during the operation to applications. Hence, it becomes hot topic in recent years. In the past, we always use the anti-creep steel generated from experiments to extend the creep deformation data of steel life plans, and is called stress and strain. But it needs substantial funds and time to obtain the data, so, it is limited to the direct analysis of the small data. Based on this, the paper uses the significant in rough set to find the each weighting of influence factor on creep life. Through different discrete methods, we found that the factor of strain is more important than stress, the results are not only in line with the traditional regression results, but they are also corresponding to the actual situation.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME