Effect Of Environmental Medium On Fatigue Life Of Expansion Joint

As an essential component of displacement compensation, expansion joints are widely used in many industrial fields. When the load is applied, some local area will yield elastic- plastic deformation. It will result in high-strain, low-cycle fatigue failure, especially when start/stop system and in varying working condition. Therefore, various studies on low-cycle fatigue of expansion joints have been done over the years, and the most authoritative one is the Expansion Joint Manufacturers Association(EJMA). EJMA gives fatigue curve of austenitic stainless steel and the faituge life calculation equation of expansion joints. However the previous studies are limited in the air condition, while in practice, expansion joints usually work in the corrosive solution, some area of the expansion joints will accumulate corrosive solution. Therefore, the influence of corrosive solution to the fatigue life of expansion joints has called many people's attention.This thesis focus on the study on fatigue life of expansion joints in the condition of 3.5% NaCl corrosive solution, the main content of this study are as follows:1. Air fatigue life prediction of expansion joints. Expansion joints'stress is measured, and compared with FEA simulation results in various displacement conditions. The fatigue life of expansion joint in air is experimentally measured.2. The corrosion fatigue life of expansion joint is measured under 3.5% NaCl corrosive solution. The real fatigue life under corrosive solution is compared with the one in air, the corrosion fatigue life is reduced greatly. Corrosive solution and stress level are the main factors, and a corrosive effect factor is proposed. Also the suggestion of expansion joint design is given.3. A new formula between crack propgation and electrical potential is proposed. Both compact test specimen and expansion joint is tested in different stress levels, and different frequncy(CT specimen only) in corrosive solution to reflect the mechanism of corrosion fatigue.4. Fatigue crack and macrographs of fracture are analyzed. Based on the...