Influence of geometric imperfections of flange joints on the fatigue load of preloaded bolts

Abstract

In an ideal flange joint configuration, the fatigue endurance of preloaded bolts is contingent upon factors such as the magnitude of preload, applied working load, and the geometric dimensions of the flange. However, real-world flanged joints often deviate from this ideal geometry, introducing imperfections that can markedly escalate the fatigue burden on bolts. This study endeavors to simulate the geometric imperfections inherent in a standard DN40 flange and ascertain their impact on bolt fatigue through a combination of empirical measurements and finite element (FE) analysis. The investigation reveals that even minor deviations in flange geometry, such as non-parallelism on the order of 0.03 mm, can exert a considerable influence on bolt fatigue, particularly when the flange gap aligns with the applied eccentric working load (same side). To mitigate the deleterious effects of these imperfections, the proposal and evaluation of employing filler material between the flanges are made. Specifically, it is demonstrated that a thin layer of liquid metal filler (KemisKit Fe21), substantially alleviates the fatigue burden on bolts. Empirical findings illustrate that this corrective measure enhances the fatigue life of bolts by a factor of more than 30 under the highest applied working load condition.