Applicability of fatigue design recommendations for thin plate welded joints by assessment of fatigue crack initiation and propagation life

Abstract

Fatigue design guidelines for welded joints are primarily based on tests of around 10mm thick joints. Fatigue strength generally decreases with increased thickness, likely due to increased stress concentration or changes in stress distribution. Thus, guidelines correct and reduce the fatigue strength of thicker joints. However, for thinner plates commonly used in railway cars, there is limited test data and it is unclear if the guidelines apply. This study conducted a 4-point bending fatigue test on a 3mm thick fillet welded joint to determine fatigue strength. Contrary to expectations, fatigue strength decreased when thickness reduced from 9mm to 3mm. However, test results showed higher fatigue strength than the recommended value, confirming that the guidelines can apply to 3mm thickness. Additionally, the study investigated the reduced fatigue strength of thin plates using the relationship between the number of cycles to crack initiation, local stress range, and crack growth analysis based on Paris' law. It found that as thickness decreases, the stress concentration at the weld toe decreases and the number of cycles to crack initiation increases. However, the ligament also shrinks, resulting in a shorter crack propagation life.