Experimental Study on Fatigue Performance of Welded Hollow Spherical Joints Reinforced by CFRP

Abstract

The risk of fatigue failure of welded hollow spherical joints (WHSJs) under alternating loads increases due to the inherent defects, the disrepair, and the demand for tonnage upgrades, of suspension cranes. The finite element analysis results revealed that the ranking of the stress concentration factor at the WHSJ was as follows: weld toe in steel tube of tube–ball connection weld > weld toe in steel tube of tube–endplate connection weld > weld toe in sphere of tube–ball connection weld > weld toe in plate of tube–endplate connection weld. Moreover, the peak stress at the weld of the tube–sphere connection was reduced by 32.93% after CFRP bonding reinforcement, which was beneficial for improving the fatigue performance. In this study, 16 full-scale specimens of Q235B WHSJs were tested by an MTS fatigue testing machine to study the strengthening effect of CFRP on the fatigue performance. It was found that the fatigue fracture of WHSJs was transferred from the tube–sphere connection weld to the tube–endplate connection after CFRP reinforcement. According to the fitted S-N curves, the fatigue strength could be increased by 13.26%–18.19% when the cycle number increased from 10,000 to 5,000,000.