PROPAGATION MODE AND CHARACTERISTICS OF FATIGUE CRACKS IN STEEL BRIDGE DECK AFTER DRILLING AHEAD OF THE CRACK TIP

Drilling the stop-hole ahead of the crack is a common maintenance method when the crack tip cannot be accurately identified or the crack length is short with a narrow operating space. The fatigue test and finite element simulation were conducted to study the crack-propagation mode and stress characteristics of the stop-hole after drilling. By monitoring the hole-edge strain, combined with simulation results and experimental phenomena, the reason for the change of crack-growth direction and path after drilling ahead of the tip was explained. Local stress characteristics of the fatigue crack before and after drilling ahead were compared to explore the influence on crack propagation. The result shows that the stop-hole will crack in advance while the original crack has not reached hole edge and two cracks will propagate in opposite direction at a rapid rate until they meet. The stop hole can guide the crack to propagate towards the stress concentration zone in front of hole edge, which is the reason for crack turning at the hole. Drilling ahead of the crack increases the stress intensity factor at the crack tip by 15% to speed up crack propagation and weaken the arresting effect. However, crack retardation can still be observed after the original crack converges with the crack initiating from hole.