Fatigue failure analysis of HSLA steel sheets holed by conventional and flow drilling processes

Résumé

Flow drilling process produces bushes for removable joints that can be threaded by forming tapping process,
reducing stages in production of components of automobile industry and in construction sheds. High strength
and low alloy steels (HSLA) are employed on several applications in the processing industry. Benefits provided
by these materials make them an efficient solution, since their high cold resistance allows reducing
weight on structures, as well as maintaining the required mechanical properties. The present study evaluated
the conventional and friction drilling processes in HSLA steel sheets with a thickness of 4.25 mm. Specimens
were subjected to cyclic loadings, with no rework after holemaking, so the resultant characteristics of each
process were maintained. Fractured surfaces were analyzed with a scanning electron microscope (SEM) to
identify the fracture mechanism in different drilling processes. Fractographies obtained on both processes
indicated that the failure mechanism occurred due to ductile fracture resulting from the nucleation, growth
and coalescence of micro cavities.
Keywords: High strength low alloy steel, conventional drilling, flow drilling, ductile fracture.