A fracture mechanics approach to fatigue crack propagation characteristics in a locally used structural steel plate

Abstract

A fracture mechanics approach was used to investigate the effects of thickness, stress ratio and configurational geometry on fatigue crack growth characteristics of a locally produced steel plate.

The experiments were performed in laboratory air at frequencies of 15.7 Hz and 23.7 Hz on two test rigs designed for that purpose. Tests were conducted at both intermediate and law crack growth rates. The thicknesses considered were 4.5 rrm, 6 nm, 12 rrm and 18mn. The stress ratios considered were 0, 0.22, 0.36 and 0.5. The configurational geometries investigated comprised the compact specimen, the centre-cracked tension specimen and the arc-shaped tension specimen.

It was found that crack growth rates increased with increasing thickness, with more pronounced effects at low crack growth rates. The fatigue crack growth rates increased with increasing stress ratios with more significant effects being observed at low crack growth rates while at the intermediate range, the effects were less pronounced. As regards the configurational geometry, no effects on crack growth rate were observed at the intermediate range, but at low crack growth rates, crack growth was found to be highest in the centre-cracked tension specimen and lowest in the arc-shaped tension specimen with the compact specimen coming in between.

Thickness and stress ratio effects have been explained using crack closure concept. The configurational geometry effects have been explained by considering plastic zone size formations.