Fatigue crack growth in notched specimens: a numerical analysis

Abstract

Fatigue crack growth (FCG) is linked to irreversible and non-linear processes happening at the crack tip, which explains different problems observed in the use of da/dN-?K curves. The replacement of ?K by non-linear crack tip parameters, namely the crack tip opening displacement (CTOD) is an interesting alternative. The objective in here is to study the effect of notches on FCG using the plastic CTOD range, ?p. M(T) specimens with lateral notches of different radius (1, 2, 4 and 8 mm were analysed numerically, keeping the total depth constant (8 mm). The increase of crack length increases ?p and therefore FCG rate. For plane stress state, the formation of the residual plastic wake with crack propagation, produces crack closure which compensates the effect of crack length and there is a stabilization of ?p. The reduction of notch radius increases ?p for all crack lengths, particularly for the shortest ones. For plane strain state there is almost no crack closure therefore ?p is higher than for plane stress state, and the effect of crack length produces a relatively fast increase of ?p.

Keywords

• Fatigue crack growth
• Notches
• Plastic CTOD
• Crack closure