A novel factor to assess the lateral constraint under mode-I loading

The stress intensity factors KIxx, KIyy and KIzz are introduced as an extension of the conventional stress intensity factor for mode-I of loading, KI. This enables us the definition of a lateral constraint index, y, as the ratio KIzz / K*Izz at the crack front, or, more generally, as sigmazz(pierwiastek (2(pi)r))/K*Izz outside the crack front, where K*Izz refers to plane strain conditions. The index y is determined numerically by means of three-diemensional finite element calculations. It facilitates the conversion between the stress intensity factor KI and the JI-integral in mode-I of loading for different specimens (CT, SENB, Arcan-Richard, etc.) of whichever thickness, thus opening new perspectives for the consideration of the influence of the lateral constraint by establishing instability conditions of cracks.