represented with a Ramberg-Osgood power hardening law with a yield stress of 350 MPa, a hardening exponent of 9, a Young’s modulus of 200 GPa and Poisson’s ratio of 0.3. Numerical results The crack driving force was monitored through the development of the J-integral and is presented in Figure 3 for the shallowest part of the re-entrant sector and the deepest crack segment of the coalesced crack. J is normalised by the yield stress (Y) and the local ligament length (t-alocal). J is presented for a series of crack depths in the re-entrant sector for the same remotely applied load. The applied load is normalised with the limit load of an uncracked geometry (P0). Amplified values of J are found in the re-entrant sector compared to the deepest crack segments for all applied loads favouring crack advance from the re-entrant sector. Error! Not a valid link. Crack tip constraint was quantified with the T stress [7,8] derived from the local bending moments and reaction forces in the line spring model. The interest was focused on the re-entrant sector which develops enhanced crack driving forces in elasticity and plasticity. Figure 4 presents T as a function of crack depth for the re-entrant sector. T is normalised with the yield stress and presented for five values of applied load, normalised with the limit load of the uncracked geometry. The magnitude of T depends on the extent of coalescence. Pronounced re-entrant sectors exhibit a compressive T stress in the initial stages of coalescence, indicating significant constraint loss. As the crack depth increases, T becomes more positive due to the bending dominated fields. Figure 4 shows that the T stress distribution saturates as the re-entrant ligament develops large scale plasticity. Error! Not a valid link.
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