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Conventional finite element analyses of cracked specimens assuming linear elastic material behaviour do not take into account geometric nonlinearities in the vicinity of a crack tip. In order to investigate the effect of these nonlinearities simple finite element calculations were carried out, using both a linear solver and an iterative geometric nonlinear solver, for both Mode I and Mode II loading. Under Mode I loading a crack tip blunts. In consequence the effect of using the nonlinear solver was to  decrease crack surface  displacements in the vicinity of a crack tip. However the effect was small and hence unlikely to be of practical significance. Behaviour under Mode II loading is fundamentally different in that a crack tip remains  sharp.  Once nodal displacements were taken into  account using the  nonlinear solver had no effect on results. In view of the results obtained it is concluded that there is no point in carrying out more sophisticated finite element calculations.