  Aneurysms are localized bulges of arteries, and they can rupture with fatal
consequences. Complex mechanobiological factors preclude in vivo testing to
assess the rupture risk of an aneurysm, and size based criteria are often used
in clinical practice to guide surgical interventions. It is often found that
tortuous and buckled aneurysms can exceed in size recommended for surgical
intervention, and yet do not rupture. This study addresses why buckled
aneurysms exhibit this intriguing behaviour by combining in vitro inflation
experiments on hyperelastic tubes with finite element calculations. Using a
biologically relevant material model for an arterial wall, we show that buckled
aneurysms can grow in size without rupturing under favourable arterial
pre-tensions. Stretch reversal phenomenon exhibited by arteries governs whether
buckling or bulging occurs first. Exponential stiffening favours the axial
propagation of an aneurysm instead of radial growth in size. The choice of
failure criteria based on Ogden's strain energy function, Gent's first stretch
invariant, and Cauchy stress are discussed. Failure maps incorporating post
bifurcation (bulging and buckling) response are constructed to delineate the
regimes of growth, buckling and rupture of an aneurysm.
