The concept of snap divergence and post-critical states are theoretically formulated for Joined Wings with the arc length technique. The true critical condition is compared with the divergence speed evaluated by solving an eigenvalue problem about a steady state equilibrium, showing how in some cases this last approach is not reliable and even nonconservative.The work assesses the difference of the nonlinear responses relative to mechanical loads (both conservative and follower ones) used to mimic the real loading condition and the aerodynamic forces.Two joined-wing configurations, characterized by a different location of the joint, are investigated. It is demonstrated that the lift/displacement response may hide the physical snap divergence occurrence, leading to non-physical interpretation of the stability properties of the system. Thus, as a consequence, use mechanical loading to mimic aerodynamic effects should be meditated since they may not give a reliable picture. Aeroelastic stiffening and softening effects are observed for the different cases, and it is discussed how practical instability situation may not be encompassed by the formal mathematical criterion (singularity of the system tangent matrix).Finally, physical interpretation of the static aeroelastic deformation is provided with particular emphasis on the conditions that lead to the snap divergence. The bending/torsion coupling at geometric (sweep angle of the wings) and material (composite materials) level for each wing can not be thought as an isolate property, since, due to the overconstrained nature of the system, the actions are transferred between different parts of the system. In other words, an intuitive approach that tries to fine tune the design of a part as an isolate entity may not lead to meaningful results.
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