Dynamic linear viscoelastic small deflection lifting surface torsional divergence and col- umn creep buckling are investigated by including inertia contributions in the governing integral- partial differential relations for the entire lifetime of the structure. Their conceptual and ana- lytical similarities are demonstrated. The behavior of time dependent transient velocities and loads during the initial load build-up phase, maneuvers, etc., is also examined. Computer sim- ulations confirm that wing and column deformations and stability (time to diverge or creep buckle) are radically altered by the presence of inertia effects - even under static loading - when compared to equivalent quasi-static results for both small and large relaxation time values, even though the accelerations are almost solely due to viscoelastic material time effects, rather than to load contributions. It is also shown that different very short time loading patterns affect wing or column displacements and critical times. It is further demonstrated that viscoelastic materials exhibiting finite long time strains are subject to additional static as well as dynamic creep buckling load constraints which do not apply to materials with unbounded long time creep strains. Wings and columns with viscoelastic materials showing finite long time strains do not exhibit instabilities until after a load threshold is reached which solely depends on material properties.
Alternate torsional creep buckling time hypotheses based on strain reversal, constancy of slopes of deflection logarithms and on deterministic and/or stochastic material time dependent failures are formulated and examined.
Viscoelastic materials exhibit degradations of relaxation moduli and failure stresses with time. Consequently, since applied moments and deflections increase in time due to creep and failure stresses decrease, it is only a matter of time before either creep buckling or material failures will occur. The concept of column/wing lifetime or survival times based on probabili- ties of failure is, therefore, formulated and evaluated including temperature effects. The failure criterion is based on combined compressive, bending and shear stresses and considers delami- nation onset as the failure condition, because of the availability of statistical experimental data necessary for probability modeling and simulations.