This paper presents an experimental and numerical study of the folding, stowage, and deployment behavior of viscoelastic tape springs. Experiments show that during folding the relationship between load and displacement is nonlinear and varies with rate and temperature. In particular, the limit and propagation loads increase with the folding rate but decrease with temperature. During stowage, relaxation behavior leads to a reduction in internal forces that signicantly impacts the subsequent deployment dynamics. The deployment behavior starts with a short, dynamic transient that is followed by a steady deployment and ends with a slow creep recovery. Unlike elastic tape springs, localized folds in viscoelastic tape springs do not move during deployment. Finite element simulations based on a linear viscoelastic constitutive model with an experimentally determined relaxation modulus are shown to accurately reproduce the experimentally observed behavior, and to capture the eects of geometric nonlinearity, time and temperature dependence. 1 Nomenclature a T = temperature shift factor c 1 , c 2 = constants in WLF equation E = uniaxial relaxation modulus E ∞ = uniaxial long-term modulus G = shear relaxation modulus h = tape spring thickness h = average tape spring thickness I = second moment of area K = bulk relaxation modulus L = tape spring length M = bending moment P = reaction force R = tape spring radius r = longitudinal radius of curvature of localized fold T = temperature T 0 = reference temperature t = time t' = reduced time u = vertical displacemenṫ u = vertical displacement rate v = horizontal displacement x = horizontal coordinate α = tape spring subtended angle ϵ = strain κ l = longitudinal curvature ν = Poisson's ratio ρ = relaxation times σ = stress θ = rotation angle 2
Thermal cycling and creep in metallic interconnects during operation of solid oxide cell (SOC) stacks could cause contact losses in the interface between the interconnect and cells. The magnitude of stress and its distribution within the SOC stack depends on the overall design of the stack and the operating conditions. In this study, stresses in different types of generic SOC stack designs caused by external loading and temperature variations through long‐term operation are investigated. The investigation includes stack designs with and without contact components combined with machined (cross‐shaped) or pressed (corrugated) interconnects. Two different generic temperature profiles in the stacks are considered. Special focus is given to stresses that can cause possible delamination of the interconnect from the cell that subsequently leads to loss of electrical contact. It is found that too rigid designs cause high stresses and creep in the interconnects, and so‐called stress reversal will cause delamination between interconnect and cell during shut‐down. Furthermore, the study also presents the effect of SOC stack design and/or thermal gradient on the magnitude of in‐plane stresses in the cells. Here it is found that it advantageous to cool the stack primarily with convection, as this causes a linear thermal profile and much lower stresses than if cooling is relying on conduction in the solids, as this causes a thermal gradient in several directions.
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