Landslides reactivate due to external environmental forcing or internal mass redistribution, but the process is rarely documented quantitatively. We capture the three‐dimensional, 1‐m resolution surface deformation field of a transiently reactivated landslide with image correlation of repeat airborne lidar. Undrained loading by two debris flows in the landslide's head, rather than external forcing, triggered reactivation. After that loading, the lower 2 km of the landslide advanced by up to 14 m in 2 years before completely stopping. The displacement field over those 2 years implies that the slip surface gained 1 kPa of shear strength, which was likely accomplished by a negative dilatancy‐pore pressure feedback as material deformed around basal roughness elements. Thus, landslide motion can be decoupled from external environmental forcing in cases, motivating the need to better understand internal perturbations to the stress field to predict hazards and sediment fluxes as landscapes evolve.

A new type of folded composite hinge is investigated for its use in precision deployable spacecraft structures. The hinge is an integral feature of a composite tube intended for use as a structural truss member. The design of the hinge allows the tube to be elastically folded for stowage even with tube wall thicknesses from 0.4 to 1.7 mm. Whether the large but primarily elastic folding stresses impart permanent deformations to the tube after it is deployed is experimentally assessed. The data show that any such permanent strain induces tip deformations, identi ed as microscopic plastic behavior, of no more than 2.5 ¹ axially and 9 ¹ laterally, depending on the composite layup. This deployment repeatability is comparable to prior measurements of mechanical deployables. Moreover, stow duration and number of stows have no measurable effect, once the initial stow-deploy cycle has been completed. There is always a signi cant viscoelastic creep recovery following deployment that increases with stowage time. However, this viscoelastic creep is recovered. An exponential curve t of the creep time response shows that the time constants of the viscoelastic recovery are independent of stow duration. Nomenclature fag = vector of coef cients, ¹m b = intercept, ¹m k = spring stiffness constant, N/m M = model order m = thermal correlation coef cient, ¹m/ ± C N = number of measurements P = probability S x = sample standard deviation, ¹m t = time, s t º; P = Student's t distribution u x = precision interval, ¹m y = tip displacement, ¹m O y = tip displacement estimate, ¹m 1T = change in temperature, ± C º = degrees of freedom ¾ 2 i = sample variance, ¹m 2 ¿ = time constant, s f¿ g = vector of time constants, s  2 = chi-squared distribution

It has been previously demonstrated that increasing structural complexity can lead to lighter weight structures. However, it is not clear that structural complexity or hierarchy enables lighter weight structures for all architectures and load cases. In this paper, the performance trends in linear truss structures are investigated as a function of self-similar hierarchy order and of loading conditions. The investigations show the order of structural hierarchy resulting in a lightest weight self-similar four longeron solid element truss-column is 2 nd (a truss made from trusses) for requirements representative of space structures. The resulting truss-column is typically an order of magnitude lighter than the corresponding 1 st order truss-column and two to four times larger in diameter. Long and lightly loaded columns are shown to have the greatest potential for mass reduction with increasing hierarchy. Optimization results for 1 st and 2 nd order self-similar triangular single-laced double-bay trusses subject to bending strength and stiffness requirements are also presented. A comparison of 1 st and 2 nd order results show a factor of 30 reduction in truss mass and a simultaneous factor of nine increase in truss diameter.

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The experimental study and analysis of a novel gossamer structural component is described. The component is a 3-m-long thin-walled isogrid column prototype that may be elastically stowed and deployed. The column has a diameter of 0.318 m, with a linear density of 46 g/m. The static and dynamic mechanical responses of the deployed prototype are examined and compared to an idealized model. These comparisons indicate global stiffness ranging from 11 to 28% and buckling strengths from 7 to 37% of the theoretically ideal performance. Initial local curvatures approaching the thickness of the isogrid ribs are found to be the primary source of this performance reduction. A modeling approach based on the postbuckled response of individual isogrid ribs is proposed for predicting the global effects of local imperfections, and good agreement with the test results is found. In general, initial rib curvatures greater than 10% of the rib thickness are predicted to result in signi cant degradations of the global structural performance. NomenclatureA = cross-sectional area, m 2 b = isogrid rib width, m c = compliance, m/N E = Young's modulus, Pa f = vibration frequency, rad/s h = isogrid rib spacing, m I = minimum rectangular moment of inertia, m 4 J = rotational inertia, kg ¢ m 2 k = stiffness, N/m (or Nm/rad) L = length, m P = axial load, N q = normalized axial load r = column radius, m t = column/rib thickness, m°= knockdown factor ± = axial de ection, m " = imperfection amplitude, m ¾ = stress, N/m 2 Á = thin-walled cylinder exponent Subscripts axial = axial properties bending = bending properties cr = critical load eff = effective properties ideal = ideal properties rib = individual rib properties