Buckling Sensitivity of Open Section Thin Shell Structures

Researchers

Fabien Royer
Sergio Pellegrino

Description

Buckling is a dominant instability in thin-shell structures and often defines their range of operation. Understanding the physics behind this phenomenon is crucial but is often complex for two main reasons. First, thin shells follow a falling, unstable post-buckling path right after buckling (sub-critical bifurcation), and therefore, the structure’s unbuckled state is metastable, making their buckling load extremely sensitive to imperfections. Second, even if it is possible to compute mathematically the buckling modes for a structure, the mode shapes seen in experiment often exhibit highly localized deformations. The common way of dealing with this complexity is to apply an empirical knockdown factor to the buckling load computed mathematically, which leads to very conservative thin shell designs. To reduce the mass of thin shell structures, one needs to depart from this approach and understand the sensitivity of the structure’s buckling to disturbances and imperfections, in the hope of finding a tighter lower bound for experimental buckling loads. Recent advances focused on characterizing this sensitivity for cylindrical and spherical shells using a probe that locally displaces the structure, causing it to buckle earlier than its buckling load. By measuring the probe reaction force, a useful tool called stability landscape of shell buckling is derived and quantify the structure’s resistance against buckling.

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Here we generalized this approach to more complex thin shell assemblies, made of open cross-section components, more complex loadings, and extend the methodology to study the whole post-buckling regime. We also extend the probing methodology to the entire structure, which reveals buckling modes that are not predicted by the classical mathematical computation.

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Finally a new pure bending testing machine has been designed and removes all redundant constraints on the test structure. It guarantees that no state of self-stress would develop in the structure and makes it particularly suitable for the study of imperfection sensitive structures.

Experimental_Stability_Landscapes.png
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Publications:

  • Royer, F., Hutchinson, J. W., Pellegrino, S., Probing the Stability of Thin Shell Structures Under Bending (In preparation: manuscript pdf)

  • Royer, F., Pellegrino, S., Buckling Sensitivity of Ultralight Ladder-Type Coilable Space Structures (In preparation: manuscript pdf)

  • Royer, F., Li, Y., Truong, A., Sommer, C., Pellegrino, S., Pure Bending Machine for The Testing of Non-Linear Structures Under Large Deformations (In preparation: manuscript pdf)

  • Royer, F. and Pellegrino, S. (2020), Buckling of ultralight ladder-type coilable space structures. SciTech 2020, Orlando (FL), AIAA-2020-1437.