Failure Analysis of Coilable Shell Longerons

Researchers

Armanj Hasanyan
Wen Luo
Christophe Leclerc
Sergio Pellegrino

Description

Thin-shell Triangular Rollable and Collapsible (TRAC) longerons are fundamental to the deployable SSPP spacecraft. Its cross-section is composed of two flanges, with an opening angle and radius theta and r, respectively, joined at the web-section of width w. In the deployed configuration of the structure, the composite TRAC longerons are used to support the photovoltaic and RF antenna tiles. To package the SSPP spacecraft efficiently, it must be tightly coiled to minimize the stowed volume. However, this can lead to material failure. In this study, the goal is to understand the fracture behavior of composite shell longerons when coiled. To investigate the failure process, an experiment is devised to coil the longerons around a rigid hub of radius R.

Schematic indicating the cross-section of a coilable TRAC longeron.

Schematic indicating the cross-section of a coilable TRAC longeron.

Experiment devised for conducting coiling experiments. 

Experiment devised for conducting coiling experiments. 

The aim of this project is to understand the relation between manufacturing methods, the resulting microstructural defects, and their effects on the performance (failure) of the longeron. During coiling, the longeron may experience local cracking, which under certain conditions (creep, fatigue, thermal cyclic loading) can grow to cause structural failure (exp. delamination at the web). As a result, understanding their effects is critical for the manufacturing and the design of the longerons. For this, micro-CT imaging is conducted to understand the manufactured induced defects and the resulting failure modes due to coiling.

A current research is also focused on characterizing microstructural defects statistically. For example, to characterize the voids at the interface in the web-section, Avizo software is used. First, the voids are segmented from the micro-CT scans of the longerons. From this, the void shape and volume are approximated by fitting an ellipsoid (i.e. length of semi-axis). This allows for statistical representation of void shape and volume through probability distributions. The goal of this study is two-fold: first, to represent the quality of the longerons after manufacturing using probability distributions. Second, to appropriately introduce the voids into a finite element model to numerically study their effects on the performance of the longerons.

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ZEISS Xradia 510 Versa 3D X-ray microscope (XRM) was used for generating the microstructural volume images of the longerons. For visualization and statistical analysis of the defects, Avizo software was used.   

Publications:

  • Hasanyan, A. D. and Pellegrino, S. (2020). Characterization of interface toughness in thin-ply composites. SciTech 2020, Orlando (FL), AIAA-2020-0694.

  • Leclerc, C. and Pellegrino, S. (2019). Reducing stress concentration in the transition region of coilable ultra-thin-shell booms. SciTech 2019, San Diego (CA), AIAA-2019-1522.

  • Leclerc, C., Pedivellano, A. and Pellegrino, S. (2018). Stress concentration and material failure during coiling of ultrathin TRAC booms. SciTech 2018. Orlando (FL), AIAA-2018-0690.