Our research focuses on the design and failure analysis of shell structures made from ultra-thin composites, specifically for deployable spacecraft and space vehicles. This work is driven by the need to create large-scale space strucgures that use origami-inspired packaging techniques to overcome the mass and volume constraints of rockets. Examples include Caltech's Space Solar Power Project (shown below), NASA's Solar Sail, and AFRL's Roll Out Solar Array (ROSA). These next-generation spacecraft rely on ultra-thin composite materials that elastically deform during packaging, passively self-deploy by releasing stored strain energy, and support structural loads once deployed in space.

Multistable Composite Shells with Steered Fibers

Multistable structures possess the ability to maintain multiple stable geometric configurations without needing a constant external load. Transitions between these states are achieved through external energy input, offering a significant advantage over traditional folding or coiling mechanisms. This characteristic is particularly beneficial for applications in the aerospace sector, especially for morphing and deployable structures. A classic example of such a structure is the tape spring shell.

In this study, we explore the use of advanced manufacturing techniques, specifically automated fiber placement (AFP) technology, to create laminates with steered fibers. This method allows for spatial variation in the properties of the shell, enabling precise control over the energy landscape and overall shape of the structure. The coupling of the initial shell geometry with these tailored material properties results in shells capable of achieving two or more stable configurations. This approach leverages fiber steering to enhance the performance and functionality of aerospace structures.

Progressive Damage Modeling of Ultra-thin Shell Structures

Ultra-thin composite shell structures, such as booms and longerons, are integral to deployable spacecraft, supporting functional elements during packaging, deployment, and in-space operation. However, these processes can induce material failure in the composite shells, impairing the integrity and overall performance of the spacecraft. For instance, during coiling around a cylindrical hub, high stress concentrations develop in the transition region between the uncoiled and coiled sections. These stress concentrations are primarily due to the formation and propagation of localized folds caused by buckling. In addition, during long-stowage times, viscoelastic mechanisms can lead to material failure and fracture. 

To predict and prevent such failures, both experimental and numerical modeling standards are essential. Developing structural or shell-scale progressive damage models is crucial for guiding the design of spacecraft structures, including material selection, shell geometry, and support mechanisms. By carefully calibrating the material damage properties and imperfections, these models can predict the formation and propagation of damage, such as localized cracks and microcracks that are not visible through visual inspection. These predictive capabilities are vital for ensuring the reliability and longevity of deployable spacecraft structures.