A micro-scale look at how parachute fibers respond under stress

Parachutes have many applications, decelerating everything from skydivers to scientific payloads to supersonic speed. Regardless of how slow a parachute slows down, two things remain constant: the parachute must withstand large amounts of force, and it is crucial to ensuring the safety of whatever it carries. To choose parachute materials that do their job effectively, it is important to have a good understanding of what happens when a parachute opens and descends.

Cutler Phillippe, Francesco Panerai and Laura Villafañe Roca, researchers at the Beckman Institute for Advanced Science and Technology, used CT scanning to study the fiber-scale properties of parachute textiles and relate them to larger-scale behavior. Their work is published in the Journal of the American Institute of Aeronautics and Astronautics (AIAA).

“We generally know how a textile affects the performance of the parachute,” said Phillippe, a graduate student in the Department of Aerospace Engineering at the University of Illinois at Urbana-Champaign. “But we do not know, from an experimental point of view, how these performances relate to the individual movements of the fibers in the textile as well as to the dynamic properties of, for example, a fiber bundle.”

If the performance of the parachute (how it behaves in the sky) is considered on the macro scale, a bundle of fibers is on the meso scale and an individual fiber represents the micro scale, the researchers said.

The researchers aimed to quantify what was happening at these smaller scales and relate this behavior to forces and interactions occurring on larger scales. This provides data to computer modelers simulating the potential behavior of untested parachutes and could inform them of new phenomena.

The researchers used a micro-CT scanner at Beckman to image two parachute textiles subjected to increasing levels of stress. Like a hospital CT scanner, micro-CT scanners use X-rays to image 2D slices of a material. These slices visualize the 3D structure of the material once assembled.

The group loaded their parachute samples onto an instrument called a tensile tester, which allowed them to gradually increase the force exerted on their textile samples. At each new force level, micro-CT scans were taken while the samples were held under stress.

The tensile tests showed the researchers how the fibers responded to different levels of stress: how they stretched, straightened, and reorganized with increasing loads. As the fiber bundles changed shape, the pores between them would also widen, which would change the way air flows through and around the parachute.

When textiles contain the same number of fibers of the same type running in both directions (up and down rather than left and right within the material), the textile is said to be isotropic. This means that it has the same properties in both directions. For example, applying a force along the vertical axis should result in the same amount of stress and strain in the material as if the force were applied along the horizontal axis.

However, the researchers observed the opposite: the textiles had different properties in different directions. During weaving, fibers running in one direction, called the warp, are held in tension on a loom, while the fibers running perpendicular to them, called the weft, are slipped between the first set of fibers. Even after the textile is removed from the loom, differences in tension during the manufacturing process mean that it is not isotropic. Specifically, the fabric is more resistant to stretching in the direction of the warp fibers.

Understanding this difference can shed light on processes such as parachute assembly. Parachutes are made up of different textile parts attached to each other, and the orientation of these parts influences the properties of the entire parachute.

Choosing the best parachute materials is crucial for safety and mission objectives. This research informs models that will be used to identify promising candidate textiles.

“IT work is very good at recreating things that have been done,” Phillippe said, “but it’s not quite at the deployment phase (pun intended) to be able to say, ‘Okay , I’ve modeled this new textile and I can definitely tell you whether or not it’s worth the cost of making a prototype.'”

Improving parachute material control models are making parachute industries and applications more cost-effective and faster. In addition to scientific missions, this work can be applied to parachutes in other contexts: for example, for use in rescue or recreational operations.

Phillippe presented his work at a symposium on interactions between fluids and structures, where he met NASA computer scientists and other programmers who incorporate research like his into their models.

“Most of the time, there’s a slight lag in communication between what computer scientists need and what experimentalists think they need, and you end up not seeing the full picture,” Phillippe said. “Getting to know everyone and hearing about their wants and needs has been very inspiring. This really helped me define what I needed to do for the rest of this work. »

Phillippe is currently using imaging microscopy to better understand the impact of textile pores on air flow and imaging textiles with the flow passing through them to visualize 3D deformation.