Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff,
Speaker 1: lor and Vogel Bomb. Here pop quiz in case you
Speaker 1: didn't read this episode title, But what do a sheet
Speaker 1: of paper being crushed into a ball and tossed into
Speaker 1: a waste basket, The front end of a car forming
Speaker 1: in a crash, and the Earth's crust gradually forming mountains
Speaker 1: over millions of years all having common They're all undergoing
Speaker 1: a physical process called crumpling, which occurs when a relatively
Speaker 1: thin sheet of material, one with a thickness that's far
Speaker 1: less than its length or its width, has to fit
Speaker 1: into a smaller area. And while it's easy to imagine
Speaker 1: crumpling as mere disarray, scientists who have studied crumpling have
Speaker 1: discovered that it's anything but The crumpling turns out to
Speaker 1: be a predictable, reproducible process governed by math. A recent
Speaker 1: breakthrough at our understanding was described in a paper published
Speaker 1: in Nature Communecations in twenty twenty one, in which researchers
Speaker 1: describe a physical model for what happens when thin sheets
Speaker 1: are crumpled, then unfolded, and recrumpled. For the article, this
Speaker 1: episode is based on how Stuffwork. Spoke via email with
Speaker 1: Christopher Ryecroft, the paper's corresponding author, who's Associate professor in
Speaker 1: the John L. Paulson School of Engineering and Applied Sciences
Speaker 1: at Harvard University. He said, from an early age, everyone
Speaker 1: is familiar with crumpling a sheet of paper into a ball,
Speaker 1: unfolding it, and looking at the complicated network of creases
Speaker 1: that form on the surface. This seems like a random,
Speaker 1: disordered process, and you might think it's difficult to predict
Speaker 1: anything at all about what happens. Suppose now you repeat
Speaker 1: this process, crumple the paper again and unfold it. You
Speaker 1: will get more creases. However, you won't double the number
Speaker 1: because the existing creases already weakened the sheet and allow
Speaker 1: it fold more easily the second time around. That idea
Speaker 1: formed the base of experiments performed several years ago by
Speaker 1: another of the papers authors, former Harvard physicist Schumel M.
Speaker 1: Rubinstein and his students. Rubinstein and his team crumpled a
Speaker 1: thin sheet repeatedly and measured the total length of the
Speaker 1: creases on that sheet, which they called mileage. Ryecroft said
Speaker 1: they found that the growth of mileage is strikingly reproducible,
Speaker 1: and each time the accrual of new mileage would get
Speaker 1: a little less because the sheet is progressively getting weaker.
Speaker 1: That finding stumped the physics community, hence the more recent research.
Speaker 1: A Ryecraft said, we found that the way to make
Speaker 1: progress was not to focus on the creases themselves, but
Speaker 1: rather to look at the undamaged facets that are outlined
Speaker 1: by the creases. Houstuffworks also spoke by email with the
Speaker 1: more recent papers lead author Yovanna A. And Jyevic, a
Speaker 1: Harvard doctoral candidate. She said, in the experiment, thin sheets
Speaker 1: of mylar, a thin film that crumples similarly to paper,
Speaker 1: were systematically crumpled several times, developing some new creases with
Speaker 1: each repetition. In between crumples, the sheets were carefully flattened
Speaker 1: and their height profiles scanned using an instrument called a profilometer.
Speaker 1: The profilometer makes measurements of the height map across the
Speaker 1: surface of the sheet, which allows us to calculate and
Speaker 1: visualize the locations of creases as an image. Because creasing
Speaker 1: can be messy and irregular, it generates noisy data that
Speaker 1: can be tough for computer automation to make sense of.
Speaker 1: To get around that problem, Andreavic hand traced the crease
Speaker 1: patterns on twenty four sheets using a tablet, PC, Adobe illustrator,
Speaker 1: and photoshop. That meant hand recording twenty one thousand, one
Speaker 1: hundred and ten facets in total. Thanks to Andreevic's labors
Speaker 1: and image analysis, the researchers could analyze how many facets
Speaker 1: of different sizes were created as the crumpling progress. They
Speaker 1: found that the size distributions could be explained by fragmentation theory,
Speaker 1: which looks at how objects are ranging from rocks and
Speaker 1: glass shards to volcanic debris and icebergs, break up into
Speaker 1: small pieces over time. Ryecroft said that same theory can
Speaker 1: accurately explain how the facets of the crumpled sheet break
Speaker 1: up over time as more creases form. We can also
Speaker 1: use it to estimate how the sheet becomes weaker after crumpling,
Speaker 1: and thereby explain how the accumulation of mileage slows down.
Speaker 1: This allows us to explain the mileage results and the
Speaker 1: logarithmic scaling that we're seen in the twenty eighteen study.
Speaker 1: We believe that the fragmentation theory provides a perspective on
Speaker 1: the problem and is especially useful to model the accumulation
Speaker 1: of damage over time. But okay, let's back up a second.
Speaker 1: Why do some objects crumple in the first place, as
Speaker 1: opposed to simply breaking apart into a lot of little pieces.
Speaker 1: It has to do with how flexible a material is.
Speaker 1: Things like paper and milar are very easy to bend,
Speaker 1: so they're not very likely to break when you apply pressure,
Speaker 1: But things like rock and glass don't bend easily, so
Speaker 1: force can make them break. Andreevic explained a crumpling and
Speaker 1: breaking are quite distinct processes, but there are some similarities
Speaker 1: we can recognize. For example, both crumpling and breaking are
Speaker 1: mechanisms of relieving stress and a material. The idea of
Speaker 1: creases protecting other regions of a sheet from damage refers
Speaker 1: to damage being localized to very narrow ridges in the sheet.
Speaker 1: In fact, the sharp vertices and ridges that form when
Speaker 1: a sheet crumples are localized regions of stretching in the sheet,
Speaker 1: which are energetically unfavorable. As a result, the sheet minimizes
Speaker 1: those costly deformations by confining them to very narrow regions,
Speaker 1: protecting the rest of the sheet as much as possible. Furthermore,
Speaker 1: your research showed that the more a sheet is crumpled,
Speaker 1: the more it resists further compression, so that increasingly more
Speaker 1: force is required to compress it. The ridges seem to
Speaker 1: line up and act as pillars that increase the strength
Speaker 1: of the crumpled sheet. There's still a lot that needs
Speaker 1: to be learned about crumpling. For example, it's not clear
Speaker 1: whether different types of crumpling of using a cylindrical piston,
Speaker 1: for example, rather than your hand it results in a
Speaker 1: different type of crease pattern. A Ryecroft said, we'd like
Speaker 1: to understand how general our findings are. In addition, researchers
Speaker 1: want to learn more about the actual mechanisms of how
Speaker 1: creases form and to be able to take measurements during
Speaker 1: the process rather than just examining the end result. A
Speaker 1: Ryecraft explained. To get around this, we're currently developing a
Speaker 1: three D mechanical simulation of a crumpled sheet, which can
Speaker 1: allow us to observe the entire process already our simulation
Speaker 1: and can create creased patterns that are similar to those
Speaker 1: seen in the experiment, and it provides us with a
Speaker 1: much more detailed view of the crumpling process. But all right,
Speaker 1: why does crumple theory matter? Gaining insights about crumpling is
Speaker 1: potentially really important to all sorts of things in our
Speaker 1: modern world. Ryecroft said, if you're using a material in
Speaker 1: any structural capacity, it is critical to understand its failure properties.
Speaker 1: In many situations, it's important to understand how materials will
Speaker 1: behave under repeated loading. For example, aircraft wings vibrate up
Speaker 1: and down many thousands of times over their lifetime. Our
Speaker 1: study of repeated crumpling can be viewed as a model
Speaker 1: system for how materials are damaged under repeated load. We
Speaker 1: expect that some core elements of our theory about how
Speaker 1: materials are weakened by fractures increases over time may have
Speaker 1: analogs in other material types, and sometimes crumpling might actually
Speaker 1: be utilized technologically. For example, crumpled graphene sheets have been
Speaker 1: suggested as a possibility for making high performance electrodes for batteries. Really,
Speaker 1: crumple theory provides insights into all sorts of phenomena, from
Speaker 1: how insects wings unfold to how DNA packs into a
Speaker 1: cell nucleus, all of which could be used to build
Speaker 1: more efficient machines. In the future. Today's episode is based
Speaker 1: on the article crumple theory. We can learn a lot
Speaker 1: from how paper crumples on how stuffworks dot com, written
Speaker 1: by Patrick J. Higer. Brain Stuff is production of by
Speaker 1: Heart Radio in partnership with how stuffworks dot Com and
Speaker 1: is produced by Tyler Klang. For more podcasts on iHeartRadio,
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