WEBVTT - Why (and How) Does Paper Crumple? 0:00:01.840 --> 0:00:07.520 Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff, 0:00:07.520 --> 0:00:11.040 lor and Vogel Bomb. Here pop quiz in case you 0:00:11.080 --> 0:00:13.800 didn't read this episode title, But what do a sheet 0:00:13.800 --> 0:00:15.960 of paper being crushed into a ball and tossed into 0:00:16.000 --> 0:00:19.040 a waste basket, The front end of a car forming 0:00:19.040 --> 0:00:22.960 in a crash, and the Earth's crust gradually forming mountains 0:00:23.000 --> 0:00:27.680 over millions of years all having common They're all undergoing 0:00:27.680 --> 0:00:31.720 a physical process called crumpling, which occurs when a relatively 0:00:31.760 --> 0:00:34.800 thin sheet of material, one with a thickness that's far 0:00:34.960 --> 0:00:37.680 less than its length or its width, has to fit 0:00:37.880 --> 0:00:43.000 into a smaller area. And while it's easy to imagine 0:00:43.040 --> 0:00:47.080 crumpling as mere disarray, scientists who have studied crumpling have 0:00:47.159 --> 0:00:50.879 discovered that it's anything but The crumpling turns out to 0:00:50.920 --> 0:00:56.320 be a predictable, reproducible process governed by math. A recent 0:00:56.360 --> 0:00:59.360 breakthrough at our understanding was described in a paper published 0:00:59.360 --> 0:01:02.880 in Nature Communecations in twenty twenty one, in which researchers 0:01:02.920 --> 0:01:06.319 describe a physical model for what happens when thin sheets 0:01:06.360 --> 0:01:12.120 are crumpled, then unfolded, and recrumpled. For the article, this 0:01:12.160 --> 0:01:14.760 episode is based on how Stuffwork. Spoke via email with 0:01:14.840 --> 0:01:18.960 Christopher Ryecroft, the paper's corresponding author, who's Associate professor in 0:01:19.000 --> 0:01:21.880 the John L. Paulson School of Engineering and Applied Sciences 0:01:21.920 --> 0:01:26.480 at Harvard University. He said, from an early age, everyone 0:01:26.560 --> 0:01:28.920 is familiar with crumpling a sheet of paper into a ball, 0:01:29.160 --> 0:01:32.399 unfolding it, and looking at the complicated network of creases 0:01:32.440 --> 0:01:36.120 that form on the surface. This seems like a random, 0:01:36.200 --> 0:01:39.639 disordered process, and you might think it's difficult to predict 0:01:39.680 --> 0:01:43.280 anything at all about what happens. Suppose now you repeat 0:01:43.280 --> 0:01:46.600 this process, crumple the paper again and unfold it. You 0:01:46.640 --> 0:01:50.520 will get more creases. However, you won't double the number 0:01:50.920 --> 0:01:54.520 because the existing creases already weakened the sheet and allow 0:01:54.560 --> 0:01:59.200 it fold more easily the second time around. That idea 0:01:59.320 --> 0:02:02.520 formed the base of experiments performed several years ago by 0:02:02.520 --> 0:02:06.280 another of the papers authors, former Harvard physicist Schumel M. 0:02:06.320 --> 0:02:10.600 Rubinstein and his students. Rubinstein and his team crumpled a 0:02:10.639 --> 0:02:13.960 thin sheet repeatedly and measured the total length of the 0:02:14.000 --> 0:02:18.920 creases on that sheet, which they called mileage. Ryecroft said 0:02:19.360 --> 0:02:22.919 they found that the growth of mileage is strikingly reproducible, 0:02:23.240 --> 0:02:26.040 and each time the accrual of new mileage would get 0:02:26.040 --> 0:02:29.640 a little less because the sheet is progressively getting weaker. 0:02:32.320 --> 0:02:36.440 That finding stumped the physics community, hence the more recent research. 0:02:37.080 --> 0:02:39.720 A Ryecraft said, we found that the way to make 0:02:39.800 --> 0:02:43.080 progress was not to focus on the creases themselves, but 0:02:43.160 --> 0:02:46.400 rather to look at the undamaged facets that are outlined 0:02:46.440 --> 0:02:50.680 by the creases. Houstuffworks also spoke by email with the 0:02:50.720 --> 0:02:54.120 more recent papers lead author Yovanna A. And Jyevic, a 0:02:54.280 --> 0:02:59.280 Harvard doctoral candidate. She said, in the experiment, thin sheets 0:02:59.280 --> 0:03:02.519 of mylar, a thin film that crumples similarly to paper, 0:03:02.800 --> 0:03:06.800 were systematically crumpled several times, developing some new creases with 0:03:06.880 --> 0:03:11.200 each repetition. In between crumples, the sheets were carefully flattened 0:03:11.240 --> 0:03:14.760 and their height profiles scanned using an instrument called a profilometer. 0:03:15.480 --> 0:03:18.440 The profilometer makes measurements of the height map across the 0:03:18.480 --> 0:03:21.120 surface of the sheet, which allows us to calculate and 0:03:21.280 --> 0:03:27.800 visualize the locations of creases as an image. Because creasing 0:03:27.919 --> 0:03:31.760 can be messy and irregular, it generates noisy data that 0:03:31.840 --> 0:03:34.400 can be tough for computer automation to make sense of. 0:03:35.120 --> 0:03:38.440 To get around that problem, Andreavic hand traced the crease 0:03:38.480 --> 0:03:42.760 patterns on twenty four sheets using a tablet, PC, Adobe illustrator, 0:03:42.840 --> 0:03:47.120 and photoshop. That meant hand recording twenty one thousand, one 0:03:47.240 --> 0:03:53.200 hundred and ten facets in total. Thanks to Andreevic's labors 0:03:53.240 --> 0:03:57.040 and image analysis, the researchers could analyze how many facets 0:03:57.080 --> 0:04:01.040 of different sizes were created as the crumpling progress. They 0:04:01.120 --> 0:04:05.400 found that the size distributions could be explained by fragmentation theory, 0:04:05.720 --> 0:04:08.760 which looks at how objects are ranging from rocks and 0:04:08.840 --> 0:04:12.800 glass shards to volcanic debris and icebergs, break up into 0:04:12.840 --> 0:04:18.800 small pieces over time. Ryecroft said that same theory can 0:04:18.839 --> 0:04:22.359 accurately explain how the facets of the crumpled sheet break 0:04:22.440 --> 0:04:25.960 up over time as more creases form. We can also 0:04:26.040 --> 0:04:29.279 use it to estimate how the sheet becomes weaker after crumpling, 0:04:29.640 --> 0:04:33.640 and thereby explain how the accumulation of mileage slows down. 0:04:34.520 --> 0:04:37.000 This allows us to explain the mileage results and the 0:04:37.040 --> 0:04:40.839 logarithmic scaling that we're seen in the twenty eighteen study. 0:04:40.920 --> 0:04:43.960 We believe that the fragmentation theory provides a perspective on 0:04:44.000 --> 0:04:47.120 the problem and is especially useful to model the accumulation 0:04:47.200 --> 0:04:52.520 of damage over time. But okay, let's back up a second. 0:04:53.080 --> 0:04:56.000 Why do some objects crumple in the first place, as 0:04:56.040 --> 0:04:59.239 opposed to simply breaking apart into a lot of little pieces. 0:05:00.279 --> 0:05:02.920 It has to do with how flexible a material is. 0:05:03.520 --> 0:05:06.559 Things like paper and milar are very easy to bend, 0:05:06.920 --> 0:05:09.719 so they're not very likely to break when you apply pressure, 0:05:10.320 --> 0:05:13.400 But things like rock and glass don't bend easily, so 0:05:13.600 --> 0:05:18.760 force can make them break. Andreevic explained a crumpling and 0:05:18.800 --> 0:05:22.680 breaking are quite distinct processes, but there are some similarities 0:05:22.720 --> 0:05:26.800 we can recognize. For example, both crumpling and breaking are 0:05:26.800 --> 0:05:30.960 mechanisms of relieving stress and a material. The idea of 0:05:31.040 --> 0:05:34.640 creases protecting other regions of a sheet from damage refers 0:05:34.680 --> 0:05:38.400 to damage being localized to very narrow ridges in the sheet. 0:05:39.279 --> 0:05:42.160 In fact, the sharp vertices and ridges that form when 0:05:42.160 --> 0:05:45.799 a sheet crumples are localized regions of stretching in the sheet, 0:05:46.160 --> 0:05:51.120 which are energetically unfavorable. As a result, the sheet minimizes 0:05:51.240 --> 0:05:55.520 those costly deformations by confining them to very narrow regions, 0:05:55.720 --> 0:05:59.760 protecting the rest of the sheet as much as possible. Furthermore, 0:06:00.120 --> 0:06:02.760 your research showed that the more a sheet is crumpled, 0:06:03.200 --> 0:06:07.479 the more it resists further compression, so that increasingly more 0:06:07.600 --> 0:06:11.480 force is required to compress it. The ridges seem to 0:06:11.560 --> 0:06:14.920 line up and act as pillars that increase the strength 0:06:15.000 --> 0:06:20.080 of the crumpled sheet. There's still a lot that needs 0:06:20.120 --> 0:06:23.719 to be learned about crumpling. For example, it's not clear 0:06:23.760 --> 0:06:27.240 whether different types of crumpling of using a cylindrical piston, 0:06:27.320 --> 0:06:29.960 for example, rather than your hand it results in a 0:06:30.040 --> 0:06:34.240 different type of crease pattern. A Ryecroft said, we'd like 0:06:34.279 --> 0:06:39.280 to understand how general our findings are. In addition, researchers 0:06:39.320 --> 0:06:41.760 want to learn more about the actual mechanisms of how 0:06:41.839 --> 0:06:44.880 creases form and to be able to take measurements during 0:06:44.880 --> 0:06:48.560 the process rather than just examining the end result. A 0:06:48.640 --> 0:06:52.440 Ryecraft explained. To get around this, we're currently developing a 0:06:52.480 --> 0:06:55.960 three D mechanical simulation of a crumpled sheet, which can 0:06:56.000 --> 0:06:59.960 allow us to observe the entire process already our simulation 0:07:00.080 --> 0:07:02.360 and can create creased patterns that are similar to those 0:07:02.400 --> 0:07:04.800 seen in the experiment, and it provides us with a 0:07:04.880 --> 0:07:11.520 much more detailed view of the crumpling process. But all right, 0:07:12.080 --> 0:07:16.400 why does crumple theory matter? Gaining insights about crumpling is 0:07:16.440 --> 0:07:19.560 potentially really important to all sorts of things in our 0:07:19.680 --> 0:07:23.920 modern world. Ryecroft said, if you're using a material in 0:07:24.000 --> 0:07:28.560 any structural capacity, it is critical to understand its failure properties. 0:07:29.240 --> 0:07:32.600 In many situations, it's important to understand how materials will 0:07:32.600 --> 0:07:37.760 behave under repeated loading. For example, aircraft wings vibrate up 0:07:37.760 --> 0:07:41.000 and down many thousands of times over their lifetime. Our 0:07:41.040 --> 0:07:43.600 study of repeated crumpling can be viewed as a model 0:07:43.640 --> 0:07:47.560 system for how materials are damaged under repeated load. We 0:07:47.680 --> 0:07:50.720 expect that some core elements of our theory about how 0:07:50.760 --> 0:07:54.680 materials are weakened by fractures increases over time may have 0:07:54.800 --> 0:08:02.160 analogs in other material types, and sometimes crumpling might actually 0:08:02.200 --> 0:08:07.680 be utilized technologically. For example, crumpled graphene sheets have been 0:08:07.720 --> 0:08:13.840 suggested as a possibility for making high performance electrodes for batteries. Really, 0:08:13.920 --> 0:08:17.480 crumple theory provides insights into all sorts of phenomena, from 0:08:17.600 --> 0:08:21.440 how insects wings unfold to how DNA packs into a 0:08:21.520 --> 0:08:24.680 cell nucleus, all of which could be used to build 0:08:24.760 --> 0:08:32.600 more efficient machines. In the future. Today's episode is based 0:08:32.640 --> 0:08:35.000 on the article crumple theory. We can learn a lot 0:08:35.040 --> 0:08:37.680 from how paper crumples on how stuffworks dot com, written 0:08:37.679 --> 0:08:40.200 by Patrick J. Higer. Brain Stuff is production of by 0:08:40.240 --> 0:08:42.480 Heart Radio in partnership with how stuffworks dot Com and 0:08:42.600 --> 0:08:45.920 is produced by Tyler Klang. For more podcasts on iHeartRadio, 0:08:46.160 --> 0:08:49.199 visit the iHeartRadio app, Apple Podcasts, or wherever you listen 0:08:49.240 --> 0:09:00.960 to your favorite shows.