1:45 PM - 3:15 PM
[O11-P66] The absorption of impact by dilatant fluids
Keywords:dilatant fluids, honey, shock absorption
Research Background
When I commuted to school by bicycle, I started wearing a helmet, and felt that the helmet was too big when stored. I thought that if I could make it smaller, it would take up less space and be more convenient. So I thought that by using a dilatant fluid, whose viscosity increases when it is subjected to physical impact, I could create a helmet that is foldable but has strong shock absorption.
What is the dilatancy phenomenon?
A dilatant fluid is a type of non-Newtonian fluid whose viscosity increases with shear rate (1), one example is potato starch dissolved in water. The dilatancy phenomenon is a phenomenon in which such fluids become stronger when subjected to impact, and the fluid becomes solid. In the case of potato starch, the potato starch particles initially float in the water, but when force is applied, the arrangement of the particles changes. When this happens, the gaps between the particles become larger, and water enters the gaps (at this time, the water is sucked into the gaps and appears dry), and the floating particles collide with each other, hardening and changing into a solid state. When the force is released, the shape collapses and the liquid returns to its original state (1).
Experimental method
Pure water, oil, carbonated water, honey and potato starch were mixed to create a fluid, and an iron ball was dropped onto it to measure the acceleration. (Equipment used: Smartphone app phyphox (3)) Initially, the liquid and potato starch were mixed at 50g:100g, and the acceleration was measured 10 times, and the amount of liquid was increased by 10g. This operation was repeated up to 90g of liquid. However, referring to previous research, the ratio of pure water and potato starch was fixed at 75g:100g (4).
Results and Discussion
The acceleration was small when there was 70g and 90g of honey. In other words, it was found that the shock absorption of the fluid is high.
However, although the acceleration was small when there were 70g and 90g of honey, at 90g it is considered that the honey is close to a solid, so it is considered that the shock absorption increases when there are 70g of honey and 100g of potato starch.
Future prospects
In this experiment, we were not able to make a helmet shape, but in the future, we will make a helmet shape with a fluid made from a liquid that has similar properties to honey. In that case, the challenge will be keeping the fluid uniform inside the helmet. In addition, although there has been previous research on making a box-shaped folding helmet, it is also necessary to devise a way to make a hemispherical helmet that fits the shape of the head.
References
(1) Kyushu University, Dilatant fluid, Dilatancy, Kyushu University Statistical Physics Laboratory Homepage, http://www.stat.phys.kyushu-u.ac.jp/~nakanisi/Physics/Dilatancy/(2025-3-21)
(2) Nagoya City Water Supply and Sewage, Does it harden when squeezed? Mysterious Liquid, Nagoya City Waterworks Bureau website https://www.water.city.nagoya.jp/uruoi_life/category/learn/145187.html (2025-03-21)
(3) Phyphox (physical phone experiments), a smartphone app developed by Aachen University of Technology
https://phyphox.org/ (2025-3-21)
(4) Igarashi Eita, Kato Otoha, Kudo Kaito, Sato Mitsuyoshi, Impact absorption performance of helmets using dilatancy, Akita Prefectural Yuri High School website, http://www.yuri-h.akita-pref.ed.jp/yuri-h-cms/assets/uploads/2022/03/ c1284e091dba05fa24231fc505db1c94.pdf
(2025-03-21)
(5) Tomoyuki Kachi, Toru Kumazaki, Yuta Mori, Strength measurement of dilatancy fluid and its application, Gifu Prefectural Ena High School website https://school.gifu-net.ed.jp/ena-hs/ssh/H31ssh/sc3/31905.pdf (2025-3-21)
(6) Yoshifumi Yamagata, Rheology in everyday life Part 1 Flow (viscosity) curves of honey and mayonnaise, https://www.jstage.jst.go.jp/article/rheology/50/4/50_343/_pdf(2025-4-13)
When I commuted to school by bicycle, I started wearing a helmet, and felt that the helmet was too big when stored. I thought that if I could make it smaller, it would take up less space and be more convenient. So I thought that by using a dilatant fluid, whose viscosity increases when it is subjected to physical impact, I could create a helmet that is foldable but has strong shock absorption.
What is the dilatancy phenomenon?
A dilatant fluid is a type of non-Newtonian fluid whose viscosity increases with shear rate (1), one example is potato starch dissolved in water. The dilatancy phenomenon is a phenomenon in which such fluids become stronger when subjected to impact, and the fluid becomes solid. In the case of potato starch, the potato starch particles initially float in the water, but when force is applied, the arrangement of the particles changes. When this happens, the gaps between the particles become larger, and water enters the gaps (at this time, the water is sucked into the gaps and appears dry), and the floating particles collide with each other, hardening and changing into a solid state. When the force is released, the shape collapses and the liquid returns to its original state (1).
Experimental method
Pure water, oil, carbonated water, honey and potato starch were mixed to create a fluid, and an iron ball was dropped onto it to measure the acceleration. (Equipment used: Smartphone app phyphox (3)) Initially, the liquid and potato starch were mixed at 50g:100g, and the acceleration was measured 10 times, and the amount of liquid was increased by 10g. This operation was repeated up to 90g of liquid. However, referring to previous research, the ratio of pure water and potato starch was fixed at 75g:100g (4).
Results and Discussion
The acceleration was small when there was 70g and 90g of honey. In other words, it was found that the shock absorption of the fluid is high.
However, although the acceleration was small when there were 70g and 90g of honey, at 90g it is considered that the honey is close to a solid, so it is considered that the shock absorption increases when there are 70g of honey and 100g of potato starch.
Future prospects
In this experiment, we were not able to make a helmet shape, but in the future, we will make a helmet shape with a fluid made from a liquid that has similar properties to honey. In that case, the challenge will be keeping the fluid uniform inside the helmet. In addition, although there has been previous research on making a box-shaped folding helmet, it is also necessary to devise a way to make a hemispherical helmet that fits the shape of the head.
References
(1) Kyushu University, Dilatant fluid, Dilatancy, Kyushu University Statistical Physics Laboratory Homepage, http://www.stat.phys.kyushu-u.ac.jp/~nakanisi/Physics/Dilatancy/(2025-3-21)
(2) Nagoya City Water Supply and Sewage, Does it harden when squeezed? Mysterious Liquid, Nagoya City Waterworks Bureau website https://www.water.city.nagoya.jp/uruoi_life/category/learn/145187.html (2025-03-21)
(3) Phyphox (physical phone experiments), a smartphone app developed by Aachen University of Technology
https://phyphox.org/ (2025-3-21)
(4) Igarashi Eita, Kato Otoha, Kudo Kaito, Sato Mitsuyoshi, Impact absorption performance of helmets using dilatancy, Akita Prefectural Yuri High School website, http://www.yuri-h.akita-pref.ed.jp/yuri-h-cms/assets/uploads/2022/03/ c1284e091dba05fa24231fc505db1c94.pdf
(2025-03-21)
(5) Tomoyuki Kachi, Toru Kumazaki, Yuta Mori, Strength measurement of dilatancy fluid and its application, Gifu Prefectural Ena High School website https://school.gifu-net.ed.jp/ena-hs/ssh/H31ssh/sc3/31905.pdf (2025-3-21)
(6) Yoshifumi Yamagata, Rheology in everyday life Part 1 Flow (viscosity) curves of honey and mayonnaise, https://www.jstage.jst.go.jp/article/rheology/50/4/50_343/_pdf(2025-4-13)