LESSON 5.3 · 2:13 · CHAPTER 5 · WHAT'S IN THE PELLET
Short fibres never reach full strength
A fibre picks up load through shear at its surface and needs a minimum length to reach its breaking stress.
Predict · at 0:39 in the video
A carbon fibre is 7 microns across and 4,000 megapascals strong. Assume the plastic grips it at 20 megapascals. What's the critical length? And are printed fibres, about 0.3 millimetres, above or below it?
About 0.7 millimetres. Printed fibres are below it. 4,000 times 7 microns, over twice 20, is 0.7 millimetres.
Further reading
This course is our own. These books go deeper.
- The economics of Big Area Additive Manufacturing, Post et al., Solid Freeform Fabrication Symposium, 2016
- Additively manufactured carbon fibre-reinforced composites: state of the art and perspective, van de Werken et al., Composites Part A, 2020
About the numbers
Simulations in this lesson are our own. Where a number rests on an assumption or a single source, the video marks it with an asterisk and says where it comes from.
Up next · 5.4 · 1:48The screw breaks fibres, mostly before you buy