3 ms·

A few commenters here suggested building the base out of flat plates for strength. But as I understood it, the maximum load was determined by the properties of

A few commenters here suggested building the base out of flat plates for strength. But as I understood it, the maximum load was determined by the properties of the plastic. The plastic became fluid, rather than the structure of the pieces failing. From TFA: >>The material is just flowing out of the way now and it's not able to take any more. We're getting a plastic failure. It means the brick keeps on deforming, without the load increasing. So, help out the not-a-real-engineer here. Doesn't that mean that changing the shape of the pieces wouldn't help? ie, even if the base were a solid sheet of Lego plastic it would just flow out of the way at that load?

wiredfool 12y ago
The picture of the squished piece looks like there it was a combination of buckling failure of the sides (a geometric instability) and a material failure along the sides (ripping, to allow the buckling failure of the sides). It doesn't look like a fluidlike or flow failure to me. FWIW, Plastic deformation here is in contrast to elastic, it's not the material. Elastic deformation is linear, Hooke's law deformation: f=kx. Plastic deformation is when elastic breaks down, and you can have additional deformation at the same (or lower) load. Generally, there's an elastic region, then a plastic region, and then total failure. The numbers suggest that legos are actually pretty similar to unreinforced masonry, the strength looks like about 4000 PSI in compression and nearly no tensile strength. That's about equivalent to bog standard concrete or concrete blocks (CMU). The main difference is that Legos are much less dense. It would be interesting to see something similar to Gothic architecture done in Legos though there would have to be some tweaking to deal with flying buttresses due to the density.

3 ms·

A few commenters here suggested building the base out of flat plates for strength. But as I understood it, the maximum load was determined by the properties of

by breischl 12y ago

wiredfool 12y ago
The picture of the squished piece looks like there it was a combination of buckling failure of the sides (a geometric instability) and a material failure along the sides (ripping, to allow the buckling failure of the sides). It doesn't look like a fluidlike or flow failure to me. FWIW, Plastic deformation here is in contrast to elastic, it's not the material. Elastic deformation is linear, Hooke's law deformation: f=kx. Plastic deformation is when elastic breaks down, and you can have additional deformation at the same (or lower) load. Generally, there's an elastic region, then a plastic region, and then total failure. The numbers suggest that legos are actually pretty similar to unreinforced masonry, the strength looks like about 4000 PSI in compression and nearly no tensile strength. That's about equivalent to bog standard concrete or concrete blocks (CMU). The main difference is that Legos are much less dense. It would be interesting to see something similar to Gothic architecture done in Legos though there would have to be some tweaking to deal with flying buttresses due to the density.