> The researchers found that the new material’s elastic modulus — a measure of how much force it takes to deform a material — is between four and six times greater than that of bulletproof glass. They also found that its yield strength, or how much force it takes to break the material, is twice that of steel, even though the material has only about one-sixth the density of steel.
The problem with this is that steel is a large class of alloys, with a wide variety of properties depending on the chemical and physical makeup of an alloy. Even "types of steel" that people are familiar with - e.g. stainless steel - are not specific alloys but themselves classes of alloys. I'm not a metallurgist but I assume there are dozens if not hundreds of alloys qualifying as steel.
So when someone writes an article saying "it's stronger than steel!" that's exciting, but it's not enough information. In this case we know it's stronger by yield strength. We can say the new material's yield strength is twice that of the weakest known steel alloy, but no more than that.
You can see here, there is a wide gulf between the weakest and strongest alloys just in this chart, which only has five alloys and a handful of different treatments. Yield strength is anywhere from 210MPa to over 1600MPa, an 8x difference.
Subchart (g) in the image shows a plot of yield strength against elastic modulus, and it looks like the plot tops out around 1.4 GPa, meaning the strongest tested configuration by yield strength is weaker than that of tempered 4140 and 4340 steels, while nearly 7x stronger than hot-rolled 1020 steel. I don't know if "2D yield strength" is different than what is shown in the amesweb.info table, though.
I think you're missing the novel polymer for the steel-forest. Its a 2d polymer (spans a plane instead of forming strings, which is new) that has material properties that make it comparable to materials that we think of as strong.
The part where it gets rigorously classified can come later. The people involved with this project were themselves probably not metallurgists.
> yield strength, or how much force it takes to break the material
That's not yield strength.
Yield strength is how much force is required to permanently deform the material.
Ultimate tensile strength is the force required to break the material.
One great thing about steels is that they tend to work-harden.
Typical 250 grade mild steel, meaning it takes in excess of 250 MPa force to permanently stretch a 10mm round diameter section, usually has an ultimate tensile strength exceeding 400 MPa.
