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There are two main objectives when designing conventional structures: strength and serviceability. We want to make sure structures have sufficient strength unde

by ggcdn 7y ago

There are two main objectives when designing conventional structures: strength and serviceability. We want to make sure structures have sufficient strength under very rare and severe loading to prevent collapse. But we also want to make sure they don't move too much under normal loading. It sounds like using silk would be a challenge to satisfy both objectives in many applications. In order to actually mobilize the tensile strength, it would require huge strains that would be incompatible with conventional materials. Or everything would need to be pretensioned up to some high stress. Likewise, for serviceability it would require either lots of strand under low stress or pretensioned strand. That's not to say these are insurmountable problems, just something Ive never thought about before.

dragontamer 7y ago
The "obvious" solution to using spider silk is to create a weave of it, like a textile, and then use the spider-silk in the form of a composite. Imagine spider silk replacing fiberglass threads for example, or carbon-fiber threads. Its not fiberglass or carbon-fibler per-se that makes the material strong, its the composite. The mixture of plastic (which provides compressive strength) with fiber (which provides tensile strength). There are a ton of composite fibers in the marketplace. I'm not a materials engineer, so I don't know exactly what people are looking for in their fibers (aside from high tensile strength). Probably low-weight, high strength... and probably low-compressive strength (or at least, people ignore the figure). "Elasticity" in spider-silk sounds interesting, but I'm not sure if thats good or bad for a composite. ----------- The composite for structures is going to be Reinforced concrete: Steel Rebar provides tensile strength, while Concrete provides compressive strength. Where spider-silk (or fiberglass / carbon fiber composites) shine, are low-weight applications. Bicycles, bullet-proof armor, and flywheels. The question is if spider-silk is actually any better than carbon fiber (or Kevlar) That's the thing: we have a LOT of manufactured fibers. Maybe spider-silk has a niche that can be used. But its competing against Carbon Fiber, Fiberglass, and Kevlar. ----------- It seems like Spider-silk has less tensile strength than Carbon Fiber / Kevlar. However, due to its flexibility, spider-silk can absorb significantly more energy before breaking (aka "Toughness"). So spider-silk might be superior for stopping bullets in a composite weave, but it would be awful as a load-bearing structure (unless that load-bearing structure were expected to be "catching" objects a lot). Hmmm... maybe a Tennis Racket would be the ideal use of Spider Silk...
- ggcdn 7y ago
  Because I'm a structural engineer, I like to think about the future of structures, not bicycles. Many good ideas came about by taking something from one obvious application and transferring it to another. I also don't think we will be using reinforced concrete in the year 2070 the same way or as extensively as we are now - the carbon footprint is too large. Maybe these new materials can spawn completely new types of structural systems that were never possible with conventional strengths and stiffness. Low weight is ultimately a goal of structural engineering as well, but not to the same extreme as sporting goods. Obviously cost comes into play, but many things that were once prohibitively expensive are now used on structures, including carbon fiber. Elasticity (or in the case of conventional materials, ductility) is a trait that has applications in seismic design, so I disagree with your last claim. The trick is combining the good parts of that material with the good traits of other materials into a composite that achieves stability under gravity and predictable deformability under seismic loads.

by ggcdn 7y ago

dragontamer 7y ago

The "obvious" solution to using spider silk is to create a weave of it, like a textile, and then use the spider-silk in the form of a composite. Imagine spider silk replacing fiberglass threads for example, or carbon-fiber threads. Its not fiberglass or carbon-fibler per-se that makes the material strong, its the composite. The mixture of plastic (which provides compressive strength) with fiber (which provides tensile strength). There are a ton of composite fibers in the marketplace. I'm not a materials engineer, so I don't know exactly what people are looking for in their fibers (aside from high tensile strength). Probably low-weight, high strength... and probably low-compressive strength (or at least, people ignore the figure). "Elasticity" in spider-silk sounds interesting, but I'm not sure if thats good or bad for a composite. ----------- The composite for structures is going to be Reinforced concrete: Steel Rebar provides tensile strength, while Concrete provides compressive strength. Where spider-silk (or fiberglass / carbon fiber composites) shine, are low-weight applications. Bicycles, bullet-proof armor, and flywheels. The question is if spider-silk is actually any better than carbon fiber (or Kevlar) That's the thing: we have a LOT of manufactured fibers. Maybe spider-silk has a niche that can be used. But its competing against Carbon Fiber, Fiberglass, and Kevlar. ----------- It seems like Spider-silk has less tensile strength than Carbon Fiber / Kevlar. However, due to its flexibility, spider-silk can absorb significantly more energy before breaking (aka "Toughness"). So spider-silk might be superior for stopping bullets in a composite weave, but it would be awful as a load-bearing structure (unless that load-bearing structure were expected to be "catching" objects a lot). Hmmm... maybe a Tennis Racket would be the ideal use of Spider Silk...

ggcdn 7y ago
Because I'm a structural engineer, I like to think about the future of structures, not bicycles. Many good ideas came about by taking something from one obvious application and transferring it to another. I also don't think we will be using reinforced concrete in the year 2070 the same way or as extensively as we are now - the carbon footprint is too large. Maybe these new materials can spawn completely new types of structural systems that were never possible with conventional strengths and stiffness. Low weight is ultimately a goal of structural engineering as well, but not to the same extreme as sporting goods. Obviously cost comes into play, but many things that were once prohibitively expensive are now used on structures, including carbon fiber. Elasticity (or in the case of conventional materials, ductility) is a trait that has applications in seismic design, so I disagree with your last claim. The trick is combining the good parts of that material with the good traits of other materials into a composite that achieves stability under gravity and predictable deformability under seismic loads.