Spider’s web resists damage
5 Mar 2012 by Evoluted New Media
It’s not just the strength of the silk that makes a spider’s web so strong, say researchers in America, it’s the stretchiness too.
Spider’s silk stretches and softens when pulled, before stiffening as the force of pulling increases – a property which was considered a structural weakness. However, researchers now think this actually makes the webs more robust. The silk’s unusual characteristic of softening and stiffening varies with the forces applied to it, and on the overall design of the web.
Markus Buehler, an associate professor of civil and environmental engineering at MIT analysed materials with different properties arranged in the same web pattern to see how they responded to localised stresses. They found that materials with other responses – those that either behaved as a simple liner spring or become more plastic as they’re pulled – perform much less effectively.
Damage to the spider’s web tends to be localised – affecting just a few threads – which can easily be replaced.
“Even if it has a lot of defects, the web actually still functions mechanically virtually the same way,” said Buehler. “It’s a very flaw-tolerant system.”
Much of the research is based on computer modelling of material properties and how they respond to stresses, but in order the test his finding, Buehler and his colleagues went into the field. They tested actual spider webs by poking and pulling at them.
Buehler was surprised by the effect – initially, the entire web was deformed, but because of the silk’s nonlinear response, only the threads where the force was applied carried the load by stretching out and becoming stiff. As the force increased, they broke, but the damage was always localised.
The findings could be useful for engineers, and may help in the development of more damage-resistant synthetic material. It may also provide design principles that might apply to networked systems like the internet or electric grid. They may also play a role in designing earthquake-resistant buildings, allowing localised damage to ensure the overall survival of the building.
