![]() They protect the weak zones when the fibers are subjected to stressors. In the computer models used by Kjellstadli, the strong zones are spread around in the material. These zones are randomly scattered throughout it. An apparently uniform material has weak and strong zones. “The strong parts of the material surround the weak parts and protect them,” says Kjellstadli.Ī material like concrete isn’t equally strong everywhere, though it may look like it. Illustration: Knut Jørgen Måløy, Department of Physics, University of Oslo #Some things crack under pressure crack#By looking at how this crack front moves, PoreLab can test its theories. This creates a situation that is close to the theoretical models. They have been sandblasted and then placed in an oven so that they are fused where there is contact between them. The picture shows how a crack (the transition from black to white) moves through two plastic sheets that are “glued” together. He has collaborated with Hansen, researcher Srutarshi Pradhan and PhD candidate Eivind Bering – also from the same department – in studying the phenomenon. The idea flies in the face of intuitive thinking, because shouldn’t the material get weaker instead? What’s going on?ĭoctoral candidate Jonas Tøgersen Kjellstadli from NTNU’s Department of Physics can explain the process for us. Strong parts protect the weak partsīut this doesn’t explain why materials can become even stronger under strain. As the animals rotted and emitted gases, they made the material porous and thus stronger. The builders of the Kristiansten fortress in Trondheim in the 17th century put the remains of dead animals into the material. People have known about these force mechanisms at least since the Middle Ages. The builders of the Kristiansten fortress in Trondheim in the 17th century put the remains of dead animals into the construction material. If there’s a crack in the concrete, the force gets distributed throughout the material due to all the holes. Something similar occurs in the porous concrete. If you drill a hole at this point, the force instead spreads around the hole and lessens the pressure on the glass. “When you get a crack in your car’s windshield, you can stop that crack from spreading by drilling a hole in it,” he says.Īn untreated crack has a high concentration of force at the tip of the crack. #Some things crack under pressure full#Why, for example, does concrete function in this way? Spreads the forceĬoncrete looks compact, but it’s actually full of tiny holes. Among other things, the researchers consider what happens in materials subjected to stress, and for the uninitiated, some of their findings are a bit unexpected. Researchers at PoreLab work mostly with porous materials, like concrete, and in their world, this sort of thing can happen. Hansen’s role as the head of PoreLab, a Center of Excellence for outstanding research at NTNU and the University of Oslo (UiO), is not exactly coincidental. “The reason concrete is so strong is because it’s so weak,” says Professor Alex Hansen, and already here our head may start to spin a little. ![]()
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