Many users choose a glass design after testing 30 samples. Possibly worrying fact: you may need thousands of tests to get statistically trustworthy results.
Sikkerhetskonferansen 2017, Norway’s largest and most authoritative conference on security, took place in Oslo 28-29 March. More than 700 people took part, including the Minister of Defence and the Minister of Justice and Public Security. Among the speakers were PhD candidates Karoline Osnes and Erik Løhre Grimsmo from SFI CASA at NTNU.
Like a lottery
Well into her second PhD year, Osnes knows one thing much better than when she started: glass is an unpredictable friend. In tests, one sample may turn out to be twice as strong as another one that is seemingly identical. Fracture in glass is a stochastic process. It is a bit like the lottery: You know there is a chance in a million that you might win. Still, not winning a hundred times doesn’t increase your chances next time around.
“This makes research on glass very challenging. One of my main messages to the conference is that we are going to need time,” she says.
What Osnes needs time to do, is to develop tools that can be used to optimize glass design. It should provide sufficient protection and be cost effective. The tools in question are numerical models that manage to predict the behaviour of laminated glass.
“At the moment we are trying to determine at what point glass fractures and how to describe the strength of the glass. Another phenomenon that needs attention is the description of crack propagation and fragmentation, she says.
“To complicate matters further, we are in the very early stages of developing tools to describe delamination.”
“An extreme ambition for our research would be to enable optimal interaction between different materials and components exposed to blast loading. The aim would be as little damage as possible. This could imply that explosion proof glass is not necessarily desirable, and that controlled failure in the glass and polymer could be used to relieve other components in a structure,” Osnes adds.
“One question turns up from time to time: why should we carry out this kind of research in Norway?”
“The obvious answer is that our research group SIMLab is world-leading on the behaviour of materials and structures subjected to impact loading. Who else should be better qualified? Besides, we have the SIMLab Shock Tube facility. This lets us perform a great number of tests under controlled circumstances,” Osnes responds.
It may be added that CASA partners keep returning to the fact that you greatly improve your chances of getting access to leading-edge research if you have something to offer yourself.
How to prevent collapse
Research on steel is another matter altogether, or so we like to think. One could say that Erik Løhre Grimsmo has alternative facts:
“It is true that we know a lot about steel. Even so, there is little research on the behaviour of beam-to-column joints in steel structures subjected to impulsive loading. As an example, we need to understand better what happens when an explosion initiates progressive collapse of a building. Good design of joints is important to prevent such collapse,” he points out.
“The aim of my research is to subject beam-to-column joints to impact loading. Subsequently, I want to validate a numerical model that we can use for further research. I also want to show how we may apply a validated model to improve design.”
The joints in his research include both bolted and welded connections.
“What do you know now, as you are close to defending your PhD thesis that you didn’t know at the outset?”
“One thing I understand better is the difference between static and dynamic behaviour of parts in a structure. One aspect is that the mass (or inertia) plays an important role under dynamic loading conditions.”
“What has been the biggest surprise in your work?”
“How demanding it is to design and carry out successful experiments. After more than three years and quite a bit of experience I discover again and again that it is possible to make suboptimal choices on how to set up an experiment.”
The beauty of research
Erik Løhre Grimsmo will defend his thesis on 20 June. His lecture at Sikkerhetskonferansen 2017 did not deal specifically with the plans for the new government administration complex in Oslo, but he did touch on the topic. He also hopes that his new employer, engineering consultants Aas-Jakobsen, will get a contract on the project.
“It would be extremely exciting to work on such a project,” he confesses.
At the same time, the beauty of generic research is revealed in the interest for the work of both Karoline Osnes and Erik Løhre Grimsmo. None of them started out with the automotive industry in mind. Yet, in both cases CASA’s car-producing partners have shown great interest.
This article was originally posted on SFI CASA Newsletter.
It was written by Albert H. Collett, Communication officer at SFI CASA, NTNU.