#AskGlaston Episode 57: Does the shard size of tempered glass vary depending on the impact strength?

This week, we’ve received the following question from Middle East:

I have observed that when we break glass in the center with a lot of force, the fragments close to the point of impact are sometimes big long shards exceeding the standard of 40 fragments. However, shards further from the center of the impact are smaller in size. Is this normal or does this mean the glass is not tempered properly? Does the shard size vary depending on the strength of the impact?

And if this means our glass is not tempered properly, what can we do to rectify this?

It is a very known behavior that the glass fragmentation depends on where you break the glass. If you break the glass in the center, you can get long shards, but if you break it on the edges, then usually the fragments are smaller. And that’s because you have different boundary conditions depending on whether you break the glass in the center or on the edge.

If you want to get smaller fragments even if you break the glass in the center, you can increase the stress level by tempering the glass at a higher temperature and with the higher cooling power. Then, the size of the fragments will get smaller. 

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About the author

Antti Aronen

An experienced researcher and engineer in the field of theoretical and experimental research, Antti is Glaston’s Senior Research Engineer in D&I. He is passionate about sharing his deep knowledge of glass products and processes with others. His PhD thesis was on glass heat treatment, and he continues to enthusiastically model the tempering process today. An innovator at heart, he has even registered some patents over the years. To counterbalance living at the top of the world in Finland, he spent nearly 4 years “down under” as a Research Fellow at the University of Sydney in Australia.

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