Divide rows of python pandas DataFrame

I have a pandas DataFrame df like this

   mat  time
0  101   20
1  102    7
2  103   15

I need to divide the rows so the column of time doesn't have any values higher than t=10 to have something like this

   mat  time
0  101   10
2  101   10
3  102    7
4  103   10
5  103    5

the index doesn't matter

If I'd use groupby('mat')['time'].sum() on this df I would have the original df, but I need like an inverse of the groupby func.

Is there any way to get the ungrouped DataFrame with the condition of time <= t?

I'm trying to use a loop here but it's kind of 'unPythonic', any ideas?