I have figured it out myself... Here's the code i used:
Private Sub CommandButton1_Click()
sheet_name = ActiveSheet.Name
MsgBox ("some message")
ActiveSheet.ChartObjects("Graph_1").Activate
ActiveChart.SeriesCollection(1).Select
ActiveSheet.ChartObjects("Graph_1").Chart.SeriesCollection(1).Values = " '" & sheet_name & "'!stress_range"
ActiveSheet.ChartObjects("Graph_1").Chart.SeriesCollection(1).XValues = " '" & sheet_name & "'!def_range"
End Sub
Hope this can be useful for anyone with the same problem as me.
Thanks