Loading Datepart in Excelsheet Name into Table

I have  excel sheet it's name is ExcelSheet20Oct2012.xlsx 

I'm looping this excel sheet into a table, so I have the name of this excelsheet stored in variable "ForEachExcelName". Now my requirement is I want to load the Datepart in the excelsheet (i.e.20Oct2012) into Date Column (Date datatype, length 8) of the destination table in "YYYYDDMM" format.

I'm using derived column to do this task, I want to know how to write a expression for this. I tried 

(DT_DATE) (SUBSTRING(@[User::ForEachExcelName],9,9)) but it is giving me error as it failing to convert DT_WSTR to DT_DATE.

Royal Thomas