Reg:Convert character to date field

Hi Experts,

i am new to BO, i am creating a universe with VBRK and VBRP tables.My requirement is that i have to spilt date by month and year wise so i need VBRK-FKDAT(Posting date) as Date field so that i can set time hierarchy in properties tab to the field . But the VBRK-FKDAT field is in Character format i tried to change the object format to the field to Date but when i made a phrase check it showed an error that expression type is not compatible.

is there any way to make the field as date field?

Regards,

Vikram Sukumar