In order to activate strain rate effects for SOLID65 elements in ANSYS-APDL, you will need to use the keyword *ELFORM,14. This keyword is followed by the element type number (which is 65 for SOLID65 elements) and then the following parameters:
1. Plastic strain rate sensitivity factor
2. Strain rate sensitivity parameter
3. Strain rate hardening parameter You can find more information about *ELFORM and the parameters it requires in the ANSYS help documentation.