I registered as a myTDK member but am unable to view members-only articles.

A. myTDK members consist of the two grades of (1) email newsletter member and (2) VIP member, depending on the items that have been registered.
Viewing members-only articles requires registration as a (2) VIP member.
Those who have not registered all of the information are registered as email newsletter members.

If you would like to change membership grades from that of an email newsletter member to that of a VIP member, please follow the procedures here (Q. I have registered for email newsletter subscription but am unable to view members-only articles.).