Until the end of July, online journals from The Institute of Mechanical Engineering are available free through Sage Publishers. The list includes all 16 sections of the Proceedings of the IMechE. When you reach the page for a specific title, you can use the search box or browse issues by clicking on the "all issues" tab.
These titles may especially be of interest to medical researchers:
Part H: Journal of Engineering in Medicine
Part L: Journal of Materials: Design and Applications
Part N: Journal of Nanoengineering and Nanosystems
Part P: Journal of Sports Engineering and Technology