I just finished my degree in mechanical engineering (specializing in biomechanics). Where are you from? What university are you going to after the army?
Unfortunately, most of my profs wrote their own notes and never really used standard textbooks. But here is a few I used as a reference
Course: Biomaterials - - Textbook: http://www.amazon.ca/Biomaterials-Science-Introduction-Materials-Medicine/dp/0125824637 Course: Ergomonics and Desgin - - Textbook: http://www.amazon.ca/Human-Factors-In-Engineering-Design/dp/007054901X
Reading Scientific Journals and Case Studies is another way to learn a lot, plus theyre usually not too long and pretty interesting