Electrical strain gauges are the most common tools used, because they are simple and inexpensive. However, the data that they provide is limited. You may refer to the reading for sub-subunit 3.3.2 for additional information.
Attribution:
Stephanie Redfern, Ranjeet (Ron) Agarwala, and Dr. Steve Gibbs. Mechanics I. The Saylor Academy 2014, http://www.saylor.org/courses/me102/