The vCalc Shear Stress equation computes the stress causing a displacement of a surface of a volume as shown in the image. In the image surface A is displaced by a distance x.
The shear strain, `gamma`, results from the shear stress, `tau`, caused by the force F||.
original author: Billy
The strain is computed as the ratio of the following:
Young, Hugh and Freeman, Roger. University Physics With Modern Physics. Addison-Wesley, 2008. 12th Edition, (ISBN-13: 978-0321500625 ISBN-10: 0321500628 ) Pg 367, eq 11.15