The engineering components of strain

For convenience these nine quantities are regrouped and denoted as follows  

The first three quantities 6xx eyy and zz correspond to the fractional expansions or contractions along the x, y and z axes of an infinitesimal element at Pi. The second three quantities eyz, e x and exy correspond to the components of shear strain in the yz, zx and xy planes, respectively. The last three quantities aJx, (Hy and ftJz do not correspond to a deformation of the element at Pi, but are the components of its rotation as a rigid body. 

ABCD is an infinitesimal square that has been displaced and deformed into the 

Here = 0i — 02 does not correspond to a deformation of ABCD but to twice the angle through which AC has been rotated. The deformation is therefore defined by the first six quantities 

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It was emphasized in Section 2.2 above that the engineering components of strain were defined. The nine tensor components of strain are defined by the symmetric strain tensor... 

In terms of the engineering components of strain e c, ete. defined in Section 2.2... 

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