ABSTRACT
Mean square elastic strains can be measured by X-ray line broadening. For comparison with experiment they are computed within the framework of linear anisotropic elasticity as the derivatives of the elastic energy with respect to the elastic constants. The dislocation density is a geometric quantity and does not depend on elastic constants. The derivative of the matrix of elastic constants with respect to a certain elastic constant is a projection matrix with the same symmetry and the derivative of the energy with respect to certain elastic constant is the spatial average of the product of strain components. The derivative of the energy with respect to an elastic compliance gives the spatial average of the product of stress components. For straight dislocations, the energy can be expressed particularly simply as quadratic form in the Burgers vector.
