  Fiber optical strain sensors are used to measure the strain at a particular
sensor position inside the fiber. In order to deduce the strain in the
surrounding matrix material, one can employ the strain transfer principle. Its
application is based on the assumption that the presence of the fiber does not
impede the deformation of the matrix material in fiber direction. In fact, the
strain transfer principle implies that the strain in fiber direction inside the
fiber carries over verbatim to the strain inside the matrix material. For a
comparatively soft matrix material, however, this underlying assumption may not
be valid. To overcome this drawback, we propose to superimpose the matrix
material with a one-dimensional model of the fiber, which takes into account
its elastic properties. The finite element solution of this model yields a more
accurate prediction of the strain inside the fiber in fiber direction at low
computational costs.
