This paper describes an investigation of the internal mechanical strain in
composite samples with barriers cast midway between point-plain electrodes in a
polyester resin. The paper also characterizes the dependence of this strain on the amount
of moisture absorbed by the sample, especially under the influence of an applied electric
field. In this work, the strain was studied for composite and homogeneous samples
exposed to high electric fields in both wet and dry conditions. Through this study, the
difference in the strain patterns between wet and dry samples is determined and the effect
of moisture, as aging element reducing the adhesion strength between the barrier and the
surrounding matrix, is highlighted.