The test sample expansion system uses a tensioning head with a base plate (3) supporting the tensioning elements on one side and a force measuring device (2), for the applied tensile stress, on the opposite side. The tensioning head has an attached mirror surface (8) onto which a light ebam (10) is directed. The reflected beam is received by a position detector (11) which is coupled to an associated electronic evaluation circuit (12). The displacement representing the expansion of the test sample (4) is detected simultaneously. Pref. the applied tensile force is measured by a piezoelectric measuring device (2).
