[en] Tests performed within the framework of earlier RWTUeV projects together with results obtained elsewhere with regard to the time dependence of fracture mechanics data show that time-effects reduced the toughness of materials, according to the nature of the test (extremely slow load rate or hold times with sustained load). Reduction in toughness has an effect on the following: - decrease in critical material data (J₀, deltasub(i)) - levelling off of the crack resistance curve J = J(Δa) and in consequence a decrease of tearing modulus. This tendency is confirmed quantitatively by recent test results. These tests were performed with the material 15 Mn Ni 63 at room temperature with hold times under sustained load and according to the appropriate standards (without hold times). The tests show that hold times cause additional stable crack growth. The resulting J-Δa curve is lower and less sloping than the curve obtained in a standardized test. The time effect should be taken into account in a safety analysis. (orig.)