@misc{yuan_on_the_1991, 
author={Yuan, H., Brocks, W.},
title={On the J-integral concept for elastic-plastic extension},
year={1991},
howpublished = {GKSS report},
note = {Yuan, H.; Brocks, W.: On the J-integral concept for elastic-plastic extension. Nuclear Engineering and Design. 1991. vol. 131, 157-173.}}