Hardness and fracture toughness models by symbolic regression Jinbin Zhao, Peitao Liu, Jiantao Wang, Jiangxu Li, Haiyang Niu, Yan Sun, Junlin Li and Xing-Qiu Chen Eur. Phys. J. Plus, 138 7 (2023) 643 Published online: 24 July 2023 DOI: 10.1140/epjp/s13360-023-04273-x