This book mainly introduces some basic phenomena and laws of highly ductile materials during elastoplastic deformation, and their engineering applications, such as the transfer and relief of stress concentration in the notch root, the mitigation of possible brittle fracture, the ductile deformation and damage, fatigue, energy absorption, plastic buckling, thermal stress problems, etc. It shows a number of revolutions in modern applications and design, which are beneficial to the safety of modern equipment, and improve applicability. In addition, the first three chapters of this book also briefly introduce the basic knowledge of elastoplastic deformation and analysis as a preliminary knowledge.