On dynamic plastic failure of structures under impact.

摘要

This thesis has conducted a series of intensive investigations on dynamic plastic failure (DPF) of structures under intense dynamic loading, which can be divided into three subtopics: on fundamentals of structural DPF, on DPF of imperfect structures, and on DPF of pre-loaded structures.; Firstly, the failure modes, failure criteria and failure thresholds of perfect structural members are surveyed and revisited. By incorporating two important effects, i.e. the interaction between the shear force and bending moment, and the weakening effect of the sliding sections during the failing process, the plastic shear failure of a clamped beam (Mode III of the three basic failure modes) and the associated failure criteria are studied in-depth, resulting in more reliable prediction of the thresholds for this important failure mode.; Then, the most efforts are dedicated to studying the DPF of imperfect structures (e.g. with pre-cracks/pre-notches). Typical examples, relevant failure criteria, novel concepts, and associated yield loci have been studied theoretically, followed by a FE modeling and two systematic experimental investigations. The main experimental findings and measurements compare favourably with the results from the theoretical analyses and the FE simulations. Compared with perfect ones, dynamic failure of pre-notched/pre-cracked structural members features evident “local behaviour” regarding to the energy dissipation, making the structure much more easily fail in a strength-controlled failure mode, i.e. crack initiation and extension leading to breakage at the pre-notched/cracked section(s). From this study, an integrated insight of the special failure modes, failure criteria and failure thresholds of imperfect (pre-notched/cracked) structural members under impact has been achieved.; Finally, by examining the three basic failure modes of a pre-tensioned clamped beam with a rigid-plastic theoretical approach, effect of axial pre-load on structural DPF is explored.; Essential advances on the simulation method and experimental technique in the field of Structural Impact have been made. Some general conclusions are also drawn.