Thin-Walled Tubes

The axial crushing of thin-walled tubes has been the subject of extensive research in the past. The existing kinematic models for predicting crushing behavior of axially loaded thin-walled tubes are systematically reviewed and analyzed. The advantages and limitations of each model are discussed. A new chain link model for circular tubes and square tubes is presented and studied in detail. Unlike the case in all existing models, the shape of folds is considered as a variable in the present model, and the dimensionless effective crushing distance is shown to be a function of this variable. Consequently, the new model for circular tubes is able to predict the mean crushing force accurately for materials having different strain hardening property and a large range of diameter to thickness ratio using a rigid-perfectly plastic material model. A plastic linearly strain-hardening model is further considered in order to predict a better accuracy the folding characters and the mean crushing force. Eccentricity is also introduced to the chain link model and is shown to predict the load-deflection history with finite load peaks. A modified chain link model for circular tubes capable of reproducing alternating high and low peaks is also outlined. The proposed kinematic models predict crushing curves more accurately than previous models. A chain link model for square tubes is also established. Because of the introduction of the shape variable, this model satisfactorily fits the gap between the theoretically completely flattened kinematically admissible field and the effective crushing distance observed experimentally. Good agreement with experimental data on mean crushing force is achieved. Finally, a discussion on material hardening, dynamic effects and effective crushing distance is given. Thesis Supervisor: Tomasz Wierzbicki Title: Professor of Applied Mechanics