Crush mechanics of square tubes

• Stauchverhalten von Vierkant-Hohlprofilen

Jafarzadeh Aghdam, Nima; Schröder, Kai-Uwe (Thesis advisor); Münstermann, Sebastian (Thesis advisor)

Düren : Shaker Verlag (2023)
Book, Dissertation / PhD Thesis

In: Aachener Berichte aus dem Leichtbau 2022,3
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2022

Abstract

Thin-walled structures are used widely for energy absorption under axial loading. This thesis investigates the crushing behavior of metallic square tubes, also known as crash boxes (CBs). These tubes are relatively thick, which results in their plastic buckling. Axial crushing of the tubes is a complex phenomenon and many open questions remain unanswered including their plastic buckling and stacking effect on their crushing behavior. Furthermore, researchers of this field deal with different challenges such as irreproducibility and unrepeatability of the experimental results. These uncertainties decrease the reliability of the designs and conducted studies. The present study first investigates the unrepeatability issue of the tubes in order to provide a reliable setup for studying their behavior. For this purpose, it examines the buckling behavior of the tubes and the creation of different folding patterns. It is shown that the coupling of local buckling modes results in the unrepeatability issue of the tubes, and remarks are provided for the design of tubes with reproducible outcomes. Understanding the mechanism of the reproducible axial impact of the tubes provides a reliable setup for studying their crushing behavior. Afterward, based on this setup, the crushing behavior of the tubes is studied. Owing to the buckling of the tube’s plates, the stress transfers to the effective width region of the plate, i.e., at the sides, and decreases at the mid-plate region. The fold length and the effective width of a tube define its energy absorption and collapse force, respectively. In the present study, a method is derived for the accurate calculation of the effective width and fold length of the plastically buckled tubes. Calculating the plastic-buckling and collapse forces of the tubes is another focus of the present study. It is shown that the buckling and collapse forces of tubes can be calculated by deriving their mid-plate width. Furthermore, a new analytical approach is derived for the calculation of the buckling and collapse forces. The introduced approach is validated by experimental results. Finally, the axially stacked tubes are examined. In lightweight structures, it is common for the tubes to be stacked on top of each other. Stacking the tubes affects their behavior importantly, and it might result in a different performance of the tube compared to its performance as a single tube. Without a clear understanding of the stacking effect, the design guidelines of the tubes can not result in a reliable design. The crushing behavior of the axially stacked tubes is investigated in the present study, and the required design guidelines are provided.

Institutions

• Chair and Institute of Structural Mechanics and Lightweight Design [415610]