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Chapter 3


Thin-walled tubes of different geometry and materials have been prevalently used as
collapsible energy absorbers in various kinds of structural applications. Such devices are
designed to collapse progressively for absorbing impact energy in a controlled manner and
converting kinetic energy in to [plastic strain energy in impact situations. There are various
types of sections of tubes they are listed below,


3.1 Circular Tube:

A circular tube is representing an efficient and light crash absorber under loading
condition. In addition, circular tubes under compression are reported to be the most prevalent
components in energy absorbing systems since they provide reasonably constant operating load.
3.1.1Types of analysis:
A number of analytical models for predicting the mean crushing load of progressive
folding of such tubes have been developed under axial quasi static and impact loading
3.1.1a Quasi static and impact loading:
The collapse response and energy absorption capability of circular tubes under quasi
static and impact loading with varying parameters namely wall thickness and tube diameter. It
was found that the energy absorption capacity of tubes in impact tests is higher by about 1.5612.3% than quasi static tests, whereas the increase in the initial peak load is between 14.3340.25%. Moreover, an important finding is that both crush load and energy absorption capacity
increase with increasing thickness and diameter.
3.1.1b Axial Loading:
Circular tube when subjected to an axial load, a circular tube collapses in an efficient
manner when it displays stable progressive collapse and deforms in the axisymmetric ring, nonaxisymmetric or mixed mode. The collapse mode depends primarily on the ratio of diameter to

thickness (D/t), the ratio of length to diameter (L/D) and the material of tubes. In general, thicker
tubes deform via an axisymmetric mode whereas thinner tubes deforms in an non-symmetrical
mode. Figure 3.1 shows typical collapse mode of circular tube under axial loading.

Fig 3.1 Typical collapse modes of circular tube under axial loading
3.1.2 Advantages:
1. A general observation tells us that circular tube has better energy absorption
2. It represents an efficient and light crash absorber under axial loading.
3.1.3 Disadvantages:
1. When its length is greater than critical length, it deforms in a global Euler
buckling mode, which is an inefficient mode for energy absorption and thus needs
to be avoided in crashworthiness applications.
2. The crush and energy absorption response of circular tubes are significantly
affected by varying geometrical, material and loading parameters.
3.2 Square Tubes:
The deformation mode of square tubes is very different to circular tubes, though the
general characteristics are similar.