Aircraft Accident Investigation Report No. ACCID01/06

CityU Professional Services Ltd
Failure Analysis of a Towbar
Department of Physics & Materials Science
City University of Hong Kong
The fracture surface on the broken off top plate is shown in Figure 4-9. It can be seen that the
bottom part of the fracture surface contained tensile fracture as well as signs of bending, causing
the appearance of layer separation. Figure 4-10 is the other part of the fracture surface, i.e. the
one at the head assembly end. It is noted that the bottom plate was sawn off near the welded
joint so as to reveal the fracture surface easily. Apart from having a fracture surface similar to
that in Figure 4-9, this figure also contains evidence that the middle part, as well as the fracture
surface, were subjected to indentation from a certain object. This will be explained later.
Figure 4-9 : Fracture surface of top plate
Figure 4-10 : Fracture surface of top plate at head assembly end
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