Explosive bursting of an aircraft fuselage
Analytical Service Pty Ltd
TECHNICAL NOTE 69

TECHNICAL NOTE 69

A short segment of the fuselage of Tu-154M was modeled as shown in Fig.1. Note that it is inverted, consistent with the description of the incident. (Smolensk, 2010.) The chairs with passengers are modeled crudely, by means of sets of blocks.

An 8 kg charge of TNT was placed near the floor, on the passenger side and detonated. The shell of the fuselage was pushed by the impulse of the explosion, it broke and opened up broadly. The frames below show how the event developed. Notice the early holes in the floor due to the close proximity of the explosive charge.

The diameter of the shell is 3.8m and the skin thickness is 1.5 mm. When bursting, the edge of the shell attained the speed of about 80 m/s.

DETAILS

Because of double symmetry, only one-quarter of the fuselage segment had to be modeled.

The shell was made from an aluminum alloy with the properties between those between 2024-T3 and 2024-T351. Although strength-wise these alloys are not regarded as particularly sensitive to the speed of deformation, the tests indicate that there is a large increase in the failure strain while under rapid loading. This was not accounted here in order to have a clearer relationship between the amount of explosive and the extent of breakage.

The effects of such explosions are dependent on the amount of explosive used. A smaller charge, say 6 kg, would also, open the shell, but not to this extent.

When this is compared with an earlier simulation conducted by Sandia Labs, the main difference is whether the skin separates from the frames or not. We have assumed strong rivets, therefore no separation was observed.

The deformation of fuselage walls as found on the ground was quite similar to what was determined here, except for the additional distortion due to impacting against the ground. There was one important difference, though. In the cross-section of the fuselage normal to its axis there are two skin joints, at about 300 off the ceiling center, on each side of that center. Such discontinuities are prone to failure, especially under dynamic loading. Yet, symmetry in shape does not usually mean a symmetry of breakage, so one of the joints failed and the other remained attached to the rest of skin.

In our model the failure was induced in the plane of symmetry. This was done to keep the model size small by being able to create only one-half of the fuselage. We have therefore sacrificed some of the realism for the sake of making modeling job easier.

The effect of the fuselage being inverted or not is marginal and it relates only to how the internal contents were dispersed during the event.

FUSELAGE SEGMENT
Time = 0

Fig. 1 Above: Over-all view of the model

FUSELAGE SEGMENT, initial breaking
Time = 8.0984

Fig. 2 Above: Early stage of opening up.

FUSELAGE SEGMENT, advanced breaking
Time = 33.498

Fig. 3 Above: Avanced stages of breaking

FUSELAGE SEGMENT, initial breaking
Time = 8.0984

Fig. 4 Above: Early stage of opening up.

FUSELAGE SEGMENT, near-final opening
Time = 90.003

Fig. 4 Above: Breakage at the end of simulation.

OPENING OF THE FUSELAGE DUE TO AN INTERNAL EXPLOSION