Development and validation of adaptive ride down safety systems

The work carried out in this project report can be split up into various categories, but the key plan ended up being to optimise the principle of energy absorption that was created in the Sirius course. If at all possible, the principle would probably then be applied in 3 applications in the interior of a personal vehicle. These applications include the steering column – that will get the primary focus, the ride down seats and also the shoulder belt load limiter.

A drop test rig, which attempted to resemble a crash situation, was created to be able to test different materials and cutting geometries. By input from VMCC, the mass of the weight and the height from which it was dropped could be determined.

A testing matrix was designed so that each cutting geometry could be tested 3 times on every material. This initial test sequence resulted in conclusion that aluminium was the best option, nevertheless it was also noticed that the test rig was not sufficient to choose the best geometry of the cutting insert. This awareness resulted in a redesign of the test rig.

In the next test setup a couple of cutting inserts were put with cutting edges directed towards one another, and the aluminium test plates fell down between. By doing this the perpendicular forces were cancelled out and the cutting procedure got far more stable. Once again, all cutting geometries were tested, but only with the aluminium test plates. After some statistical analysis, the choice of most optimal cutting geometry could possibly be decided. With both the material and cutting geometry chosen, other parameters may very well be analyzed.

Various cutting depths were tested to see if a dependence between depth and force could be found. A nearly linear relationship was discovered when the cutting depth was plotted with the cutting force, but a rather different behaviour was found when the specific cutting force was plotted beside the force. This implies that if both cutting inserts features nearly the same cutting depth the force is linear to the cutting depth, but if they differ, particularly at low cutting depths, the linearity is broken.

Tests with varying temperatures had been carried out. A number of tests were carried out both at -15 C and 55 C, but no big differences could possibly be seen in regards to the tests performed at room temperature.

To conclude the energy absorbing principle, the tests performed in this work demonstrate that the steadiness of the force level is highly dependent of the material. The cutting geometry only has a little influence, while the temperature and the velocity has little to none.

Source: Lulea University of Technology

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