AUTOMOBILE PARTS

AUTOMOBILE PARTS

CRUMPLE ZONE

DECELERATION CURVES

SAFETY CAGE

FRONT and REAR IMPACT

FRONT OFFSET IMPACT

ROLL OVER

ROLL OVER

Optimal crash pulses The stiffness of the available front structure determines the deceleration pulse during a crash. This pulse should have a certain shape, ensuring minimal risk for the occupant. During a heavy collision, there are three important phases: Crash initiation phase. above the trigger value of about 6 km/h. 2. Airbag deployment phase. This relative velocity should be sufficiently low, The deceleration of the car should be sufficiently low in this phase. 3. Occupant contact phase. High decelerations may occur . The frontal car structure should be stiff enough to decelerate.

Research has shown that for optimal occupant safety in a collision with 48 km/h impact velocity, the first phase lasts between 10 and 30 ms, the second phase lasts 35 ms and the last phase fills up the remaining time to a total of maximal 90 ms. In the first and second phase, the optimal relative velocity values are 8 km/h each. Figure shows a crash pulse as a function of time against a rigid wall with full overlap optimized for low injury values (HIC and Chest-G). This curve is achievable for a large number of current cars.

Figure shows the three phases of a collision with impact velocity of 56 km/h in a velocity-deformation graph, calculated with the preceding graph (already optimized crash) but adjusted for the higher velocity. Because higher velocities do not significantly change the time duration, the same crash initiation time of 15 ms and an airbag deployment time of 35 ms are assumed. The crash duration is 90 ms with a total deformation length of 78 cm.

Figure 2.6 shows two additional characteristics on both sides of the graph of Figure 2.5. The upper graph is an example of an offset (40 per cent overlap) crash and the lower graph is an example of a full overlap crash with the same vehicle. The two extreme characteristics are positioned as close as possible around the graph of the optimal (lowest injury values) crash situation. In this case the vehicle has a weighted design, the average deceleration of two extreme crash situations is optimal.

The material selected for the five mentioned profiles was FeP03 (Euro), a commonly used steel (for specifications see Table 3.11). Over the length of the longitudinal member, the profile thickness was kept constant at 2.0 mm. This value is realistic and generally gives a stable folding pattern. The dimensions of the profiles were chosen to have the same perimeter resulting in a constant mass per unit of length, see Table 3.1. The undeformed length of each profile is 350 mm.

The results of the simulations , which concern a collision with a 56 km/h impact speed, a mass of 1100 kg, and a normal angle of incidence are shown in Figure 3.1.

Results To put these conclusions into the practice of designing a car that has to sustain a wide range of frontal collisions, it is advocated to use a rectangular profile in a lying orientation instead of the profiles which are expected to absorb significantly more energy. The reason is that it is more important to give adequate protection for the whole range of load directions rather than to optimize the longitudinal member for minimal mass only. This rectangular profile, which must be constructed heavier to match the energy absorption of the well absorbing profiles with a load direction of zero degrees, will offer a much better energy absorption at oblique load angles in return. For the same amount of energy absorption as the circular profile, the thickness of the rectangular profile must increase with about √2 resulting in about 700 gram added mass