Comparison between different layups for the impact attenuator 1. Introduction and preconditions The impact attenuator (IA) which i s covered at this tests will be used at a race car of the Formula Student series. The goal is to fulfill the requirements of the given rules with the lightest possible design. In the rules, there is stated that the peak deceleration of a 300 kg car may not exceed 40 g. Furthermore, the maximum mean deceleration is limited too with 20 g. The impact velocity must be at least 7 m/s which results in a kinetic energy of 7350 J to absorb by the impact attenuator. For the tests, a pendulum with an inertia that represents the 300 kg was used. The initial displacement of the pendulum was chosen in a way that the required 7 m/s are reached. Due to fabrication reasons, the same design of the IA was used with different layups. In total, 6 different layups were tested.
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joanneum racing graz
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2. Comparison of the Layups 2.1.
Impact Attenuator V1
The layup for the first version is shown in the table below: Orientation
Fabric Twill Fabric Twill UD Layer Fabric Twill Fabric Twill Fabric Twill Fabric Twill UD Layer Fabric Twill Fabric Twill
Total number of main layers: 8 Total weight: 1268 g
Figure 1 shows the deceleration over time and displacement for impact attenuator V1. It is visible, that the deceleration is near to the top limit, so the number of plies can be reduced.
Figure 1: Deceleration over time and displacement – V1
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joanneum racing graz
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Impact Attenuator V2
The layup for the second version is shown in the table below: Orientation
Comment
0°/90° ±45° 0° 0°/90° 0°/90° 0° ±45° 0°/90°
Fabric Twill Fabric Twill UD Layer Fabric Twill Fabric Twill UD Layer Fabric Twill Fabric Twill
Total number of main layers: 6 Total weight: 1061 g
Figure 2 shows the deceleration over time and displacement for impact attenuator V2.
Figure 2: Deceleration over time and displacement – V2
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joanneum racing graz
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Impact Attenuator V3
The layup for the third version is shown in the table below: Orientation
Comment
0°/90°
Fabric Twill
±45° 0° 0°/90° 0°/90° 0° ±45° 0°/90°
Kraibon Fabric Twill UD Layer Fabric Twill Kraibon Fabric Twill UD Layer Fabric Twill Fabric Twill
Total number of main layers: 6 Total weight: 1265 g
Figure 3 shows the deceleration over time and displacement for impact attenuator V3. The fact that the peak deceleration decreased although the displacement decreased too shows the potential of Kraibon, because more energy has been absorbed within less displacement – we’ve continued with removing layers.
Figure 3: Deceleration over time and displacement – V3
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joanneum racing graz
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Impact Attenuator V4
The layup for the fourth version is shown in the table below: Orientation
Comment
0°/90°
Fabric Twill
0° ±45° 0°/90° ±45° 0° 0°/90°
Kraibon UD Layer Fabric Twill Fabric Twill Fabric Twill UD Layer Kraibon Fabric Twill
Total number of main layers: 5 Total weight: 860 g (Optimized – overlaps..)
Figure 4 shows the deceleration over time and displacement for impact attenuator V4.
Figure 4: Deceleration over time and displacement – V4
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joanneum racing graz
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Impact Attenuator V5
The layup for the fifth version is shown in the table below: Orientation
Comment
0°/90° 0°
Fabric Twill UD Layer Kraibon Fabric Twill Fabric Twill Kraibon UD Layer Fabric Twill
±45° ±45° 0° 0°/90°
Total number of main layers: 4 Total weight: 860 g
Figure 5 shows the deceleration over time and displacement for impact attenuator V5. The peak deceleration exceeded the limits. Impact attenuator V5 was not able to absorb 7350 J.
Figure 5: Deceleration over time and displacement – V5
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joanneum racing graz
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Impact Attenuator V6
The layup for the sixth version is shown in the table below: Orientation
Comment
0°/90°
Fabric Twill
0° ±45° 0° 0°/90°
Kraibon UD Layer Fabric Twill UD Layer Kraibon Fabric Twill
Total number of main layers: 3 Total weight: 840 g
Figure 6 shows the deceleration over time and displacement for impact attenuator V6. The graph shows a saddle point at 0,23 m, because the margin of the pendulum was reached and the rest of the remaining energy was not absorbed completely by the impact attenuator. Impact attenuator V6 was also not able to absorb 7350 J.
Figure 6: Deceleration over ti me and displacement – V6
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joanneum racing graz
09.04.2016
3. Conclusion The lightest design that fulfills the requirements is V4. The heaviest one is V1. In the table below, a comparison of both is shown: Version Weight Number of main layers Kraibon used Peak deceleration Mean deceleration Max. Displacement (=Deformation)
V1
V4
1268 g 8 No 39 g 11,4 g 0,17 m
860 g 5 Yes 28 g 11,3 g 0,21 m
Impact attenuator V4 is the best suited option because it is the lightest one that fulfills our requirements.
