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67 Field Example (courtesy of Ontario Ministry of Transportation) FE Model Figure 55. Rail flattening--field example vs. finite element model. lations showed stable exit velocities. The 50 percent and At this time, the vehicle was still moving into the guardrail 75 percent simulations also showed a relatively large amount and was just starting to be redirected. The static deflection of lateral skidding and upward motion as the vehicle was contours for 2575 percent flattening were very uneven. This exiting the guardrail. This skidding motion was caused was due to vibrations induced in the rail when the pickup by the edge of the vehicle bed catching on a fold in the truck bed slapped the guardrail. guardrail near a post, which also contributed to the decrease in yaw. 13.3 Discussion Figure 60 presents approximate damage contours for the guardrail. All of the damage contours were measured starting A full series of simulations, with flattening ranging from at post 9 (position = 0) up to post 21 (position = 22860 mm). 25100 percent, were run to determine whether rail flatten- For all simulations, except the 100 percent flattening simula- ing posed a risk to vehicle and occupant safety. It was found tion, the maximum dynamic deflection occurred at 165 ms. that the vehicle became unstable above 75 percent flattening. Figure 56. Rail flattening simulations before impact: 25% flattening (top left), 50% flattening (top right), 75% flattening (bottom left), and 100% flattening (bottom right).

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68 Figure 57. Flattening simulation results at t = 0.7s. 25% flattening (top left), 50% flattening (top right), 75% flattening (bottom left), and 100% flattening (bottom right). At 100 percent flattening, the vehicle rolled over as it exited by the end of the simulation. Such a large change in the vertical the guardrail. position of the vehicle can be an indicator of vaulting. However, A key factor in the exit behavior of the vehicle was the mo- in this case the vehicle was redirected before this could occur. tion of the front left tire. Figure 61 shows the vertical displace- The undamaged simulation showed the lowest amount of ver- ment of the center of the front left and rear left tires over time, tical tire motion, which was an indicator of vehicle stability. In relative to each tire's original position at the start of the simu- the plot of the front left tire displacement for the undamaged lation. The simulation of 100% flattening showed the greatest simulation, the time at which the wheel struck and rolled over displacement of the tire, reaching over 1600 mm (63 inches) a post can be easily discerned by the peaks in the displacement. Table 27. Results for rail flattening simulations. Un- 25% 50% 75% 100% damaged Flattening Flattening Flattening Flattening Impact Conditions Speed (kph) 100 100 100 100 100 Angle (deg) 25 25 25 25 25 Exit Conditions Speed (kph) 53 56 59 60 73 Angle (deg) 14.5 12.1 9.1 10.7 10.0 Occupant Impact Velocity X 7.51 7.3 7.5 6.8 5.9 (m/s) Impact Velocity Y 5.54 5.5 5.7 5.7 5.7 (m/s) Ridedown X (G) -11.77 -14.7 -10.9 -14.1 -7.4 Ridedown Y (G) -12.27 11.4 -11.6 -12.3 -11.4 50 ms Average X (G) -6.68 -5.6 -6.0 -6.1 -5.4 50 ms Average Y (G) -6.82 -6.6 -7.1 -6.9 -7.2 50 ms Average Z (G) -3.85 3.3 -3.7 -4.1 2.6 Guardrail Deflections Dynamic (m) 0.69 0.74 0.75 0.75 0.80 Static (m) 0.55 0.57 0.44 0.43 0.62 Vehicle Rotations Max Roll (deg) -14.4 -15.8 -16.7 15.2 Roll Max Pitch (deg) -9.9 -12.3 20.2 -20.7 > 18 Max Yaw (deg) 40.3 38.3 38.0 38.0 33.5

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69 90 X - Roll 70 Y - Pitch Z - Yaw Angular Displacement (degrees) 50 30 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -10 -30 -50 Time (s) 90 90 X - Roll X - Roll 70 Y - Pitch 70 Y - Pitch Z - Yaw Z - Yaw Angular Displacement (degrees) Angular Displacement (degrees) 50 50 30 30 10 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -10 -10 -30 -30 -50 -50 Time (s) Time (s) 90 90 X - Roll X - Roll 70 Y - Pitch 70 Y - Pitch Z - Yaw Z - Yaw Angular Displacement (degrees) Angular Displacement (degrees) 50 50 30 30 10 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -10 -10 -30 -30 -50 -50 Time (s) Time (s) Figure 58. Roll, pitch, and yaw curves for flattening simulations: undamaged (top), 25% flattening (middle left), 50% flattening (middle right), 75% flattening (lower left), and 100% flattening simulations (lower right).

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70 100 X Velocity Y Velocity 80 Z Velocity Total Velocity 60 Velocity (kph) 40 20 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -20 Time (s) 100 100 X Velocity X Velocity Y Velocity Y Velocity 80 Z Velocity 80 Z Velocity Total Velocity Total Velocity 60 60 Velocity (kph) Velocity (kph) 40 40 20 20 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -20 -20 Time (s) Time (s) 100 100 X Velocity Y Velocity 80 Z Velocity 80 Total Velocity 60 60 Velocity (kph) Velocity (kph) X Velocity 40 40 Y Velocity Z Velocity Total Velocity 20 20 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -20 -20 Time (s) Time (s) Figure 59. Velocity curves for flattening simulations: undamaged (top), 25% flattening (middle left), 50% flattening (middle right), 75% flattening (lower left), and 100% flattening simulations (lower right).

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71 1200 Static Deflection Contour Max Deflection Contour (t=0.165s) 1000 Distance from Guardrail (mm) 800 600 400 200 0 0 5000 10000 15000 20000 25000 Guardrail Lengthwise Position (mm) 1200 1200 Static Deflection Contour Static Deflection Contour Max Deflection Contour (t=0.165s) Max Deflection Contour (t=0.165s) 1000 1000 Distance from Guardrail (mm) Distance from Guardrail (mm) 800 800 600 600 400 400 200 200 0 0 0 5000 10000 15000 20000 25000 0 5000 10000 15000 20000 25000 Guardrail Lengthwise Position (mm) Guardrail Lengthwise Position (mm) 1200 1200 Static Deflection Contour Static Deflection Contour Max Deflection Contour (t=0.165s) Max Deflection Contour (t=0.295s) 1000 1000 Distance from Guardrail (mm) Distance from Guardrail (mm) 800 800 600 600 400 400 200 200 0 0 0 5000 10000 15000 20000 25000 05 0001 0000 150002 0000 25000 Guardrail Lengthwise Position (mm) Guardrail Lengthwise Position (mm) Figure 60. Guardrail damage contours for flattening simulations: undamaged (top), 25% flattening (middle left), 50% flattening (middle right), 75% flattening (lower left), and 100% flattening simulations (lower right).

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72 1800 1800 Undamaged Undamaged 1600 1600 25% Flattening 25% Flattening 50% Flattening 50% Flattening 1400 1400 75% Flattening 75% Flattening 100% Flattening 100% Flattening Vertical Displacement (mm) Vertical Displacement (mm) 1200 1200 1000 1000 800 800 600 600 400 400 200 200 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.2 0.4 0.6 0.8 1 1.2 -200 -200 Time (s) Time (s) Figure 61. Displacement of vehicle tires for the flattening simulations: front left tire (left) and rear left tire (right). The vehicle instability at greater than 75 percent flattening When the rail was 100% flattened, a different behavior was was caused by the vehicle riding up the flattened rail. Both observed. Because of the higher top height of the rail and the the flatness of the rail and the lower bottom height of the flatness of the surface, the force of the collision was distrib- rail were contributors to the rollover. As shown in Figure 62, uted over a larger portion of the fender. These factors pre- a maximally flattened rail extends both higher and lower vented the rail from penetrating the space above the tire. The than an undeformed rail would and also presented a much lower bottom height of the rails also presented a problem. As smoother surface. the tire was forced upward by contact with the posts, the ele- In the undamaged simulation, because of the height of the vation of the tire increased so that the majority of the tire was rails, the collision force was concentrated on the front of the on or above the rails. This, combined with a slight outward fender, leading to extensive crush on the front left corner of slope in the rail caused by the crash damage, provided a ramp the vehicle. This deformation allowed the top half of the rail for the tire to ride up. The increase in rail height, which was to penetrate the space above the front left tire. The presence concentrated on the left side of the vehicle, imparted a rolling of the rail above the tire provided a downward force that pre- motion that the vehicle was unable to recover from. vented the tire from moving upward. The upward motion The vehicle exit speed also varied by the degree of flatten- caused by the left tires hitting the post bases was counteracted ing. For the undamaged simulation the exit speed was 53 kph, by the downward force exerted by the rail. whereas for the 100 percent flattening simulation the exit Figure 62. Height of the rails relative to the vehicle: undamaged (left) and 100% flattening (right).