Blog Post | Staging a Car Crash | RICSAC 3
In this latest installment, we continue with our exploration of the Research Input for Computer Simulation of Automobile Collisions (RICSAC) test series. These tests make excellent benchmarks with which to study just how quickly and accurately Virtual CRASH can reproduce accident cases.
Before reading ahead it is highly recommended to review the following:
Here we will review RICSAC 3. We will follow a similar procedure as in our prior posts.
The final result is shown below:
In the RICSAC 3 collision, a 1974 Ford Torino is made to impact a stationary 1974 Ford Pinto. The figure below depicts the impact configuration, as well as pre and post-impact trajectories. The figure is obtained from Figure 15 of Reference [1]. We will start by importing and scaling this crash diagram [2]. Due to the known scale inaccuracies of the Smith and Noga diagrams, the scale will be adjusted to confirm to the published impact positions and points-of-rest.
We would like to use our knowledge of the post-impact trajectory, orientation, and rest position, to help us obtain reasonable estimates of the pre-impact speeds of both vehicles.
On page 2-38 of Reference [3], we can find the "Summary Form" for RICSAC 3. This is shown as Table 1 below.
Table 1
The "Crash Test Summary" can be found on page 9-4 of Reference [4]. This is shown below as Table 2.
Table 2
Finally, we show the "Vehicle Test Weights" form from page 9-21 of Reference [4]. This is shown as Table 3 below.
Table 3
We will create an axis object and plot the impact and rest positions noted in the Table 1 above. We will also place markers at the impact and rest positions as we did in the Chapter 12 exercise. Due to the known scaling error of the Smith and Noga diagrams, the scale tool was aligned with the 9 meter embedded scale, but the scale tool length was set to 31.5 feet. The image was then reasonably aligned with the impact and rest position markers shown above.
With our crash diagram, and Tables 1, 2, and 3, we are now ready to proceed with our simulation.
In our simulation, we will reuse the same vehicles from our prior RICSAC simulations. The Skoda Felicia will be used as an exemplar for the Pinto, and an AMC Matador will be used as a Torino exemplar.
Using data from Tables 1, 2, and 3, as well as in Expert Autostats, we input the following values for our two vehicles:
Just as we did in the RICSAC 1 and RICSAC 2 examples, we're first going to conduct a quick post-impact trajectory analysis to get reasonable estimates of the post-impact speeds needed for each vehicle to travel along its final trajectory.
Using this simple procedure, we arrive at a post-impact velocity of 14.082 mph for the Pinto and 11.7 mph for the Torino. Approximating this impact as a collinear, we can solve for the Torino's pre-impact speed by [5]:
The results are shown below:
Thus, we can expect to find reasonable simulation solutions using a 20.6 mph pre-impact speed for the Torino. Allowing for potential variations in final speeds, we find a reasonable pre-impact speed window of 19 mph to 22 mph for the Torino.
Next, we set up our full simulation. We again use clones of our vehicles with physics removed and set at the final recorded positions to act as targets for our simulation results.
Adjust the initial position of the Torino, and adjust the steering angles, Torino's initial speed, and impulse centroid and restitution value until reasonable convergence is obtained. Here we show the final ees object settings used after creating a user contact (note depth of penetration = 0):
A steering angle of 0.5 degrees was given to the Torino and a 1.01 degrees to the Pinto at time = 0 seconds. The final results are shown below:
Here we find excellent agreement overall between the simulation and data. The final positions were simulated to better than 0.5 feet and final orientations to within 5 degrees. The Torino's pre-impact speed was found to within 1 mph. The Delta-V values were found to better than 1.7 mph, and PDOFs to better than 3 degrees. Note, here PDOF is defined with 0 degrees directed forwards and 90 degrees to the left. This convention means that a frontal collision with a rearward directed force has a PDOF of 180 degrees.
[1] “Examples of Staged Collisions in Accident Reconstruction,” R. Smith and J. Noga, NHTSA, US DOT.
[2] Importing and Scaling Images and Diagrams (VC5 | VC4 | VC3 | Public Safety)
[3] “Research Input for Computer Simulation of Automobile Collisions, Volume IV. Staged Collision Reconstructions,” NHTSA, US DOT, DOT HS 805 040.
[4] Research Input for Computer Simulation of Automobile Collisions, Volume II. Staged Collision Reconstructions,” NHTSA, US DOT, DOT HS 805 040.
[5] See page 526, "Fundamentals of Traffic Crash Reconstruction, Volume II," Daily, Shigemura, and Daily, IPTM.
