Rollover Analysis: minimum speeds and roll velocity approximation

[MSI]

For latest Mar 2022 post, click here

Q: Do you have methods to calculate the roll rates for a vehicle rollover?

A: In addition to our list of references Rollover speed versus the number of rotations?

We also have posted up some equations from our book McHenry Accident Reconstruction

• Minimum Lateral Speed for Tripping Type Rollover
  • which also includes a couple pages on 'Speed Required for a Lateral Rollover Beyond 90 degrees'

The following figures added Mar 2022 for convenience:

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fig 85.jpg (68.05 KiB) Viewed 323 times

Here is the list of references cited in the link above:

speed for rollover references.jpg (78.46 KiB) Viewed 323 times

[MSI]

Q: We are interested in vehicle's velocity peak roll rate, angle and time. we have the approximate traveling speed from the scene evidence.

A: From that list of references on Rollover tests the last reference Rollover Crash Tests on Dirt: An Examination of Rollover Dynamics includes a list of Peak Roll Rate & Mean Roll Rate (repeated below)
However for a particular accident the roll rate may vary due to things like

• trip type?
  • was is a curb, soft soil? vehicle component failure?
  terrain type:
  • downslope, upslope, variations in elevation
    terrain material: dirt, grass, hard packed, soft, moist
  vehicle exterior interaction?
  • The shape and structure of the vehicle will influence how it interacts with local terrain
    a van v a passenger car v a pickup truck, etc,
    different vehicle structure interaction with local terrain can vary the rollover rate and response)

I might suggest use of a simulation program like our msmac3D and model the specific vehicle and terrain (survey? point cloud?) to test and refine the speed from scene evidence and then also the roll (and pitch) rates.

roll rates.jpg (63.05 KiB) Viewed 1269 times

[MSI]

We have accumulated some steer induced rollover tests as part of our msmac3D validations.
Below are some of the measured time history plots of the roll angle and roll velocities from some of the tests.
We added something to help identify the test so you can find additional information.
We'll try to update this soon as part of our validation paper and include more comprehensive information.
However we post these up now to be responsive to the question.
Note that the roll rates for these flat surface steer induced rollovers are less than for dolly launched rollover tests (cited above).

1997 Toyota 4Runner Rollover.jpg (162 KiB) Viewed 1263 times

1989 Explorer roll.jpg (146.16 KiB) Viewed 1263 times

toyota test roll rate.jpg (104.58 KiB) Viewed 1263 times

[MSI]

Q: In determining a vehicle's peak roll rate, is it simply the degrees it rolls during the period of time which is degrees per second or is it much more complicated than that?

A: Peak Roll Rate is the measured rolling rate, measured in deg/sec during a rollover test.
You'll note in that the test result summary (see above) they list the peak and then the mean or average roll rate.
The mean or average roll rate is sometimes computed in 3 different ways:

• 1) by averaging the roll rate throughout the test (sampling measurements every tenth of a second and then taking an average) (deg/sec)
• 2) taking the total amount of roll and dividing by time, (deg/sec) or
• 3) taking the total roll and dividing by distance (deg/foot)

In a lot of rollovers you may observe measurements with wildly changing rolling rates (see above) as components strike the ground.
Vans you will find have rolling rates which are generally more consistent than other vehicles (a box rolls easier than a vehicle with a smaller top than the base)
When the tires hit and the tire/suspension gets possibly damaged or when the roof buckles or deforms, these all can change the roll rate rapidly.
Also variations in the local terrain can change the rolling rate during a rollover.

[MSI]

Question on another forum about full scale tests for end-over-end rollovers
Can't recall any specific crash test which included an end-over-end vault but recall have seen some (might come to me later)
In the meantime the following is a page out of our book McHenry Crash Reconstruction 2008 which includes some equations to consider in calculating a minimum speed to produce an end-over-end vault.
We've also created a separate topic:

• End-Over-End Rollover Analytical Relationships

To which we will add any additional information/references as we come across them/recall them.

EndOverEndVaultEquations.png (166.96 KiB) Viewed 785 times

[MSI]

Some additional references posted on Napars Facebook Page

A link with a good review of a range of rollover testing techniques, including the "critical sliding velocity" (CSV):

• See Critical Sliding Velocity
  • From the National Academies of Sciences, Engineering, and Medicine. 2002.
    An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance:
    Special Report 265. Washington, DC:
    The National Academies Press. https://doi.org/10.17226/10308.
• "critical sliding velocity" also comes up in SAE 1999-01-1336 (from NHTSA site so FREE)
  
  • Measured Vehicle Inertial Parameters-NHTSA’s Data Through November 1998
    • This paper is primarily a printed listing of the National Highway Traffic Safety Administration’s (NHTSA) Light Vehicle Inertial Parameter Database. This database contains measured vehicle inertial parameters from SAE Paper 930897, “Measured Vehicle Inertial Parameters -NHTSA’s Data Through September 1992” (1), as well as parameters obtained by NHTSA since 1992.
      The proceeding paper contained 414 entries. This paper contains 82 new entries, for a total of 496. The majority of the entries contain complete vehicle inertial parameters, some of the entries contain tilt table results only, and some entries contain both inertia and tilt table results.
      This paper provides a brief discussion of the accuracy of inertial measurements. Also included are selected graphs of quantities listed in the database for some of the 1998 model year vehicles tested.

From the NAPARS facebook post it continues...

• , which is a catalog of the vehicle inertial parameters recorded by NHTSA, and light examination of the relationships contained therein. By "Inertial parameters", we mean mostly weight and moments of inertia, but it includes some other dimensional info, too. Since it was tax dollars that paid for it (more or less), the paper is available to the public on the NHTSA website: https://www.nhtsa.gov/.../VRTC/ca/capub ... 1-1336.pdf
  There is a ton of interesting data in there, though it took me a while to figure out the tables - pay close attention to the headers. The data sets roll over across 2 pages.

[MSI]

Note: Added figures and references to the first post on this topic.