Rollover Analysis: minimum speeds and roll velocity approximation

[MSI]

For latest Mar/Jun 2022 posts, page down or 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 901 times

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

speed for rollover references.jpg (78.46 KiB) Viewed 901 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 1847 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 1841 times

1989 Explorer roll.jpg (146.16 KiB) Viewed 1841 times

toyota test roll rate.jpg (104.58 KiB) Viewed 1841 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 1363 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.

[MSI]

Adding a few more references, more to come

SAE paper 2008-01-0172 Rollover Dynamics: An Exploration of the Fundamentals
Carter, Luepke, Henry, Germane, Smith

• ABSTRACT
  • Research focusing on automotive rollovers has garnered a great deal of attention in recent years. Substantial effort has been directed toward the evaluation of rollover resistance. Issues related to crashworthiness, such as roof strength and restraint performance, have also received a great deal of attention. Much less research effort has been directed toward a more detailed study of the rollover dynamics from point-of-trip to point-of-rest.
    The reconstruction of rollover crashes often requires a thorough examination of the events taking place between point-of-trip and point-of-rest. Increasing demands are placed on reconstructionists to provide greater levels of detail regarding the roll sequence.
    Examples include, but are not limited to, roll rates at the quarter-roll level, CG trajectory (horizontal and vertical), roll angle at impact, and ground contact velocity.
    Often the detail that can be provided in a rollover reconstruction is limited by a lack of physical evidence. However, there are many cases where the physical evidence – both on the vehicle and the ground – allows for detailed re-positioning of the vehicle during the roll sequence. Using such a high level of detail would lead one to believe that the reconstruction of the rollover dynamics will be an accurate representation of the actual event. But, just how accurate will it be?
    This paper seeks to examine the commonly used constant deceleration method of rollover reconstruction in light of detailed analyses of actual rollover tests. By comparing methods used in the field to detailed experimental observations this paper will provide an understanding of the accuracy and limitations of those methods. The underlying data that provide the foundation for this article are derived from two highspeed soft-surface dolly rollover tests of sport utility vehicles.
  CONCLUSIONS
  1. The effective deceleration for both tests in this study was 0.55g, considering the typical range of 0.4g to 0.6g used in reconstruction.
  2. The actual OTG acceleration in a rollover event will be highly non-linear with segments that may exceed 1g when in contact with the ground and
     segments that approach zero when the vehicle becomes airborne.
  3. Use of the constant acceleration model results in both underestimation as well as overestimation of OTG speeds at various points during the roll sequence using the typical range of deceleration values.
  4. In these tests the constant acceleration model generated OTG speeds that exceeded the measured OTG speed by 50% or more at various times during the roll sequence using the typical range of deceleration values.
  5. Roll rate as a function of time and distance in both tests appears to demonstrate a triangular pattern.
  6. Use of the constant acceleration model can provide a reasonable approximation of peak roll rates and to a certain extent the profile of the roll rate versus time history.
  7. The extent of the agreement between reconstructed and actual roll rates will depend on a number of factors, including the effective deceleration used and the number of quarter-roll positions that can be established.
  8. The peak roll rates in these tests were best approximated when an effective deceleration of 0.45g was used in the reconstruction computations.
  9. Roll angle as a function of distance demonstrated a bi-linear relationship and was very similar for both tests.
  10. Use of the constant deceleration model generally underestimates the time duration of a rollover event using the typical range of deceleration values.
  11. Reconstructed kinetic energy generally overestimates the actual kinetic energy in a rollover crash.
  12. For SUV’s rolling over on a flat dirt surface the effective deceleration, based on this study, will range from 0.45g and 0.55g.
  13. . A multiphasic approach to reconstructing rollovers is suggested by the results of this study and should be further investigated for applicability to reconstructing real-world rollovers.

SAE 2002-01-0942 A Comparison of Rollover Characteristics for Passenger Cars, Light Duty Trucks and Sport Utility Vehicles
Scott Altman, Dean Santistevan, Clarence Hitchings, Jerry G. Wallingford and Bill Greenlees

• ABSTRACT
  • The evaluation of a rollover accident requires the assessment of a large amount of information in order to completely analyze the accident and determine the vehicle dynamics throughout its roll sequence. This information includes the physical evidence available through examination of the accident site, the vehicle and any photographs or documentation of the accident scene.
    Many times there is a lack of scene data available complicating a thorough evaluation of the vehicle path and roll distance during the rollover. Inspection of the vehicle reveals the minimum number of rolls the vehicle experienced during the rollover event, leaving the roll distance traveled as one of the many unknown variables.
    This paper compares the roll distance, roll speed and number of rolls for dolly testing and real world rollovers. An evaluation of the roll distance and number of rolls for passenger cars, light trucks and sport utility vehicles is compiled and compared to one another. Relationships were found and discussed.
  CONCLUSIONS
  1. The results of this study for the reconstructed accidents illustrate the expected non-linear relationship between the speed of the vehicle at trip/tip-up and the roll distance. In addition a direct relationship can be seen between the speed of the vehicle at trip/tip-up and the number of rolls. This Leads to the number of rolls of the vehicle being directly related to the roll distance.
  2. The average roll distance per roll for vehicles that roll one time or less is approximately 14m (45.9ft.). The average roll distance per roll for vehicles that roll more than two times is constant between 16.1m (52.8ft.) and 16.9m (55.4ft.). These values for average roll distance are much greater for the reconstructed rollovers than for the dolly tests.
  3. It was observed that the speed of SUV’s at trip/tipup was on average higher than the other vehicle classes probably due to the lower yaw angle at
     initiation of rollover.
  4. The use of dolly tests to relate roll distance, trip/tipup speed, and number of rolls is not an effective tool for use in rollover accident reconstruction.
  5. The relationship between roll distance, trip/tip-up speed, and number of rolls observed were not affected by the trip/roll surface for reconstructed
     rollover accidents.

[MSI]

Had to add that the report above
SAE paper 2008-01-0172 Rollover Dynamics: An Exploration of the Fundamentals
the first conclusion

• The effective deceleration for both tests in this study was 0.55g, considering the typical range of 0.4g to 0.6g used in reconstruction.

Is right in line with the 1972 work of the late Phil Hight:

• An often cited value for the average ground deceleration factor for rollovers is 0.40-0.65 and is based on reported values found in a 1972 report by Hight ( Hight, P.V., Siegel, A.W., Nahum, A.M., “Injury Mechanisms in Rollover Collisions”, SAE paper 720966).
  
  • It should be noted that the values reported were not measured values but were calculated from “estimated rollover speeds” based on “other road users’ statements, highway geometry, braking and centrifugal skid marks, critical cornering speeds, etc.”. However more recent measurements of drag on rolling vehicles support the general range of the estimates cited in the Hight report.
  (from another forum topic References on Rollover speed versus the number of rotations?)