Below are my quick notes for the FIRST of the Occupant Protection: Accident Reconstruction sessions.
I was typing as fast as I could while listening to the presenters, so I apologize in advance if there are any typos or inaccuracies. These are not exact quotes, just my notes on the sessions. This is just to give you an idea of what was presented, if you are interested you should probably get the paper. I may have missed one or two sessions as well. I tried my best to catch everything. Ill post the second session soon:
SESSION I:
Acceleration and Braking Performance of School Buses
Charles Funk, Exponent
Testing performed on type A and type C school busses. Tested acceleration and braking performance using Vericom DAQ. Multiple drivers were used; from inexperienced to experienced bus drivers. Results show initial acceleration g spike and then settled at lower level. These are close to passenger car acceleration rates. 10% difference between all the different drivers (normal accel), 6 % difference for rapid acceleration.
Low Speed Acceleration of Tractor-Semitrailers Equipped with Automated Transmissions
Kerry Drew
Two tractors (different HP) with different loads (3700 lbs and 0). Automated transmissions, still have clutch, but only used when starting from stop. 100m acceleration test, (small uphill grade .0037 m/m). Started tractor in 1st 2nd and 3rd gears. two accelerator positions (60% and 100%). In general there was not much difference in acceleration between unloaded but significant difference between loaded. Compared these results to calculated constant acceleration. Assumptions of constant accel should be made cautiously. Vehicle HP was made little difference for unloaded vehicles.
Application of Air Brake Performance Relationships in Accident Reconstruction and Their Correlation to Real Vehicle Performance
Al Dunn
Brake force is non-linear. Looked at relationship between PSI and brake torque. Looked at Heusser model and the variables associated with model. Details procedure to find brake force as a function of pushrod stroke. Showed relationship between static stroke and torque output. Able to calculate an adjusted drag factor from data from braking tests. Compared new model to test data. For most cases, model matches test data (not for many disabled brakes).
Analysis of Motorcycle Braking Performance and Associated Braking Marks
Al Dunn
Tested 1995 BMW with ABS, 2003 Buell, 2005 Harley 1200. Used VBox III at 100 hz for data acquisition. Tested at speeds of 25 45 and 60. Tested 3 riders with 3 braking strategies (front, rear, both). Calculated stopping distance by integrating velocity. Calculated drag factor. Also calculated confidence interval on those results. BMW with ABS had highest drag factor. Similar results for others. At higher speeds, some motorcycles had higher drag factors at higher speeds. Analysis was done for braking differences between front, rear and both. Also performed all the same tests on a wet surface. Analyzed braking marks for the test and showed differences between braking strategies. Calculated the braking speeds from measured braking marks showed a 10% error on average. Rear brake does not always improve stopping distance.
Rollout Deceleration of Modern Passenger Vehicles
Daniel Desautels
Quantify vehicle rolling deceleration for late model vehicles, including CVT and hybrid vehicles. Studied post-impact roll (in or out of gear, automatic transmission and manual). Many classes and makes were tested. Used non-contact speed sensor (5th wheel), Vbox 100Hz and handheld GPS. Calculated deceleration values for small speed increments. Plotted deceleration over speed (coasting). CVT produces different results from manual and automatic transmissions. Average deceleration rates were presented as well.
An Integrated Model of Rolling and Sliding in Rollover Crashes
James Funk
Proposed rollover model is an extension of model proposed by Chen and Guenther previously. Model is focused on two parameters: translational velocity vs time and roll velocity vs time. Breaks down model into two phases, tumbling phase (sliding and rolling). Proposed modeling producing velocity and roll rate as a function of time consisting of trip phase airborne phase, sliding phase and rolling phase. Broke down model into a simple free body diagram. Breaks up equations into four parameters in sliding and rolling phase. Used 12 rollover tests to validate model.
A Critique of Critical Speed Yaw Mark Research
Shane Richardson presented by Tia Orton
Study aims to quantify error in critical speed formula. Not a challenge of the validity of the critical speed formula. Author states that small errors in the field have a large effect on calculations. Paper shows sensitivity of yaw measurements. Extensive literature review was done to analyze theory on yaw critical velocity. Author summarizes literature review and makes important notations on benefits and flaws. Author provides suggestions for documenting yaw markings. A list of recommendations, from the literature review, is compiled. Case study was also presented. Critical speed formula is a viable solution. It is only really accurate to 10 - 15%.
Empirical Testing of Vehicular Rotational Motion
Duane R. Meyers
Analyzed previously published model for friction during rotation. Measured deceleration of a vehicle while it is rotating and measuring vehicle trajectories. Vericom and Vbox was used as data acquisition. Test conducted at the WI state patrol with a 2005 Crown Victoria. Disabled ABS and provided ability to shut off brake valves to one side of vehicle. Tested at over 50 mph, applied hard braking to one side of the vehicle. Conclusions: Simplified models in literature were validated to testing with small error.
Analysis of Critical Speed Yaw Scuffs Using Spiral Curves
Jeremy Daily
Author reviewed classical critical speed yaw analysis. Investigates yaw marks with a decreasing radius. A yaw test was performed. The position data (x,y) was plotted. That data was attempted to be fitted as a function. Spiral was curve fit to the yaw markings. This curve fit was optimized with total least squares. Non-linear problem requires an iterative solution. The yaw markings were fit to many mathematical formulations of spiral types. Author compared the different spiral formulations to the actual test data. The author has created spreadsheets for calculating the spiral parameters at:
http://tucrrc.utulsa.edu/Publications.html
Comparison of Calculated Speeds for a Yawing and Braking Vehicle to Full-Scale Vehicle Tests
Neal Carter
Author compared multiple models for calculating speeds for yawing and braking vehicles. Also compared these models to non-braking models. Conducted some dynamics tests with a 2008 Chevy Malibu. Driver was told to brake for one test and let the vehicle come to rest in another test. Author shows the results of the tests and how the different models compare to the test data.