Automotive Accident Reconstruction

Donald E. Struble holds a BS, MS, and PhD from California Polytechnic State University, Stanford University, and Georgia Institute of Technology, respectively, all in engineering with an emphasis on structuralmechanics. Dr. Struble was assistant professor of aeronautical engineering at Cal Poly, manager of the Research Safety Vehicle program and senior vice president of Engineering and Research at Minicars, Inc., and president of Dynamic Science in Phoenix, Arizona. He is a member of SAE, AAAM, and Sigma Xi, the Scientific Research Society. Formerly senior engineer at Collision Safety Engineering in Phoenix, Arizona, and president of Struble–Welsh Engineering in San Luis Obispo, California, he is now retired.

General Principles


An Exact Science?


Units, Dimensions, Accuracy, Precision, and Significant Figures


Newton's Laws of Motion


Coordinate Systems


Accident Phases


Conservation Laws


Crush Zones


Acceleration, Velocity, and Displacement


Crash Severity Measures


The Concept of Equivalence


Objectives of Accident Reconstruction


Forward-Looking Models (Simulations)


Backward-Looking Methods


References


Tire Models


Rolling Resistance


Longitudinal Force Generation


Lateral Force Generation


Longitudinal and Lateral Forces Together


The Backward-Looking Approach


Effects of Crab Angle


References


Subdividing Noncollision Trajectories with Splines


Introduction


Selecting an Independent Variable


Finding a Smoothing Function


Properties of Splines


Example of Using a Spline for a Trajectory


A Program for Reverse Trajectory Calculation Using Splines


Introduction


Developing Velocity-Time Histories for Vehicle Run-Out Trajectories


Other Variables at Play in Reverse Trajectory Calculations


Vehicle Headings and Yaw Rates


Example Reverse Trajectory Calculation


Yaw Rates


Secondary Impacts with Fixed Objects


Verifying Methods of Analyzing Post-Crash Trajectories


The RICSAC Crash Tests


Documenting the Run-Out Motions


Data Acquisition and Processing Issues


Separation Positions for the RICSAC Run-Out Trajectories


Side Slap Impacts


Secondary Impacts and Controlled Rest


Surface Friction


Sample Validation Run


Results of Reverse Trajectory Validation


References


Time-Distance Studies


Purpose


Perception and Reaction


Constant Acceleration


Example of Constant Acceleration Time-Distance Study


Variable Acceleration


References


Vehicle Data Sources for the Accident Reconstructionist


Introduction


Nomenclature and Terminology


Vehicle Identification Numbers


Vehicle Specifications and Market Data


Vehicle Inertial Properties


Production Change-Overs and Model Runs


Sisters and Clones


Other Information Sources


People Sizes


References


Accident Investigation


Introduction


Information Gathering


Scene Inspection


Vehicle Inspection


Crush Measurement


References


Getting Information from Photographs


Introduction


Photographic Analysis


Mathematical Basis of Photogrammetry


Two-Dimensional Photogrammetry


Camera Reverse Projection Methods


Two-Photograph Camera Reverse Projection


Analytical Reverse Projection


Three-Dimensional Multiple-Image Photogrammetry


References


Filtering Impulse Data


Background and Theory


Analog Filters


Filter Order


Bode Plots


Filter Types


Digital Filters


FIR Filters


IIR Filters


Use of the Z-transform


Example of Finding the Difference Equation from the Transfer Function


Bilinear Transforms


References


Digital Filters for Airbag Applications


Introduction


Example of Digital Filter in Airbag Sensor


References


Obtaining NHTSA Crash Test Data


Contemplating Vehicle Crashes


The Crush Zone


Accelerometer Mount Strategy


Other Measurement Parameters and Transducers


Sign Conventions and Coordinate Systems


Processing NHTSA Crash Test Accelerometer Data


Summary of the Process


Downloading Data from NHTSA's Web Site


Identifying the Accelerometer Channels to be Downloaded


Downloading the Desired Channels


Parsing the Data File


Filtering the Data


References


Processing NHTSA Crash Test Acceleration Data


Background


Integrating the Accelerations


Filtering the Data


Filter( j) Subroutine


Parsing the Data File


NHTFiltr.bas Program Output


Averaging Two Acceleration Channels


Using the NHTSA Signal Browser


References


Analyzing Crash Pulse Data


Data from NHTSA


Repeatability of Digitizing Hardcopy Plots


Effects of Plotted Curve Quality


Accuracy of the Integration Process


Accuracy of the Filtering Process


Effects of Filtering on Acceleration and Velocity Data


Effect of Accelerometer Location on the Crash Pulse


Conclusions


Reference


Downloading and Analyzing NHTSA Load Cell Barrier Data


The Load Cell Barrier Face


Downloading NHTSA Load Cell Barrier Data


Crash Test Data Files


Grouping Load Cell Data Channels


Computational Burden of Load Cell Data Analysis


Aliasing


Example of Load Cell Barrier Data Analysis


Using the NHTSA Load Cell Analysis Software


References


Rollover Forensics


Introduction


Measurements of Severity


Evidence on the Vehicle


Evidence at the Scene


References


Rollover Analysis


Introduction


Use of an Overall Drag Factor


Laying Out the Rollover Trajectory


Setting Up a Reverse Trajectory Spreadsheet


Examining the Yaw and Roll Rates


Scratch Angle Directions


Soil and Curb Trips


References


Vehicle Structure Crash Mechanics


Introduction


Load Paths


Load-Deflection Curves


Energy Absorption


Restitution


Structural Dynamics


Restitution Revisited


Small Car Barrier Crashes


Large Car Barrier Crashes


Small Car/Large Car Comparisons


Narrow Fixed Object Collisions


Vehicle-to-Vehicle Collisions


Large Car Hits Small Car


Barrier Equivalence


Load-Deflection Curves from Crash Tests


Measures of Crash Severity


References


Impact Mechanics


Crash Phase Duration


Degrees of Freedom


Mass, Moment of Inertia, Impulse, and Momentum


General Principles of Impulse-Momentum-Based


Impact Mechanics


Eccentric Collisions and Effective Mass


Using Particle Mass Analysis for Eccentric Collisions


Momentum Conservation Using Each Body as a System


The Planar Impact Mechanics Approach


The Collision Safety Engineering Approach


Methods Utilizing the Conservation of Energy


References


Uniaxial Collisions


Introduction


Conservation of Momentum


Conservation of Energy


Momentum Conservation for Central Collisions


Reference


Assessing the Crush Energy


Introduction


Constant-Stiffness Models


Sample Form Factor Calculation: Half-Sine Wave Crush Profile


Sample Form Factor Calculation: Half-Sine Wave Squared


Crush Profile


Form Factors for Piecewise-Linear Crush Profiles


Sample Form Factor Calculation: Triangular Crush Profile


Constant-Stiffness Crash Plots


Example Constant-Stiffness Crash Plot


Constant-Stiffness Crash Plots for Uniaxial Impacts by Rigid


Moving Barriers


Segment-by-Segment Analysis of Accident Vehicle Crush


Profiles


Constant-Stiffness Crash Plots for Repeated Impacts


Constant Stiffness with Force Saturation


Constant Stiffness Model with Force Saturation, Using Piecewise


Linear Crush Profiles


Constant-Force Model


Constant-Force Model with Piecewise Linear Crush Profiles


Structural Stiffness Parameters: Make or Buy?


References


Measuring Vehicle Crush


Introduction


NASS Protocol


Full-Scale Mapping


Total Station Method


Loose Parts


Other Crush Measurement Issues in Coplanar Crashes


Rollover Roof Deformation Measurements


References


Reconstructing Coplanar Collisions, Including


Energy Dissipation


General Approach


Development of the Governing Equations


The Physical Meaning of Two Roots


Extra Information


Sample Reconstruction


References


Checking the Results in Coplanar Collision Analysis


Introduction


Sample Spreadsheet Calculations


Choice of Roots


Crash Duration


Selecting Which Vehicle is Number 1


Yaw Rate Degradation


Yaw Rates at Impact


Trajectory Data


Vehicle Center of Mass Positions


Impact Configuration Estimate


Vehicle Headings at Impact


Crab Angles at Impact


Approach Angles


Restitution Coefficient


Principal Directions of Force


Energy Conservation


Momentum Conservation


Direction of Momentum Vector


Momentum, Crush Energy, Closing Velocity, and


Impact Velocities


Angular Momentum


Force Balance


Vehicle Inputs


Final Remarks


References


Narrow Fixed-Object Collisions


Introduction


Wooden Utility Poles


Poles that Move


Crush Profiles and Vehicle Crush Energy


Maximum Crush and Impact Speed


Side Impacts


References


Underride/Override Collisions


Introduction


NHTSA Underride Guard Crash Testing


Synectics Bumper Underride Crash Tests


Analyzing Crush in Full-Width and Offset Override Tests


The NHTSA Tests Revisited


More Taurus Underride Tests


Using Load Cell Barrier Information


Shear Energy in Underride Crashes


Reconstructing Ford Taurus Underride Crashes


Reconstructing Honda Accord Underride Crashes


Reconstructing the Plymouth Reliant Underride Crash


Conclusions


References


Simulations and Other Computer Programs


Introduction


CRASH Family of Programs


SMAC Family of Programs


PC-CRASH


Noncollision Simulations


Occupant Models


References


Index





Catalog no. K20381


October 2013


c. 488 pp.


ISBN: 978-1-4665-8837-0


$149.95 / GBP95.00





Shelving Guide/Bookshop Category: Automotive Engineering


Contact Editor: Jonathan Plant


Keywords


Reconstruction


Crush energy


Velocity change (delta-V)


Rollovers


Conservation of energy


Conservation of momentum


Newton's Second Law


Trajectory analysis


Structural stiffness


Restitution


Filters, digital


Planar impacts


Impact velocity


Vehicle crashes


Crash tests


Photogrammetry


Time-reverse


Drag factor


Pole impacts


Underride crashes