Automotive Accident Reconstruction Practices and Principles

Automotive Accident Reconstruction: Practices and Principles introduces techniques for gathering information and interpreting evidence, and presents computer-based tools for analyzing crashes. This book provides theory, information and data sources, techniques of investigation, an interpretation of physical evidence, and practical tips for beginners. It also works as an ongoing reference for experienced reconstructionists. The book emphasizes three things: the theoretical foundation, the presentation of data sources, and the computer programs and spread sheets used to apply both theory and collected data in the reconstruction of actual crashes. It discusses the specific requirements of reconstructing rollover crashes, offers background in structural mechanics, and describes how structural mechanics and impact mechanics are applied to automobiles that crash. The text explores the treatment of crush energy when vehicles collide with each other and with fixed objects. It delves into various classes of crashes, and simulation models. The framework of the book starts backward in time, beginning with the analysis of post-crash vehicle motions that occurred without driver control. Applies time-reverse methods, in a detailed and rigorous way, to vehicle run-out trajectories, utilizing the available physical evidence Walks the reader through a collection of digital crash test data from public sources, with detailed instructions on how to process and filter the information Shows the reader how to build spread sheets detailing calculations involving crush energy and vehicle post-crash trajectory characteristics Contains a comprehensive treatment of crush energy This text can also serve as a resource for industry professionals, particularly with regard to the underlying physics.

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 Noncol

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.