1st Edition

Automotive Accident Reconstruction Practices and Principles

By Donald E. Struble, Ph.D. Copyright 2013
    498 Pages 14 Color & 119 B/W Illustrations
    by CRC Press

    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

    Noncollision Simulations

    Occupant Models

    References

    Index

    <pr>Catalog no. K20381

    October 2013

    c. 488 pp.

    ISBN: 978-1-4665-8837-0

    $149.95 / £95.00

    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

    Biography

    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.