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.

Table of Contents

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

Write a review

Your Name:


Your Review: Note: HTML is not translated!

Rating: Bad           Good

Enter the code in the box below: