The Active Bumper System MIME 1501 - 1502 Technical Design Report Capstone Design Course Report Project #9 Final Report Design Advisor: Prof. Blucher Design Team Matt Bonnell, Seth Pointer Erik Bodurtha, Ralph Castro April 13, 2004 Department of Mechanical, Industrial, and Manufacturing Engineering College of Engineering, Northeastern University TABLE OF CONTENTS ABSTRACT. ................... ... .... .... ........ il •• � ••••••••••••••••• * •••••••••••••• " ..······*··· iv 1.0 PROJECT OVERVIEW......................................................... 1 1.1 Introduction. .................. ..... 1 1.2 Problem Statement..................... .............................. ......... 1 1.3 Crash Test Data........................................................ ......... 1 2.0 REQUIREMENTS.................................................................. 3 2. 1 Extended Collapsible Structure . .... 0...................................... 3 2. 1.1 Force and Acceleration....................... .................... 3 2. 1.2 Structure Collapse.. .................................. ............ 4 2. 1.3 Durability ..... ....... .... .... ... 0 •• 0 ..... .... ... ............ ..... 4 2.2 Sensing System .................................................................. 4 2.3 Deployment... ........................................... ....................... 4 2.4 Locking................... .. ......... .......................................... 5 3.0 CURRENT TECHNOLOGIES................................................ 5 3. 1 Sensing Systems . ... .............. ... .... ........... .......... ....... ...... ... 5 3.2 Crumple Zones ................................................................... 6 3.3 Aluminum Foam............................................................. .... 6 4.0 ANALYTICAL INVESTIGATIONS.......................................... 6 4.1 Target Energy Absorption................ ....... ................. ............ 6 5.0 EXPERIMENTAL INVESTIGATION.......................................... 8 5.1 Test Procedure................................................................ ... 8 5.2 Test Results and Analysis..................................................... 8 5.3 Application of Results ........... ............. ....... ........... .............. 14 5.4 Effect of System.......... .. .......... ...... .... .......................... 15 6.0 DESIGN DETAILS............................................................... 15 6. 1 Final Design Assembly ......................................................... 15 6.2 Extended Sub-Assembly ........................................................ 16 6.3 Base Sub-Assembly............... ............................................... 17 7.0 POST-DESIGN ANALYSIS................... ..................................... 18 7.1 Bending Moment and Shear ................................................... 18 7.2 Spring Plunger Stress..... ................. ............... ..... ........... 19 8.0 RECOMMENDATIONS........................... ................................... 20 8.1 Metal Types................................. ........... ......................... 20 8.2 Geometries ........................................................................20 8. 3 Foam Considerations ............................................................ 20 8.4 Deployment Force ...............................................................20 8.4.1 Frictional Force................................................... 21 8.4.2 Explosive Force...................... ............................ 21 9.0 CONCLUSIONS..................................................................... 22 APPENDIX A............................................................................... 24 APPENDIX B............................................................................... 27 APPENDIX C............................................................................... 29 APPENDIX D............................................................................... 32 APPENDIX E............................................................................... 33 LIST OF FIGURES AND TABLES FIGURES: 1. Chest g's vs. Injury Probability...................................... 2 2. System Deployment Threshold....................................... 5 3. Kinetic Energy vs. Velocity........................................... 7 4. Force vs. Distance for Metal Samples.............................. 9 5. Cumulative Energy...................................................... 10 6. Foam Force vs. Displacement........................................ 11 7. Foam Cumulative Energy............................................... 12 8. Force vs. Distance Foam/Skin Assembly........................... 12 9. Cumulative Energy Foam/Skin Assembly........................... 13 10. Crushed Samples....................................................... 14 11. Final Design Assembly.................................................. 15 12. Column Sub-Assemblies............................................... 16 13. Bending and Shear Stress on Structure............................ 19 14. Spring Plunger Stress.................................................. 19 15. Frictional Force......................................................... 21 TABLES 1. Full Frontal Impact Deceleration Data................................ 2 2. Energy Absorbed by 12 inch Specimens.............................. 10 3. Percentage of Residual Kinetic Energy Absorbed.................. 11 Abstract This report describes the development of an active front bumper system for small automobiles. This system anticipates a collision and extends a structure from the front of the car, increasing the length over which the collision takes place. The increased length dissipates the energy of the accident over a greater amount of time and reduces the force transferred to the vehicle's occupants, lowering their risk of severe injuries. The main components of this design are a sensing system and a collapsible structure that extends from the front of the automobile prior to impact. This project focuses on the design of the collapsible structure. The final design recommendation for the structure is a series of six columns that collapse in much the same way as a modem vehicle's front frame, or "crumple zone'. Each column has an aluminum foam center surrounded by a thin steel frame. The columns are 12 inches in length with a 3 inch square cross section, and are connected to the front bumper of the automobile. 1.0 Project Overview 1.1 Introduction Safety has been at the forefront of automotive design for several decades. From the first seatbelts to airbags and anti-lock brakes, new technologies are continually being used to protect occupants in automobiles. Thanks to these developments, people have a greater chance than ever of walking away from serious accidents. Yet despite the continuous efforts to make vehicles safer, there is still room for improvement. In recent years consumer demands have led to higher speed limits on highways and an increase in the number of large vehicles, such as SUV' s, on the roads. These circumstances increase the risk to drivers and passengers, especially those who still drive small cars. Safety technology needs to constantly adapt to the ever changing dynamic of daily travel, as there are still thousands of people severely injured or killed in automobile accidents every year. 1.2 Problem Statement The majority of severe accident-related injuries occur as a result of frontal collisions. These types of accidents are extremely dangerous because when a car collides head-on with another vehicle or object it decelerates rapidly, which translates a large g-force to the occupants. A high enough g-force can cause severe spine and neck injuries, and even death. The development of energy-absorbing crumple zones in the early 90's helped reduce the g-force translated to occupants and their risk of serious injury. However, the crumple zone is limited in the amount of energy it can absorb because the front frame of a car is only a few feet long. Cars with larger front ends would be able to absorb more energy, but such vehicles are less practical and desirable for everyday use. Therefore, a structure that could be stored in the front frame of a car and extended before an accident to help absorb impact energy would strike an ideal balance between safety and design. 1.3 Crash Test Data New cars go through several crash tests to determine the risk of injuries to occupants. The full frontal test is the most applicable to this project. The National Highway Traffic Safety Administration (NHTSA) performs this test as part of their New Car Assessment Program. In this test a vehicle crashes into a fixed barrier at 35 miles per hour, and a computer analyzes the effects on seat belted crash dummies. The results show high occupant decelerations as energy is absorbed by the front of the car. Table 1 shows deceleration data for various small cars, which the active bumper system would help the most. The decelerations from this test are simulations of head-on collisions with vehicles of the same size, with each traveling at 35 mph. If the other vehicle was larger or moving faster these values would increase. 1 Table 1 -Full frontal impact deceleration data [1] Deceleration Data from NHTSA Full Frontal Impact Tests (35mph collision into fixed barrier) 2004 Make & Model Driver's Side Chest Deceleration (g) Safety Rating (out of 5 stars) Acura RSX 2-DR. 43 5 BMW Z4 Convertible 46 4 Chevrolet Cavalier 2-DR.