Engineering & Crash Testing

1. Engineering & Crash Testing

2. Number one killer of teenagers: • Teen drivers have crash rates 3 times those of drivers 20 and older per mile driven. Immaturity leads to speeding and other risky habits, and inexperience means teen drivers often don't recognize or know how to respond to hazards.

3. Crash testing definition: • A crash test is a form of destructive testing usually performed in order to ensure safe design standards in crashworthiness and crash compatibility for various modes of transportation or related systems and components. (Wikipedia)

4. Types of crash tests: • Frontal-impact tests: which is what most people initially think of when asked about a crash test. These are usually impacts upon a solid concrete wall at a specified speed, but can also be vehicle-vehicle tests. SUVs have been singled out in these tests for a while, due to the high ride-height that they often have. • Offset tests: in which only part of the front of the car impacts with a barrier (vehicle). These are important, as impact forces (approximately) remain the same as with a frontal impact test, but a smaller fraction of the car is required to absorb all of the force. These tests are often realized by cars turning into oncoming traffic. Small Overlap tests: this is where only a small portion of the car's structure strikes an object such as a pole or a tree, or if a car were to clip another. This is the most demanding test as it loads the most force onto the cars structure at any given speed. These are usually conducted at 15-20% of the front vehicle structure. • Side-impacttests: these forms of accidents have a very significant likelihood of fatality, as cars do not have a significant crumple zone to absorb the impact forces before an occupant is injured. • Roll-overtests: which tests a car's ability (specifically the pillars holding the roof) to support itself in a dynamic impact. More recently dynamic rollover tests have been proposed as opposed to static crush testing (video).[1] • Roadside hardware crash tests: are used to ensure crash barriers and crash cushions will protect vehicle occupants from roadside hazards, and also to ensure that guard rails, sign posts, light poles and similar appurtenances do not pose an undue hazard to vehicle occupants. • Old versus new: Often an old and big car against a small and new car,[ or two different generations of the same car model. These tests are performed to show the advancements in crashworthiness. • Computer model: Because of the cost of full-scale crash tests, engineers often run many simulated crash tests using computer models to refine their vehicle or barrier designs before conducting live tests.

6. Computer crash simulation:

7. Crash test dummy: • The dummy's job is to simulate a human being during a crash, while collecting data that would not be possible to collect from a human occupant. • All frontal crash tests in the United States are conducted using the same type of dummy, the Hybrid III dummy. This guarantees consistent results. A dummy is built from materials that mimic the physiology of the human body. For example, it has a spine made from alternating layers of metal discs and rubber pads.

9. The dummies contain three types of instrumentation: • Accelerometers • Load sensors • Motion sensors

10. Accelerometers: These devices measure the acceleration in a particular direction. This data can be used to determine the probability of injury. Acceleration is the rate at which speed changes. For example, if you bang your head into a brick wall, the speed of your head changes very quickly (which can hurt!). But, if you bang your head into a pillow, the speed of your head changes more slowly as the pillow crushes (and it doesn't hurt!).

11. Load Sensors Inside the dummy are load sensors that measure the amount of force on different body parts during a crash. The graph above shows the force in Newtons in the driver's femur (the thigh bone), during a 35-mph frontal crash. The maximum load in the bone can be used to determine the probability of it breaking.

12. Movement SensorsThese sensors are used in the dummy's chest. They measure how much the chest deflects during a crash. The scan above shows the driver's chest deflection during a crash. In this particular crash, the driver's chest is compressed about 2 inches (46 mm). This injury would be painful, but probably not fatal.

13. Survival: • Obviously, the ideal crash would be no crash at all. But, let's assume you are going to crash, and that you want the best possible chances of survival. How can all of the safety systems come together to give you the smoothest crash possible? • Surviving a crash is all about kinetic energy. When your body is moving at 35 mph (56 kph), it has a certain amount of kinetic energy. After the crash, when you come to a complete stop, you will have zero kinetic energy. To minimize risk of injury, you would like to remove the kinetic energy as slowly and evenly as possible.

14. Survival, cont.: • Ideally, your car has seatbelt pre-tensioners and force limiters; they both tighten up the seatbelts very soon after your car hits the barrier, but before the airbag deploys. The seatbelt can then absorb some of your energy as you move forward towards the airbag. Milliseconds later, the force in the seatbelt holding you back would start to hurt you, so the force limiters kick in now, making sure the force in the seatbelts doesn't get too high. • Next, the airbag deploys and absorbs some more of your forward motion while protecting you from hitting anything hard.

15. Survival, cont.: • The most recent advancement in safety equipment is known as a smart air bag. These air bags can deploy with different speeds and pressures, depending on the weight and seating position of the occupant, and also on the intensity of the crash.

16. What are my chances of being seriously injured? • A lot of research has been done (and is still being done) to classify injuries. Crash-test researchers came up with a standard called the Abbreviated Injury Scale (AIS) for classifying different injuries. • Each injury is assigned a rank based on how severe it was: 1 is just minor cuts and bruises; 3 indicates a serious injury that requires immediate medical treatment and may be life threatening; 6 is fatal.

17. STAR Rating systems • Researchers have used crash test data to determine the likelihood of injuries that may be sustained in a crash. In addition, that data was used to create the NHTSA's star system. This system makes automobile safety ratings easier for consumers to understand when buying a car.

19. Engineers: • 1. What types of engineers would be involved in crash testing? • 2. What type of data would they collect? • 3. How would physics be used in these tests? • 4. What types of equipment would they use in these crash tests scenarios?

20. Your engineering challenge: • How would you design a crash testing simulation in the high school engineering lab? • What materials, models, sensors, data, etc. will you utilize? • What will you use for vehicles, track, wall, etc.? • What will be your testing constants. Variables? • How will you collect your data? • How will you interpret and present your data? • Design it, draw it and explain it using the above criteria.

21. Materials available in lab: • Knex • Legos • Pvc pipe • Hose, tubing, plastics • Pully, string, weights, etc. • Wheels, gears, motors, etc. • Lumber, plywood • Rubber bands, paper clips, clamps, etc. • Others available, please ask…