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How cars are tested


Forum: Car Seat Safety

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July 15th, 2008, 05:51 AM
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Join Date: Sep 2005
Posts: 467
Most of us probably never put a lot of thought into what a car is going to do in a crash, and that has probably always been the case, even back when dashboards were heavy gage steel covered only with paint and seatbelts weren't even an available option. Fortunately, car makers do put a lot of thought into crash safety and so does the government who has a lot of regulations which every car design sold in the US must meet.

There are differences in terminology and even methodology between the different automotive manufacturers, but generally speaking here are the key milestones in the process:

1) Concept testing - the initial design is tested using some sort of basic mock-up of the design. Often the design may be changed in the proces of being tested to address any issues that might arise during testing.

2) Design testing - at this point, the design is usually intended to be the design that will go into production. The parts are made with prototype processes - meaning they are made in lower numbers using machines that aren't dedicated to making those parts, so it takes longer and at higher cost to make the parts.

Tooling to make parts in numbers for production are usually being made, but that tooling typically costs in the range of $60,000 to $250,000 for 1 tool to make usually 1 piece of the car, and can take from 6 months to 1 year to make.

3) Production testing - this level of testing is done to test parts made using the same tooling that will make the parts in production.

Two more things to know about testing in general:

Each test is usually done with a number of test samples, usually 3 at a minimum and often 6 parts or assemblies. This is done to establish a degree of reliability.

Testing for each stage is done at multiple levels, often each component is tested individually and as part of a complete vehicle... Quite often it will also be tested as part of a subassembly. A vehicle will usually go through a schedule of different tests, but component and assembly testing usually only puts a component or assembly through a single test that is intended to simulate the expected life of the car or some multiple of how many lifetimes the car is expected to live (usually 10 years is 1 life)

No test component will ever be used on a production car that is sold to the general public. Parts, cars and assemblies are kept for a specific period of time, such as 6 months, in case they are needed for analysis then they are disposed of as scrap metal (or whatever material they are made of.)

Federal Motor Vehicle Safety Standards (FMVSS)

Here is NHTSA's page listing what the various FMVSS are, they cover crash avoidance, crashworthiness, post crash standards and other regulations - such as fuel economy.

http://www.nhtsa.dot.gov/cars/rules/...VSS/index.html

One that I dealt with a lot while I was working on convertible tops (which would relate to anything in the interior of the car) was FMVSS 302 - flammability of interior materials. It specifies burn resistance and is intended to prevent deaths and injuries from vehicle fires, including ignition sources like matches and cigarettes.

FMVSS 572 specifies crash test dummies, specificly an average male, a 6-year old, 3-year old, 9-month old 6-month old and newborn infant.

FMVSS 213 specificaly relates to child restraint systems.

Crash testing

This is usually done on more than one vehicle, with one vehicle used for one test. Test engineers may spend weeks placing sensors on the vehicle. Crash test dummies are usually reusable and are themselves loaded with sensors to measure the movement at many of their joints, which are pretty close to the human skeleton, and measure pressure at critical points which may be impacted in a crash.

Each test is recorded on multiple cameras to capture different view angles, each camera may be recording 100 frames every second.

There are crash tests to simulate a head-on collision, rear collision, side collision, roll-over accidents.. Usually the most damaging test is the offset barrier test, where the car collides with a hard object hitting half of the front of the car.

These tests are being done on basicly new cars. Vehicle testing does not usually involve crash testing anything that would represent an aged car. For the most part, this isn't a concern on newer cars or cars up to 10 years old because they are coated and designed with drainage to prevent corrosion that might deteriorate a car's crashworthiness, but extreme conditions might result in rust that would make a car less safe - but that degree of rusting out would be pretty obvious to most consumers.

Toyota had some SEVERE problems with that on their trucks, and they have a silent recall program in place to buy back rusted out trucks from a certain timeframe.

About computer analysis

Finite Element Analysis is a computer method or analysing the strength of a part under predicted loading conditions. It is a method that is used to refine designs so that the number of design changes needed before a part will pass a test is fewer, but on a new vehicle this is not used as a substitute for testing. Some late design changes, such as cost reductions, may utilize computer analysis in place of testing, but this is only utilized when the computer analysis can show the part will perform as well or better than a previous design that has already passed testing.

How FEA works is this: In its simplest form, pulling on a bar of metal with a certain load creates a certain amount of stress. If the stress is higher than the metal can stand, it will stretch then break. FEA simulates a part with a whole bunch of pyramids interconnected, and each edge of the pyramid is like one of these bars of metal. There may be thousands to hundreds of thousands of elements in a part, and if you've been through algebra and tried to solve a simple quadratic equation with 3 terms... Solving a stress problem with hundreds of thousads of elements is that much harder.

The output is in the form of a picture of the part color coded by stress levels, usually red is the highest stressed area and this is what is looked at in terms of how high the stress is and where it is located.

Some historical notes (don't read this part while you're eating)

Crash testing has been around longer than crash test dummies, and crash test dummies have helped a lot to improve the understanding of how a crash affects a passengers. Before there were crash test dummies, crash testing was done using cadaevers.

If you've seen the movie "Tucker" the attitude towards safety of the '50's is probably accurately displayed. There was a genuine concern that putting safety improvements in cars would create a perception that they were unsafe. When Ford began a safety campaign in 1956 to offer optional safety equipment like lap belts and padded dashboards... It didn't really sell that well.

I've had a 1955 Ford, and the 1956 Ford dashboard is pretty much the same, except that it had the option of having a 1/4" foam pad covered by vinyl on top of it... It really was more show than real protection as you'd still be hitting your head on a piece of steel...

As a show of how strong the '55 Ford dashboard is, I onced dropped a 35 lb iron engine head on it from a 3 foot high workbench. It didn't dent.

My dad once told me a story of how his dad took him to see a crashed '55 Ford at an impound lot. It had struck a bridge abutment at 100 miles per hour, and there wasn't exactly enough space anymore between the seat and the dashboard for a person.

Modern crashworthiness advances allow Formula 1 drivers to walk away from 100 MPH + crashes with walls with sprained ankles (or be carried away with broken ankles, but at least very much alive.) Maybe race car technology is the next level and passenger cars aren't quite there, but we've come a long way for understanding crashes and minimizing injuries in the past few decades.
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