*This is a very preliminary writeup*

- NOTE: If you don't have our msmac3D software, Please also see the post below which includes links to directly get the NHTSA crash test data and HOWTO calculate the A&B Coefficients

We have a link in the 3D Graphics HELP Button to direct link to the NHTSA CASH Test database

- If from
**Medit3D**:**Tools menu**of msmac3D we have the**Lsqfit - A&B Coefficient Calculator**(same program as discussed below)- Menu item
**Databases**and select**NHTSA Crash Tests**which brings up the test selection menu (on Left see below) which allows you to select Make, then Model, Then Year

- From the datasheet take the average crush, test weight,

From the data on the sheet Record the following (numbers listed in red):- the average crush
**C1,C2,C3,C4,C5,C6**

Add these 6 crush measurements and divide by 6

- the
**Veh Speed**Test Impact Speed - The
**Weight**aka Test Weight - The
**LENCNT**aka Length of Contact- for some reason they don't present in inches in () like other nums, so simply divide by 25.4

- The
**Test#**aka Test number - Note that if photos, videos, reports available these buttons will activate you can review them/collect them/etc

We also recommend you check the Sisters and Clones Database from Greg Anderson- We have an older version of that Sisters Clones Database available if you pop out to Medit3D Grid: Database Menu->
It is probably 10 or so years old so for vehicles made in past decade and for refinements of the database please consider a subscription to the Sisters and Clones database

- the average crush

- An instructional video on the LSQFIT will be posted and linked here soon

We selected the 1985 Ford Escort

- From the Prasad SAE 900412 Report A Study Using the Repeated Test Technique
- one of the datapoints was bad (50 mph/50 inches) or simply skewered the results (see below for details)
- We added 3 more tests from 81-84 which the sisters & Clones Database said are the same body

And the chart created and A,B CRASH3 Coefficients and also AKV Stiffness were as follows:

CRASH was developed as a preprocessor for the SMAC simulation program

To Help NHTSA with their statistical NASS study get starting speeds for SMAC

NHTSA Later adopted CRASH since 'the errors will wash out in the large sample size' and that they were 'looking for trends'

However now CRASH and damage analysis have been used in individual crash reconstrctions

Reasons to be cautious when using CRASH or other damage analyses:

- Most CRASH or damage analysis techniques are based on a single data point and assumption of 'no-damage' intercept
- Be sure to check the source of the data for any crush coefficients you use
- below we present the data for a 1985 Ford Escort
- Some of the data was first presented by Prasad SAE 900412 Report

First a summary of what would be the Crash B coefficient (and corresponding AKV for SMAC) with the data as presented and then dissected:

- Note that these charts and comparisons demonstrate how depending on a single crash test and assumption of 'no damage' intercept may produce very different results for a vehicle's CRASH3 A&B Coefficients virtual crush stiffness .

And realize that most Crush Coefficients sold are based on a single Crash Test at approx 35 MPH and then an assumed 'no damage' intercept.

More write up on this will follow in the next week or so

this first collection from the Prasad SAE 900412 Report has an outlier (the green dot on chart behind data) which skewers the fit away from the other points:

Here is what the fit looks like if you remove that outlier:

Next we added the extra crash tests (sisters/clones of the test vehicle) but again with the outlier (green dot on chart behind data)

Note once again the fit is skewered

And now with that outlier removed, note how much better the least square fit matches the data

Now we simply go with 'what if only single tests available (we found 3):

We do it again with a low speed test from that Prasad paper:

These next 3 are what if only 1 test available for the Escort?

- And which test?
- and how much do the A/B fits change?

- This demonstrates the sensitivity and possible changes in the A & B CRASH3 Coefficients depending on test results
- and why it is important to use MORE than a single test and an assumption for the 'no damage' intercept!

Below you see depending on which individual test is chosen (or if only one ran, which one?)

the CRASH3 A & B Coefficients would be:

If based on all 3 tests:- NHTSA 3 Test: A = 213 lb/in^2 B = 58 Lb/in

- NHTSA 3 Test and Low speed Test: A = 207 lb/in^2 B = 64 Lb/in

- NHTSA Test #407: A = 188 lb/in^2 B = 55 Lb/in
- NHTSA Test #452: A = 221 lb/in^2 B = 63 Lb/in
- NHTSA Test #509: A = 190 lb/in^2 B = 70 Lb/in

Below are the individual fits: