In the tools menu of msmac3D we have the Lsqfit - A&B Coefficient Calculator (same program as discussed below)
and we have now added a link to it to the Ver 3.3 3DGraphics HELP Button with a direct link to the NHTSA CASH Test database
and all Tests are then listed:
Select a Test from the list of tests for the make/mode/yr/etc and then:
- From the datasheet take the average crush, test weight,
From the data on the sheet Record the following (numbers listed in red):
We also recommend you check the Sisters and Clones Database from Greg Anderson
- the average crush
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 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
- 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
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:
Note once again the fit is skewered
- 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