Stiffness Coefficients

[nseisel]

I am a newly certified reconstructionist. My training was conducted by a local police department with most of the topics taught by IPTM. One concept we did not dive into very much was calculating stiffness coefficients for crush profiles. A and B values are the ones I am struggling with. I can get G values based on A and B values just fine. Can anyone point me in the right direction of being able to do this?

[mchenrysoftware]

It is pretty straight forward
i have a page on our McHenry Forum

• HOWTO Calculate CRASH3 A & B Coefficients, AKV (for SMAC)
  Which includes the steps to calculate A & B
  I note it uses tools in our msmac3D software
  For those without the msmac3D software I will edit and add instructions on how to retrieve NHTSA Crash Test Data for ANY vehicle from the NHTSA online crash test search engine and then HOWTO calculate the A & B Coefficients.

Main point is to get all related crash tests (and sisters and clones)
and then do fits on each all together and see if any outliers, etc. etc

Our McHenry Forum also has a lot of information on Damage analysis
see

• CRASH, Damage Analysis
  Includes detailed information on damage analysis (not just CRASH!)

• 
  Crash Reconstruction Topics
  All things related to Crash Reconstruction

Let me know if any additional questions

Brian
McHenry Software

[mchenrysoftware]

OK added the instructions, please see:

• Additional Instructions for A&B Calculations
  for folks without msmac3D software

[nseisel]

Thank you for the timely reply.

If I do not have access to these software programs, do you know of an actual list of formulas I can use to calculate values for b1 and then A and B?

The formula used by IPTM is as follows:

DeltaV= change in velocity
b0= zero crush speed (in/sec)
L= overall length of crush (in)
W= weight (lbs)
G= gravity (in/secsquared)

b1= (DeltaV - b0)/ L = (1/sec)
A= (W x b0 x b1)/ (G x L) = (lb/in)
B= (W x b1squared) / (G x L) = (lb/ insquared)

Does this seem correct?

[mchenrysoftware]

Ooops!
Thanks for the reminder.
I forgot to also include the conversion factors for going from the Least Square Linear fit b0 & b1 (Campbell) to A & B (Crash)
Same as the IPTM you mentioned
see:

• Crush Coefficients Conversions: CRASH (McHenry), Campbell, WinSMASH (Prasad)

[nseisel]

Okay, good to know I was doing it correctly by hand. Thank you for your help!

[Lasaman]

tagging along this topic on stiffness coefficients...

I came across an opposing expert who presented some stiffness coefficients (A & B) for semi-trucks with no reference.
I have not seen any published studies for stiffness coefficients (A & B) for semi-trucks.
He is an ex-MAIT officer, so I have to ask, is there some police cheat sheet that they use?

Thank you.

[mchenrysoftware]

here's a related topic
Truck Crush Properties

brian

[Lasaman]

Thank you sir.

[Hebert]

tagging along this topic on stiffness coefficients...

I came across an opposing expert who presented some stiffness coefficients (A & B) for semi-trucks with no reference.
I have not seen any published studies for stiffness coefficients (A & B) for semi-trucks.
He is an ex-MAIT officer, so I have to ask, is there some police cheat sheet that they use?

There were some SAE papers that suggested some pretty generic numbers (i.e.: 960897 "Updating vehicle Class Categories" by Sidall and Day) which included "Generic Data for Trucks and Dollys" as well as another table for "Trailers and Barriers." Far from being a "police cheat sheet," this came from a paper published by the Society of Automotive Engineers. If there Is a "police cheat sheet," it's most probably some sort of generic "rule of thumb" nonsense and is likely followed by more than just police reconstructionists.

In my experience, those are mostly, as the name implies, pretty generic approximations. I haven't seen any sort of meaningful specific stiffness data based on actual tests such as one might find for a passenger car either.