**Q: Could you answer my following questions? These questions concern car accident.**

Pictures are enclosed to this e-mail. I'll be grateful for your answer.

1. Program Crash3 assumes, that the profile of deformation (the width and depth of deformation) of car body has to be uniform in vertical direction. Does Picture 1 depict this properly?

Pictures are enclosed to this e-mail. I'll be grateful for your answer.

Pic. 1. In accident which interests me, large truck (weight about 43 mT = 43 000 kg) struck at passenger car.

Picture 2 shows the real appearance of damages of passenger car. Sill and floor were deformed partially (they slipped under the truck). Wheels were separated.

Pic. 2. Is following equation (1) valid in this case (this is equation 2.48 from “Crash3 Technical Manual”)?

Can we use damage profile, as shown in Picture 3 (hatched area)?

Are the coefficients of stiffness (A [lb/in] and B [lb/in2]) still valid?

Equation (1) Pic. 3. 2. To which Vehicle Class Category of passenger cars belongs AUDI 80 B3 (according to SAE 960897)?

3. In “Crash3 Technical Manual” you use unit lb. Is this the unit of mass (pound), or is this unit of force (pound multiplied by gravitational acceleration)?

**A: First realize that CRASH3 was developed as a pre-processor for the SMAC program and so there are a lot of simplifying assumptions (as with any mathematical model)**

When Ray McHenry/Calspan delivered SMAC to NHTSA they couldn’t come up with an initial speed, so Ray developed CRASH which NHTSA embraced as adequate for their statistical studies where the possible errors wash out in the sample size.

Fast forward 40 years and today folks consider damage analysis as a bonified crash reconstruction tool and make erroneous statements about it’s accuracy.

The original crush tables (A,B) were based on a small sample of crash tests.

Today generally folks try to find actual tests of a vehicle or a ‘clone’ (similar) vehicle to base their A&B crush coefficients on.

We of course caution that A& B coefficients based on a single test do not constitute a scientifically accurate technique and so should be used only as a first approximation method and then other techniques (combining trajectory AND damage like with SMAC) provide a better technique.

Here are a few forum topics on the subject

- What Speed should I Use to Calculate CRASH3 A&B Coeff?
- Should a CRASH type damage analysis include induced damage?
- Review of CRASH Damage analysis and the NHTSA "reformulation"
- Magnification Factor v Energy Correction Factor

With that said, the following are answers to your specific questions:

1. Program Crash3 assumes, that the profile of deformation (the width and depth of deformation) of car body has to be uniform in vertical direction. Does Picture 1 depict this properly?

**Yes your picture is approximate. Of course you are showing a side impact where some of the limitations of CRASH3 are most apparent due to the wide variation of the approximate crush stiffness if the sill or the wheels are included in the impact.**

Picture 2 shows the real appearance of damages of passenger car. Sill and floor were deformed partially (they slipped under the truck). Wheels were separated. Is following equation (1) valid in this case (this is equation 2.48 from “Crash3 Technical Manual”)? Can we use damage profile, as shown in Picture 3 (hatched area)?

Are the coefficients of stiffness (A [lb/in] and B [lb/in2]) still valid?

**The coefficients in the CRASH3 tables were created in the 1970s (during the crash3 update and some issues are in the tables)**

See Where can I find the RICSAC crush measurements?

**See answer above. Tables based on wheelbase so compare in table.**

3. In “Crash3 Technical Manual” you use unit lb. Is this the unit of mass (pound), or is this unit of force (pound multiplied by gravitational acceleration)?

**lb = pounds is weight which INCLUDES the gravitations acceleration.**

If Mass used it does not include gravitational acceleration.