What is the CRASH Energy Correction Factor (ECF)?

Questions/Topics Related to the CRASH computer program
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brian
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What is the CRASH Energy Correction Factor (ECF)?

Post by brian »

Q: What is the Energy Correction Factor (ECF) used in Damage Analysis?
A: Crush properties of vehicles are measured and fitted for crush directions that are perpendicular to the involved end or side of a vehicle. However, in an oblique collision, a component of the tangential friction force acts to increase the effective crush resistance in the direction of crushing and thereby, the absorbed energy. Therefore, an Energy Correction Factor (ECF) is needed for applications of crush coefficients to oblique collisions.
For further information, please see the section on Energy Correction Factor(ECF) from our book McHenry Accident Reconstruction.
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MSI
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Re: What is the CRASH Energy Correction Factor (ECF)?

Post by MSI »

Q: I want to ask you a question about CRASH3 algorithm. There is a correction factor in CRASH3 ( 1+ tan^2. alpha). Is the alpha angle PDOF angle here? It is limited to 45 degrees to make the factor maximum 2. If it is PDOF angle, can we say that PDOF angle is limited to 45 degrees? Because i saw it can take higher values in planar impact mechanics applications of Brach.
A: Alpha is "the angle of crushing relative to a perpendicular to the involved end or side of the vehicle". It may be the same as PDOF, but for example, in side impacts Alpha is adjusted by 90 degrees. The limitations of 2 is for the correction factor based on Alpha and not on the angle Alpha.
From one of our recent publications on ECF
  • "On the basis of a recognition of the limitations on energy absorption that are imposed by realistic levels of tangential friction, a revised form of the ECF was proposed in 1986. Applications of the ECF since that time have generally been restricted to the angular range of ± 45 degrees so that only a limited evaluation of the effects of the revised ECF was possible"
Also see our related discussions on With respect to Brach do you mean Brach values for PDOF? Or some suggestion for correction factor that Brach suggests? And could you please provide an example as in what reference and on what page?
Please also see Some Momentum Misconceptions for limitation of momentum and planar impact mechanics which include simplifying assumptions such as instantaneous exchange of momentum, etc.
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Re: What is the CRASH Energy Correction Factor (ECF)?

Post by MSI »

Q: In planar impact mechanics spreadsheet in the Brach book "Vehicle Accident Analysis and Reconstruction Methods", there are PDOF angles, not correction factors. For example, in that example PDOF 1= -1.5 degrees and PDOF 2 = 65.5 degrees. Thats why i asked if PDOF is limited to 45 degrees in CRASH 3. Because when we take that alpha angle as PDOF and use 65.5 degrees for ECF, it is higher than 2.

A: There is no limit on the Alpha angle in CRASH. However, the maximum ECF is limited to 2.0. So if the angle produces an ECF greater than 2.0, simply use 2.0.
In the example you cited in the Brach book (p 160, 161) the comparison of CRASH3 damage (uncorrected for tangential impules) with his Planar Impact mechanics calculations is rigged!

For additional detailed informaiton, please see our topic
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Re: What is the CRASH Energy Correction Factor (ECF)?

Post by MSI »

Q: And one more question: how is the alpha angle defined? It seems hard to define it according to the figure in The Algorithms of Crash, page 28 (see below), moment arms of resultant collision force'
A: Alpha is basically the PDOF. Internally in CRASH3 it is based upon the PDOF. The only adjustment is that for side impacts where the perpendicular is other than 0 degrees. The adjustment is that the angle must be normalized such that it is relative to the perpendicular to the end or side of 0 degrees. So for example a side impact with a PDOF of 100 degrees would have an Alpha of 10 degrees (100-90).
crash p28.jpg
crash p28.jpg (40.61 KiB) Viewed 4800 times
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Re: What is the CRASH Energy Correction Factor (ECF)?

Post by MSI »

Q: In this ECF thread you mention "Looking at the Brach book Table 6.2, the listing for the RICSAC staged collision analysis, the value for MU for identical impacts varies arbitrarily" and also present values for RICSAC 9 from the book in Figure 7.14, p 145 and Figure 7.13, p 142.
I currently do not have the book, can you provide those tables?

A: Yes
We have posted them to our Topic Planar Impact Model Assumptions
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Re: What is the CRASH Energy Correction Factor (ECF)?

Post by MSI »

The Brach book was updated to 2nd edition (edition 1 2005, edition 2 2011)
No changes w/r to posting above.
For additional information please see Topic Planar Impact Model Assumptions
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Re: What is the CRASH Energy Correction Factor (ECF)?

Post by MSI »

Some subject material from replies moved to other subjects to streamline information.
See posts above with related new links.
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