Refinement of DeltaV in CRASH damage analysis

Questions/Topics Related to the CRASH computer program
#CRASH #EDCRASH #PC-CRASH
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MSI
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Refinement of DeltaV in CRASH damage analysis

Post by MSI »

The McHenry Team remain scientifically tinkering on many things and are in the process of soon making some refinements to the DeltaV calculation procedure for the CRASH damage analysis.
The following is an introduction/abstract:

ABSTRACT:
  • In statistical investigations of injuries and exposure in automobile collisions (like NHTSA's NASS which is now renamed CISS), it has long been recognized that the best measures of exposure severity are the direction and magnitude of the Impact Speed Change (DeltaV) of the collision. Most investigations of highway accidents for statistical studies like NASS do not have access to detailed scene data (e.g., positions and headings at impact and rest, tire and gouge marks, ets.), and so the measurement and interpretation of damage dimensions constitutes the most readily available and often used basis for estimation of the directions and magnitudes of the DeltaV for those statistical studies.

    The original CRASH program (1976) constituted an early effort to obtain uniform estimates of DeltaV on the basis of Vehicle damage for use in the NHTSA statistical studies.

    Fast forward 45+ years later and the CRASH damage analysis procedure has been widely misused in litigation related individual case reconstructions. While there has been an abundance of published criticisms of the early forms of the CRASH program over the past 45+ years (for example see related forum topic) , there have been no significant refinements in the analytical approach or improvements of the accuracy of the damage analysis procedures marketed and used by crash investigators, police, etc.:
    • The main ‘refinements’ to CRASH have been a “reformulation” by NHTSA which was mainly to create a separate program (WinSMASH) used ONLY by NHTSA and so no harassment and subpoena's from the litigation circus. The WinSMASH program damage analysis is essentially the same as the CRASH program except for using individual vehicle 'crush coefficients':
      • NHTSA created an online crash test database of mainly 35 MPH NCAP barrier crash tests.
      • NHTSA also performed a number of multiple impacts on vehicles to try to better define the crush properties of some vehicles over a range of speeds.
        • HOWEVER, there have been no refinements of the underlying analytical foundations of CRASH aside from the “reformulation” which was essentially simply changing the variable names.
      • In 1997 we published 4 papers (which all made SAE transactions as top 10% papers for that year) and one included suggestions for refinement of CRASH to address restitution.
        • The paper received unwarranted and erroneous pushback from the members of the cottage industry selling clones of CRASH and crush coefficients for CRASH and so we temporarily abandoned our pursuit of improvements of CRASH damage analysis for the past 25 years (we've had more important things to do than waste time trying to educate stubborn mules)
      • Other attempts at refinement of the CRASH damage analysis method have been random and arbitrary such as:
        • ‘airgap’ approximations and adjustments based mainly on 'photographs??!' by commercial crush coefficient vendors with no objective scientific basis.
        • Papers suggesting arbitrary and subjective "crush stiffness zoning" on vehicles with NO supporting crash tests data for 'zones' and so it thereby creates an arbitrary and subjective attempt at a solution procedure. (links to follow)
    Our current efforts are aimed at scientifically and objectively updating the CRASH damage analysis procedure to improve the accuracy of the DeltaV of damage analysis on the basis of a 'hands free' analytical approach:
    1. Modifications to insure force equilibrium at the time of peak force
    2. Refinements in the definition of the impact configuration on the basis of the damage centroids and the Principle Direction of Force (PDOF)
      • While comparing and averaging the centroid the collision partners at an approximated separation positions and orientations to insure coincident exchange of momentum between the vehicles
    3. Addressing the effects of induced damage introduced for offset collisions
      • Approximating the additional energy which is required to induce significant induced damage
    4. Checking the compatibility of the reported residual crush values and making automatic adjustments where necessary.
      • Automating the adjustment process based on a scientific basis to remove subjectivity from the process
    5. Checking the elastic ranges of input crush properties and making adjustments, as required, to be realistic.
    6. Restitution effects will be included in the refined DeltaV calculations.
We expect to publish some additional information and a scientific paper in the near future. Stay Tuned!
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