m-smac Reconstruction Checklist
The following is a summary of ideas which should be considered as you setup a new m-smac accident reconstruction project.
• Collect all information, vehicle types, makes, models, scene evidence, damage measurements
• Create a scene diagram: Use a CAD program and save as a DXF file
o Import the file (Tools à Import à Import DXF) to convert a DXF file to a SCE type file
o You should save the CAD file as a DXF ver 12.0 prior to importing
• Vehicles setup
o Initial positions and velocities-
o From your scene diagram prepared above make note of the approximate initial X,Y, Psi for each vehicle.
• From simple conservation of momentum equations (programs like CRASH) determine a first approximation of the impact speeds.
• Damage –
o measure areas of damage (per SAE paper 880072)
o determine L, M, C1-C6
o input these on m-smac input card 80 and 85 for use as targets
• Vehicle weights and measurements
o From databases or other
sources -> medit32 Databases menu: 
• Determine the weight distribution and calculate the CG location (include estimate of occupants and cargo)
o calculate the CG location and inputs A, B, XF, XR, YS, etc.
§ see the SMAC Input manual for definitions of these inputs
§ medit32 Help->SMAC input Manual
o Most inputs for weight and dimensions are on input card 2 (veh#1) and input cards 3 (veh#2)
o Moments of Inertia
§ See the SMAC Input manual or McHenry Reconstruction book for approximation techniques
o Tire Cornering Stiffness
§ see SMAC Input manual for approximation techniques
§ first approximation use 16% of weight on tire
o Collision Model inputs: Crush Stiffness, Inter-vehicle friction, etc
§ Inputs on msmac Card 13 & 14
§ See SMAC Input Manual - section Parameter Estimation: Collision Model Inputs for additional information
o Obtain crash tests from the NHTSA Crash Test database or
§ the NHTSA website: http://www-nrd.nhtsa.dot.gov/database/nrd-11/veh_db.html
§ Use medit Tools – Lsqfit program to calculate A & B.
§ Generally start with B value for AKV
o Inter-vehicle friction
§ start with default value of 0.55
§ vary if vehicle interaction warrants
• sliding interactions may warrant lower intervehicle friction coefficient,
• override and/or ‘snagging’ interactions may warrant higher values.
• Note components of the vehicles “snagged” start by increasing the intervehicle friction and then test the use of the snag option
• Snag option inputs are on m-smac input card 16
• See SMAC input Manual section Parameter Estimation - Snag Option for additional information
o Friction coefficients
§ Roadway – per approximation tests or drag sled tests
o Braking, steering –
§ Setup impact configuration and/or run pre-impact maneuvers with approximations for steering and braking.
o Run through impact.
§ Vary pre-impact maneuvers to achieve a match of the general areas of damage
• Using the time of impact from the simulation, modify the braking and steering tables to introduce braking and steering effects produced by the collision interaction
The remainder of the task is to iterate to achieve an acceptable match of the measured damage areas, the evidence from the scene (tire marks,, etc.) and the approximate positions at rest.
Demos & Tutorials