Stiffness Coefficients a and B
Definition
Vehicle-specific constants derived from staged barrier crash tests. A is the force threshold below which no permanent crush occurs (N/m width). B is the slope of the force-crush relationship (N/m² of crush area). Both are published in the NHTSA crash test database.
- Coefficient A
- Force threshold below which no permanent crush occurs (N/m width)
- Coefficient B
- Slope of the force-crush relationship (N/m2 of crush area)
- Source
- Staged barrier crash tests
- Database
- Published in the NHTSA crash test database
Common questions
Why are coefficients A and B specific to each vehicle model rather than universal constants?+
They come from actual staged barrier crash tests of that vehicle, capturing its particular structural stiffness and crumple behaviour, so using another model's coefficients would misrepresent how much force it takes to produce a given amount of crush.
What happens to a crush-energy speed estimate if the wrong A and B values are used?+
Because the coefficients directly scale the relationship between measured crush depth and absorbed energy, using coefficients from a stiffer or softer vehicle than the one involved will systematically overstate or understate the calculated impact speed.
Related terms
- CRASH3
- Calspan Reconstruction of Accident Speeds on the Highway version 3: a mathematical model that relates permanent crush depth to absorbed energy through...
- Dynamic Crush
- The maximum deformation depth at the moment of peak force during impact, before any elastic recovery. Dynamic crush is larger than residual...
- Energy Equivalent Speed (EES)
- The speed at which a vehicle would strike a rigid fixed barrier to absorb the same amount of energy as observed from...
- Residual Crush
- The permanent, non-recoverable deformation depth remaining after the elastic springback of the vehicle structure. This is what is measured at the scene...
- SMAC
- Simulation Model of Automobile Collisions: a trajectory and damage simulation that uses CRASH3-type stiffness data to model full collision kinematics, including vehicle...