DISCUSSION: Friction decrement with speed

In general, on wet surfaces, the effective tire-surface friction coefficient decreases with speed and c_μ (card 12:field 7) can be used to simulate the decrease. The effective friction coefficient, used in all SMAC calculations, is computed as:

                    μ_effective = μ₀ - μ_{0 *} c_{μ *} |v| 

where :

μ₀ =the nominal coefficient of friction, and  |v| =the absolute value of the tire speed in inches/sec.

Some manuals for other versions of SMAC have recommended the use of a value of C_μ=0.0003 sec/in. This value should not be used for dry pavement. The use of this value for dry pavement results in the following μ_effective for a μ₀₌0.70:

          Speed in MPH              XMU                              Speed in MPH              XMU

                    0                         0.70                                   40                        0.55

                   20                        0.63                                      60                        0.48

For dry pavement applications a reduction in the effective friction coefficient is normally not as apparent as in wet road applications.

Therefore, for dry pavement, normally you should set C_μ=0.0.

NOTE: An additional option of different CMU form Vehicle 1 and Vehicle 2 has been added. Simply set CMU2 = some value other than 0.0 and it will set CMU2 for ONLY Vehicle 2. CMU will then be used ONLY for Vehicle 1.

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Collision Model, Crush Properties