( 1+\beta^{-2} \right )$$" style="width:284px;height:30px;"></p><div><ul><li><b>Equivalent time</b>:</li></ul></div><p><img src="ContactForceN_ElastoPlasticLinear_eq04386676940021557440.png" alt="$$K_{n} = 1.198 \left ( \dot{\delta}_{n}^{0}R_{eff}E_{eff}^{2}\sqrt{m_{eff}} \right )^{2/5} \left ( exp \left ( -\frac{tg^{-1}(\beta)}{\beta} \right ) \right )^{2}$$" style="width:359px;height:40px;"></p><p>The unloading stiffness coefficient <img src="ContactForceN_ElastoPlasticLinear_eq06940021353607503515.png" a