  In this study, we numerically investigated the mechanical responses and
trajectories of frictional granular particles under oscillatory shear in the
reversible phase where particle trajectories form closed loops below the
yielding point. When the friction coefficient is small, the storage modulus
exhibits softening, and the loss modulus remains finite in the quasi-static
limit. As the friction coefficient increases, the softening and residual loss
modulus are suppressed. The storage and loss moduli satisfy scaling laws if
they are plotted as functions of the areas of the loop trajectories divided by
the strain amplitude and diameter of grains, at least for their small values.
