  Stars grazing supermassive black holes (SMBHs) on bound orbits may produce
periodic flares over many passages, known as repeating partial tidal disruption
events (TDEs). Here we present 3D hydrodynamic simulations of sun-like stars
over multiple tidal encounters. The star is significantly restructured and
becomes less concentrated as a result of mass loss and tidal heating. The
vulnerability to mass loss depends sensitively on the stellar density
structure, and the strong correlation between the fractional mass loss $\Delta
M/M_*$ and the ratio of the central and average density
$\rho_{\mathrm{c}}/\bar\rho$, which was initially derived in disruption
simulations of main-sequence stars, also applies for stars strongly reshaped by
tides. Over multiple orbits, the star loses progressively more mass in each
encounter and is doomed to a complete disruption. Throughout its lifetime, the
star may produce numerous weak flares (depending on the initial impact
parameter), followed by a couple of luminous flares whose brightness increases
exponentially. Flux-limited surveys are heavily biased towards the brightest
flares, which may appear similar to the flare produced by the same star
undergoing a full disruption on its first tidal encounter. This places new
challenges on constraining the intrinsic TDE rates, which needs to take
repeating TDEs into account. Other types of stars with different initial
density structure (e.g., evolved stars with massive cores) follow distinct
evolution tracks, which might explain the diversity of the long-term luminosity
evolution seen in recently uncovered repeaters.
