L'articolo consigliato, che costituisce lo standard ISRM attuale; tende a confermare le mie precedenti osservazioni sul preferibile utilizzo di 2 tipi di martelli per diverse tipologie di rocce.
Aydin A. 2009. Suggested method for determination of the Schmidt hammer rebound hardness: Revised version.
Int. J. Rock Mech. & Mining Sci. 46, 3, 627-634
The earlier ISRM suggested method [1] endorsed the use of
only the L-type SH. However, for a given plunger tip diameter
and radius of curvature, the impact energy of the SH
determines its range of applicability. Accordingly, this
limitation should be kept in mind in selecting the hammer
type. For instance, the standard L- and N-type hammers, with
respective impact energies of 0.735 and 2.207Nm, should be
used with caution when the UCS of the rock material or
discontinuity wall is outside the range of 20–150MPa, where
sensitivity decreases and data scatter increases. The N-type
hammer is less sensitive to surface irregularities, and should be preferred in field applications; while the L-type hammer has
greater sensitivity in the lower range and gives better results
when testing weak, porous and weathered rocks.
