martellando literally means hammering, so I guess your notes should be strongly marked and detached. one of the pieces in my repertoire calls for martellando in a short section with very dissonant chords. i usually lift my hands high enough that when I drop and hit the keys, it sound as if i'm "hammering" down the notes. for that piece, i don't use the sustain pedal to achieve a dry, hammered effect. I guess you can use the pedal in other contexts to produce an "echoing" effect of the martellando.