There are a limited number of ways an edge blow can be effective against plate armor, and an account of a deed of arms at Noseroy in 1519, comprising some fifty encounters at the barriers, illustrates them.
It is just barely possible for a sword to cut through a helmet under optimal conditions “…there was given a stroke of the sword on the crest of an armet that opened it to daylight.” This was a single handed sword stroke. Cutting through a helmet, however, won’t necessarily injure the wearer. The edge not only has to penetrate, but create a long enough cut to reach flesh beneath. This is immensely difficult. Modern examples of test cutting with Japanese swords demonstrate that a two handed grip, windup from a position behind the wielder’s back, and a rigidly braced helmet are required to make a record breaking cut 13 cm long. Even an impressive cut like this may not be sufficient to let the blade reach flesh, depending on the shape of the helmet and the amount of space provided by the padding and suspension system within it.
Cutting metal can actually be counterproductive in terms of the damage done to the opponent, since much of the force of the blow is expended in making the cut, leaving less to be transferred to the target as shock and momentum.
Gauntlets are much more vulnerable to cutting. The plates are thinner and there is little air space and padding between them and the hand. Further, some types of gauntlets protect the fingers with overlapping scales riveted to leathers. It is possible for a blade to slip between the scales and cut the fingers even if the scale is not penetrated.
“Jean de Chantrans of the enterprise fought two and did not fight any more, because he was wounded in the hand.” Also, there were many other “gauntlets cut and many wounded in the hands to the effusion of blood.” These injuries were all done with two-handed swords.
Arms are another point of potential vulnerability, although less so than the hands. The plates of a vambrace are often relatively thin compared to the helmet or breast, and a relatively short cut to the forearm could reach flesh. Claude d’Anglure was wounded in the arm “to the effusion of blood” by a single handed sword stroke. It’s possible, however that the stroke was a thrust to the inside of the elbow, and his was the only arm wound reported.
A sword doesn’t have to cut to be effective. During the fighting with two handed swords there were “many basinets and armets driven in.” A deeply dented helmet can be driven into the wearer’s skull, and even if the helmet isn’t dented enough force can be transmitted through the padding to stun or worse. Claude de Vienne was wounded in the head “to the effusion of blood” by a single handed sword stroke. Fighting with a two handed sword the count de Bussy “gave such a stroke to (Jean) de Falletans, on the armet, that he kneeled in the sand.” The prince d’Oranges “gave a stroke of the sword on the crest of the armet of Phillipe de Falletans so that he had to take three steps back from the barrier and was unable to fight any more that day.”
Likewise, a non penetrating blow to the gauntlet can deliver enough force to injure the hand within it. The small plates of gauntlet fingers don’t spread the force of a blow over a very large area, and finger plates and scales don’t seem to have had any padding beyond that provided by the leathers they were riveted to.
Finally, an edge blow can be effective not by injuring an opponent directly, but by damaging his armor. During the combat with two handed swords many guardbraces were “avalez” or “swallowed”. This word is also used in medieval French to describe hose rolled down below the knee. If the lace or strap that supported the top of a guardbrace was cut or broken, it would tend to slide down onto the rest of the armharness, and “avalez” would be an apt term for such a failure. This would not only leave the shoulder vulnerable but seriously impede free movement of the arm.
An edge blow could be effective against an opponent armored in plate if it was properly aimed. At Noseroy, the points of vulnerability were heads, hands, and to a lesser extent arms. Because the combats were fought over waist-high barriers they do not show to what extent legharness might or might not be vulnerable to edge blows.