A knife assembly comprising: a knife blade of which a front edge is a cutting edge, the knife blade being a corrugated knife blade comprising a corrugated part having a continuous shape defining a periodic pattern of peaks and valleys over a certain distance; a holder configured for supporting the knife blade ; a clamp arranged for clamping the knife blade onto the holder ; and a fastening mechanism cooperating with the holder and clamp for securing and clamping the knife blade to a clamped state in which it is clamped between the clamp and the holder with the cutting edge protruding at a front side of the knife assembly; the clamp having first clamping portions which are arranged along a first clamping line at a front side of the clamp and are provided for in the clamped state contacting the knife blade at a complementary contact line on the knife blade rearward from the front edge of the knife blade; characterised in that the clamp has an inwardly corrugated shape complementary to that of the knife blade and comprises second clamping portions , formed by inwardly bevelled parts of the clamp with a shape corresponding to complementary contact surfaces of the knife blade , the second clamping portions being positioned in a second clamping region which extends up to a distance rearward from said first clamping line and being provided for in the clamped state contacting the knife blade at the complementary contact surfaces, such that in the clamped state the clamp contacts the knife blade with the first clamping portions and the second clamping portions which together provide a contact over a width of the knife blade. a knife blade of which a front edge is a cutting edge, the knife blade being a corrugated knife blade comprising a corrugated part having a continuous shape defining a periodic pattern of peaks and valleys over a certain distance; a holder configured for supporting the knife blade ; a clamp arranged for clamping the knife blade onto the holder ; and a fastening mechanism cooperating with the holder and clamp for securing and clamping the knife blade to a clamped state in which it is clamped between the clamp and the holder with the cutting edge protruding at a front side of the knife assembly; the clamp having first clamping portions which are arranged along a first clamping line at a front side of the clamp and are provided for in the clamped state contacting the knife blade at a complementary contact line on the knife blade rearward from the front edge of the knife blade; characterised in that the clamp has an inwardly corrugated shape complementary to that of the knife blade and comprises second clamping portions , formed by inwardly bevelled parts of the clamp with a shape corresponding to complementary contact surfaces of the knife blade , the second clamping portions being positioned in a second clamping region which extends up to a distance rearward from said first clamping line and being provided for in the clamped state contacting the knife blade at the complementary contact surfaces, such that in the clamped state the clamp contacts the knife blade with the first clamping portions and the second clamping portions which together provide a contact over a width of the knife blade. <EOS>