In this paper, we describe the three-dimensional effect of a blade line end on the pushing shear of paperboard. In order to reveal the deviation of cutting line force caused by the strain constraint of the unseparated zone, the relationship between the cutting line force and the indentation depth of a blade was experimentally investigated by varying the tip thickness of the blade, the length of the blade, and the length of the unseparated zone of paperboard. The following results were obtained. (1) The first peak (or inflection) of line force fC1 tends to decrease in a certain range of unseparated-zone length a and a certain range of blade-tip thickness w, while fC1 is almost constant with a in the case of a sharp blade. (2) The second peak of line force fC2 is increased in a certain range of a. (3) A formula of the approximate relationship of fC2 with respect to the blade length was experimentally derived.
