Owning to the lack of understanding of the polycarbonate sheet's shearing behavior, this research work focused on revealing the unstable cutting characteristics of a 0.5 mm thickness polycarbonate worksheet subjected to a straight punch/die shearing. Mechanical conditions (such as the tool clearance and feed velocity) of the shearing process were varied and investigated. Through the experimental results, it was revealed that: (i) an overlapping (negative) punch/die clearance was not suitable for burrless cutting of the worksheet. (ii) When using a positive 2-20% clearance, two primary cracks were initiated in the vicinity of the cutting tool corners, where only one of the two cracks was largely propagated into the bulk of the worksheet. This deviated propagation strongly deteriorated the quality of the sheared profile of the polycarbonate worksheet. (iii) The deviated propagation of the crack seemed to be affected by an in-plane/lateral unbalanced stress state in the worksheet. (iv) As the shearing velocity varied ranging from 0.05 to 1.0 mm s(-1), the characteristics of the cutting load resistance were slightly variant, while the velocity seemed to have almost no effect on the pattern of crack initiation and its propagation. Moreover, the shearing problem was numerically studied based on a two-dimensional finite element analysis method by varying the constitutive equation of the worksheet. In order to discuss about the crack propagation, a state of two dimensional stresses in the worksheet was simulated. (C) 2015 Elsevier B.V. All rights reserved.