Scratch behavior of polycarbonate by Rockwell C diamond indenter under progressive loading

Rockwell C diamond indenter with a spherical tip of radius of 108 μm was used to slide on bulk polycarbonate under linearly increasing normal load from 5 mN to 20 N in order to investigate deformation and damage of ductile polymers during scratching. The peak value of the ratio of residual depth over penetration depth corresponds to a critical normal load, which can be used as the piecewise point for the subsection functions describing variation of tangential load, penetration depth and residual depth with normal load. The true adhesion interfacial friction coefficient was found to be 0.3 for contact between PC and diamond by three-dimensional model. Residual groove widths were found to be proportional to the square root of normal load, and provided useful information to characterize the radius of spherical tip. Values of fracture toughness of PC obtained by scratch-based methodologies under sufficiently large normal loads associated with brittle fracture and crack plane, are in excellent agreement with literature values. The material is under triaxial compressive stress state, making the flow and shear stresses much larger than the ones for uniaxial tensile test. •True adhesion friction coefficient can be obtained by three-dimensional model rather than two-dimensional model.•Fracture toughness of polycarbonate can be measured by scratch-based methodologies.•Scratch-based approaches of assessing fracture toughness of PC are only applicable under large loads.•The radius of spherical tip can be characterized by residual scratch groove widths.•Flow and shear stresses during scratching are larger than the ones for uniaxial tension.