Direct extraction of rate-dependent traction–separation laws for polyurea/steel interfaces

Polyurea coatings on steel form tough, flexible and chemically resistant surfaces, making them ideal for a variety of applications. An important issue for polyurea coatings in some cases is their adhesion to steel under various loading conditions in aggressive environments. In this paper, adhesion was examined using steel/polyurea/steel sandwich specimens and interfacial fracture mechanics. The mode 1 and mode 2 interfacial fracture behaviors were characterized by two independent traction–separation laws. The traction–separation laws were measured directly by recording the J-integral and the end-opening displacement in the directions normal and tangential to the steel/polyurea interface. In each case, the traction was initially nonzero, increased with increasing separation, reached its peak value and then decreased with further increasing opening. Strong rate-dependent effects were found for both modes of fracture and were attributed to the interfacial behavior. Porosity introduced during the processing of the polyurea affected the traction–separation laws and associated fracture mechanisms.