Dynamic tensile strength of polyurea

Dynamic tensile strength of polyurea is measured at an ultrahigh strain rate of 1.67 × 107s−1by generating spall failures inside thick polyurea coatings bonded to steel plates using laser-generated stress waves of several nanoseconds in duration. Specifically, thick polyurea films were cast on a steel plate whose backside was provided with water glass–covered Al film. The Al film was melted by focusing a high-energy Nd:YAG laser pulse over 3-mm-diameter area. Exfoliation of the Al generated a compressive stress wave toward the polyurea coating, which turned tensile upon reflection from the free surface. At a threshold laser energy, the amplitude of the returning tensile stress wave exceeded the dynamic tensile strength of polyurea. The stress wave profile inside the steel plate was interferometrically recorded at the threshold laser fluence and was used in a wave mechanics simulation to calculate the peak tensile stress. The polyurea was modeled as a viscoelastic solid.