A dynamic four point bending test setup has been developed, which allows stable crack growth on notched asphalt concrete beams. The purpose of this setup is to be able to characterize the crack growth resistance of asphalt concrete mixes in the crack opening mode. The developed test is dynamic and force controlled, using a haversine force signal. Crack propagation was measured with crack foils, and was also calculated from the ripple amplitude of the measured compliance. The crack opening displacement was measured at the notch opening. The specimens were beams of dense asphalt concrete, sized 60x60x450 cubic mm. The experiments were performed at 0 centigrade and 30 Hz, at which the flexural tensile strength was (7 + 1) MPa, the stiffness modulus was 19 GPa, and the phase angle of the stiffness was 7 degrees. Notches of 5 mm deep or more acted as starter cracks. Stable crack growth was observed up to the last 10 to 20 mm of the beam. After that the crack growth became unstable. The conditions of the experiments were chosen to last between 1000 and 1000 000 load repetitions. The conditions for plane strain were fulfilled, and plastic deformation at the crack tip was not dominant. Thus linear elastic behaviour may be assumed. (A)
Abstract