The accelerated mechanical fatigue performance for sinusoidal horizontal oscillations (at the natural frequency of the flexible post-delineator test specimen, 16-in. Free length) was investigated for four types of post delineators. One was an x-shaped post made of polycarbonate material, two were fiberglass-reinforced thermoplastic posts (t- and c-shapes) and the other was a round polyethylene tube. Three test specimens were tested for the following post conditions: new post, post put into the ground and driven over once with the rear-tire of a slow-driving tractor, post driven over twice (in same direction), and post driven over three times (in same direction). The results indicate that the x-shaped polycarbonate material post breaks off after a relatively low number of cycles (fewer than 150, 000), whereas the two fiberglass-reinforced posts survive 5 million cycles and show moderate damage (cracks) and do not show an excessive static horizontal deflection when subjected to a 1.5 Kg (14.7 Newtons) horizontal pull force. The round polyethylene post also survives 5 million cycles and on some test specimens shows a few cracks on the portion of the tube that is inside the holding fixture. For all four post types tested, there appear to be rather small detrimental effects related to the number of times a post was slowly driven over and its subsequent fatigue performance at 5 million cycles. Based on the test results, it is recommended that 16-in. Free length post delineator test specimens (at least 3 specimens per type of post) be tested and that they be subjected to a minimum of 5 million cycles. If all three specimens survive the 5 million cycles (not broken) and their horizontal static deflection (1.5 Kg) is less than 2.5 In. (16-In.Free length), the post type has passed the accelerated mechanical fatigue evaluation test.
Abstract