Laminates containing 25 percent of tough (unaged) maraging steel plates and 75 percent of brittle (aged) maraging steel plates were prepared by a special diffusion bonding and heat treating technique so that the thickness of the tough constituent was either 0.02, 0.04, 0.06, or 0.08 in. Compact tension fracture toughness specimens were machined so that the laminates were parallel to the sides of the specimens. They were then fractured according to the recommendations of the ASTM and three indices of toughness were measured: KIc, as recommended by the ASTM, Komax based on the maximum load and original crack length and Kimax, based on the maximum load and instantaneous crack length. Four tests were performed at each thickness of the tough constituent; two each at crack lengths of approximately 0.30 and 0.55 in. The plane-strain fracture toughness of the laminates was slightly higher than KIc of the monolithic brittle constituent and was independent of either crack length or the dimensions of the tough constituent. Regardless of the thickness of the tough phase the composite toughness was highest for specimens containing cracks 0.30 in. long when the throughness was measured in terms of Komax or Kimax. The thoughnessas a function of thickness exhibited a relative maximum when the tough phase was 0.04 in. thick and a relative minimum when the tough phase was 0.06 in. thick for both the 0-30 and 0.55-in. crack lengths. The experimental results are in broad agreement with a proposed model for crack extension in the divider orientation.
The primary aim of this study is to support the policy decisions on selection of a work zone layout that would have least deterrence to the traffic flow on busy urban arterials carrying heterogeneous traffic. The traffic flow characteristics were recorded with two cameras and the speed variation was obtained by plying probe vehicles fitted with Global Positioning Systems (GPSs) repeatedly in the section. The traffic stream speed and capacity of the various types of work zone sections were analyzed and it is found that near side lane closure has a relatively least effect on capacity (15 %) whereas the effect of run around type closure is maximum (46 %). The reasons for the variations in speed and capacity at these types of work zones were examined and reported. Besides, the application of the study results with respect to planning of work zone layout is discussed.
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