Experimental investigations of internal energy dissipation during fracture of fiber-reinforced ultra-high-performance concrete

Split-cylinder fracture of fiber-reinforced ultra-high-performance concrete (UHPC) was examined using two complementary techniques: X-ray computed tomography (CT) and acoustic emission (AE). Fifty-mm-diameter specimens of two different fiber types were scanned both before and after load testing. From the CT images, fiber orientation was evaluated to establish optimum and pessimum specimen orientations, at which fibers would have maximum and minimum effect, respectively. As expected, fiber orientation affected both the peak load and the toughness of the specimen, with the optimum toughness being between 20% and 30% higher than the pessimum. Cumulative AE energy was also affected commensurately. Posttest CT scans of the specimens were used to measure internal damage. Damage was quantified in terms of internal energy dissipation due to both matrix cracking and fiber pullout by using calibration measurements for each. The results showed that fiber pullout was the dominant energy dissipation mechanism; however, the sum of the internal energy dissipation measured amounted to only 60% of the total energy dissipated by the specimens as measured by the net work of load. It is postulated that localized compaction of the UHPC matrix as well as internal friction between fractured fragments makes up the balance of internal energy dissipation.     

LEVEL OF PROFICIENCY AND MULTIDIMENSIONAL VIEWPOINTS ABOUT PROBLEM SIMILARITY.

THE OBJECT OF THIS RESEARCH WAS TO DETERMINE WHETHER INDIVIDUAL CONSISTENCIES IN JUDGMENTS OF PROBLEM SIMILARITY ARE RELATED TO THE PROFICIENCY LEVEL OF THE JUDGES. 51 RADAR CONTROLLERS OF VARYING LEVELS OF EXPERIENCE AND COMPETENCY WERE ASKED TO JUDGE THE DEGREE OF SIMILARITY AMONG 30 AIR-TRAFFIC CONTROL STIMULI USING THE METHOD OF SUCCESSIVE INTERVALS. THESE DATA WERE ANALYZED ACCORDING TO THE "POINTS-OF-VIEW" PROCEDURES DEVELOPED BY TUCKER AND MESSICK. 4 DIMENSIONS OF VIEWPOINT WERE EXTRACTED REPRESENTING 4 MAJOR SUBGROUPS OF SS, EACH OF WHICH EXHIBITED CONSISTENTLY DIFFERENT EMPHASES IN THEIR JUDGMENT OF STIMULUS SIMILARITY. RESULTS INDICATED THAT (1) ASSIGNMENT TO A VIEWPOINT GROUP WAS RELATED TO TRAINING AND COMPETENCY LEVEL, AND (2) SS WITH GREATER PROFICIENCY TENDED TO VIEW THE STIMULI, NOT IN TERMS OF THEIR PHYSICAL CHARACTERISTICS, BUT RATHER IN TERMS OF THE RESPONSES THAT WOULD BE REQUIRED FOR AIR-TRAFFIC CONTROL. (PsycINFO Database Record (c) 2010 APA, all rights reserved)