Browsing by Author "O'Brien, David A."

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    Automated Pavement Condition Assessment Using Laser Crack Measurement System (LCMS) on Airfield Pavements in Ireland
    Mulry, Brian; Jordan, Michael; O'Brien, David A. (2015-06-04)
    Pavement condition surveys which identify pavement distress types, severities and quantities and provide a condition index or rating are an essential part of any pavement management system and an invaluable tool in the evaluation of a pavement's performance. Traditionally, distress data has been collected manually on foot, where the pavement is examined by eye, and the distress data is measured by hand. For airfield pavements, this often involves significant disruption to or closure of runways which can be very inconvenient and costly. Further modifications in Ireland have led to the development of more rapid visual inspection methods using a driven windshield survey procedure and more recently, using forward view digital video. This paper describes a case study where automated data collection and processing using Laser Crack Measurement System (LCMS) technology was used to establish and graphically report the pavement condition on two major runways at Dublin and Cork Airports, Ireland. The runways at both airports were constructed with asphalt-surfaced pavements. The data collection for the study included manual walking surveys, visual surveys from forward view digital video, and the collection of intensity and range three-dimensional (3D) imagery using an LCMS mounted on a high speed vehicle. The type, severity and extent of the pavement distress data were identified from the manual survey, the digital video, and using automated extraction from the LCMS 3D imagery. The data were processed and evaluated using the Micro PAVER pavement management system and the condition reported using the US Army Corps of Engineers Pavement Condition Index (PCI). The imagery and distress data from the LCMS survey were graphically reported using colour-coded thematics in ArcGIS and Google Earth GIS formats, and the detailed distress data was also mapped in AutoCAD layers. The paper examines and compares the pavement condition results obtained from the manual, video and LCMS data collection methods, and outlines the findings in using LCMS technology to automatically identify, geo-locate and graphically report pavement condition and distress data for airfield pavements.
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    Finite element stress analysis of idealized composite damage zones
    O'Brien, David A. (Virginia Tech, 1977)
    This study was concerned with linear and nonlinear stress and failure analysis of an idealized damage zone in a laminated composite under compressive loading. The following conclusions can be made from results of the analysis. 1. A boundary layer exists around the damage zone; it is similar to the boundary layer along the free edges. 2. Interlaminar stresses in the boundary layer around the damage zone are similar to those produced at the free edge. 3. The interlaminar stresses around the damage zone may be as large or larger than those at the free edge depending upon the fiber orientations and stacking sequence. 4. The boundary layer associated with the damage zone extends as far or farther into the interior of the laminate as does the free edge effect, depending on fiber orientation and stacking sequence. 5. Only laminated materials with more than one fiber orientation are affected by the damage zone. 6. Lamination theory is valid in interior regions away from free edges and the damage zone. 7. The presence of a damaged zone induces interlaminar stresses in an interior region away from free edges and the damage zone. 8. Due to interlaminar stresses produced in an interior region, failure, defined by a Tsai-Wu failure criterion, may initiate in the interior away from free edges and the damage zone. 9. The cutout extending down to a ±45 interface may produce large stress concentrations near the edge of the damage zone, depending upon the fiber orientations and stacking sequence. 10. Elastic results adequately predict where failure initiates for the laminate considered. 11. A damaged [90/±45/0]s laminate fails at approximately 60 percent of the load carried by an undamaged laminate. 12. For a [90/±45/0]s laminate, initial failure occurs at the free edge in the 0° layer. Subsequent failure in the interior of the 0° layer as well as at the free and cutout edges of the other layers leads to total failure. This investigation indicates that future areas of study should include: 1. Linear and nonlinear analysis of hygrothermal effects in laminates with idealized damage zones. 2. A three layer damage zone (cutout) in an eight layer laminate. 3. The effects of varying geometric parameters such as cutout width and layer thickness. 4. More detailed nonlinear analysts. 5. An improved method for modeling failure and unloading of an element. 6. Experimental study of specimens with idealized damage Zones to compare with theoretical analysis. 7. Analysis capability for bending of unsymmetric laminates.