The Crack Garden took a giant concrete slab that served as a central gathering area and created a series of cracks filled with different plants. The project reinvigorates the area by creating permeable space for plants to grow.
Crack Infrastructure Design Suite 2009 Crack
The cracks turn a barren, lifeless space into one that provides food for homeowners and a pleasant space for relaxing. From certain vantage points the lines of plantings stack up to present a more densely planted experience.
Some months ago, the City again declared war on drivers who block the box, i.e. go through red lights and block intersections. The crackdown lasted precisely 24 hours. The usual headlines about a ticket blitz appeared, and that was that.
On October 8, 2009, FHWA Office of Research, Development, and Technology Associate Administrator, Michael F. Trentacoste accepted the designation of Associate in the Forum of European Highway Research Laboratories (FEHRL) on behalf of the Agency. FHWA received strong support for application and was sponsored by three national laboratories in France, Czech Republic, and the Netherlands. The active participation will be managed by the Turner-Fairbank Highway Research Center (TFHRC). The FHERL provides a coordinated structure of the interests of more than 30 national research and technical centers from Europe, together with associated institutes from Israel, South Africa and now, the United States. The FEHRL is engaged in road engineering research topics including safety, materials, environmental issues, telematics, and economic evaluation. The effort to establish a collaboration platform with FERHL was initiated by FHWA Office of Research, Development, and Technology Director Debra S. Elston, the co-chair of the 2008 international scan on transportation research program administration. One of the scan team's implementation strategies is to build international relationships and institutionalize cooperation in transportation research to achieve global goals and leverage knowledge and resources.
Crack-free concrete? Although much progress has been made in reducing concrete's propensity to crack, the goal remains elusive. A novel approach to this problem is the focus of "High-Performance Stress-Relaxing Cementitious Composites for Crack-Free Pavements and Transportation Structures," an EAR Program project launched by the FHWA in 2008 and conducted at Texas A&M University's Texas Transportation Institute.
The December 2009 edition of Popular Science lists the Diverging Diamond Interchange (DDI) as one of the Best Inventions of the year. FHWA's TFHRC had a major role in identifying, evaluating, and assisting Missouri DOT in constructing the design featured in the issue. FHWA's Federal Land Highway Hoover Bridge Bypass Project is listed as another winner of an engineering award. See the December 2009 issue of Popular Science at: www.popsci.com
FHWA's Office of Safety Research and Development has just updated the 2009 Beta Release of the Crash Prediction Module (CPM) to support the upcoming Highway Safety Manual, Part C- Predictive Methods. It is now available for free downloading at www.ihsdm.org. The CPM is one of six existing modules available from FHWA's 2008 Public Release of the Interactive Highway Safety Design Model (IHSDM). IHSDM is a suite of software analysis tools for evaluating the safety and operational effects of geometric design decisions on two-lane rural highways.
In this paper we present a novel test methodology for the generation of varying degrees of pre-damage in small soda-lime glass cylinders by dynamic loading in combination with a subsequent contactless damage quantification. In the first step, 13 glass specimens are placed in demountable aluminum confinements. The confinements are then impacted by flyer plates at different impact velocities between about 70 m/s and 400 m/s. Two high-speed cameras are used to investigate the velocities and the planarity of the impacts. Afterwards, three-dimensional visualizations of the recovered specimens are generated using conventional CT-imaging at a micro-CT-device and phase-contrast imaging at a beamline of a synchrotron. A concept is developed to determine the crack volumes by means of a region-growing algorithm. For five selected specimens, the mean total crack volume is determined as a function of the impact velocity. The developed methods are a first step to improve the predictive power of existing numerical simulation models of glasses and ceramics in scenarios with high velocity impact or ballistic penetration. In the specimens, defined, quantifiable damage is generated that can later be characterized, e.g. in triaxial compression tests, to obtain damage-dependent yield curves. This concept turns out to be a significant improvement in comparison to the characterization tests of previous studies, which used loosely poured glass quartz powder or specimens that had been pre-damaged quasi-statically without quantification of the degree of damage.
Several studies have focused on visualizing the onset and propagation of damage in transparent materials. Senf et al. (Senf et al. 1994, 1995) developed edge-on-impact experiments, which enabled the observation of crack nucleation and propagation in single glass plates. This procedure has later been continued and improved by Strassburger et al. (Strassburger et al. 2005a, b, 2007b, 2010; Strassburger and Senf 1995). The more complex morphology of damage in multi-layer glass laminates was studied by Bless et al. (Bless and Chen March 2010) for high velocity impact (1118 m/s).
Promising alternative methods of visualizing the internal fracture process are techniques based on X-ray CT. Several studies (e.g. Chen et al. 2014; Luo et al. 2012; Hudspeth et al., 2013) have demonstrated that experiments observed by phase-contrast imaging (PCI) are well suited for the visualization of cracks in brittle materials even in highly dynamic events. For example, Chen et al. (2014) conducted edge cutting on borosilicate glass while monitoring the time-dependent failure process with high-speed X-ray PCI capabilities.
Figure 5 shows a photograph of the recovered sabot and the aluminum plate on the left side. On the right side, a photograph of the recovered confinement, after the removal of the cover plate, is displayed. The pre-damaged SLG cylinder is visible in the center of the confinement appearing dark since the internal crack surfaces diffuse the light.
A further significant improvement, compared to previous studies, is the contact-free investigation of the pre-damage prior to a possible measurement of the residual strength. An extensive CT test series is carried out in order to analyze and quantify the crack volume in the pre-damaged SLG cylinders. X-ray CT scans are conducted at two different facilities, at a micro-CT device of the Ernst-Mach-Institut and at the synchrotron beamline of the Paul Scherrer Institut.
For the identification of the crack volume, a software tool developed by the Australian National University (ANU) is used. Utilizing the advanced 3D image processing and segmentation techniques of the software, an analysis method for the SLG specimens is developed. As a result, the pre-damage of selected specimens is quantified and parameterized.
In order to get a first estimate of the generated damage, the recovered SLG specimens were placed on top of a bright light source and transmitted light images were taken. Figure 6 shows the images of twelve specimens. The crack areas inside the SLG specimens diffract the transmitted light leading to a darker appearance of regions with a higher crack density. The images are arranged by rising impact velocities from left to right and top to bottom. At the lowest impact velocities of about 70 m/s, only a few crack areas are visible. Large areas appear bright indicating that the impact generated only a coarse fragmentation. At higher impact velocities, the amount of visible crack areas significantly increases. At the highest velocities, above 250 m/s (pictures in the bottom row), the SLG specimens are strongly fragmented and a dense network of crack areas is visible.
Although these transmitted light images clearly show the dependence of the impact velocity on the generated degree of damage, they are not suitable for a systematic quantification. The amount of the transmitted light is strongly dependent on the position and orientation of the crack areas as well as the position of the light source and the camera settings. Furthermore, in some cases, a thin layer of aluminum residues, attached at the SLG surface, obstructed the light transmission.
The presented method of taking a microsection enables a better visualization of the pre-damage, however, the specimen is destroyed in the process making a characterization of the residual strength in a subsequent triaxial pressure test impossible. Furthermore, for a defined quantification of the whole volume, other methods are required. A more advantageous method is therefore a contactless and non-destructive determination of the total crack volume by means of conventional X-ray CT and PCI. These characterization techniques are presented in the next section.
In order to get a contactless and non-destructive determination of the total crack volume, tomographic experiments were conducted at two different CT facilities. The objective of the CT is to create a three-dimensional image of a specimen. On the one hand, high-resolution absorption-based X-ray CTs were carried out at the Fraunhofer EMI by means of a micro-CT system. On the other hand, PCI measurements were conducted at a synchrotron beamline of the Paul Scherrer Institut (PSI). X-ray CT is a method of generating image data by means of X-ray transmission. An in-depth description of the principles is provided for example by Buzug (Buzug 2008) or Goldman (Goldman 2007a, b). For additional information on the PCI method, the reader is referred e.g. to Chen et al. (2014); Zernike (1942); Gureyev and Wilkins (1998).
However, with the resulting images of the conventional absorption radiography, a quantitative evaluation of the degree of damage is very difficult. The analyzed specimens contain fine crack structures that exhibit relatively low density differences. In addition, the aluminum sleeve surrounding the glass cylinder lowers the achievable contrast. Furthermore, distinct beam-hardening (Seibert and Boone 2005) and ring artifacts (Hsieh 2009; Schulze et al. 2011) are present, which obscure the crack structures. 2ff7e9595c