Yin H.,Gemini Technologies Inc.
Road Materials and Pavement Design | Year: 2015
While a reflective cracking propagation rate of 25 mm per year is well accepted by airport pavement engineers, the mechanism of reflective cracking under field conditions has not been fully investigated. A recently completed project sponsored by the Federal Aviation Administration (FAA) led to the development of the Temperature Effect Simulation System (TESS). After an in-depth evaluation of the TESS, full-scale tests to mechanically simulate thermally induced reflective cracking were conducted. A large simulation matrix was first developed to select promising joint opening and displacement rates using three-dimensional viscoelastic-based finite element analyses. A test pavement was then built, instrumented, and tested at the FAA National Airport Pavement Test Facility (NAPTF). This paper describes the successful full-scale test, crack monitoring under accelerated loading, and the data analysis used to evaluate the crack development. Main research conclusions included: (1) “25 mm per year” was quite conservative for thermally induced reflective cracking; (2) Once bottom-up reflection cracks reached a critical length, the crack evolution became very aggressive. For that reason, it is hypothetical to sandwich a strain-relieving hot mix asphalt interlayer between the Portland cement concrete slabs and the new overlay to minimise overlay stresses and to tolerate horizontal movements at the joint. Furthermore, significant insights into the mechanisms and mitigation of thermally induced reflective cracking were obtained and presented. Findings from this study are of immediate assistance to airports supporting light to medium weight aircraft and experiencing significant temperature cycling. © 2014, © 2014 Taylor & Francis.
Yin H.,Gemini Technologies Inc.
International Journal of Pavement Engineering | Year: 2013
The bottom-up fatigue damage in flexible pavements is typically assessed through the tensile strains at the bottom of the asphalt layer. The fatigue damage is then correlated using a calibration factor to the fatigue cracking. Therefore, the success of any pavement design depends on the accuracy and efficiency of employed mechanistic parameters, such as stress and strain. A procedure that can accurately and rapidly predict pavement strain response when traffic and environmental data are provided is desirable. In this study, an analytical procedure was developed to predict pavement response using a mixed pool of tensile strains from instrumentation and 3D FE simulation. Statistical features make the developed procedure powerful and efficient such that the strain responses due to every individual axle pass can be predicted. A demonstration example of predicting tensile strains under multiple-axle loading conditions is provided to facilitate application of the procedure to other data-sets. The maximum difference of 9 microstrain in response implies a reasonable accuracy of the analytical procedure. As demonstrated by using a full-depth flexible pavement section, the analytical procedure is effective and of immediate assistance to experimentally compare design alternatives. © 2013 Taylor and Francis Group, LLC.
Yin H.,Gemini Technologies Inc
International Journal of Pavement Research and Technology | Year: 2013
Reliable determination of pavement response to variable environmental and traffic conditions is essential for successful mechanistic design of asphalt concrete (AC) pavements. By measuring the responses directly, the assumptions and simplifications are notof concern. However, the introduction of the instrumentation into the pavement structure may itself inherently and significantly affect the pavement responses. This concern has led to questions about what is actually being measured by in-situ gages. When comparing measured and predicted responses, can one set of information be considered the "ground truth?" In this paper, the impact of gage instrumentation on localized strain responses in AC pavements is evaluated through finite element (FE) simulations. The distinct feature of the developed 3-D FE model is the inclusion of elastic strain gages in viscoelastic AC layers. These strain gages were modeled in both longitudinal and transverse directions at multiple depths within the AC layers. Influencing factors such as pavement temperature, vehicle speed, contact pressure, tire wander, and AC mixture were considered. FE simulations reveal that the inclusion of a strain gage results in considerably lower strain responses than otherwise predicted. This is manifested most at high pavement temperatures, low vehicle speeds, and high contact pressures. The presence of a strain gage may result in a prediction error of up to 73 percent for the conditions and materials considered. © Chinese Society of Pavement Engineering.
Yin H.,Gemini Technologies Inc
International Journal of Pavement Research and Technology | Year: 2012
Pavement deflection data coupled with backcalculation analysis are widely used to estimate the layer moduli of pavement structures for rehabilitation design and for pavement asset management. This paper presents a mechanistic approach to simulate full-depth flexible pavement responses when subjected to falling weight deflectometer (FWD) loads. The FWD testing is conducted at pavement locations instrumented with strain gauges, pressure cells, and thermocouples. For the selected full-depth asphalt concrete (AC) pavement structure, layer moduli are first backcalculated from FWD data, assuming that the AC and subbase materials are linear elastic, and that the subgrade can be treated as a nonlinear elastic material. The backcalculated AC moduli are compared to laboratory values, adjusted for load duration and temperature. The adjusted laboratory values for the surface layers are consistently lower, averaging about 70 percent of the backcalculated values. The adjusted laboratory values for the bituminous concrete base course (BCBC) are about 10 percent higher than the backcalculated values. The backcalculated layer moduli are then employed to predict horizontal strains in bound materials and vertical stresses in unbound materials through three-dimensional (3-D) finite element simulations. Finally, simulated responses and pavement responses from embedded instrumentation devices during the FWD loading are compared. An average prediction error of 30 percent was found through comparison of the simulated and measured pavement responses, with the predicted responses exceeding the measured responses in every case. © Chinese Society of Pavement Engineering.
Gemini Technologies Inc. | Date: 2014-06-23
A monocore for a sound suppressor that significantly enhances the trapping and delay of the gases exiting from the sound suppressor due to the design, location, and configuration of slanted baffles and angled half-baffles, and a plurality of rods. The slanted baffles help define the blast chamber, expansion chambers, and exit chamber of the monocore. The plurality of rods may be positioned in the blast chamber or the expansions chambers. The plurality of rods may vary in length. The plurality of rods may also replace the angled half-baffles.
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