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Perpetual Pavements, if properly designed and rehabilitated, it can last longer than 50 years without major structural rehabilitation. Fatigue endurance limit is a key parameter for designing perpetual pavements to mitigate bottom-up fatigue cracking. The endurance limit has not been implemented in the Mechanistic Empirical Pavement Design Guide software, currently known as DARWin-ME. This study was conducted as part of the National Cooperative Highway Research Program (NCHRP) Project 9-44A to develop a framework and mathematical methodology to determine the fatigue endurance limit using the uniaxial fatigue test. In this procedure, the endurance limit is defined as the allowable tensile strains at which a balance takes place between the fatigue damage during loading, and the healing during the rest periods between loading pulses. The viscoelastic continuum damage model was used to isolate time dependent damage and healing in hot mix asphalt from that due to fatigue. This study also included the development of a uniaxial fatigue test method and the associated data acquisition computer programs to conduct the test with and without rest period. Five factors that affect the fatigue and healing behavior of asphalt mixtures were evaluated: asphalt content, air voids, temperature, rest period and tensile strain. Based on the test results, two Pseudo Stiffness Ratio (PSR) regression models were developed. In the first model, the PSR was a function of the five factors and the number of loading cycles. In the second model, air voids, asphalt content, and temperature were replaced by the initial stiffness of the mix. In both models, the endurance limit was defined when PSR is equal to 1.0 (net damage is equal to zero). The results of the first model were compared to the results of a stiffness ratio model developed based on a parallel study using beam fatigue test (part of the same NCHRP 9-44A). The endurance limit values determined from uniaxial and beam fatigue tests showed very good correlation. A methodology was described on how to incorporate the second PSR model into fatigue analysis and damage using the DARWin-ME software. This would provide an effective and efficient methodology to design perpetual flexible pavements.
lack of time pressure and urgency to the given situations. If these expected results hold, there may be implications for both undergraduate engineering curriculum and real-world engineering endeavors.
The hardware will consist of electric motors functioning as a generator by reversing the rotation of the motor (regenerative braking). Using the dynamometer with the additional motor system paired with a local battery, the entire system can be run off by their tuning service. When considering the Dynojet and Dynapack dynamometer, it was calculated that an estimated return of 81.5% of electricity used can be generated. Different factors such as how frequent the dyno is used and for how long affect the savings. With a generous estimate of 6 hours dyno run time a day for 250 business days and the cost of electricity being 13.19 cents/kwh the Dynapack came out to $326.45 a year and $1424.52 for the Dynojet. With the return of electricity, the amount saved comes out to $266.18 for the Dynapack and $1161.50 for the Dynojet. This will alleviate electrical costs dramatically in the long term allowing for performance shops to invest their saved money into more tools and equipment.