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La sicurezza di un tracciato stradale: velocità di progetto, aderenza trasversale e sopraelevazione.
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Studio sulla tenacita' alla frattura di un acciaio inossidabile martensitico AISI 410 mediante provini tipo Charpy-V con raggio di fondo intaglio variabile
No full textEvaluating consistencyof two-lane rural highways: an approach for little twisty alignments
No full textOne technique used to improve road safety is to check the consistency of the alignment. Design consistency implies that road geometry and environment does not violate either the expectation or the ability of the motorist to guide and control a vehicle in a safe manner and in predictable ways.
One of the most common consistency measure is check speed variation along the alignment. A fundamental question in checking consistency is the speed upon which the road alignment should be based.
The design speed concept was used, in the past, and is used again in some standard like Italian one. Recently, in many standards, the use of design speed, to check consistency or to determine individual geometric elements like superelevation rates, was replaced by operating speed, indicated like 85th percentile speed.
Operating speed is the real answer to the driver expectancy and is, generally, higher than design speed. In particular all studies have indicated that operating speeds exceed design speeds less than 90 km/h at horizontal curves on rural two lane highways.
A recent research in the Department of civil Engineering of University of Trieste on two lane rural highways, showed that, on roads with little twisty alignments, the operating speeds, on horizontal curves and tangents, was not only always higher than design speeds but even higher than maximum permissible speed of road category; for that reason was impossible to use design speed of Italian standards to check consistency on these roads. Moreover it was impossible to use operating speed for checking consistency because these speeds were higher than maximum permissible speed.
In these road it should be made provision for a speed control in order to limit the maximum operating speed to the maximum permissible speed.
The results of the study indicate that it is possible to use speed consistency on roads with little twisty alignment, according with Italian speed limits, only if there is a control of the maximum operating speed, moreover it is suggested a particular kind of speed control.
Speed control was realized limiting inferiorly the curvature change rate (CCR) of the road section according with the environmental speed
Study of hot deformation behaviour of 2205 duplex stainless steel through hot tension tests
No full textThe hot working behaviour of duplex stainless steels has been studied in the literature mainly through hot torsion or hot compression tests. The aim of this paper is to investigate the hot deformation behaviour of a duplex stainless steel type 2205 (F51) through hot tension tests, which are easier to carry out and can offer some additional information about the maximum sustainable strain in tension before starting of irreversible damage. In fact, even under the uniaxial compressive action of a forging press, tensile stresses may develop in some zones of the forged product. These zones become most critical and the knowledge of the limiting conditions are important.
Three different test temperatures were selected, namely 900 °C, 1000 °C and 1100 °C. The hot working behaviour was characterized by fitting the mean flow stress, strain rate and temperature relationship with the hyperbolic sine function defined by Sellars and Tegart. An activation energy Q equal to 430 kJ/mol was obtained for plastic straining at high temperature. It corresponds to values, obtained with hot torsion or hot compression tests, reported in the literature where a large variation in activation energy is also found for duplex stainless steels. It was explained by considering the intrinsic two-phase nature of the investigated steel. The ductility in the different hot working conditions was characterized by the true strain at the onset of damage formation under prevailing tensile stress conditions. The role of the microstructure as well as of damage formation during deformation on the shape of the flow stress curves was analyzed
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