1,720,984 research outputs found
The effects of the cold expansion degree on the fatigue crack growth rate in rail steel
No full textThis study investigates the effects of the cold-expansion degree on the fatigue strength of rail steels. Two degrees of cold-expansion, 2% and 4%, and two stress levels were investigated. Results indicate that cold-expansion postpones crack initiation and extends fatigue life, especially with higher degrees of cold-expansion and lower stress levels. Linear superposition principle coupled with the weight function method results in an overestimated fatigue life of cold-expanded specimens, suggesting that reliable predictions can be achieved if both the residual stresses redistribution due to propagating crack and the crack closure effects due to plastic wake generation are considered in the simulations
An Optimized machine for fast grape cooling by cryogenic fluid
No full textE’ stato progettato e realizzato un impianto per il raffreddamento rapido di una quantità di uva fresca da inviare ad una macchina (Crushers-Destemmer Machine)- (mash-destemming) pigia-diraspatrice, mediante l’utilizzo di fluido criogenico: CO2 liquida. Il raffreddamento realizzato dall’impianto considerato avviene in circa 8 s. La macchina gestisce una portata di uva di circa 2- 3 ton /h di uva, con salto termico dell’uva considerata regolabile (T ing – T usc) fino a 20 °C. Tale processo risulta necessario quando si vuole effettuare il processo di criomacerazione delle uve che consente di ottenere vini di alta qualità. La criomacerazione può essere effettuata anche con l’utilizzo di gruppi frigoriferi tradizionali di grandi capacità. Però questi gruppi frigoriferi, oltre a presentare elevati consumi energetici e costi impiantistici molto alti, che devono essere ammortizzati solo su un utilizzo esclusivamente stagionale, molto spesso danneggiano il prodotto raffreddato, a causa dell’attrito generato dal passaggio nelle tubazioni, provocando formazione di feccia grossolana che inficia la qualità del prodotto finito. Ciò è evitato utilizzando l’impianto considerato. Esso è formato da una tavola vibrante che consente la stratificazione dell’uva realizzando uno strato di un grappolo d’uva, sonde di temperatura ad infrarosso per la lettura della temperatura degli acini di uva, ugelli per l’iniezione di CO2 liquida, elevatori a nastro coibentati per mantenere costante la temperatura finale dell’uva, macchina diraspatrice che opera in ambiente inertizzato (poiché è presente solo la CO2 ,non c’è più l’aria) e alla temperatura di criomacerazione. Il ciclo nel suo insieme è gestito da un PLC che, regolando la quantità di CO2 da immettere, controlla la Temperatura dell’intero process
Simplified equipment for unsaturated soil hydrostatic compression tests
No full textIn this paper, soil mechanical property variations in moisture and granulometry have been
investigated. Investigations were performed to compare hydrostatic compression test (HCT) responses
and evaluate the compression index, Cc, which is an indicator of the soil's susceptibility to compaction-
induced damage. The experiments were performed on 24 soil samples typologies. Each sample was
obtained by combining three types of soil (types A, B and C) with a relative content varying from 0 to
100% in 20% increments. Soil type A had a granulometry ranging between 0.5 and 1 mm, type B
between 0.25 and 0.5 mm, and type C less than 0.25 mm. These samples were representative of a sandy
soil, chemically inactive, and had various granulometries and initial moisture contents. A cell for HCT
was set up to allow the initial volume measurement of the test pieces and the subsequent changes
during HCT with an estimated error less than 0.1 cm3. All samples were pre-compacted and prepared
in agreement with the actual standards. The experimental data are reported in diagrams; the data
allowed comparison of the mechanical behaviours between the considered unsaturated soils and
underlined how soil moisture and granulometry affect soil response during HCT. Furthermore, because
of the methodology used, the equipment was very economical
Optimization of a device for a fumigation process
No full textAn equipment was designed and realized that has allowed to perform the fumigating process optimization for the foodstuff. The equipment, easy to use, allow to exhaust completely the Magnesium of alluminium phosphide pellets and to reduce the phosphine production time from 5 days to 2 days. In addition it is particularly convenient during the fumigazion in cold periods
Optimization of a device for the fumigation process
No full textIt has been optimized a device that performs the dried agricultural products disinfestation by fumigation process with phosphine gas. Moreover, it allows to completely exhaust the active principle contained in the pellets of magnesium and aluminium phosphide used in the fumigation process, and to complete the phosphine production process, ordinarily of 5 days, in 2 days.
Further, the device results particularly convenient during the fumigation process performed in cold periods; in facts, it is equipped with a pellets heating device that improves the phosphine production. Further it allows the continuous remixing of the pellets during the fumigation process and the control of the humidity by mean of water injection. The prototype is composed of :
- cylindrical tray in stainless steel, containing the pellets of magnesium and aluminium phosphide, and it is connected to an electrical heater with a thermostatic device for the tray temperature control;
- electric engine for the rotation of the cylindrical tray;
- two bars that sustain 5 harmonic steel sheets with the extremity folded up downward with an angle of 90°. Such sheets, thanks to their elasticity, follow the fund of the tray. Besides they are of different length, so that they allow a good remixing. By mean ANSYS code it has been possible also to evaluate the goodness of the performed remixing.
- a water sprinkler connected to an electrical valve that performs the environmental hygrometric control. In such way the value of the environmental humidity is kept optimal to have the maximum phosphine production and therefore the considered process results very fast.
In the definition of the device geometries it has been used a 3D CAD program: Solid Works. It has allowed to define a parametric model of the considered device. Some experimental tests have been performed to determine the amount of water flow to obtain the optimal humidity value and to avoid dangers of fires caused by the pellets, sprinkling a water quantity ranged from 1/40 to 10 ml for every 1⁄4 of round of the cylindrical tray.
Moreover some tests have been performed to determine the optimal heating temperature considering 4 different temperatures: 30, 40, 50, 60 °C, and evaluating the phosphine quantity produced in such conditions. Besides the process of remixing has been optimized, performed by the steel sheets opportunely shaped. All of this has allowed to completely exhaust the magnesium and aluminium phosphide contained in the inlet pellet
Thermoplastic polyurethane composites for railway applications: experimental and numerical study of hybrid laminates with improved impact resistance
Full text linkDue to the introduction of highly restrictive safety and pollution legislations in the railway industry, weight reduction has become an increasingly important topic over the last decade. Carbon fibre-reinforced polymers (CFRPs) constitute an excellent alternative to traditional materials, due to their highly specific in-plane mechanical properties. Their use in railway industry, however, is currently hindered by their weak out-of-plane properties. Bogies and underframes are often subjected to impact loadings caused by objects and debris surrounding the tracks (i.e. ice, ballast) that become airborne during the train transit and impact lower part of the carriage. While metal structures absorb impact energy via plastic deformation, barely visible impact damage can occur in CFRP, weakening the component, and often leading to catastrophic failures. This work proposes a method for the improvement of impact absorption performance of railway composite structures via the addition of a thermoplastic polyurethane (TPU) coating to CFRP laminates. The thermomechanical behaviour of the thermoplastic layer was investigated with dynamic mechanical analysis and differential scanning calorimetry analysis to optimize the manufacturing process, while damping tests were carried out to demonstrate its unaltered energy absorption ability in the final manufactured structure. TPU/CFRP plates (150 × 100 mm2 of in-plane size) were subjected to 2, 3 and 5 J impacts, and the results were compared with those of traditional CFRP laminates. Non-destructive test (NDT; i.e. C-scan, phased array) and compression-after-impact test were carried out on the impacted samples to assess the damaged area and residual in-plane mechanical properties. Results show that the TPU layer modifies the energy absorption mechanism, preventing the propagation of damage within the CFRP and resulting in undamaged samples even at the highest energy. To predict the TPU/CFRP impact behaviour and identify the best process parameters to optimize impact energy absorption, a finite element model was developed and validated using experimental data. The comparison showed good correlation, and a fine approximation of the different impact mechanisms was observed with a maximum error of 5% between experimental and simulated output values. The experimental and numerical results show that the TPU/CFRP laminates constitute a novel solution for the manufacturing of lighter and safer railway composite structures.</p
Flexural fatigue behaviour of pervious concrete: Lifetime evaluation and statistical model development
No full textAnalysis of a plant for the cryo-maceration of the grapes
No full textA plant for the grapes cryo-maceration that uses the direct injection of CO2 has been studied. Such types of plants allow to obtain wines of high quality, however sometimes because of a bad use of them, it is possible that can rise serious drawbacks. Therefore such search is aimed to study the most critical part of such plant, that is the zone where the injection of the CO2 happens, that is situated in proximity of a divergent tube. After having determined the geometric characteristics of the materials and the thermodynamic characteristics of the fluids (CO2 and mashed grape) a numerical simulation of the thermodynamic exchange between the two considered fluids has been performed, and they have been examined some characteristic conditions
obtaining helpful data results to be used for the optimization of the use of the considered plant
A thermoplastic polymer coating for improved impact resistance of railways CFRP laminates
No full textDue to the superior specific mechanical properties and low density of composite materials, their demand has risen prolifically within several industrial fields over the last decade including railway industry. The latter considers composite materials as a much more attractive alternative to standard metallic solutions. However, while composite materials have already been used in the manufacturing of parts of rolling stock (overhead structures, cab fronts, seats, doors), there is currently no procedure to certify a rail vehicle built entirely - or in large part - from non-metallic materials. In this context, safety based technological improvements criteria are mandatory for any transportation system. One of the safety features for a train is the missile protection, which indicates that the vehicle shell must not permit any flying objects to penetrate the coach/vehicle. Hence, the analysis of the characteristics of composite impact damage is mandatory to apply mitigation actions against structural integrity detriment, also considering that even though regulation requirements for composite structures exist, they are not comprehensive enough to improve the overall structural safety. The aim of this paper was design and characterisation of Carbon Fibres Reinforced Polymer (CFRP) laminates hybridised with thermoplastic polyurethane (TPU), to enhance impact energy absorption and satisfy light weight requirements. In order to simulate flying ballast, a Low Velocity Impact (LVI) tests campaign was carried out at different impact energy levels (2 J and 3 J) by mean of a drop tower impact test on 150 x 100 mm CFRP specimens with and without TPU. Impacted samples were subjected to a non-destructive analysis campaign using Phased array to evaluate the extent of internal damaged areas and the results showed a significant benefit towards impact damage tolerance when a thin polyurethane layer is applied on CFRP components. Results from the experimental campaign show significant benefit against impact damage tolerance due to the thermoplastic material damping properties which are able to modify the energy absorption mechanism, reducing the extent of the internal delamination
Fatigue crack growth rate dependency on cold expansion degree in railway steel
No full textThe increase of railway track occupancy due to high speed trains introduction in the morning and cross-border transportation of hazardous and non-hazardous materials during late hours, require particular attention for the fatigue design as well as the maintenance planning of railway superstructures. For this purpose, strategies finalized to increase the fatigue strength of railway structural parts assume great interest for railway engineers. Cold expansion technique, for example, is less expensive than other mechanical and thermal treatments, but in the literature there are no data concerning its use in the railway field, being almost all available studies focused on aluminum parts. In this paper, fatigue crack growth response of drilled specimens extracted from rails submitted or not to cold expansion are presented. Two degree of cold-expansion, 2% and 4%, are investigated in terms of fatigue crack growth rate, and the results compared to those obtained with not-expanded specimens. It is found that cold expansion postpones fatigue crack initiation, and that this effect is more pronounced for increasing degree of cold expansion. A preliminary predictive model was developed, based on the sum of the Stress Intensity Factors calculated with the weight functions and concerning the residual stress field induced by cold expansion, and the one generated by the external loads
- …
