1,721,063 research outputs found
Model for phase transition during heat treatment in eutectoid steel
No full textSteel heat treatments are very important industrial processes which involve microsctructural transformations. In the shop practice the design of these processes is conducted on empirical basis using the so called Bain curves, which cannot describe the phenomenon in its globality. Here, a two dimensional model for an eutectoid steel is proposed which takes into account either diffusive or displacive transformations. The first law of the thermodynamics as well as the dynamic equilibrium equation and an evolution equation for the diffusive phase transformations are involved in the model, together with a description of the internal energy. © AES-Advanced Engineering Solutions
Water Evaporation and Condensation by a Phase-Field Model
No full textWe develop a phase-field model for the liquid-vapor phase transition. The model aims to describe in a thermodynamically consistent way the phase change phenomenon coupled with the macroscopic motion of the fluid. The phase field ε describes the liquid fraction at any point and the overall water density is a function of the phase field and the pressure. An extra gaseous substance (e.g. air) is allowed in the system and contributes to the mechanical pressure. The phase transition is described by a Ginzburg-Landau equation. The parameter that drives the transition is the partial vapor pressure, which is the relevant quantity for condensation and evaporation phenomena. Moreover, a velocity-dependent term contributes to the phase change in the transition layers where a vapor pressure gradient exists
Triassialità
No full textDeriva da assiale, a sua volta da asse, dal lat. ăxe(m); con il prefisso tri-, col valore di tre. Generalmente la T. indica uno stato spaziale definito su tre assi, in contrasto con uno stato piano o monoassiale. La T. si ritrova in matematica nelle coordinate cartesiane estese allo spazio (x, y, z), negli assi principali delle quadriche o ancora come sistema di riferimento nei metodi della rappresentazione grafica. Allo stesso modo nello stato tensionale la T. indica uno stato che necessita di una descrizione tridimensionale, e viene descritto da un tensore caratterizzato da nove componenti. Queste possono ridursi a tre (tensioni principali) se lo stato viene riferito a direzioni privilegiate chiamate direzioni principali. Un particolare stato tensionale é lo stato idrostatico caratterizzato dalla uguaglianza delle tre tensioni principali. La T. degli stati tensionali oltre che per via matriciale può essere descritta per via grafica. Una nota costruzione grafica é la costruzione dei cosiddetti circoli di Mohr
Mechanical characterization of straw bales for use in construction
No full textFrom the point of view of environmental awareness, construction sustainability is a theme that is gaining considerable attention. This has brought to a re-discovery of the use of straw as a construction material, a technology that has been widely used in the past centuries. Straw is a natural material having excellent insulating capabilities, considerable mechanical properties when packed in bales and is relatively low cost (it is indeed a by-product of farming activity). Two are the techniques adopted in straw bale construction: post-and-beam, where the load is sustained by a wooden frame and straw bales are used merely as infill material; and load-bearing, where the entire load is sustained by the plastered straw bale walls. Especially regarding the latter technique, there is a need for a deeper understanding of the mechanical properties of straw bales. The characterization of the material is made difficult by the variability brought about by the variety of plants from which straw can be obtained, unpredictability of the baling process, moisture content in the bale and other parameters. Moreover, there is not a standard regulating the productive chain of straw bales to be used for construction. In this paper, a literature review on the tests performed on single unplastered straw bales is conducted and, based on this, some ideas are proposed for the development of a model describing the mechanical behavior of straw bales
Mechanical characterization of five species of Italian bamboo
No full textHigh mechanical performance coupled with sustainability gives to bamboo a high potential to substitute conventional construction materials in various applications. In particular, there are countries in which this material has been used in construction for millennia and represents an asset, on the contrary, there are countries where there is still not enough knowledge of the structural properties of locally-grown bamboo. In these cases, it is important to extend the knowledge of the mechanical properties of local bamboo species supported by the development of suitable standardised testing procedures. In this view, the paper presents the results of an experimental study for the mechanical characterization of five bamboo species cultivated in Italy (Phyllostachys bambusoides, edulis, iridescens, violascens and vivax). For compressive tests, the used methodology is compliant with ISO Standards; for tensile test, the procedure suggested by ISO is very difficult to apply so different set ups have been proposed and in the second part of the paper a critical discussion about ISO methodology and its possible improvements are reported. The findings from this research shed light on current challenges and on the possible future steps for a wider uptake of natural materials in constructions
Structural design of an Italian bamboo house in an Italian regulatory context: Revisiting a small building built in Costa Rica with tropical bamboo
Full text linkA residential building designed by the architect Anna Zanetti and already built in Costa Rica using Guadua angustifolia and Dendrocalamus asper is redesigned, choosing the municipality of Bologna, in the north part of Italy, as the construction site and Moso (Phyllostachys edulis) cultivated in Italy, as structural material. The redesign is performed in the context of Italian standards. The paper demonstrates how it is possible to design a building using European bamboo, geometrically smaller in respect to the tropical one, in compliance with the Italian national standards NTC2018 with the aid of Bamboo International standards (ISO 22156). All the members are multi-culms and the connections are chosen without perforations
Swelling and shrinking behaviour of bamboo and its application on a hygro-mechanical model
No full textBamboo exposed to variations in humidity is prone to cracking, which can reduce its usability. As a natural material, bamboo’s hygroscopicity causes dimensional changes, influenced by the gradient distribution of fibres throughout the wall thickness.
This study evaluated the dimensional changes resulting from variations in
moisture content. Hygroscopic coefficients were extracted and applied in a finite element model to assess the circumferential stresses generated during sorption and desorption processes. Conditioning tests showed that open ring samples tend to close during sorption and open during desorption, due to the predominant swelling and shrinking behaviour of the fibre cells. The developed finite element model successfully replicated the aperture behaviour and dimensional changes in the thickness of open ring bamboo samples. The optimized parameters were subsequently used to predict the stresses under varying humidity conditions in closed-ring samples. The circumferential stresses ranged from 9.8 MPa to -12.5 MPa from the inner to the outer layer in the saturated condition, and from − 7.1 MPa to 11.4 MPa in the dried condition. The values achieved reflect stresses that can lead to cracks and the failure of bamboo, thereby demonstrating the model’s ability to predict the hygroscopic behaviour of the material
Investigation over the parameters affecting the mechanical behaviour of small prismatic straw bales for use in construction
No full textStraw bale construction is a building technique offering many advantages: it provides excellent hygro-thermal insulation; it ensures good performance against earthquakes; and it is sustainable. From a mechanical point of view, straw bales can act as a surviving cell for the building in case of calamity. For this reason, measuring the mechanical properties of straw bales is important for the comprehension of the behaviour of straw bale buildings. Despite the fact that the use of straw bales in construction has been constantly increasing since the ‘80s, the behaviour and the performance of straw bale buildings have not been fully assessed so far. Using a recently developed test methodology (Maraldi et al., 2016), an analysis of the performance of small prismatic straw bales under monotonic compressive loads has been conducted. Force-displacement curves obtained from the tests have been fitted with a two-parameter rheological model to extract bales performance indicators. Results show that bales laid flat are stiffer than bales laid on-edge. However, if the influence of bales initial geometry is disregarded by considering stress and strain instead of force and displacement, no difference in the elastic modulus between flat and on-edge orientation appears. Furthermore, bales stiffness and elastic modulus are dependent on the initial density of the bale. It has been also found that straw bales exhibit a typical deformation pattern which depends on the baling process and that the Poisson’s ratio does not remain constant along the longitudinal direction during loading, whereas it is null along the transverse direction
Multilevel analysis of six species of Phyllostachys bamboo and Arundo donax: preliminary survey on Italian grown stands
Full text linkThe paper focuses on a multilevel analysis considering six species of bamboo of the Phyllostachys family (P. bambusoides, edulis, iridescens, viridiglaucescens, violacescens, and vivax) and Arundo donax grown in temperate climates, most of them not already studied in the literature. The analysis is divided into three levels. The analysis at the first level (the microscopic scale) includes an anatomical study to assess the shapes and dimensions of the vascular bundles and the sclerenchymatic and parenchymatic tissues. At the second mesoscale level, the percentage and distribution of the fibres, voids and parenchyma are calculated. At the third level, the macroscopic one, a discussion of the influence of the microscopical properties on mechanical properties is carried out. Despite the limited number of specimens analysed at the microscale level, differences between species emerged from the analysis and influenced the macroscopic characteristic values. In particular, the morphology of the components differs, especially in the case of Arundo donax, which presents a unique distribution of its components along the culm wall. Different contents of each component are observed for the species analysed. Moreover, an innovative analysis that focuses on the presence and distribution of voids is presented, which
have a fundamental role in the mechanical behaviour of this material. The analysis did not account for the influence of the environment on composition or anatomical and physical characteristics
Thermal treatment of bamboo with flame: influence on the mechanical characteristics
Full text linkThe mechanical properties of bamboo are susceptible to degradation due to both physical and biological agents. Among the non-chemical treatments, we studied the influence of a short-time heat treatment, using an LPG-gas torch, on the mechanical properties of a bamboo (Phyllostachys viridiglaucescens) growing in Italy. The response was very encouraging as we found no significant reduction in either elastic modulus or tensile, compressive and bending strength.
Several samples were subject to tension, compression and bending tests to compare the responses of the treated and untreated culms. The average tensile elastic modulus was slightly greater for the untreated culms. The average tensile strength of the untreated culms was only slightly greater, and the differences can be assumed to be insignificant from a structural point of view. The average value of the treated culms compressive elastic modulus was slightly greater than that of the untreated ones. The compressive strength was essentially the same. The bending mechanical behaviour was barely influenced by the thermal treatment.
A microscopic investigation (optical and electron microscopy) was undertaken to investigate the possible deterioration of the bamboo microstructure due to the heat treatment. No appreciable damage was detectable in the treated material.
The proposed heat treatments can be considered as a reliable and sustainable protection practice for bamboo culms
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