196,288 research outputs found
Non-linear rheological model of straw bales behavior under compressive loads
No full textThe use of straw bales in construction has been continuously increasing over the last years, because straw offers advantages over the use of conventional materials in terms of sustainability, hygro-thermal insulation properties and has good mechanical properties. In this paper, a simple rheological model for the description of the mechanical behavior of straw bales based on biconical springs is proposed. Given the geometry and the density of a straw bale, the model predicts the mechanical response in terms of force and displacement. The effectiveness of the model is verified through the comparison of the force–displacement diagrams obtained in experimental compressive tests for bales laid flat and on edge. It is shown that the model is able to reproduce the results of a series of straw bale compressive tests
Modelling displacive and diffusive phase transition in steel
No full textThe heat treatment of steels is a process of fundamental importance for manipulating the properties of the steel.
We present a consistent thermodynamic framework for modelling the heat treatment process which is able to capture both displacive and diffusive mechanisms. The present formulation is applicable to the a grain size level of observation. Some salient features of the thermodynamic framework are highlighted, especially those
associated with surface energies, and a number of numerical experiments are presented
A continuous/discontinuous Galerkin formulation for a strain gradient-dependent damage model
No full textThe numerical solution of strain gradient-dependent continuum problems has been hindered by continuity demands on the basis functions. The presence of terms in constitutive models that involve gradients of the strain field means that the continuity of standard finite element shape functions is insufficient. Despite a resurgence of research interest in strain gradient continuum models to represent micro-mechanical effects, a sound, effective and simple framework for the numerical solution of strain gradient-dependent problems is lacking. Here, a formulation is presented which allows the use of finite element shape functions for the solution of a prototype strain gradient-dependent damage model. The formulation is examined in two dimensions for the simulation of crack propagation. Particular attention is paid to the application of non-standard boundary conditions
Simulazioni di transizioni di fase diffusive e deformative (Towards modelling diffusive and displacive phase transitions)
No full textIl calcolo degli organi di macchina richiede una descrizione molto accurata delle caratteristiche del materiale; ciò non può prescindere dalla descrizione dei trattamenti termici ai quali il pezzo è stato sottoposto. La simulazione dei trattamenti termici degli acciai viene normalmente affrontata mediante modelli di natura fenomenologica che fanno largo uso di leggi empiriche per descrivere l’evoluzione della microstruttura all’interno del pezzo. Tuttavia, l’impiego di leggi empiriche richiede un’apposita taratura dei parametri del
modello; inoltre tali leggi, per loro natura, non chiariscono fino in fondo le ragioni fisiche per le quali i fenomeni in gioco avvengono. Ne consegue che tale metodo è fortemente limitato nella sua generalità.
Il problema può essere affrontato nella sua globalità, ossia prendendo in considerazione gli effetti termici, meccanici e di transizione di fase, partendo da una descrizione della struttura interna del materiale a scala
microscopica ed inserita in un contesto termodinamicamente consistente.
In particolare, in questo lavoro viene proposto un modello a parametri di fase alla scala microscopica capace di descrivere trasformazioni di fase sia diffusive sia deformative e dunque di modellare, rispettivamente, la trasformazione da austenite a perlite e quella da austenite a martensite. Il modello, per la formulazione e la
sua natura, risulta consistente con i principi della termodinamica e permette una descrizione delle trasformazioni diffusiva e deformativa e dei fenomeni termici in un contesto unificato.
Le equazioni sulle quali si basa sono: l’equazione del moto, il bilancio della massa di carbonio (che porta alla equazione di Cahn-Hilliard) e l’equazione del calore completa, che deriva dal bilancio di energia interna. A causa della natura non-locale del modello e della presenza di equazioni differenziali alle derivate parziali fino al quarto ordine, la soluzione del problema così formulato risulta complessa da un punto di vista computazionale; per questo motivo è stato messo a punto uno strumento numerico sofisticato ma robusto. Sono stati inoltre condotti alcuni test numerici che mostrano le potenzialità dell’approccio. Il modello risulta capace di cogliere le principali caratteristiche esibite alla scala microscopica dalle transizioni di fase perlitica e martensitica, le interazioni fra queste e l’influenza dei fenomeni meccanici e termici
MECHANICAL BEHAVIOR OF STRAWBALES FOR USE IN CIVIL AND RURAL CONSTRUCTION
No full textOver the last thirty years, the use of strawbales as a construction material has re-gained a lot of popularity for several reasons: baled straw has superior thermal insulation properties; buildings made with straw-bales are less expensive; straw is a by-product, hence its usage can help reduce the costs and emissions related to its disposal; structures built with strawbales can resist earthquakes better than those built according to traditional techniques. In the context of using materials and techniques sustainable for the environment, strawbale construction appears a more than promising choice establishing a strong link with the territory as well.
Indeed, straw has been extensively used as a construction material since pre-history; more recently, strawbale houses were built in Nebraska at the end of the 19th century. The use of strawbales in construction returned popular in the late 80's (King, 2003); in some countries, this has been also supported by the development of design standards. In Italy, the lack of similar codes represents an obstacle; the procedure to have a design approved is tedious and discourages builders. In spite of this, however, strawbale houses have been and are currently being built.
A deep understanding of the mechanical behavior of straw and of the material typically used in the rendering of strawbale walls is crucial for the development of construction techniques employing load-bearing strawbale walls. In the literature, studies on the mechanical properties of strawbales and strawbale assemblies have appeared since the rediscovery of this construction technique (Zhang, 2000; Vardy, 2009). Such studies report results of experimental tests conducted on single bales and on stacks of multiple bales, plastered or unplastered, loaded both on-edge and flat. However, very few of them provide some modeling to substantiate the results.
In this paper, a review of the relevant literature regarding the mechanical properties of single unplastered straw bales is proposed and critically analyzed in order to provide guidance for future modeling; furthermore, the procedure for a comparative LCA between the options of building with conventional materials and with straw bales is sketched out and preliminary results of such an analysis are discussed
Experimental evaluation of straw bales mechanical performance
No full textThe use of straw bales in construction is becoming increasingly widespread in the last years. Straw bale building offers advantages over the use of conventional materials in terms of sustainability, hygro-thermal insulation properties and ensures good mechanical properties.
In this paper, a discussion on the behavior of single unrendered straw bales under compressive load is carried out. Starting from the data obtained from an extensive experimental campaign conducted on bales of several materials, a simple interpretation of the deformation of the bales under compression has been proposed
A non-isothermal phase-field model for shape memory alloys: Numerical simulations of superelasticity and shape memory effect under stress controlled conditions
No full textA phase-field–based model has been employed for numerical tests on the mechanical response of a shape memory alloy. The model consists of a time-dependent Ginzburg–Landau equation for a scalar order parameter describing the local phase of the material (austenite or martensite), coupled with the balance of linear momentum and the heat equations; the mechanical effect of the martensitic phase transition is described in terms of a uniaxial deformation strain along a fixed direction, making the model suited for predictions over monodimensional specimens. A number of numerical simulations under stress-controlled conditions have been performed to investigate the mechanical behaviour of the model; the results obtained are analysed in relation to the experimental evidences available in the literature and previous investigations under strain-controlled condition
Experimenting growing media through local bio-resources valorisation: A design-oriented approach for living walls
No full textIn the context of densely populated urban areas, vertical greenery systems are gaining momentum for their role in reintroducing nature and enhancing buildings sustainability. Despite this trend, the absence of a standardised methodology for designing sustainable vertical greenery systems and guidelines for selecting appropriate growing media for this technology are two crucial gaps in academic research. This study addresses this by testing six alternative growing media derived from local bio-resources (dried M. spicatum, hazelnut shells, coffee grounds, hemp stalks, grinded cork, and raw sheep wool) and comparing them with a standard growing medium. The experiment was conducted over 120 days, monitoring the health and growth of three plant species - C. comosum, S. wallisii, and M. spicata. Innovative tools, such as a multi-criteria matrix and the Mean Leaf Growth Index, were introduced to assess sustainability and plant development. The findings highlight promising outcomes for hazelnut shells-based, hemp stalks-based, and grinded cork-based growing media, showcasing their lightweight and stable attributes compared to standard growing medium and assuring good plants health and growth. In contrast, raw sheep wool-based, M. spicatum-based, and coffee grounds-based growing media present challenges in plant health and growth, despite interesting attributes concerning lightweight and low water demand. This research contributes to shaping a design-by-components strategy for more sustainable vertical greenery systems, emphasizing the crucial role of circular bio-resources in nature-based technological innovations
Stress-based formulation for non-linear analysis of curved beams
No full textThe linear and non-linear analysis of curved beams is a very classical but still very discussed topic in literature. The most commonly used approach is the displacement approach, which is affected, as it is well known by locking phenomena.
A viable alternative to overcome the problem of locking encountered is represented by equilibrium formulation in static linear analysis and mixed formulations in dynamic and non-linear analysis. In particular, in non linear analysis of beams formulations based on a Hellinger-Reissner variational principle or modified Hu Washizu principle have been proposed in literature.
In this paper a valid alternative is proposed for the non-linear analysis of an arbitrarily curved, extensible, shear flexible, elastic planar beam. The proposed formulation is based on a new variational principle expressed in terms of stress components. In particular, the unknowns are represented by the bending moment and by a variable from which the shear and the axial force can be expressed and by the generalized forces at the extremities of the bar. The Euler-Lagrange equations of this principle are the elasto-kinematic relations related to the curvature and the moment equilibrium equation. The effectiveness of the approach is illustrated through numerical examples. A comparison in terms of displacements and stress with the other formulations available in literature ends the paper
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