1,721,012 research outputs found
Mechanical characterisation of bamboo for construction: the state-of-practice and future prospects
Get PDFMethods for material characterisation of bamboo necessary for the structural design of bamboo and its expanded use in the construction sector are described. Directions for revising the nascent existing ISO 22157:2019 standard and future directions for this standard are discussed. Critical needs identified include i) improved performance of standard shear and flexural tests; ii) the need to establish protocols and methods for quantifying the long-term behaviour of bamboo and its degradation under environmental exposure; and, iii) establishing the efficacy of emerging methods of bamboo treatment. Requirements are placed in the test standards – grading – structural design ecosystem and are intended to guide future revisions of test and design standards
Stress-based formulation of non-linear planar deformations of elastic straight and curved beams
No full textIn this paper a formulation of non-linear analysis of an arbitrarily curved, extensible, shear flexible, elastic planar beam is presented. The formulation is based on a new variational principle expressed in terms of stress components. The Euler-Lagrange equation of this principle are the elastokinematic equation related to the curvature and the moment equilibrium equation. The effectiveness of the approach is illustrated through numerical examples
A mixed stress model for linear elastodynamics of arbitrarily curved beams
No full textThis work presents a mixed stress finite element for linear elastodynamics of arbitrarily curved beams based on a modified Hellinger-Reissner functional. A rational approach to choose the stress approximation is proposed. In particular, the self-equilibrated stress is augmented by some stress modes obtained from the lower-order displacement approximation using the equilibrium equations, in such a way that the total number of stress modes is equal to the number of strain modes. The rationale is to preserve all the interactions among the stresses, proper of a curved structure without compromising the flexibility of the element. An arbitrarily curved geometry is described using a parametric Hermitian interpolation scheme tuned by minimizing the initial curvature of the arch. The effectiveness of the present approach is numerically demonstrated
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
Assessing the mechanical properties of bamboo cultivated in Italy
No full textThe excellent mechanical performance of bamboo, coupled with its sustainability, have
boosted the use of this plant as a structural material in the last decades. There are countries
in which this material has been used in construction for millennia and represents an asset.
On the other hand, there are countries where still there is not enough knowledge of the
structural properties of locally-grown bamboo. The available studies and data in the
literature refer to American or Asian bamboo, and constructions in other parts of the world
are made with these imported materials. Expanding the knowledge of bamboo mechanical
properties to other species can facilitate its diffusion as a structural material in parts of
the world where bamboo is not traditional as such. In order to accomplish this, a very
important step is the development of standardised testing procedures. In this paper, the
results of an experimental campaign for the mechanical characterization of Phyllostachys
Viridiglaucescens grown in Italy is presented. This species is one of the most common
bamboo species cultivated in temperate climate. Compressive tests, tensile tests, shear
tests and bending tests were performed. The methodology is mainly compliant with the
International Standards; however, to cope with the particular physical properties of Italian
bamboo, the testing methodology was modified, where needed, with respect to that
prescribed by the International Standards
Un modello misto agli sforzi nella dinamica degli archi
No full textABSTRACT Linear dynamics of curved beams has been studied with a mixed stress formulation. The stress description has been been divided into three parts: one in equilibrium with loads, one autoequilibrated and the last one in equilibrium with inertia forces. The latter has been obtained by integration from a displacement field such that the numeber of strain mode is equal to the number of stress modes. A particular geometry description has been developed using a known set of inter element point coordinates and the tangent and coordinates of the extremities of the whole arch. This representation is based upon modified hermitian function tuned by two shape parameters which add flexibility to the classical description. These parameters are then calculated through the minimization of the curvature of the whole arch. The methods has been validated with a benchmark in which there is an exact solution of reference
A macroscale phase-field model for shape memory alloys with non-isothermal effects: Influence of strain rate and environmental conditions on the mechanical response
No full textA Ginzburg–Landau model for the macroscopic behaviour of a shape memory alloy is proposed. The model is essentially one-dimensional, in that we consider the effect of the martensitic phase transition in terms of a uniaxial deformation along a fixed direction and we use a scalar order parameter whose equilibrium values describe the austenitic phase and the two martensitic variants. The model relies on a Ginzburg–Landau free energy defined as a function of macroscopically measurable quantities, and accounts for thermal effects; couplings between the various relevant physical aspects are established based on thermodynamic principles. The theoretical model has been implemented within a finite-element framework and a number of numerical tests are presented which investigate the mechanical behaviour of the model under different conditions; the results obtained are analyzed in relation to experimental evidence available in the literature. In particular, the influence of the strain rate and of the ambient conditions on the response of the model is highlighted
A unified thermodynamic framework for the modelling of diffusive and displacive phase transitions
No full textA thermodynamically consistent framework able to model both diffusive and displacive phase transitions is proposed. The first law of thermodynamics, the balance of linear momentum equation (in the linearized strain approximation) and the Cahn–Hilliard equation
for solute mass conservation are the governing equations of the model, which is complemented by a suitable choice of the Helmholtz free energy and consistent boundary and initial conditions. To highlight thermo-chemo-mechanical interactions, some numerical
tests are performed in which the phase transition is triggered by setting the value of the initial temperature; a time–temperature–transformation diagram is determined
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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