83 research outputs found
Growth of a flexible fibre in a deformable ring
No full textWe study the equilibrium configurations related to the growth of an elastic fibre in a confining flexible ring. This system represents a paradigm for a variety of biological, medical, and engineering problems. We consider a simplified geometry in which initially the container is a circular ring of radius R. Quasi-static growth is then studied by solving the equilibrium equations as the fibre length l increases, starting from l = 2R. Considering both the fibre and the ring as inextensible and unshearable, we find that beyond a critical length, which depends on the relative bending stiffness, the fibre buckles. Furthermore, as the fibre grows further it folds, distorting the ring until it induces a break in mirror symmetry at l > 2 pi R. We get that the equilibrium shapes depend only on two dimensionless parameters: the length ratio mu = l/R and the bending stiffnesses ratio kappa. These findings are also supported by finite element simulation. Finally we experimentally validate the theoretical results showing a very good quantitative prediction of the observed buckling and folding regimes at variable geometrical parameters
Thermo-mechanical response of poly(methyl methacrylate) (PMMA) large volumes exposed to time-dependent environmental conditions
No full textLow thermal conductivity and elevated absorbance of large bulky volumes of poly(methyl methacrylate) (PMMA) exposed to moderately aggressive environmental conditions may cooperate to determine critical mechanical conditions, kindling unexpected high thermal stresses values which lead the material to failure. From the engineering point of view, this can be explained as the result of two concomitant phenomena which activate a cascade of events: very sharp thermal gradients engendered by transient thermal processes induced by cyclic environmental conditions, combined with significant bulk heat generation due to the high thermal inertia of massive PMMA volumes, in turn aggravating the steepness of the thermal gradients, may in fact ingenerate severe stress regimes, potentially undermining the structural stability of the material. Moving from these considerations, the present study is aimed to investigate possible rupture of PMMA blocks experiencing heating processes as a consequence of their exposure to outdoor cyclic environmental conditions. The problem is approached by means of both rigorous analytical arguments and the Finite Element based numerical methods, finally exploiting the theoretical outcomes to formulate a hypothesis which might explain the still unclear phenomenon of the sudden breaking of the PMMA structure, named Huge Wine Glass and designed by the world famous Japanese architect Toyo Ito, which occurred in Pescara (Italy) in 2009
Visco-elastic and thermal-induced damaging in time-dependent reshaping of human cornea after conductive keratoplasty
No full textWith the aim of investigating the role played by both the radiofrequency-induced thermal damaging and the viscoelasticity of the tissue in human cornea surface reshaping—time dependent key factors for the success of the surgical outcome in the short-term post-intervention period—the Conductive Keratoplasty (CK, a surgical technique used for the correction of farsightedness) has been simulated with reference to the protocol adopted for moderate hyperopia. By means of a transient thermal analysis, the amount of the local thermal-induced tissue damaging has been computed in order to remap the constitutive properties of the corneal tissue. Successively, a mechanical non-linear analysis has been performed for predicting the corneal curvature around the optical zone during the post-surgery period. The study aims to contribute some firm thermo-mechanical roots to better understand the corneal tissue response to thermal insults and its reshaping predictability in a long period
Third-order nonlocal elasticity in buckling and vibration of functionally graded nanoplates on Winkler-Pasternak media
No full textThe focus of the present work is to present an analytical approach for buckling and free vibrations analysis of thick functionally graded nanoplates embedded in a WinklerPasternak medium. The equations of motion are derived according to both the thirdorder shear deformation theory, proposed by Reddy, and the nonlocal elasticity Eringen's model. For the first time, the equations are solved analytically for plates with two simply supported opposite edges, the solutions also turning helpful as shape functions in the analysis of structures with more complex geometries and boundary conditions. Sensitivity analyses are finally performed to highlight the role of nonlocal parameters, aspect and side-to-thickness ratios, boundary conditions, and functionally graded material properties in the overall response of plates and cylindrical shells. It is felt that the proposed strategy could be usefully adopted as benchmark solutions in numerical routines as well as for predicting some unexpected behaviors, for instance, in terms of buckling load, in thick nanoplates on elastic foundation
Competition between elasticity and adhesion in caterpillar locomotion
No full textIn recent years, there has been a growing interest in understanding animals’ locomotion mechanisms for developing bio-inspired micro- or nano-robots capable of overcoming obstacles and navigating in confined environments. Among non-pedal crawlers, caterpillars exhibit one of the most stable and efficient gait strategies, utilizing muscle contractions and substrate grip. Although several approaches have been proposed to model their locomotion, little is known about the competition between body elasticity and adhesion, which we demonstrate playing a central role in crawling gait. Preliminarily, experimental observations and measurements were performed on Pieris brassicae larvae, gaining insights into fundamental features characterizing caterpillar locomotion and estimating key geometrical and mechanical parameters. A minimal but effective one-dimensional discrete model was thus conceived to capture all the relevant aspects of the movement. Inter-mass springs model the deformable body units, Winkler-like constraints with an adhesion threshold reproduce elastic interactions and attaching/detaching events at prolegs-substrate interface, and a triggering muscle contraction initiates the larva’s crawling cycle, generating the observed travelling wave. After demonstrating theoretically that caterpillars move obeying quasi-static laws, we proved robustness of the proposed approach by showing very good agreement between theoretical outcomes and experimental evidence, so paving the way for new optimization strategies in soft robotics
Stability of tunnels according to depth and variability of rock mass parameters
No full textEven with the most recent advances in rock mechanics, the stability assessment of underground tunnels continues to involve many uncertainties in the parameters which can significantly affect the calculated factors of safety. In the present work, a straight characterization which can help to evaluate the risk of a tunnel collapse with respect to the depth of excavation is proposed. Following a consolidated Limit Analysis approach and by means of the Hoek-Brown failure criterion, the galleries are divided into shallow, intermediate and deep according to the variability of the mechanical parameters of the rock mass with depth. A solution to the problem of impending collapse in the case of variable rock properties is proposed and examples are presented and discussed both from an analytical and a numerical standpoint
The role of viscoelasticity and stress gradients on the outcome of conductive keratoplasty
No full textA mechanical analysis of the conductive keratoplasty on hyperopic eyes has been carried out, and the attention has been focused on incorporating the actual viscoelastic properties of the human corneal tissue and on the stress gradients induced by the intervention. By avoiding unnecessary complications which may obscure the essential behaviour of the model, the results are in very good agreement with the clinical and experimental findings and suggest that the major role in the commonly observed decrease of the initial degree of the refractive correction might be played by the stress gradients at the intervention spots, which are likely to influence the wound-healing. The study aims to contribute some firm mechanical roots to the predictability of the outcome of an increasingly popular technique that, notwithstanding several advantages with respect to ablative interventions, at present cannot be considered completely satisfactory
A different approach for the assessment large domes based on revisited classic theory fundamentals
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