Semi-analytical static analysis of nonlocal strain gradient laminated composite nanoplates in hygrothermal environment

AbstractIn this work, the bending behavior of nanoplates subjected to both sinusoidal and uniform loads in hygrothermal environment is investigated. The present plate theory is based on the classical laminated thin plate theory with strain gradient effect to take into account the nonlocality present in the nanostructures. The equilibrium equations have been carried out by using the principle of virtual works and a system of partial differential equations of the sixth order has been carried out, in contrast to the classical thin plate theory system of the fourth order. The solution has been obtained using a trigonometric expansion (e.g., Navier method) which is applicable to simply supported boundary conditions and limited lamination schemes. The solution is exact for sinusoidal loads; nevertheless, convergence has to be proved for other load types such as the uniform one. Both the effect of the hygrothermal loads and lamination schemes (cross-ply and angle-ply nanoplates) on the bending behavior of thin nanoplates are studied. Results are reported in dimensionless form and validity of the present methodology has been proven, when possible, by comparing the results to the ones from the literature (available only for cross-ply laminates). Novel applications are shown both for cross- and angle-ply laminated which can be considered for further developments in the same topic

Production and characterization of lattice samples with solid shell in 17-4 PH stainless steel by Laser Powder Bed Fusion technology

In this work, 17-4 PH stainless steel square-based lattice structures with solid shell were manufactured by Laser Powder Bed Fusion. Face Centered Cubic unit cell was chosen as lattice cell geometry. The main aim of this work was to study the role of the shell in the mechanical behavior under compression load and to identify any critical issue due to the connection of the shell with lattice part. This is a relevant topic since often lattice structure are integrated with solid walls and the study of the relative behavior can support the understating of the performance of complex components. The manufactured samples were tested in as-built and heat-treated condition. In detail, solution and aging treatment was performed as a conventional route for 17-4PH steel. In particular, microhardness and compressive tests were performed, and the mechanical behavior and the fracture mechanisms of the samples were investigated. Furthermore, the defects, the geometry of the struts and the connection with the solid part were analyzed. The detachment of the shell from the lattice did not occur. In fact, the solid part followed the deformation of the structure. The microstructural evolution after heat treatment was found to be responsible for an increase in hardness, strength and deformation for the investigated structures

Compressive behavior of Co-Cr-Mo radially graded porous structures under as-built and heat-treated conditions

Additive manufacturing research is continuously growing, and this field requires a full improvement of the capability and reliability of the processes involved. Of particular interest is the study of complex geometries production, such as lattice structures, which may have a potentially huge field of application, especially for biomedical products.In this work, the powder bed fusion technique was utilized to manufacture lattice structures with defined building angles concerning the build platform. A biocompatible Co-Cr-Mo alloy was used. Three different types of elementary cell geometry were selected: Face Centered Cubic, Diagonal, and Diamond. These cells were applied to the radially oriented lattice structures to evaluate the influence of their orientation in relation to the sample and the build platform. Moreover, heat treatment was carried out to study its influence on microstructural properties and mechanical behavior. Microhardness was measured, and compressive tests were performed to detect load response and to analyse the fracture mechanisms of these structures.The results show that the mechanical properties are highly influenced by the cell orientation in relation to the building direction and that the properties can be further tuned via HT. The favorable combination of mechanical properties and biocompatibility suggests that Co-Cr-Mo lattices may represent an optimal solution to produce customized metal implants

Oxidative stress and cardiovascular disease

The endothelium is one of the most important, and certainly the most extensive, organs involved in cardio- vascular homeostasis. The endothelium-derived vasoactive factors inhibiting smooth muscular cells contraction and proliferation, and platelet function, include nitric oxide (NO), prostacyclin and endothelial-derived hyperpolarizing factor. However, endothelial cells can also produce vasoconstrictive, proaggregant, promitogen mediators, such as thromboxane A2, prostaglandin H2, endothelin 1, and angiotensin II. Therefore, any impair- ment of endothelial function may trigger the typical chain of events of atherogenesis, characterised by vasocon- striction, cellular proliferation and thrombosis. In this regard, the biological link between endothelial dysfunction and atherosclerosis is a reduced bioavailability of NO. However, the precise mechanisms by which the endothelial dysfunction occurs remain still unclear. A decreased bioavailability of NO can be caused by its enhanced reactive oxygen species (ROS) breakdown. Oxidative stress may represent a common mechanism by which different cardiovascular risk factors cause endothelial dysfunction and trigger atherothrombotic process

Comparing accuracy of three remote sensing methods to evaluate soil impact related to forest operations

Monitoring soil impacts related to forest operations is crucial to reach the sustainable forest management goal. On the other hand, field survey to assess such kind of impact is usually costly and time consuming. Therefore, the possibility of using remote and proximal sensing technologies to analyze forest soil impacts could be very helpful for forest managers. According to this, the aim of the present work was the evaluation of reliability of three different remote sensing tools for the assessment of soil impacts related to forest operations. The study area consisted in an oak coppice located in the Municipality of Castel Giorgio (Terni District, Central Italy). The different tested technologies were Sentinel-2, Google Earth and an unmanned aerial vehicle equipped with an RGB sensor. After forest utilization, images of the study area were obtained by the above-mentioned systems, and a photo-interpretation process allowed the identification of skid trails patterns produced by the operators during the extraction of timber. The three theoretical skid trails patterns were compared with the real one, obtained by field relief with Global Navigation Satellite Systems (GNSS) technology. The obtained results showed that all these systems still need some improvements for an effective application in the Italian forest sector, concerning soil impacts evaluation after forest operations

The effect of 2-D surface irregularities on laminar-turbulent transition: A comparison of numerical methodologies

Laminar-turbulent transition prediction is of practical interest in aircraft design since transition affects important aerodynamic quantities such as drag and heat transfer. Extended laminar flow on aerodynamic surfaces is an effective way of reducing aircraft drag. One of the major challenges for the implementation of laminar-flow surfaces is the potential for any irregularity to move transition upstream. Under low-disturbance environment, boundary-layer transition results from the growth and breakdown of different flow instabilities. In 2-D flows the scenario is dominated by Tollmien-Schlichting (TS) instabilities. Common wing-surface irregularities, such as two-dimensional steps, gaps or waviness can alter the growth characteristics of TS waves and therefore must be taken into account at the design stage

Preservation of Abandoned Historic Centres — The Case of Poggioreale antica (Sicily)

Among the fourteen towns most damaged by the earthquake that struck western Sicily in 1968, Poggioreale was subjected to total relocation a few kilometres away, and to the transfer of its whole population. More than half a century later, the damaged settlement is still largely recognisable and has been experiencing a new season of interest for some years now, both from the local community and various kinds of outsiders who imagine economic spin-offs of an uncertain nature in its enhancement. The research we present questions the chance of survival for the settlement, forgotten for decades, in the context of interventions aimed at its reuse. Alternative strategies are discussed: on the one hand, that of bringing the ancient centre back to life, even in part, with a limited inclusion of collective functions and without claiming to inhabit it again; on the other hand, and in the authors’ opinion, more likely, that of reusing the ruins as an archaeological area preserving their memory in a different form. In either case, the kinds of operations to be carried out on the body of the ancient buildings for their physical preservation play a key role. These issues are addressed as a whole through the canonical procedure of correlating the phases of knowledge, interpretation, and definition of minimal and compatible intervention criteria

DNS of the interaction of crossflow instabilities with forward-facing steps

Previous studies on the interaction between stationary crossflow (CF) vortices and a forward-facing step (FFS) have shown a significant influence on the laminar-turbulent transition (e.g. [1, 2]). In a recent experimental investigation, Rius-Vidales & Kotsonis [3] found that the effect of the step height on the transition location is non-monotonic. An unprecedented transition delay (w.r.t to the case without FFS) occurs when the incoming stationary CF vortices interact with a shallow FFS. Instead, the interaction with a higher FFS leads to an upstream advancement of the transition front location. The present work aims to numerically reproduce the experimental setup in [3] through direct numerical simulation (DNS). The current investigation’s final goal is to understand further the flow physics behind the observed behaviour in the experiments

Tollmien-Schlichting waves over forward-facing steps: An experimental and numerical study

This work presents an experimental and numerical investigation jointly conducted by TU Delft and DLR on Tollmien-Schlichting (TS) waves interaction with a Forward-Facing Step (FFS). Experiments are conducted at the TU Delft low turbulence anechoic wind tunnel on an unswept flat plate model. Single-frequency disturbances are introduced using controlled acoustic excitation. The temporal response of the flow in the vicinity of the step is measured using Hot-Wire Anemometry (HWA). In addition, the global effect of the step on laminar-turbulent transition is captured using Infrared Thermography (IR). Two-dimensional (2-D) Direct Numerical Simulations (DNS) performed at DLR provide detailed information at the step. Experimental and DNS results in clean and step case conditions present very good agreement. Both methods predict large distortion of the TS waves downstream of the step, where DNS results present different growth trends between velocity components of the TS waves. Furthermore, negative and positive regions of the production term are observed to correlate with streamwise positions where the disturbances appear tilted in and against the mean shear, respectively. These findings point towards the presence of different growth mechanisms triggered by the step which could modify the level of amplification of disturbances far downstream