Search results for "STIFFNESS"
showing 10 items of 524 documents
On stiffness and damping of vibro-impact dynamics of backlash
2021
We consider the instantaneous stiffness and damping of the vibro-impact in a backlash pair. Opposed to the existing and mostly used models of the backlash, we address the problem of contact and separation, and the associated force propagation within a mechanical pair, from a viewpoint of the vibro-impact dynamics. We discuss the impact forces with the coefficient of restitution as a principal factor which shapes the transient backlash response.We show that a common approach to modeling the backlash by means of a dead-zone in a restoring force is unsuitable for correctly capturing the mechanical impact. We exemplary demonstrate a qualitative accord between an experimental backlash response a…
Topology Optimization Design of Internal Reinforcements in a Sailing Dinghy
2021
AbstractIn this paper, a novel approach has been followed based on FEM simulation and Topology Optimization tools to locate and model the reinforcements inside the hull of a sailing dinghy. This process assumes that the inner volume included between the hull and the deck is, at the beginning of the simulation, filled with material; then a portion of this inner volume is eroded until a final free form shape of the reinforcements is obtained. A key point of this procedure is the definition of the optimization constrains because the final shape of the reinforcements must fulfill several requirements such as weight, stiffness and stress. At the end of the optimization procedure, the final shape…
Investigation of buckling characteristics of cracked variable stiffness composite plates by an eXtended Ritz approach
2021
Abstract Variable Angle Tow (VAT) composite plates are characterized by in-plane variable stiffness properties, which opens to new concepts of stiffness tailoring and optimization to achieve higher structural performance for advanced lightweight structures where damage tolerance consideration are often mandatory. In this paper, a single-domain eXtended Ritz formulation is proposed to study the buckling behaviour of variable stiffness laminated cracked plates. The plate behaviour is described by the first order shear deformation theory whose generalized displacements, namely reference plane translations and rotations, are expressed via suitable admissible trial functions. These consist of a …
Effect of progressive collapse of central column on the push-down response of two-span beam-column substructures
2021
Abstract In this paper, a simplified model is proposed for hand calculation of the push-down curve of reinforced two-span beam-column substructures with the mid-span column subjected to a vertical load inducing progressive collapse response. The model takes into account the flexural, arch and catenary strength mechanisms and the axial stiffness of RC compressed columns. The model was validated against experimental data available in the literature. The expressions derived, in a closed form, were useful for hand calculation of push-down responses and robustness evaluation of RC framed structures. The derived explicit expressions can be applied in a step-by-step manner for tracing nonlinear be…
Aortic Stiffness in HIV Infection with and without Antiretroviral Therapy. A Meta-analysis of Observational Studies
2020
Background: The risk of Cardiovascular (CV) events is higher in HIV-infected patients (HIV+) compared to HIV-uninfected persons (HIV−). Large artery stiffness, a well-documented predictor of adverse CV prognosis, may mediate this enhanced risk. It is usually assessed by measuring aortic Pulse Wave Velocity (aPWV). Studies examining arterial stiffness in HIV+ yielded inconsistent results. We performed a meta-analysis with the aim to evaluate the association of HIV infection and its therapy [Antiretroviral Therapy (ART)] with aPWV. Design and Method: The Standardized Mean Difference (SMD) and corresponding 95% confidence intervals were calculated for aPWV in different comparison groups. Stati…
Synthesis and Characterization of a New Fully Aromatic LCP
1996
Abstract Liquid crystal polymers (LCP)are a relatively new class of polymers with very interesting and unusual properties. In particular, easy processability and outstanding mechanical and barrier properties make them very attractive. Unfortunately the high stiffness of their chains often leads to compounds having very high melting points and consequently to unprocessable materials. By adding a flexible segments in the chain backbone the LCPs become processable at lower temperatures but lower properties are displayed. A new rigid liquid crystalline polymer, having excellent physical properties, good processing temperature and a good cost/performance compromise, is described in this work. Th…
Phase Separation and Nematic Order in Lyotropic Solutions: Two Types of Polymers with Different Stiffnesses in a Common Solvent
2021
The interplay of the isotropic-nematic transition and phase separation in lyotropic solutions of two types of semiflexible macromolecules with pronounced difference in chain stiffness is studied by Density Functional Theory and Molecular Dynamics simulations. While the width of the isotropic-nematic two-phase coexistence region is narrow for solutions with a single type of semiflexible chain, the two-phase coexistence region widens for solutions containing two types of chains with rather disparate stiffness. In the nematic phase, both types of chains contribute to the nematic order, with intermediate values of the order parameter compared to the corresponding single component solutions. As …
Bio-based rigid high-density polyurethane foams as a structural thermal break material
2020
Abstract Sustainable development of building industry implies increasing usage of green materials. With this aim and for the intended application as a structural thermal break material, rigid high-density polyurethane foams have been manufactured using polyols derived from renewable resources - tall oil fatty acids. Thermal conductivity, compressive strength and stiffness of the foams of density ranging from ca. 100 to 680 kg/m3 have been determined. Comparison of the bio-based foams with reference foams derived from petrochemical resources demonstrated similar performance characteristics thus suggesting that bio-based foams can also serve as structural thermal break materials. Analytical m…
Estimation of the elastic constants of highly porous cellular plastics reinforced with fibres embedded in foam struts
2015
In order to enhance the mechanical properties of polymer foams, fillers of different materials and sizes are being applied. Fibrous fillers shorter than the characteristic foam cell dimensions have the potential of efficient reinforcement, due to their high aspect ratio, without detrimentally interfering with foam structure. A theoretical model is developed for evaluation of the effect of filler on foam stiffness. The elastic response of rigid polymer foams filled with short fibres, of length commensurable with that of foam struts, is modelled by using the orientational averaging technique. Explicit expressions for components of the stiffness tensor of composite foams are derived in terms …
Topology-Sensitive Microfluidic Filter for Polymers of Varying Stiffness
2017
The separation of polymers based on their size, rigidity, and topology is an essential but also highly challenging task for nanoscience and engineering. Using hybrid molecular dynamics simulations that correctly take into account hydrodynamics, we have designed microfluidic channels for separating linear from ring polymers in dilute solutions. We establish that the transport velocity of the polymers is independent of their topology and rigidity when the channel walls are smooth and repulsive. However, when the walls are decorated with attractive spots arranged on lines parallel to the flow, ring polymers exhibit an order of magnitude higher transport velocity compared to linear chains. The …