Search results for "dynamics."
showing 10 items of 9637 documents
Experimental and Numerical Study on Linear Friction Welding of AA2011 Aluminum Alloy
2014
Linear Friction Welding (LFW) is a solid-state joining process used for non-axisymmetric components. LFW involves joining of materials through the relative motion of two components undergoing an axial force. In the process, the heat source is given by the frictional forces work decaying into heat and determining a local softening of the material and eventually the needed bonding conditions. In the paper, an experimental and numerical campaign is proposed for AA2011 aluminum alloys welding. Different case studies are considered with fixed oscillation frequency and varying pressure at the interface between the specimens. Constant oscillation amplitude and specimens geometry is used. The calcu…
Different Space Charge Behavior of Materials Used in AC and DC Systems
2017
The aim of the present work is to evaluate the behavior, from the space charge accumulation phenomenon point of view, of three different XLPE specimens used as insulation materials in high voltage systems. Considering that under DC stress the charge accumulation is more relevant as compared to the AC case, in the specimens for DC applications additives are typically added. In this work, three different specimens are analyzed. One is a free additive sample used conventionally under AC stress and two others include different additives that are used under DC stress. In order to measure the space charge accumulation, the Pulsed Electro Acoustic (PEA) method has been employed. For each sample, t…
Effect of plastic deformation on photoluminescence of ZnTe bulk monocrystals
1999
Abstract In this work ZnTe bulk single crystals have been deformed by axial compression with the aim of analyzing the luminescence properties related to intrinsic structural defects like dislocations. Plastic deformation greatly decreases the overall PL response, near-band-edge luminescence as well as deep level-related emissions. Results indicate a close relationship between the so-called Y1 and Y2 bands and the density of generated dislocations. Plastic deformation also produces an emission band at 603 nm whose intensity is proportional to the amount of introduced deformation.
The interphase model applied to the analysis of masonry structures
2014
Abstract Masonry material presents a mechanical response strongly dependent on the static and kinematic phenomena occurring in the constituents and at their joints. At the mesoscopic level the interaction between the units is simulated by means of specific mechanical devices such as the zero thickness interface model where the contact tractions and the displacement discontinuities are the primary static and kinematic variables respectively. In many cases the joint response depends also on internal stresses and strains within the interface layer adjacent to the joint interfaces. The introduction of internal stresses and strains leads to the formulation of the interphase model, a sort of enha…
Mechanisms of polymer crystallization from flowing solutions
1978
The recent experimental results on flow-induced crystallization by Pennings and coworkers show that extremely rigid polyethylene fibers can be obtained in a shear flow. On the other hand, the mechanism by which these flow-induced crystals are produced is still open to investigation. In this work a few aspects of fibrous crystal growth are theoretically investigated. The molecular dynamics of chains partly attached to the crystal and partly immersed in the solution is considered. The influence of temperature and of geometrical factors is also discussed.
Determination of the apparent activation energy of dielectric relaxation phenomena by means of the representation of ε” as a function of T at constan…
1984
Abstract The main purpose of this work is to justify the use of the positions of the maxima of e” versus T curves when calculating the apparent activation energy in secondary dielectric relaxations or in the relaxation associated with the glass transition. To exemplify this, phenomenological models as well as experimental results for methacrylic polymers are discussed.
Linear versus Three-Arm Star Polybutadiene: Effects of Polymer Architecture on the Thermodynamic Solution Behavior
2012
The interaction of linear and of three-arm star polybutadiene (PB) with THF was studied in the temperature range between 25 and 55 °C. Information for dilute solution rests on light scattering experiments; Flory–Huggins interaction parameter χ stem from vapor pressure measurements as a function of φ, the volume fraction of polymer. Despite the minute divergence in the architecture, the second osmotic virial coefficients of the two PBs differ noticeably. The present work demonstrates that these disparities become much more pronounced as φ increases and that they depend strongly on temperature. These findings are interpreted on the basis of an approach accounting for the effects of chain conn…
Experimental and numerical study of composite T-joints for marine application
2010
Abstract The aim of this work was to study the behaviour of composite T-joints used in marine applications. The effect of several parameters was investigated. In particular, three configurations were studied; i.e. with adhesive and with two different over-laminations. Moreover, the joined sections were made of different materials. These joints were subjected to a tensile load in the plane of the sheet. To quantify the effect of different designs on the strength, a variance analysis was performed. Finally, a numerical model was developed using a commercial finite element code (Ansys).
A Promising New Method to Estimate Drug-Polymer Solubility at Room Temperature
2016
The established methods to predict drug-polymer solubility at room temperature either rely on extrapolation over a long temperature range or are limited by the availability of a liquid analogue of the polymer. To overcome these issues, this work investigated a new methodology where the drug-polymer solubility is estimated from the solubility of the drug in a solution of the polymer at room temperature using the shake-flask method. Thus, the new polymer in solution method does not rely on temperature extrapolations and only requires the polymer and a solvent, in which the polymer is soluble, that does not affect the molecular structure of the drug and polymer relative to that in the solid st…
Investigations on the linear friction welding process through numerical simulations and experiments
2012
Abstract Linear Friction Welding (LFW) is a solid-state joining process applied to non-axisymmetric components. LFW involves joining of materials through the relative motion of two components undergoing an axial force. In such process the heat source is given by the frictional forces work decaying into heat determining a local softening of the material and eventually bonding conditions. In the paper the authors present a designed and assembled laboratory fixture for LFW operations and the results of an experimental and numerical campaign aimed to weld steel parts. The dedicated fixture permitted to highlight the effect of the most important process parameters. Process conditions allowing ef…