Search results for "deformation"
showing 10 items of 515 documents
Time dependent viscoelastic rheological response of pure, modified and synthetic bituminous binders
2016
Bitumen is a viscoelastic material that exhibits both elastic and viscous components of response and displays both a temperature and time dependent relationship between applied stresses and resultant strains. In addition, as bitumen is responsible for the viscoelastic behaviour of all bituminous materials, it plays a dominant role in defining many of the aspects of asphalt road performance, such as strength and stiffness, permanent deformation and cracking. Although conventional bituminous materials perform satisfactorily in most highway pavement applications, there are situations that require the modification of the binder to enhance the properties of existing asphalt material. The best kn…
The elastic interaction of high-spin and low-spin complex molecules in spin-crossover compounds
1988
Several transition metal compounds show a transition from the low-spin (LS) to the high-spin (HS) electronic state with increasing temperature. The cooperative nature of the transition is usually parametrised by an interaction constant Gamma , the origin of which is still under discussion. In the frame of the lattice expansion mode, the interaction Gamma is attributed to the elastic interaction between the spin-changing ions as a result of the deformation of the crystal accompanying the transition. The authors calculate the complete elastic energy originating from the so-called image pressure in closed form by considering the crystal as an isotropic homogeneous elastic medium with the spin-…
Plastic Deformation of Single Nanometer-Sized Crystals
2008
We report in situ electron microscopy observations of the plastic deformation of individual nanometer-sized Au, Pt, W, and Mo crystals. Specifically designed graphitic cages that contract under electron irradiation are used as nanoscopic deformation cells. The correlation with atomistic simulations shows that the observed slow plastic deformation is due to dislocation activity. Our results also provide evidence that the vacancy concentration in a nanoscale system can be smaller than in the bulk material, an effect which has not been studied experimentally before.
Effect of type, size and deformation on the polarizability of carbon nanotubes from atomic increments
2006
The interacting induced dipole polarization model is used for the calculation of the dipole–dipole polarizability α. The method is tested with single-wall carbon nanotubes (SWNTs) as a function of nanotube radius and elliptical deformation. The results are similar to ab initio reference calculations. For the zigzag tubes, the polarizability follows a remarkably simple law. The calculations effectively differentiate among SWNTs with increasing radial deformations. The polarizability and related properties can be modified continuously and reversibly by the external radial deformation. These results suggest a technology in which mechanical deformation can control chemical properties of the car…
Beta-forging of Ti6Al4V titanium alloy powders consolidated by HIP: Plastic flow and strain-rate relation
2014
Ti6Al4V is probably the best known and studied titanium alloy, not only for aerospace applications. Nevertheless the deformation behavior still represents a challenge if any modification in the deformation process is required or introduced. This work deals with deformation behavior description of Ti6Al4V HIPped powders during high temperature deformation tests carried on in the Beta-region. Laboratory compression and tensile tests have been coupled with relaxation tests in order to achieve robust data about strain rate sensibility m-coefficient and activation energy Q. These results have been fitted for the assessment of a more general exponential deformation law. The final result is a “Dor…
Characteristics of mechanical metamaterials based on buckling elements
2017
Metamaterials are composed of structural elements and derive their properties mainly from the inner structure of the elements, rather than the properties of their constituent material. By designing an unstable structural element as the building block of a metamaterial, many interesting effective material properties can be obtained. The deformation and dissipation mechanisms of such a material built from unstable structural elements is studied in detail. To do so a combination of analytical, semi-analytical, and numerical models are applied to a single buckling element, a periodic cell, and finite size combinations of buckling elements including gradients in the properties of the building bl…
Radiation effects on stress evolution and dimensional stability of large fusion energy structures
2021
Abstract We assess the effects of neutron irradiation on the deformation and stress evolution of large-scale fusion energy structures. This is accomplished through non-linear finite element structural analysis of the coupled thermal and mechanical fields at the Beginning-Of-Life (BOL), at 45 dpa, and at 90 dpa. Radiation effects include volumetric swelling and the influence of radiation on the mechanical properties. The system studied here is a large section of a full inboard module of an integrated structure comprising the First Wall and Blanket (FW/B) of a Dual Cooled Lithium-Lead (DCLL) energy conversion unit in the Fusion Nuclear Science Facility (FNSF). The structural material is the f…
Melting and multipole deformation of sodium clusters
1999
Melting and multipole deformations of sodium clusters with up to 55 atoms are studied using an ab initio molecular dynamics method. The melting temperature regions for Na20, Na40, and Na 55 + are estimated. The melting temperature region determined here for Na 55 + agrees with the one determined experimentally. The dominating deformation type observed at the liquid phase for Na20 and Na40 is octupole deformation and for Na14 and Na 55 + quadrupole deformation.
Computer simulation of metal flow in the hot upsetting of a high-strength aluminium alloy
1993
Abstract The effects of metal-working temperature on the hot axisymmetric upsetting of AA 7012 aluminium alloy were investigated in the temperature range of from 250 to 400°C, at a strain rate of 4 s −1 . The material behaviour was studied by means of simulative methods based on the analysis of torsion-test results which have shown that when the strain increases, the flow stress increases to a peak value and then decreases to a fracture value. Furthermore, the flow stress decreases with decreasing strain rate and with increasing temperature. Constitutive equations, describing accurately the hot deformation behaviour of the material, were defined and used subsequently in a numerical model th…
Laboratory and in-situ tests for estimating improvements in asphalt concrete with the addition of an LDPE and EVA polymeric compound
2019
Abstract Pavement deformation is a critical issue in the design of pavement structures and the related mixture. Asphalt concretes may be very sensitive to this problem, in compliance with the viscoelastic behaviour of the adopted bitumen. To improve the material performance, many attempts have been made to introduce in the mixture other materials as “modifiers” or “additives” for increasing the permanent deformation resistance and the elastic modulus of the material. Among the different possible materials, polymers determined significant improvements in the road pavement performance. In this paper, the authors tested the adoption of a specifically engineered polymeric compound, in order to …