Hollow Discs Research Articles

Multi-criteria decision-making applied to the sustainability of building structures based on Modern Methods of Construction

Since the establishment of the Sustainable Development Goals, great concern has arisen on how to diminish the impacts that result from construction activities. In such context, Modern Methods of Construction (MMC) rise as a powerful way to reduce life cycle impacts through optimizing the consumption of materials. This paper focuses on the sustainability assessment of different modern construction techniques applied to concrete structures of single-family houses. The life cycle performance in terms of sustainability is compared between a conventional reference design, a precast design, a lightweight slab design with pressurized hollow discs, and a design based on double-wall structural elements. The sustainability is assessed through a set of 38 indicators that address not only the economic and environmental response of the designs, but also their social impacts as well. Five of the best known Multi-Criteria Decision-Making (MCDM) techniques (SAW, COPRAS, TOPSIS, VIKOR and MIVES) are applied to derive the life-cycle performance of each design into a single sustainability score. Since there is no consensus on which MCDM method works best in sustainability assessments, a Global Structural Sustainability Index (GSSI) combining and weighting the above is proposed here to aid the analysis of the results obtained. The results show that consideration of the three dimensions of sustainability leads to balanced designs whose preference need not coincide with those derived from each one-dimensional life cycle approach.

Influence of the Bauschinger Effect on the Distribution of Residual Stresses in a Thin Hollow Hyperbolic Disc under External Pressure

There are materials whose forward flow curve is practically independent of plastic strain (perfect plasticity) but the Bauschinger effect reduces the elastic range with flow reversal. A new model that is capable of describing such behavior of material under plane stress conditions has been recently proposed. An important class of structures in which the state of stress can often be accurately approximated by plane stress conditions is thin hollow discs. It is therefore of interest to use the new model for determining the distribution of residual stresses in thin discs subject to various loading conditions, followed by unloading. This paper presents a solution for the residual stresses and strains in a hollow hyperbolic disc loading by external pressure, followed by unloading.

Vibration Analysis for an Ultrasonic Transducer Coupled with Interior and Exterior Piezoelectric Discs

This research deals with an ultrasonic transducer coupled with piezoelectric discs of two types, solid and hollow. The interior solid disc is an exciter and the exterior hollow disc is an ultrasound sensor. The characteristics of the radial and axial vibrations in the axisymmetric motions were investigated theoretically, and verified experimentally. The piezoelectric governing equations were derived theoretically by virtue of mechanical displacements and electric potential, and their solutions produced characteristic equations yielding natural frequencies. The theoretical analysis was enhanced by three-dimensional mode shapes obtained using finite element analysis. The experimental results verified the theoretical analysis. Another experiment showed that the transducer excites ultrasound at the interior disc, and senses it at the exterior disc. The study showed that an ultrasonic transducer coupled with piezoelectric solid and hollow discs could be designed by determining a suitable diameter for each disc.

An investigation of cutting forces and tool wear in turning of Haynes 282

Superalloys belong to the group known as difficult to cut materials, and inside this category of material Haynes 282 is considered a novel material with huge applicability subjected to automobile, aerospace and gas turbine industries. The characterization of machining of this new material evidences a lot of importance. Therefore, this paper presents an experimental investigation into the effect of lubricant pressure and material heat treatment on cutting forces, machined surface quality and tool wear evolution on turning of superalloy Haynes 282. Face turning of hollow discs with fixed cutting conditions with cemented carbides tools where carried out to evaluate machinability.The results show that Haynes 282 Alloy in solution annealing Large Grain Solution (LGS) state has better machinability than precipitation hardened Large Grain Aged (LGA) state in terms of force levels and tool wear. In terms of coolant pressure effect, a significant improvement is not observed in the case of High pressure coolant (HiPC).

Description of reversed yielding in thin hollow discs subject to external pressure

This paper presents an elastic/plastic model that neglects strain hardening during loading, but accounts for the Bauschinger effect. These mathematical features of the model represent reasonably well the actual behavior of several materials such as high strength steels. Previous attempts to describe the behavior of this kind of materials have been restricted to a class of boundary value problems in which the state of stress in the plastic region is completely controlled by the yield stress in tension or torsion. In particular, the yield stress is supposed to be constant during loading and the forward plastic strain reduces the yield stress to be used to describe reversed yielding. The new model generalizes this approach on plane stress problems assuming that the material obeys the von Mises yield criterion during loading. Then, the model is adopted to describe reversed yielding in thin hollow discs subject to external pressure.

From Nanofibrous Hollow Microspheres to Nanofibrous Hollow Discs and Nanofibrous Shells.

Nano- and microsized structures are of central importance to advanced materials and nanotechnologies, which have tremendously impacted both biomedical and physical sciences. Herein, novel emulsification and thermally induced phase separation (TIPS) techniques to fabricate linear polymers into nanofibrous hollow objects are reported for the first time. Through manipulating the emulsification conditions, the evolution of the emulsion structure can be controlled and nanofibrous hollow microspheres with a controllable opening size and nano-fibrous shells can be fabricated. Through adjusting the rheological properties of the emulsions, nanofibrous hollow discs are also created. A new mechanistic hypotheses of the nanofibrous hollow object formation is proposed: the nano- and microscaled structures are independently determined by TIPS and the emulsification process, respectively. Guided by this theory, the nanofiber formation conditions for two further additional polymers (polyacrylonitrile and Nylon) under TIPS are identified, and solid/nanofibrous non-hollow/hollow microspheres are created from these two additional polymers under TIPS and emulsification for the first time. Therefore, the developed strategy is applicable to various polymer systems, and can broadly impact nano- and microfabrication technologies.

Forging of hollow sintered powder preforms

The forging of sintered metal powder preforms is currently arousing interest in many parts of the world as an economic method of producing components from metal powders. The present investigation has been undertaken with a view to studying the deformation characteristics of hollow sintered copper powder discs at room temperature. A theoretical analysis based on the energy method is presented for the estimation of deformation load using yield criterion for porous sintered materials and an appropriate interfacial friction law. Experiments have also been conducted which involved the forging of hollow discs of electrolytic copper powder at room temperature under axisymmetric conditions. In order to illustrate the validity of the theoretical approach, the theoretical and experimental results have been compared and presented graphically.

Elastic stress analysis of partially loaded hollow discs

This study develops and discusses solutions for the calculation of stress and displacement components in a two-dimensional elastic hollow disc. The solutions have many applications in civil, mechanical and mining engineering; such as roller disc cutter design in mechanical excavation engineering. Previously, solutions for the state of stress in circular-shaped domains have mainly considered the boundary loads as a pair of concentrated forces acting along the disc’s diameter at its circumference. In this study, the two internal and external circular boundaries of the hollow disc are under a general uniform loading, for which Lamé problem is a special case. The solution methodology is based on Michell’s expansion in polar coordinates and Fourier series representation of general boundary conditions developed for plane problems (plane strain and plane stress), encompassing all possible combinations of loading conditions at the boundaries. Displacement and stress components are constrained by equilibrium equations to ensure that they are single-valued and continuously-differentiable equations. Stresses are normalized with respect to either the applied internal pressure or the solutions from the special Lamé case, in which both boundaries at the radii r=a and r=b>a, are fully-loaded with uniform stresses p and q. Several solutions are developed in terms of design graphs. These solutions are applicable to both plane strain and plane stress problems through a conversion factor dependent on Poisson’s ratio. Results from various geometrical configurations and loading conditions show that the maximum value of the compressive normal stress is neither greater than the applied internal pressure (p) nor the external pressure (q=pa/b), while the maximum tensile stress generated in the disc reaches a value almost twice the internal pressure (p), and the maximum shear stress is not greater than one third of the internal pressure.

Mathematical model for mass and heat transfer in multilevel reactor for pyrolysis of used tyres

AbstractA new vertical pyrolysis reactor with multiple hollow discs was developed to pyrolyse waste tyres into carbon black, liquid oil and fuel gas. Based on the assumptions of an annular–granular heap, a constant angle of repose and uniform physical properties, a mathematical model for the mass transfer in a multilevel reactor is presented, which provided formulae for several important parameters, such as height, volume of each granular heap, retention time and effective covering ratio. According to the penetration model of particle heat transfer and the kinetic model of tyre pyrolysis, the exit temperature T out and rubber remnant content X out in granular heaps were effectively predicted by a straightforward stepwise calculation procedure, and the maximum pyrolytic capacity was calculated as well. The model and equations were applied in a pilot scale system (3000 ta−1). In the results, the theoretical predictions of maximum pyrolytic capacity and exit temperature are shown to be in satisfactory agreem...

Stress Analysis of an Orthotropic Rotating Disc under Thermal Loading

In this study, a thermal stress analysis on a glass-fiber/epoxy orthotropic rotating hollow discs is investigated. A closed form solution is performed using polynomials under some considerations. The temperature distribution is chosen to vary parabolically from inner surface to outer surface along the radial sections. The distributions of the tangential and radial stress components are given in figures. When the temperature is increased further, the tangential stress component decreases at the inner surface, whereas increases at the outer surface, and radial stress component are reduced. The radial displacement is calculated analytically and has a higher value at the outer surface than at the inner surface.

Nonreciprocal devices using ferrite ring resonators

Novel nonreciprocal components based on hollow ferrite discs, i.e. ferrite ring resonators, are discussed. Some three-port and four-port components are analysed, and some design guidelines are presented. It is shown that a ring structure requires a smaller diameter and ferrite thickness than a disc structure for the same frequency. A ring also provides another variable in design and permits ports to be connected to the inside as well as the outside. Novel components and increased component density may therefore be possible at the expense of bandwidth.

Stress intensity factors for multiple edge cracks in rotating hollow discs

The calculation of stress intensity factors for one to four equal length, equally spaced radial edge cracks at the inner and outer surfaces of a rotating hollow circular disc is presented. The technique used for the solutions is the modified mapping-collocation method. Data are presented for two wall ratios.

Contact Methods for Creep and Elasticity Investigations in Polymer Mechanics

Abstract A new method for measuring values of elastic and creep moduli of plastics is proposed. The method is based on an observed phenomenon found while investigating behaviour of compressed hollow discs. According to this observation a ratio of internal and external diameters has been found, ensuring a displacement of a diameter of the disc depending on one material compliance only. Outlines of a theoretical solution and some experimental results are given.

Spatial frequency peaks in the responses of the locust DCMD axon to rotation of periodic patterns, lines and dot arrays

Responses in the locust descending contralateral movement detector (DCMD) neurone to rotation of various types of test pattern were recorded. Peaking of response at high spatial frequencies was found for both radial and chordal patterns of uniform stripes, but the type of result was different in the two cases. The distance of the pattern from the eye had a marked effect on the result obtained for radial patterns, which could not be accounted for simply in terms of the reduction in whole-pattern subtense which accompanied greater distances. Reduction in pattern area, by masking at a fixed distance, produced a steep fall in response only when the reduction reached one-eighth of the total area. Single line objects were more effective than complete gratings for comparable subtenses, and the response to such objects rose smoothly and monotonically with subtense. Parallel pairs of thin lines were not discriminated from solid lines of the same subtense at angles below about 0.2°. Above this angle there was marked discrimination, the solid lines becoming much more effective. This result was in general true for both black lines on white and white lines on black. However, in contrast to the monotonic rise shown by solid lines for either contrast, there was an initial peak in the paired-line response, occurring in the range 0.12° (white on black) to 0.2° (black on white). Single discs also showed a smooth rise with increase in subtense. Circles (‘hollow discs’) were less effective than discs. Rotation of arrays of black dots produced peaking in response at about 0.38°, far exceeding the response for a single dot of the same size. Above 1.5° the response to a single dot exceeded that to an array. It was concluded that, as in the experiments with on/off stimulation with stationary targets reported earlier, spatial frequency peaks occurred also for moving targets, but only when these had a subdivided nature, e.g. periodic lines, paired lines or dot rasters. The peaks found were in the same range as those for stationary targets, i.e. 0.3–0.1°, or about 3–10 cycles/degree.