Hemispherical Dome Research Articles

Forming limit evaluation of adhesive bonded sandwich steel sheets and numerical prediction

AbstractIn the present work, the effect of hardener to resin ratio of epoxy adhesive on the formability of adhesive bonded steel sheets has been studied. Forming limit curve has been evaluated by hemispherical dome tests at predefined strain‐paths. They are predicted by finite element simulations using strain mapping method. Cohesive zone model has been used to model the interface between skin and adhesive core. An improvement in the forming limit of sandwich steel sheets has been observed when the hardener to resin ratio is changed from 0.6 : 1 to 1 : 1 due to the improved plasticity of adhesive core layer at 1 : 1 ratio as compared to others. The forming limit of sandwich sheet made at 1 : 1 ratio is equivalent to base steel sheet of same thickness and grade. This shows the potential use of sandwich sheet in place of base steel sheet. The forming limit curve predictions agree well with experimental data for base sheet, while reasonable agreement is observed in case of sandwich sheet. Numerical prediction of interface delamination show insignificant influence of hardener to resin ratio on the onset of delamination and significant effect of strain‐paths.

Theoretical predictions and experimental investigation on three stage hemispherical dome in superplastic forming process

Superplastic blow-forming technique is one of the fastest manufacturing methods for producing complicated components in automobile industries. The uniform thickness distribution where obtain in a multiple geometry component is a common problem during superplastic forming process. To prevail over this, a more than two stage superplastic forming process has been attempted using a three-step hemispherical die to form a cup-shaped 5083 aluminium alloy sheets. The superplastic forming process (SFP) parameters like thickness profile, forming time, optimum pressure, dome height and temperature were measured experimentally. Theoretical models and computational using the finite element code (ABAQUS) have been developed and validated with experimental results. Thin profile was obtained at the minimum forming time and optimum forming pressure.

Flexible Multielectrode Arrays With 2-D and 3-D Contacts for In Vivo Electromyography Recording.

We present a system for recording in vivo electromyographic (EMG) signals from songbirds using hybrid polyimide-polydimethylsiloxane (PDMS) flexible multielectrode arrays (MEAs). 2-D electrodes with a diameter of 200, 125, and 50 μm and a center-to-center pitch of 300, 200, and 100 μm, respectively, were fabricated. 3-D MEAs were fabricated using a photoresist reflow process to obtain hemispherical domes utilized to form the 3-D electrodes. Biocompatibility and flexibility of the arrays were ensured by using polyimide and PDMS as the materials of choice for the arrays. EMG activity was recorded from the expiratory muscle group of anesthetized songbirds using the fabricated 2-D and 3-D arrays. Air pressure data were also recorded simultaneously from the air sac of the songbird. Together, EMG recordings and air pressure measurements can be used to characterize how the nervous system controls breathing and other motor behaviors. Such technologies can in turn provide unique insights into motor control in a range of species, including humans. An improvement of over 7× in the signal-to-noise ratio (SNR) is observed with the utilization of 3-D MEAs in comparison to 2-D MEAs.

The role of different sliding resistances in limit analysis of hemispherical masonry domes

A limit analysis method for masonry domes composed of interlocking blocks with non-isotropic sliding resistance is under development. This paper reports the first two steps of that work. It first introduces a revision to an existing limit analysis approach using the membrane theory to find the minimum thickness of a hemispherical dome under its own weight and composed of conventional blocks with finite isotropic friction. The coordinates of an initial axisymmetric membrane surface are the optimization variables. During the optimization, the membrane satisfies the equilibrium conditions and meets the sliding constraints where intersects the block interfaces. The results of the revised procedure are compared to those obtained by other approaches finding the thinnest dome. A heuristic method using convex contact model is then introduced to find the sliding resistance of the corrugated interlocking interfaces. Sliding of such interfaces is constrained by the Coulomb’s friction law and by the shear resistance of the locks keeping the blocks together along two orthogonal directions. The role of these two different sliding resistances is discussed and the heuristic method is applied to the revised limit analysis method.

THE HISTORY OF CONSTRUCTION AND ARCHITECTURE OF THE SVYATO-TROITSKAYA CHURCH IN THE PRYMORSK CITY, ZAPOROZHYE REGION

The article presents the history of construction and architecture of the Svyato-Troitskaya church in the Prymorsk city, Zaporozhye region. The temple, consecrated in 1838 in the estate of Count V. V. Orlov-Denisov, is one of the oldest architectural monuments of the Zaporozhye region in the style of classicism. The classicism style in architecture is accompanied by a symmetrical-axial composition and restraint of decorative finishes. The role of classicism in the architecture of temple construction in Ukraine of the XIX century is analyzed. The imperial decree of 1806 with the regulation of church construction in accordance with real needs was accompanied by the publication of albums of standard designs that were sent to all provinces. The role of a model project in the construction of the temple is shown for the first time. The features of the construction of the Svyato-Troitskaya church in the style of classicism are analyzed: proportionality, symmetry, a minimum of architectural details, decoration with elements of classical antiquity - strict columns and antique details, porticoes and pediments on the facades. Architectural decisions and church features: the dome is based on powerful pylons formed by the intersection of longitudinal and transverse walls; rectangular pilasters protruding on the facades under triangular gables, form a flat portico; semicircular shallow niches are located above the window and doorways of a rectangular shape; the temple ends with a hemispherical dome on a cylindrical drum with eight window openings. The restoration of the temple of the 1980s is considered, after which the Svyato-Troitskaya church was included in the register of cultural heritage of Ukraine. The article presents the history of the сossack family, who deserved the count's dignity, shows the role of its representatives in the history of the fatherland. Explores the life of Count V. Orlov-Denisov, who worked on the construction of Svyato-Troitskaya church in the Obitochnoe village.

Finite Element Method For The Parametric Exploration Of Domestic Composite Liquid Petroleum Gas Cylinder With Steel

Conventional Steel Cylinders used for LPG cylinder for domestic applications are not manufactured in a single joint but are welded. While composite cylinders are manufactured in a single joint, Composite components cannot be welded like the steel cylinder. Composite Cylinders are winded using Filament Winding technique. Compared to Steel Cylinders, Composite Cylinders are costlier. Composite cylinders are safer than steel cylinder. Composite Cylinders due to a rubber lining inside, they are 100% leak proof. If mass production of composite cylinders are done then the cost may get reduced. This paper summarizes the design and analysis of the manufacturing of Liquid petroleum gas (LPG) Cylinder using Glass Fibre Reinforced Plastic (GFRP) material. Further, the stresses and deformations that may develop due to internal pressure loading on the LPG Cylinder with GFRP material are to be analysed. Hence finite element analysis is applied with ANSYS software to simulate the corresponding analysis. Then the parametric comparative analysis of the LPG Cylinder with steel and GFRP material is also carried out assuming hemispherical end dome and considering cylinder without end frames. A significant saving in the weight of the LPG Cylinder, significant increase in the deformation and volumetric strain is observed with GFRP material against steel.

A numerical approach on achieving uniform thickness distribution in pressure thermoforming

Pressure thermoforming is one of the most widely used thermoplastic processing technique where a polymer sheet is deformed using gas pressure. Pressure forming is not suitable in applications such as airplane canopies where precise control over dimensions is required, because of the drawback of uneven thickness distribution of the product. The current work seeks to find a way to use the pressure forming technique to produce components having uniform thickness distribution. The deformation process of PMMA sheet into a hemispherical dome using pressure thermoforming is numerically analyzed and the concept of provision of initial thickness distribution to the sheet is proposed.

Algorithmically Optimized Hemispherical Dome as a Secondary Optical Element for the Fresnel Lens Solar Concentrator

The significance of this work lies in the development of a novel code-based, detailed, and deterministic geometrical approach that couples the optimization of the Fresnel lens primary optical element (POE) and the dome-shaped secondary optical element (SOE). The objective was to maximize the concentration acceptance product (CAP), while using the minimum SOE and receiver geometry at a given f-number and incidence angle (also referred to as the tracking error angle). The laws of polychromatic light refraction along with trigonometry and spherical geometry were utilized to optimize the POE grooves, SOE radius, receiver size, and SOE–receiver spacing. Two literature case studies were analyzed to verify this work’s optimization, both with a spot Fresnel lens POE and a spherical dome SOE. Case 1 had a 625 cm2 POE at an f-number of 1.5, and Case 2 had a 314.2 cm2 POE at an f-number of 1.34. The equivalent POE designed by this work, with optimized SOE radiuses of 13.6 and 11.4 mm, respectively, enhanced the CAP value of Case 1 by 52% to 0.426 and that of Case 2 by 32.4% to 0.45. The SOE’s analytical optimization of Case 1 was checked by a simulated comparative analysis to ensure the validity of the results. Fine-tuning this design for thermal applications and concentrated photovoltaics is also discussed in this paper. The algorithm can be further improved for more optimization parameters and other SOE shapes.

Experimental study on the effects of incremental forming and friction stir welding on formability of AA5083 sheet

This article presents investigations on the effects of incremental forming and friction stir welding on the formability of AA5083 through comparison of experimentally predicted forming limit curves. Initially hemispherical dome stretching test was performed to predict forming limit curve for the parent sheet in conventional forming from plane strain to biaxial stretching strain path. Forming limit curve in case of single point incremental forming of parent sheet was also determined by conducting groove test. Formability in single incremental forming was found to be far better than that in conventional forming from the comparison of the forming limit curves for both the cases. Friction stir welded blanks were prepared by varying tool shoulder diameter, welding speed and tool rotational speed as input parameters following three levels of inputs parameters according to the central composite design matrix. Optimal welding parameters were selected based on the weld quality judged by bending angle of free bend test of the welded blanks and visual inspection. Forming limit curve for friction stir welded sheet was generated through incremental forming groove tests of the blanks made by optimal welding parameters. Formability of welded sheet was found to decrease compared to the parent sheet due to the severe plastic deformation and work hardening during the welding operation.

Limits and Potential of 3D Printing Technologies for Construction of Concrete Shells

Concrete shells are a very effective type of building structures due to their ability to bridge large spans with minimal construction thickness. This type of building structures built on the medieval vaulting techniques and, regarding the use of reinforced concrete over the last 100 years, it has overcome the limitations of the masonry vaulting technologies and enabled to increase the span of structures to tens of meters. The construction technology to realize concrete shells using monolithic casting into formwork is besides abovementioned advantages characterized by high labour and thanks to the cost and manufacturing intensity of double curved formwork panels it allows economical realization of only selected structural geometries. Its considerable limitation is, besides the costly production of double curvature formwork, also the laborious installation of formwork and falsework structures. The solution seems to be in line with the upcoming transition to Construction 4.0 robotizing the construction technology of shells that could create a similar increase in productivity and design possibilities as was the technological transition between vaults and shells. One of the promising technologies of robotic production seems to be digital fabrication methods and, in particular, 3D printing or in other words additive manufacturing. This wasteless technology, which has been used to date for experimental projects mainly for the realization of vertical bearing structures, has, despite the first attempts at realizing vaults, a number of technological limitations. In this article, authors aim to summarize and indicate possible constraints of on site 3D printing of domes. They further indicate the possible ways to overcome these limitations and suggest two different means of on site 3D printing of hemispherical dome and the dome based on the catenary profile using extrusion nozzles with different profiles. Finally they discuss the Eurocode requirements for concrete shells and suggest technological solutions for on site 3D printed shells in terms of structural reinforcement.

A 6 MW/m2 High Heat Flux Testing Facility of Irradiated Materials Using Infrared Plasma-Arc Lamps

Assessing the effect of neutron irradiation of plasma-facing materials has been challenging due to both the technical and radiological challenges involved. In an effort to address the radiological challenges, a facility was developed to conduct high heat flux testing (HHFT) of inherently small samples of neutron-irradiated materials. A new line-focus reflector was designed and fabricated at Oak Ridge National Laboratory for a plasma-arc lamp (PAL) to attain a source heat flux of 12 MW/m2. The new reflector was fabricated with two ports for monitoring specimen condition during HHFT. At the same operational conditions for PAL, the absorbed heat flux in tungsten was increased from 1.39 MW/m2 with the uniform irradiance reflector to 5.12 MW/m2 for the line-focus reflector. This fourfold increase in the heat flux, at the same PAL electrode lifetimes, enabled cost-effective facility operation for a high number of cyclic high heat flux tests. Specifically, the test section is confined to a hemispherical dome, and specimens are bolted directly to a water-cooled copper alloy rod. Temperature measurement in the PAL facility was a main challenge due to a limited line of sight. For the first time in a PAL facility operating at high heat fluxes, the specimen surface temperature was directly measured during HHFT with a pyrometer. The HHFT data, which were obtained in this upgraded PAL facility, demonstrated the facility readiness for irradiated materials.

Forming-limit strains of perforated steel sheets under biaxial stress state

The forming-limit strains of cold-rolled steel sheets perforated with regularly arranged round-, square-, and cross-shaped holes were experimentally and theoretically estimated. Two types of hole arrangements, i.e. square and triangular patterns, were considered for each hole shape and the experimental forming-limit strains were determined using the hemispherical dome test (also known as Nakazima test). The theoretical forming-limit curves were computed using the finite element method with Hill's quadratic yield function and a plastic instability criterion determined from the external force power. By comparing the experimental results and theoretical calculations under proportional loading, the formability prediction performance of the theoretical approach was evaluated. It was found that although the approach is not applicable for the triangular array of cross-shaped holes, it can achieve partially acceptable prediction for the other cases.

One-lens camera using a biologically based artificial compound eye with multiple focal lengths

This work presents the fabrication of a one-lens camera using a biologically inspired artificial compound eye with multiple focal lengths. Traditional camera designs that consist of many separated lenses are difficult to assemble due to tight tolerance. The one-lens camera design is demonstrated experimentally in this work to avoid tolerance buildups. This structure is based on the principles of both the human eye as well as an insect’s compound eye. The artificial compound eye is a curved hexagonal microlens array, like an ommatidial array, wherein each artificial ommatidium collects light with a small angular acceptance. The ommatidia, in a typical hexagonal arrangement of 37 lenses, are arranged across a hemispherical photopolymer dome. The curved hexagonal array helps us to achieve a compact and wide field-of-view camera module. The fabrication process for the curved array is divided into two parts: creation of a planar hexagonal multi-lens array, and a replication process. To create the planar array, we use inkjet printing technology with the hydrophilic confinement effect to establish microlens shapes with different profiles. Next, the replication process converts the planar array into a curved shape. The spherical configuration of the hexagonal array is accomplished by applying the template architecture to a reconfigurable surface shape, that is, a photopolymer duplication using a deformed elastomer membrane with the hexagonal array pattern. In our experimental demonstration, microlenses in four rings with different focal lengths are fabricated on a single hemispherical lens with radius of curvature of 2.4 mm. The thickness of our proposed system is 3.04 mm, the f-number is 1.68, and the diagonal field of view is 92.6 deg. Above all, our presented camera module system uses a single one-piece lens.

Forming of Adhesive-Bonded Sandwich Sheets with a Rubber Pad

The effect of a rubber pad, its quality, and diameter, on the forming limit of adhesive-bonded sandwich steel sheets is studied using hemispherical dome tests. The forming limit curve (FLC) is predicted with finite element simulations and the strain mapping method. The FLCs of sandwich sheets are compared with that of base, i.e., 0.4- and 1.2-mm-thick sheets. The forming limit of sandwich sheets when formed using rubber pads improve significantly, and is equivalent to that of the base sheet of equivalent thickness formed without a rubber pad. The rubber pad leads to a uniform strain distribution due to a cushioning effect provided by the rubber pad which also delays the onset of interface delamination. The polyurethane rubber performs better compared with the silicone rubber in improving the FLC. The effect of the rubber pad diameter is insignificant. The FLCs and forming height predicted by numerical simulations are reasonably accurate, when compared with the experimental results.

Tensile and Fracture Properties of Commercially Pure Titanium (CP-70) Hemispherical Forgings

Commercially pure (CP-70) titanium is used as the metallic liner for composite overwrapped pressure vessels used in satellite launch vehicles. The metallic liner is fabricated from domes machined out of CP-70 titanium forgings. During the hot closed-die forging of CP-70 domes from billets, the amount of deformation varies location to location, due to the non-uniform flow of material in the die cavity. This non-uniform strain distribution in the hemispherical dome results in microstructural variations along the forging axis which will remain even after annealing. The aim of the present work is to study the tensile properties, impact strength and fracture toughness of CP-70 hemispherical forging in annealed condition from top end to bottom end of domes in radial and circumferential directions with a view to understand the variation in mechanical properties to asses the design margin. Study revealed significant amount of the work-hardening difference within a forged dome even after annealing.

A comprehensive stress indicator for evaluating plant water status in almond trees

This study evaluated a comprehensive plant water stress indicator that integrates the leaf temperature and the environmental conditions that can provide feedback on the plant response to irrigation scheduling. This quantity—Comprehensive Stress Indicator (CSI)—is based on the reformulation of the leaf energy balance equation. Specifically, CSI is the ratio of the temperature difference between a dry leaf (i.e., a leaf with a broken stem) and a live leaf (on the same tree) [i.e., Tdry-Tleaf] and the difference between the vapor pressure inside the stomatal cavity at saturation and the vapor pressure of the air at ambient temperature [i.e., es(TL)-e(TA)]. The required measurements to compute CSI include dry leaf temperature, live leaf temperature, relative humidity, and air temperature at the tree being monitored. In this study, all measurements were obtained using a sensor suite called the leaf monitor. Leaf monitors were connected to a wireless mesh network to communicate the data to a website. The leaf monitor included two thermal infrared sensors, one for the dry leaf and one for the live leaf, both of which were housed in the same unit with almost identical environmental conditions due to a diffusing hemispherical dome that enclosed these sensors. The CSI is a dynamic indicator with a value for every data sample collected. For a single indicator representing each day, the CSI was evaluated in two ways. First, the CSI was integrated with respect to time from 10 A.M. to 6 P.M. to obtain the Integrated Comprehensive Stress Indicator (ICSI). Second, the CSI was averaged from 1 P.M. to 3 P.M. to obtain the Average Comprehensive Stress Indicator (ACSI). Both ICSI and ACSI were compared to other stress indicators, including the existing Crop Water Stress Index (CWSI) and Integrated Degrees Above Non-Stressed (IDANS). Results show that ICSI and ACSI are satisfactorily correlated with midday stem water potential (SWP). The ICSI and ACSI indicators may be more convenient than other stress indicators because they require measurements only at the tree being monitored.

Prediction of material behavior during biaxial stretching of superplastic 5083 aluminum alloy

In order to predict the flow behavior of a superplastic Al-Mg alloy sheet under near biaxial tension mode, finite element simulation was performed using commercial FE software (ABAQUS). To capture the time-dependent plastic behavior of the material, three constitutive models, i.e., the Voce model, a power law, and a newly introduced variable m value viscoplastic (VmV) model, were implemented in FE simulations. The models’ parameters were assessed from the three uniaxial stress-strain curves ranging from 10−3 to 10−1 s−1. To validate the simulation results, Nakazima hemispherical dome testing was performed under isothermal conditions using a constant strain rate of ~ 0.01 s−1 at 450 °C. After the tests, the thickness of the deformed parts was measured and the volume fractions of cavities at different locations were assessed using X-ray micro-tomography, and the impact of the strain path on the rate of cavitation was discussed. Based on the obtained results, when the material behavior was modeled using the VmV model, the accuracy of the prediction was about 2 and 5 times better than the ones from power law and Voce model, respectively. It was also observed that the volume fraction of the cavities exponentially increases with equivalent plastic strain and it depends on the strain path history.

Influence of altitude on aero-optic imaging quality degradation of the hemispherical optical dome.

We investigated the influence of altitude on aero-optic imaging quality degradation of the hemispherical optical dome. Boundary conditions for the aerodynamic heating effect of the optical dome were calculated by solving the Reynolds-averaged Navier-Stokes equations provided by FLUENT. The finite element model and the thermal-structure simulation results of the optical dome were obtained using ANSYS. The 3D nonuniform refractive index field of the optical dome was obtained according to the thermal-optical effect. The optical tracking method based on the fourth-order Runge-Kutta algorithm was adopted to simulate the optical transmission through the optical dome. The Strehl ratio (SR), encircled energy, distorted target images, and peak signal-to-noise ratio were presented for imaging quality evaluation. The variation rules of these imaging quality evaluation parameters were obtained in the altitude range of 0-45km. The results showed that, in the same flight conditions, with the increase of altitude, peak signal-to-noise ratio (PSNR) of the distorted image, and SR result were increased, and radiuses of dispersion spots, including 80% energy, were decreased; therefore, the influence of aero-optics effect on imaging quality degradation was gradually weakened.

On the shape optimisation of the force networks of masonry structures

A novel lumped stresses network approach for the analysis of the mechanical behaviour of masonry structures is presented. It is formulated through a network of lumped stresses, making use of polyhedral stress functions and a variational approximation of the continuous equilibrium problem. The proposed method allows for modelling masonry structures as no-tension elements and gives, in the case of curved masonry members, the optimised surface through a predictor-corrector procedure and the stress function describing the membrane stress. The given approach offers a useful tool for predicting the crack pattern of unreinforced masonry structures and the associated stress fields. It is validated against some benchmark case studies dealing with a hemispherical dome, a groin vault, a cloister vault and a masonry beam.

Quantitative Analysis of Tip Growth, Phototropic Responses, and Other Blue Light-Dependent Photoresponses of Vaucheria.

The coenocytic tip-growing alga Vaucheria exhibits positive and negative phototropism, apical expansion, polarotropism, and branch induction from the illuminated region of the cell, all of which are caused by blue light. The bending response of Vaucheria is a blue light-mediated growth response. Differently from diffuse-growing cells or organs, the apical hemispherical dome of the Vaucheria cell is the site of not only maximum growth activity but also the site of blue light perception. Thence the phototropic response is initiated by the bulging mechanism: that is, a quick shift of the growth center to the adjacent subapical flank region. Since tip growth is driven by localized exocytosis, both phototropic bending and branch induction are considered to be closely related blue light-responses. Here I describe first how to prepare a highly useful culture medium for most freshwater algae, to establish unialgal and axenic culture of Vaucheria, and then describe several simple illumination systems using ordinary and/or inverted microscopes for the measurements of tip growth and for analyses of phototropism, polarotropism, and blue light-induced branching. Brief information is also included concerning the nature and function of aureochrome, the newly discovered, ochrophyte-specific blue light receptor. Aureochrome mediates blue light-induced branching, but its role in the phototropic response is still not elucidated.