Foam Shell Research Articles

Influence of Mixing and Standing Times on the Rheological Properties and Performance of Coatings for Lost Foam Shell Casting

Influence of Mixing and Standing Times on the Rheological Properties and Performance of Coatings for Lost Foam Shell Casting

Safe Reduction of Intermammary Distance in Implant Breast Augmentation Without Fat Grafting.

Over the latest 15 years, breast augmentation with implant has been progressively refined technically and artistically. However, little attention is usually given to the intermammary space. The aim of this article is to report author's experience and technique in the safe reduction of the intermammary space in breast augmentation with implants without fat grafting. From July 2019 to July 2021, 62 consecutive patients undergoing cosmetic breast enhancement with implant and requesting a reduction of the intermammary space were retrospectively evaluated. Preoperatively, breast features were registered for all patients. Preoperative intermammary distance ranged from 2.3 to 7 cm (5.4 ± 0.74). The average follow-up time was 20 months (range 12 to 36 months). All implants were anatomical silicon-gel filled implants with micropolyurethane foam shell. No major early and late complications were experienced. The outcomes were graded as excellent in 45 breasts (72.6 %), very good in 15 (24.2%), good in the two cases (3.2%) with minor delayed wound healing (less than 1 cm) which solved conservatively within 1 month. Patients' satisfaction was high to very high. Postoperative intermammary distance was reduced in all cases and ranged from 1 to 4.5 (mean 2.6 ± 0.52 cm) CONCLUSION: The intermammary distance can be safely reduced with implant only in all cases who seek it, both via submuscular and via subfascial approach by a precise medial pocket dissection and implantation of micropolyurethane foam-coated implant, which guarantee device's stability during the healing process avoiding malposition. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Modified Polyethylene Foams for Insulation Systems.

Effective insulation of buildings and other industrial objects requires the use of materials and system solutions that ensure maximum uniformity and density of insulation shells. The study focuses on the development of insulation systems based on expanded polyethylene and, in particular, on the development of modified polyethylene with reduced flammability containing a flame-retardant modified montmorillonite clay, which does not hinder gas formation, and silicate nanofillers in layered construction. Active experiments based on mathematical design methods allowed us to establish an analytical relationship between flame-retardant and modifier consumption and extruder pressure and response functions: average density of polyethylene foam and flammability criterion. The flammability criterion was taken as the oxygen index of the modified polyethylene foam. A foaming agent masterbatch was used as the flame retardant. Analytical optimization of mathematical models obtained as a result of active experiments allowed us to determine the optimal flame-retardant consumption, which was 3.7-3.8% of the polymer mass. Optimised systems for average density and oxygen index of flammability of modified polyethylene were obtained. A nomogram for predicting the material properties and selecting the composition, and an algorithm for a computer program for evaluating the properties of modified polyethylene foam as a function of the values of various factors, were developed. Taking into account the possible expansion of the scope of application of rolled polyethylene foam and seamless insulation shells based on it, possible solutions for insulation systems were studied using the program THERM, and a combined insulation system was adopted.

Design of an Innovative Hybrid Sandwich Protective Device for Offshore Structures

Lightweight foam sandwich structures have excellent energy absorption capacity, combined with good mechanical properties and low density. The main goal of this study is to test the application of an innovative hybrid sandwich protective device in an offshore wind turbine (OWT). The results are useful for offshore structure applications. Different lightweight materials (aluminum foam, agglomerated cork, and polyurethane foam) were investigated using experimental tests and numerical simulations. Closed-cell aluminum foam showed the best performance in terms of the energy absorption capacity during an impact. As such, a Metallic Foam Shell (MFS) device was proposed for the fender of offshore wind turbines. A finite element model of a ship-OWT collision scenario was developed to analyze the response of a fender with the MFS device under repeated impacts. The proposed MFS fender can be used efficiently in a wide temperature range, allowing it to be used in harsh climatic conditions.

Flexural wave dispersion characteristics of imperfect Ti-6Al-4V foam circular cylindrical shells in a thermal environment

The present paper is mainly focused on analyzing the flexural wave dispersion of imperfect Ti-6Al-4V foam circular cylindrical shells in a thermal environment. The pores were supposed to be distributed across the thickness (z-direction) in the form of three different patterns as follows: symmetric porosity distribution (SPD), asymmetric porosity distribution (ASPD) and uniform porosity distribution (UPD). Besides, various kinds of temperature variations, including sinusoidal, linear and uniform temperature variations, were studied. The strain-displacement relationship of the shell was derived based on the first-order shear deformable theory (FSDT) of shells. Hamilton’s principle was also applied to obtain the governing equations of metal foam shells which were then solved using an analytical method. Finally, influences of different parameters including circumferential wave number, different kinds of temperature variation, temperature change, radius to thickness ratio , types of porosity distribution across the thickness, porosity coefficient and mode number on the variations of phase velocity and wave frequency were investigated and the results were illustrated and discussed.

Nondestructive Evaluation of Aluminium Foam Panels Subjected to Impact Loading

Aluminium foam sandwich structures have excellent energy absorption capacity, combined with good mechanical properties and low density. Some of the authors of this paper proposed an innovative Metallic Foam Shell protective device against flying ballast impact damage in railway axles. A closed-cell aluminium foam was chosen for the Metallic Foam Shell device. The main goal of this study was the experimental investigation of the impact responses of aluminium foam panels. Low velocity impact tests were carried out at different energies on different types of aluminium foam panels in order to investigate the effects of some parameters, such as core thickness, skin material and layer. Tests were conducted at repeated impacts on aluminium foam panels without and with skins made of aluminium and glass fibre-reinforced polymer. The experimental results were compared and the impacted panels were investigated by means of the nondestructive techniques ultrasonic phased array and digital radiography.

Evolution behavior of laser welding in hybrid structure between open-cell aluminum foam and solid aluminum shell

Hybrid structure between porous core and solid shell can combine lightweight open-cell structure of porous materials with good strength of solid shell. Laser welding is considered as an effective process to join porous metal with solid metallic shell. In this study, the evolution behavior of laser welding by a continuous wave (CW) disk laser welding between open-cell aluminum alloy (cast AC2A alloy) and aluminum sheet (wrought AA6063 alloy) was investigated. X-ray transmission system and a high-speed camera were performed during laser welding to investigate the dynamic keyhole, porosity formation, plasma plume, and spatter formation. Laser keyhole became unstable during entering and passing the vacancies of porous aluminum, which consequently resulted in bubble formation in the molten pool.

Design and optimization of Metallic Foam Shell protective device against flying ballast impact damage in railway axles

Ballast impacts can initiate surface defects that cause abrupt failure of the axle and derailment of the railway vehicle. According to the Federal Railroad Administration the axle and bearing failure costs around 89 million dollars and causes 46 derailments in the US per year (2005–2010). In this study, the authors have suggested a novel protective mechanism (Metallic Foam Shell – MFS) by using a lightweight sandwich panel. At the first step, a preliminary study is conducted, followed up by the numerical simulations to determine the applicable materials. At the next step, experimental tests were performed to assess the efficiency of the suggested device against flying ballast impacts. An extended non-destructive (NDT) evaluation has been performed in order to find the most suitable technique for damage detection of the proposed device when on-service. The studied cases were GFRP and Aluminium sandwich panels, having an aluminium foam core with different densities and thicknesses. The results showed that the MFS can absorb up to 90% of the initial impact energy and significantly decrease the chance of rebounding impact to the other components. Moreover, the results were also analysed in order to propose the most reliable NDT method for this specific application.

Void Free Fuel Solidification in a Foam Shell FIERX Target

Void Free Fuel Solidification in a Foam Shell FIERX Target

On the use of Chebyshev polynomials in the Rayleigh-Ritz method for vibration and buckling analyses of circular cylindrical three-dimensional graphene foam shells

This study aims to perform free vibration and buckling analyses of circular cylindrical shells made of three-dimensional (3D) graphene foam. Three kinds of porosity distribution are considered including two kinds of symmetrical distribution and uniform distribution. The Kirchhoff-Love shell theory is utilized to establish the mathematical model of 3D graphene foam (3D-GF) shells. Natural frequencies and buckling loads of the shells under various boundary conditions are obtained via the Rayleigh-Ritz method in conjunction with Chebyshev polynomials. Results show that the mechanical characteristics of the 3D-GF shells are significantly affected by the porosity coefficient and porosity distribution. Moreover, the effect of porosity coefficient is closely related to boundary conditions of the shells. It is also shown that as the porosity coefficient increases, the porosity distribution effect on the mechanical characteristics of 3D-GF shells becomes increasingly significant.

Vibration analysis of porous metal foam shells rested on an elastic substrate

In this article, the vibration problem of an embedded cylindrical shell consisted of porous metal foam is solved via an analytical method with respect to the influences of various porosity distributions. Three types of porosity distribution across the thickness are covered, namely, uniform, symmetric, and asymmetric. The strain–displacement relations of the shell are assumed to be derived on the basis of the first-order shear deformation shell theory. Then, the achieved relations will be incorporated with the Hamilton’s principle in order to reach the Navier equations of the cylindrical shell. Next, the well-known Galerkin’s method is utilized to calculate the natural frequencies of the system. The influences of both simply supported and clamped boundary conditions are included. In order to show the accuracy of the presented method, the results of the present research are compared with those reported by former published papers. The reported results show that an increase in the porosity coefficient can decrease the frequency of the shell. Also, the stiffness of the system can be lesser decreased while symmetric porosity distribution is chosen.

Laser welding for joining of open-cell aluminum foam to solid shell

Laser welding of open-cell aluminum foam and solid shell was performed with the objective of fabricating promising hybrid metallic materials. In this study, a feasibility of laser welding of a solid A6063 aluminum sheet to an open-cell AC2A aluminum foam was investigated. The effects of various laser-welding parameters such as laser power, welding speed, and defocused distance in addition to the pore size of aluminum foam were evaluated in terms of the shear strengths of the welded joints between the aluminum solid sheet and porous plate. Increases in weld joint width (w) and penetration depth (d) were effective to an increase in the tensile shear strength of solid-porous material joint.

Nonlinear vibration of metal foam cylindrical shells reinforced with graphene platelets

This paper performs nonlinear vibration analysis of metal foam circular cylindrical shells reinforced with graphene platelets. An improved Donnell nonlinear shell theory is employed to formulate the present model. The graphene platelet reinforced material properties are evaluated by the Halpin–Tsai equation. Different types of porosity and graphene platelet (GPL) distribution are taken into account. Governing equations are derived via Hamilton's principle and then they are transformed to ordinary differential equations using the Galerkin method. Afterwards, nonlinear frequencies of the system are solved by using the multiple scale method. Our findings demonstrate that GPL reinforced metal foam (GPLRMF) shells exhibit hardening-spring vibration characteristics. The nonlinear to linear frequency ratio of the shell closely relates to the porosity distributions and GPL patterns. The effect of geometrical size of graphene platelets on nonlinear vibration characteristics of GPLRMF cylindrical shells is also highlighted.

Mechanical stability of metal foam cylindrical shells with various porosity distributions

The paper deals with the nonlinear buckling analysis of imperfect cylindrical shells made of porous metal foam subjected to axial compression. For the metal foam shells, porosities are dispersed by uniform, symmetric, and asymmetric distributions in the thickness direction. Using Donnell shell theory and von-Karman nonlinear kinematics, nonlinear equilibrium equations are derived. The critical buckling load and buckling equilibrium curves for both perfect and imperfect shells are solved by using the Galerkin's procedure. A comprehensive investigation into the influence of porosity coefficient, imperfections, porosity distribution, and geometry on the buckling behaviors of the cylindrical shell is performed.

Fabrication of Millimeters-Sized Poly(Divinylbenzene) Foam Shells from Controllable Double Emulsion in Microfluidic Device

A geometrically confined dripping was employed to enable precise control over the dimension and structure of millimeters-sized double-emulsion precursors of poly(divinylbenzene) foam shells in a new kind of double Y-shaped compound channels. Due to the 3D axial-symmetric microfluidic device, a more stable and robust flow field was maintained to obtain a continuous and regular emulsification. Various factors were systematically investigated for the precise size control of dripping in confined channel geometry, such as outlet channel size, fluid properties and flow rates. It was seen that phase properties and synergistic effects of main factors played key roles in determining droplet size. Thus, we used the optimized microfluidic approach to fabricate predetermined size foams to satisfy inertial fusion energy experiments, ranging from 4 to 4.6[Formula: see text]mm in diameter with a 50–300[Formula: see text][Formula: see text]m wall thickness and a coefficient of variation [Formula: see text]%. The results presented in this work provided a practical guideline for creating size-desired polymersome from comparable double emulsions.

Vibration analysis of circular cylindrical shells made of metal foams under various boundary conditions

This study investigates the free vibration of metal foam circular cylindrical shells under various boundary conditions. The elasticity modulus and mass density of the shells vary gradually and continually in the thickness direction. Two types of porosity distribution are taken into account including symmetrical and unsymmetrical distributions. Love’s shell theory is employed to formulate the governing equations and then the Rayleigh–Ritz method is utilized to solve natural frequencies of the system. The results show that the porosity coefficient has important effect on the natural frequencies of metal foam shells. Its effect also relates to the boundary conditions of the shells. Moreover, different porosity distributions make the metal foam shells possess different vibration characteristics, which is quite obvious at large porosity coefficient. As the circumferential wave number increases, the natural frequencies of the metal foam shells tend to the same under various boundary conditions. Additionally, the present results are verified by the comparison with the published ones in the literature.

Compressive properties of granular foams of adhesively bonded steel hollow sphere blocks

Steel hollow spheres adhesively bonded together as a granular composite metal foam, is a special type of porous metal that aims to combine low weight, with ductility and energy absorption. Hollow spheres comprising steel foam shells were coated with a thermally activated epoxy in order to form different specimen geometries upon moulding and curing. The collapse propagation and energy absorption of steel hollow sphere blocks, comprising spheres of different sizes, was investigated experimentally, quantifying quasi-elastic and nonlinear properties of the steel hollow sphere assemblies in compression and comparing them with analytical and semi-empirical rules based on porous metal density and sphere packing. The results identify the initiation and nature of damage and highlight the merits of the material in absorbing high compressive deformations without significant loss of integrity.

Microfluidic‐assisted controllable formation of millimeter‐scale poly(divinylbenzene) foam shells

We demonstrated a practical microfluidic approach to fabricate extremely monodisperse millimeter‐sized poly(divinylbenzene) (PDVB) foam shells with the comparable double emulsion templates. At millimeter scale, the emulsification process was more complex and more difficult to control due to the very large characteristic sizes and velocities. A new kind of three‐dimension co‐axial microfluidic chip including a Y‐shaped compound channels was designed to maintain more stable and robust flow field and regular emulsification. The hydrodynamic features of the double‐emulsion droplet formation were investigated. The results showed perfect encapsulation and continuous emulsification could be obtained by one‐step dripping (Caouter ∈ (0.018,0.09)). The size of the outlet channel would be comparable with the target droplet. Besides, droplet diameters could similarly be plotted as a function of capillary number close to the general microfluidic ones. After photo‐polymerization and supercritical drying, spherical and concentric PDVB foam shells were obtained to satisfy the inertial fusion energy experiments with large diameter (3–5.45 mm), thin wall thickness (50–250 μm), low density (50–300 mg/cm3), and a less than 0.1% polydispersity. POLYM. ENG. SCI., 58:1184–1192, 2018. © 2017 Society of Plastics Engineers

Foam core composite sandwich plates and shells with variable stiffness: Effect of the curvilinear fiber path on the modal response

This paper presents the free vibration analysis of composite sandwich plates and doubly curved shells with variable stiffness. The reinforcing fibers are located in the external skins of the sandwich structures according to curved paths. These curvilinear paths are described by a general expression that combines power-law, sinusoidal, exponential, Gaussian and ellipse-shaped functions. As a consequence, the reinforcing fibers are placed in these orthotropic layers in an arbitrary manner, in order to achieve the desired mechanical properties. The effect of this variable fiber orientation on the natural frequencies is investigated by means of several parametric studies. As far as the structural theory is concerned, an equivalent single layer approach based on the well-known Carrera Unified Formulation is employed. The Murakami’s function is added to the kinematic model to capture the zig-zag effect, when the soft-core effect is significant. Thus, several higher order shear deformation theories are taken into account in a unified manner. The differential geometry is employed to describe the reference surface of doubly curved shells and panels, which are characterized by variable radii of curvature. The numerical solution is obtained using the generalized differential quadrature method, due to its accuracy and stability features. The present solution is compared with the results available in the literature or obtained by finite element commercial codes.

Improvement of District Heating Network Energy Efficiency by Pipe Insulation Renovation with PUR Foam Shells

The paper includes description of an experiment where the insulation of 532 m long 1200mm pipe section was replaced with prefabricated polyurethane (PUR) foam shells. As a result reduction of heat losses in comparison with old insulation by 3.35 times was calculated. After successful experiment full renovation of DH main pipe (total pipe length is 10730 m) insulation was performed. Renovation of main pipeline was finished in summer 2015. The first results show that relative heat losses in Eastern part of Tallinn supplied by renovated DH main pipe were decreased from 20.2% to 16.0%.