Papers by Orestes Marangos
Advances in the experimental investigation of the mechanical properties of Carbon Nanoweld
Nanoweld® carbon Fabric for Carbon Reinforced Plastics is a bio-inspired carbon fabric that promi... more Nanoweld® carbon Fabric for Carbon Reinforced Plastics is a bio-inspired carbon fabric that promises improved strength for low weight, aiming to meet the needs of the transportation for lighter and stronger structures. The proprietary process re-introduces internal geometry as an important design parameter in composite reinforcement leading to microfibre-nanofibre-nanoparticle fractal networks taking inspiration from archetypal natural structures such as feathers. The presentation will describe the carbon fabric manufacturing process and focus on the outcomes of the evaluation testing for the mechanical properties of the nanowelded fabrics. The polymeric nanofibre-carbon fibre bonds on randomly selected scaffold samples were examined with Scanning Electron Microscopy, before and after mechanical testing in tension and flexure. The local failure characteristics have been recorded, indicating the merits and pitfalls of the quality of the nanofibre-carbon fibre bonds in 3 cases, where ...
Characterisation of thin walled sandwich structures comprising steel hollow spheres for the core
Steel hollow sphere assemblies are a special type of metal foams that can offer low weight, energ... more Steel hollow sphere assemblies are a special type of metal foams that can offer low weight, energy dissipation and ductility [1, 2]. The composite manufactured using thermosetting epoxies can be attractive as core in hollow sections and sandwich configurations, ameliorating shortcomings of precursor powder metallurgy, such as more uniform cell size as well as lower cost and better tensile responses compared to sintered assemblies [3]. The work herein describes the design and mechanical testing of steel foam-epoxy composites to estimate the static and cyclic properties of these composites. This included static properties in compression of sphere assemblies, including the crushing propagation [4]. 4-point bending tests were utilized to capture shear modulus and shear strength in the sphere assembly core, sandwiched by two steel plates. Two types of sphere assembly sandwich cores were tested, the first one being 3 layers of 4.5 mm diameter spheres(referred to as ‘SFS4’) and the second ...
Machines, 2021
Fiber reinforced composites are increasingly used in high value applications. A novel technology ... more Fiber reinforced composites are increasingly used in high value applications. A novel technology (NanoWeld®) enhancing the structural integrity of the interlayer has demonstrated promising results; however, manufacturing issues related to scalability need to be overcome. The developed technology relies on consolidating thermoplastic nanofiber nonwoven veils onto technical dry fabrics through roll-to-roll ultrasonic welding. The enhanced technical dry fabrics can be further processed as any other technical fabrics for the composites industry. An alternative solution for consolidation is proposed here, based on a thermo-compressive approach to address the scalability issue. A finite element model has been employed to simulate the operating conditions and provide information for optimization of the process. Its results demonstrate that consolidation is achieved rapidly, indicating that the production rate could be accelerated. The quality of enhanced technical dry fabrics produced usin...
The Scanning Acoustic Microscope (SAM) is a powerful tool for understanding the mechanical charac... more The Scanning Acoustic Microscope (SAM) is a powerful tool for understanding the mechanical characteristics of substrates with micro-scale near-surface graded layers. To interpret the SAM results from such substrates, a theoretical model was developed that incorporated the interaction of focused ultrasonic field, with a substrate having a near-surface graded layer. The focused ultrasonic field model was formulated in terms of spherical wave expansions. The substrate wave propagation was computed with a multilayered stiffness method. The bridging between the two models was accomplished by utilizing the angular spectrum. A commercial SAM was used to characterize a dentin substrate subjected to acid-etching. Calibration and a homotopic measurement protocol were developed for data accuracy and meaningful data comparison from pre and post etching states. The reflection coefficients from the SAM measurement for the etched dentin exhibited frequency dependent attenuation. The developed theoretical model was successfully applied to explain the observed frequency dependent phenomenon. iv
Assessing the performance of electrospun nanofabrics as potential interlayer reinforcement materials for fiber-reinforced polymers
Composites and Advanced Materials, 2021
Multiscale-reinforced polymers offer enhanced functionality due to the three different scales tha... more Multiscale-reinforced polymers offer enhanced functionality due to the three different scales that are incorporated; microfiber, nanofiber, and nanoparticle. This work aims to investigate the applicability of different polymer-based nanofabrics, fabricated via electrospinning as reinforcement interlayers for multilayer-fiber-reinforced polymer composites. Three different polymers are examined; polyamide 6, polyacrylonitrile, and polyvinylidene fluoride, both plain and doped with multiwalled carbon nanotubes (MWCNTs). The effect of nanotube concentration on the properties of the resulting nanofabrics is also examined. Nine different nanofabric systems are prepared. The stress–strain behavior of the different nanofabric systems, which are eventually used as reinforcement interlayers, is investigated to assess the enhancement of the mechanical properties and to evaluate their potential as interlayer reinforcements. Scanning electron microscopy is employed to visualize the morphology an...
Mechanics Research Communications, 2018
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Dentinoenamel junction
Material-Tissue Interfacial Phenomena, 2017
The dentinoenamel junction provides the connection between material systems of dissimilar composi... more The dentinoenamel junction provides the connection between material systems of dissimilar compositions and mechanical properties. The characteristics of the region proximal to this junction contributes to the effectiveness of the mechanical performance of this interface. This chapter discusses the current understanding of this junction region with respect to its structure, composition, and mechanical behavior. Some new findings using alternative techniques that permit multiscalar homotopic measurements of composition and mechanical properties are described. Results from preliminary microscale finite element models based on realistic idealizations are then discussed to illustrate the effect of structure and composition on the mechanical behavior. The presented information shows the need for further research from both the characterization and the modeling viewpoints so that the superior properties of this robust junction can be beneficially harnessed.
Mathematical model for anomalous creep in model dentin adhesives
ABSTRACT We have recently measured creep deformations in a model dentin adhesive under a variety ... more ABSTRACT We have recently measured creep deformations in a model dentin adhesive under a variety of moisture conditions. These measurements have indicated that the rate of creep and total creep strain increase substantially when dry stored photopolymerized model adhesive is mechanically loaded under changing moisture conditions. Objective: The aim of the study is to develop a mathematical model to explain the creep behavior of a model dentin adhesive under conditions that simulate the wet, oral environment. Methods: A micromechanical approach is applied to model the rate-dependent behavior of dentin adhesives. In this approach, the structural components are modeled as directional rheological elements that undergo water-induced damage. The derived model is used to predict the creep response of model dentin adhesive samples that have been tested under different moisture conditions. Results: The model replicates the observed creep behavior, including the high creep rate and total creep strains obtained in the experiments. For the samples tested under constant moisture conditions, the behavior is found to be linear viscoelastic over a large range of stress-level. The stress range for linear behavior is approximately 30% of the overall failure stress of the adhesive under slow loading (~160MPa for dry case and ~60MPa for submerged samples loaded at 0.0075N/min). For the samples that are stored dry and tested in submerged conditions, the behavior is found to be highly nonlinear even at low stress-levels (~4.5MPa). Conclusions: The high degree of nonlinearity for samples that are stored dry and tested in submerged conditions is traced to the simultaneous water induced damage/softening of structural components and the application of the external load. In the oral environment, the interplay of mechanical loads and water-induced damage can lead to creep-failure of adhesives under function. Supported NIH/NIDCR R01 DE014392, DE014392-08S109
Continuum Mechanics and Thermodynamics, 2018
Scanning acoustic microscopy (SAM) has been applied to measure the near-surface elastic propertie... more Scanning acoustic microscopy (SAM) has been applied to measure the near-surface elastic properties of materials. For many substrates, the near-surface property is not constant but varies with depth. In this paper, we aim to interpret the SAM data from such substrates by modeling the interaction of the focused ultrasonic field with a substrate having a near-surface graded layer. The focused ultrasonic field solutions were represented as spherical harmonic expansions while the substrate solutions were represented as plane wave expansions. The bridging of the two solutions was achieved through the decomposition of the ultrasonic pressure fields in their angular spectra. Parametric studies were performed, which showed that near-surface graded layers exhibit distinctive frequency dependence of their reflectance functions. This behavior is characteristic to the material property gradation profile as well as the extent of the property gradation. The developed model was used to explain the frequency-dependent reflection coefficients measured from an acid-etched dentin substrate. Based on the model calculations, the elastic property variations of the acid-etched dentin near-surface indicate that the topmost part of the etched layer is very soft (3-6 GPa) and transitions to the native dentin through a depth of 27 and 36 microns.
Micro-scale Analysis of Compositional and Mechanical Properties of Dentin Using Homotopic Measurements
Lecture Notes in Computational Vision and Biomechanics, 2012
Mechanics of Hard Tissues, Chapter 18
Anomalous creep in model dentin adhesive under changing moisture conditions
In the mouth, the interplay of chemical and mechanical stresses can lead to a change in the mecha... more In the mouth, the interplay of chemical and mechanical stresses can lead to a change in the mechanical properties of the adhesive. Objective: The aim of the current study is to investigate the creep behavior of a model dentin adhesive under conditions that simulate the wet, oral environment. Methods: The composition of the model dentin adhesive: bisphenol-A diglycidyl ether dimethacrylate (bisGMA), 2-hydroxyethyl methacrylate (HEMA) [HEMA /bisGMA, 45/55 w/w], with 3-component photoinitiator system: camphorquinone (0.5wt%), 2-ethyl-4-aminobenzoate (0.5wt%) and diphenyliodonium hexafluorophosphate (0.5wt%). Rectangular beam specimens, 1mm1mm cross-section and 15mm length, were made. These beam specimens were subjected to a load of 4.5 MPa at a frequency of 5Hz under four different environmental conditions for 24hr-48hrs (25oC). Series 1: samples stored dry and tested dry, series 2: samples submerged in water for 5 days and tested submerged in water, series 3: specimens stored dry and ...
Dentin/Adhesive Interface in Teeth
Parametric study of the effect of phase anisotropy on the micromechanical behaviour of dentin–adhesive interfaces
Journal of The Royal Society Interface, 2005
A finite element (FE) model has been developed based upon the recently measured micro-scale morph... more A finite element (FE) model has been developed based upon the recently measured micro-scale morphological, chemical and mechanical properties of dentin-adhesive (d-a) interfaces using confocal Raman microspectroscopy and scanning acoustic microscopy (SAM). The results computed from this FE model indicated that the stress distributions and concentrations are affected by the micro-scale elastic properties of various phases composing the d-a interface. However, these computations were performed assuming isotropic material properties for the d-a interface. The d-a interface components, such as the peritubular and intertubular dentin, the partially demineralized dentin and the so-called "hybrid layer" adhesive-collagen composite, are probably anisotropic. In this paper, the FE model is extended to account for the probable anisotropic properties of these d-a interface phases. A parametric study is performed to study the effect of anisotropy on the micromechanical stress distributions in the hybrid layer and the peritubular dentin phases of the d-a interface. It is found that the anisotropy of the phases affects the region and extent of stress concentration as well as the location of the maximum stress concentrations. Thus, the anisotropy of the phases could effect the probable location of failure initiation, whether in the peritubular region or in the hybrid layer.
Journal of Materials Science, 2008
In 2003 Nature Materials article, Keckes et al. presented deformation properties of a variety of ... more In 2003 Nature Materials article, Keckes et al. presented deformation properties of a variety of woods in relation to deformation of their individual wood cells.
Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2010
The objective of the current study is to characterize the viscoelastic and fatigue properties of ... more The objective of the current study is to characterize the viscoelastic and fatigue properties of model methacrylate-based dentin adhesives under dry and wet conditions. Static, creep, and fatigue tests were performed on cylindrical samples in a 3-point bending clamp. Static results showed that the apparent elastic modulus of the model adhesive varied from 2.56 to 3.53 GPa in the dry condition, and from 1.04 to 1.62 GPa in the wet condition, depending upon the rate of loading. Significant differences were also found for the creep behavior of the model adhesive under dry and wet conditions. A linear viscoelastic model was developed by fitting the adhesive creep behavior. The developed model with 5
Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2012
There have been reports of the sensitivity of our current dentin adhesives to excess moisture, fo... more There have been reports of the sensitivity of our current dentin adhesives to excess moisture, for example, water-blisters in adhesives placed on over-wet surfaces, and phase separation with concomitant limited infiltration of the critical dimethacrylate component into the demineralized dentin matrix. To determine quantitatively the hydrophobic/ hydrophilic components in the aqueous phase when exposed to over-wet environments, model adhesives were mixed with 16, 33, and 50 wt % water to yield well-separated phases. Based upon high-performance liquid chromatography coupled with photodiode array detection, it was found that the amounts of hydrophobic BisGMA and hydrophobic initiators are less than 0.1 wt % in the aqueous phase. The amount of these compounds decreased with an increase in the initial water content. The major components of the aqueous phase were hydroxyethyl methacrylate (HEMA) and water, and the HEMA content ranged from 18.3 to 14.7 wt %. Different BisGMA homologues and the relative content of these homologues in the aqueous phase have been identified; however, the amount of crosslinkable BisGMA was minimal and, thus, could not help in the formation of a crosslinked polymer network in the aqueous phase. Without the protection afforded by a strong crosslinked network, the poorly photoreactive compounds of this aqueous phase could be leached easily. These results suggest that adhesive formulations should be designed to include hydrophilic multimethacrylate monomers and water compatible initiators.
Journal of Biomedical Materials Research, 2004
The interfacial microstructure and spatial distribution of the modulus of elasticity have a profo... more The interfacial microstructure and spatial distribution of the modulus of elasticity have a profound effect on load transfer at the dentin/adhesive (d/a) interface. The microstructure is influenced by the varying degree of demineralization of intertubular and peritubular dentin during etching as well as the depth of adhesive penetration into the hybrid layer. These factors lead not only to a unique microstructure in the vicinity of the dentinal tubules, but also to a mechanically graded hybrid layer. This article investigates the micromechanical stress distribution at a d/a interface with the use of finite element analysis (FEA). Such analysis is now feasible given the newly measured moduli of elasticity at micro-and nanoscales. The results indicate that the morphological and micromechanical properties of the d/a interface affects the stress field such that the fracture/failure is likely to initiate in the stress-concentration zone of peritubular dentin next to the hybrid/exposed-collagen layer. The results suggest that devising a full-depth high modulus hybrid layer may considerably reduce the stress concentration zone and the magnitude of stress concentration in the peritubular dentin next to the hybrid/exposed-collagen layer.
Rock-Joint Micromechanics: Relationship of Roughness to Closure and Wave Propagation
International Journal of Geomechanics, 2011
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Papers by Orestes Marangos