An Experimentally Validated Micromechanical Model for Elasticity and Strength of Hydroxyapatite Biomaterials

2008 ◽  
Vol 1132 ◽  
Author(s):  
Andreas Fritsch ◽  
Luc Dormieux ◽  
Christian Hellmich ◽  
Julien Sanahuja
Keyword(s):  
Micromechanical Model ◽  
Strength Properties ◽  
Micromechanical Modeling ◽  
Uniaxial Tensile ◽  
Structure Property ◽  
Mechanical Stiffness ◽  
Statistical Correlations ◽  
Continuum Micromechanics ◽  
Structure Property Relationships ◽  
Good Agreement

ABSTRACTHydroxyapatite biomaterials production has been a major field in biomaterials science and biomechanical engineering. As concerns prediction of their stiffness and strength, we propose to go beyond statistical correlations with porosity or empirical structure-property relationships, as to resolve the material-immanent microstructures governing the overall mechanical behavior. The macroscopic mechanical properties are estimated from the microstructures of the materials and their composition, in a homogenization process based on continuum micromechanics. Thereby, biomaterials are envisioned as porous polycrystals consisting of hydroxyapatite needles and spherical pores. Validation of respective micromechanical models relies on two independent experimental sets: Biomaterial-specific macroscopic (homogenized) stiffness and uniaxial (tensile and compressive) strength predicted from biomaterial-specific porosities, on the basis of biomaterial-independent (‘universal') elastic and strength properties of hydroxyapatite, are compared to corresponding biomaterial-specific experimentally determined (acoustic and mechanical) stiffness and strength values. The good agreement between model predictions and the corresponding experiments underlines the potential of micromechanical modeling in improving biomaterial design, through optimization of key parameters such as porosities or geometries of microstructures, in order to reach desired values for biomaterial stiffness or strength.

Micromechanical Modeling of Two-Phase Steels

2000 ◽  
Vol 653 ◽  
Author(s):  
Mikael Nygårds ◽  
Dilip Chandrasekaran ◽  
Peter Gudmundson
Keyword(s):  
Micromechanical Model ◽  
Tensile Tests ◽  
Micromechanical Modeling ◽  
Uniaxial Tensile ◽  
The Finite Element Method ◽  
Stress Strain ◽  
Two Phase ◽  
Representative Cell ◽  
Strain Data ◽  
Good Agreement

AbstractA two-dimensional micromechanical model based on the finite element method is presented to model two-phase ferritic/pearlitic steels, by aid of generalised plane strain elements. A periodic representative cell containing 100 ferrite grains, and the desired fraction pearlite is used. By applying periodic boundary conditions, loading by an average stress or strain state is possible.Uniaxial tensile tests were performed on specimens containing the ferrite and pearlite microstructures, and on two-phase materials containing 25% and 58% pearlite respectively. The stress-strain data of the pearlite material is used to fit a laminar dependent Taylor relation to represent the pearlite workhardening. Thereafter, laminar spacings in the two-phase materials are measured, and the total stress-strain response of the materials is modelled. Comparisons between generated data and experiments show good agreement up to a strain of 2%.

A Micromechanical Model of the Tensile Behavior of Woven Fabric

1997 ◽  
Vol 67 (6) ◽  
pp. 445-459 ◽  
Author(s):  
M. L. Realff ◽  
M. C. Boyce ◽  
S. Backer
Keyword(s):  
Micromechanical Model ◽  
Tensile Behavior ◽  
Woven Fabric ◽  
Uniaxial Tensile ◽  
Stress Strain ◽  
Strain Behavior ◽  
Yarn Properties ◽  
Micromechanical Approach ◽  
Uniaxial Tensile Stress ◽  
Good Agreement

This work takes a micromechanical approach to fabric tensile modeling. The entire uniaxial tensile stress-strain behavior of the fabric is modeled from the constitutive yarn properties (tensile, bending, flattening, and consolidation behavior) and the original fabric geometry. Techniques for measuring these yarn properties are described. In most cases, there is good agreement between the theoretical and experimental results for several fabrics of differing weave and yarn construction. Modified approaches are suggested for those cases where prediction of fabric stress-strain behavior deviates from the experimental data.

Micromechanical modeling of solid-type and plate-type deformation patterns within softwood materials. A review and an improved approach

Holzforschung ◽  
2007 ◽  
Vol 61 (4) ◽  
pp. 343-351 ◽  
Author(s):  
Karin Hofstetter ◽  
Christian Hellmich ◽  
Josef Eberhardsteiner
Keyword(s):  
Mass Density ◽  
Micromechanical Model ◽  
Structural Features ◽  
Shear Loading ◽  
Micromechanical Modeling ◽  
Environmental Scanning ◽  
Length Scale ◽  
Continuum Micromechanics ◽  
Load Carrying ◽  
Solid Type

Abstract Wood exhibits a highly diverse microstructure. It appears as a solid-type composite material at a length scale of some micrometers, while it resembles an assembly of plate-like elements arranged in a honeycomb fashion at the length scale of some hundreds of micrometers. These structural features result in different load-carrying mechanisms at different observation scales and under different loading conditions. In this paper, we elucidate the main load-carrying mechanisms by means of a micromechanical model for softwood materials. Representing remarkable progress with respect to earlier models reported in the literature, this model is valid across various species. The model is based on tissue-independent stiffness properties of cellulose, lignin, hemicellulose, and water obtained from direct testing and lattice-dynamics analyses. Sample-specific characteristics are considered in terms of porosity and the contents of cellulose, lignin, hemicelluloses and water, which are obtained from mass density measurements, environmental scanning micrographs, analytical chemistry, and NMR spectroscopy. The model comprises three homogenization steps, two based on continuum micromechanics and one on the unit cell method. The latter represents plate-like bending and shear of the cell walls due to transverse shear loading and axial straining in the tangential stem direction. Accurate representation of these deformation modes results in accurate (orthotropic) stiffness estimates across a variety of softwood species. These stiffness predictions deviate, on average, by less than 10% from corresponding experimental results obtained from ultrasonic or quasi-static testing. Thus, the proposed model can reliably predict microscopic and macroscopic mechanical properties from internal structure and composition, and is therefore expected to significantly support wood production technology (such as drying techniques) and mechanical analyses of timber structures.

Micromechanical Modeling of Connective Soft Tissues

2015 ◽  
Author(s):  
Ali Fallah ◽  
Mohammad Taghi Ahmadian ◽  
Keikhosrow Firoozbakhsh
Keyword(s):  
Soft Tissues ◽  
Micromechanical Model ◽  
Transversely Isotropic ◽  
Collagen Fibers ◽  
Micromechanical Modeling ◽  
Macroscopic Behavior ◽  
Nano Scale ◽  
Structures And Properties ◽  
Scale Structures ◽  
Good Agreement

In this paper, a physically motivated micromechanical model for connective soft tissues like tendon and ligament is presented. A representative volume element (RVE) is introduced based on the crimped pattern of collagen fiber in the tissue. In order to investigate the macroscopic behavior of tissue, numerical homogenization and appropriate periodic boundary conditions are used. Neglecting the effects of nano scale structures and properties on tissues macroscopic behavior leads to linear transversely isotropic model for collagen fibers. Comparison of obtained result with available experimental one, shows that this assumption leads to inaccurate results. Including the effects of nano scale structures into the presented model leads to a nonlinear transversely isotropic constitutive model for collagen fibers which leads to results that are in good agreement with experimental results.

scholarly journals A Review of Experimentally Informed Micromechanical Modeling of Nanoporous Metals: From Structural Descriptors to Predictive Structure–Property Relationships

Materials ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3307 ◽  
Author(s):  
Claudia Richert ◽  
Norbert Huber
Keyword(s):  
Network Structure ◽  
Topological Analysis ◽  
High Surface ◽  
Functional Materials ◽  
Model Systems ◽  
Micromechanical Modeling ◽  
Suitable Model ◽  
Structure Property ◽  
Structure Property Relationships ◽  
Nanoporous Metals

Nanoporous metals made by dealloying take the form of macroscopic (mm- or cm-sized) porous bodies with a solid fraction of around 30%. The material exhibits a network structure of “ligaments” with an average ligament diameter that can be adjusted between 5 and 500 nm. Current research explores the use of nanoporous metals as functional materials with respect to electrochemical conversion and storage, bioanalytical and biomedical applications, and actuation and sensing. The mechanical behavior of the network structure provides the scope for fundamental research, particularly because of the high complexity originating from the randomness of the structure and the challenges arising from the nanosized ligaments, which can be accessed through an experiment only indirectly via the testing of the macroscopic properties. The strength of nanoscale ligaments increases systematically with decreasing size, and owing to the high surface-to-volume ratio their elastic and plastic properties can be additionally tuned by applying an electric potential. Therefore, nanoporous metals offer themselves as suitable model systems for exploring the structure–property relationships of complex interconnected microstructures as well as the basic mechanisms of the chemo-electro-mechanical coupling at interfaces. The micromechanical modeling of nanoporous metals is a rapidly growing field that strongly benefits from developments in computational methods, high-performance computing, and visualization techniques; it also benefits at the same time through advances in characterization techniques, including nanotomography, 3D image processing, and algorithms for geometrical and topological analysis. The review article collects articles on the structural characterization and micromechanical modeling of nanoporous metals and discusses the acquired understanding in the context of advancements in the experimental discipline. The concluding remarks are given in the form of a summary and an outline of future perspectives.

Structure-property relationships of PE/PP sandwiched films

1987 ◽  
Vol 45 ◽  
pp. 454-455
Author(s):  
J. Petermann ◽  
G. Broza ◽  
U. Rieck ◽  
A. Jaballah ◽  
A. Kawaguchi
Keyword(s):  
Mechanical Tests ◽  
Polymer Materials ◽  
Ionic Crystals ◽  
Structure Property ◽  
Polymer Systems ◽  
Structure Property Relationships ◽  
Oriented Films ◽  
Materials Used ◽  
Polymer Laminates ◽  
Heated Glass

Oriented overgrowth of polymer materials onto ionic crystals is well known and recently it was demonstrated that this epitaxial crystallisation can also occur in polymer/polymer systems, under certain conditions. The morphologies and the resulting physical properties of such systems will be presented, especially the influence of epitaxial interfaces on the adhesion of polymer laminates and the mechanical properties of epitaxially crystallized sandwiched layers.Materials used were polyethylene, PE, Lupolen 6021 DX (HDPE) and 1810 D (LDPE) from BASF AG; polypropylene, PP, (PPN) provided by Höchst AG and polybutene-1, PB-1, Vestolen BT from Chemische Werke Hüls. Thin oriented films were prepared according to the method of Petermann and Gohil, by winding up two different polymer films from two separately heated glass-plates simultaneously with the help of a motor driven cylinder. One double layer was used for TEM investigations, while about 1000 sandwiched layers were taken for mechanical tests.

Approaches for TEM imaging of cavitation in toughened nylon

1989 ◽  
Vol 47 ◽  
pp. 352-353
Author(s):  
Barbara A. Wood
Keyword(s):  
Morphological Characteristics ◽  
Structure Property ◽  
Polymer Systems ◽  
Selective Staining ◽  
Structure Property Relationships ◽  
Rubber Toughened ◽  
Shear Yield ◽  
Controversial Topic ◽  
Selection Of ◽  
Diamond Knife

A controversial topic in the study of structure-property relationships of toughened polymer systems is the internal cavitation of toughener particles resulting from damage on impact or tensile deformation.Detailed observations of the influence of morphological characteristics such as particle size distribution on deformation mechanisms such as shear yield and cavitation could provide valuable guidance for selection of processing conditions, but TEM observation of damaged zones presents some experimental difficulties.Previously published TEM images of impact fractured toughened nylon show holes but contrast between matrix and toughener is lacking; other systems investigated have clearly shown cavitated impact modifier particles. In rubber toughened nylon, the physical characteristics of cavitated material differ from undamaged material to the extent that sectioning of heavily damaged regions by cryoultramicrotomy with a diamond knife results in sections of greater than optimum thickness (Figure 1). The detailed morphology is obscured despite selective staining of the rubber phase using the ruthenium trichloride route to ruthenium tetroxide.

Catalyst Halogenation Enables Rapid and Efficient Polymerizations with Visible to Near-Infrared Light

2020 ◽  
Author(s):  
Alex Stafford ◽  
Dowon Ahn ◽  
Emily Raulerson ◽  
Kun-You Chung ◽  
Kaihong Sun ◽  
...  
Keyword(s):  
Near Infrared ◽  
Transient Absorption ◽  
Reaction Times ◽  
Infrared Light ◽  
Structure Property ◽  
Light Emitting ◽  
Structure Property Relationships ◽  
Nir Light ◽  
Light Intensities ◽  
Emission Quenching

Driving rapid polymerizations with visible to near-infrared (NIR) light will enable nascent technologies in the emerging fields of bio- and composite-printing. However, current photopolymerization strategies are limited by long reaction times, high light intensities, and/or large catalyst loadings. Improving efficiency remains elusive without a comprehensive, mechanistic evaluation of photocatalysis to better understand how composition relates to polymerization metrics. With this objective in mind, a series of methine- and aza-bridged boron dipyrromethene (BODIPY) derivatives were synthesized and systematically characterized to elucidate key structure-property relationships that facilitate efficient photopolymerization driven by visible to NIR light. For both BODIPY scaffolds, halogenation was shown as a general method to increase polymerization rate, quantitatively characterized using a custom real-time infrared spectroscopy setup. Furthermore, a combination of steady-state emission quenching experiments, electronic structure calculations, and ultrafast transient absorption revealed that efficient intersystem crossing to the lowest excited triplet state upon halogenation was a key mechanistic step to achieving rapid photopolymerization reactions. Unprecedented polymerization rates were achieved with extremely low light intensities (< 1 mW/cm<sup>2</sup>) and catalyst loadings (< 50 μM), exemplified by reaction completion within 60 seconds of irradiation using green, red, and NIR light-emitting diodes.

A Review on Camptothecin Analogs with Promising Cytotoxic Profile

2019 ◽  
Vol 18 (13) ◽  
pp. 1796-1814 ◽  
Author(s):  
Sk. Abdul Amin ◽  
Nilanjan Adhikari ◽  
Tarun Jha ◽  
Shovanlal Gayen
Keyword(s):  
Cell Lines ◽  
Cancer Cell ◽  
Cancer Cell Lines ◽  
Structure Property ◽  
Cytotoxic Potential ◽  
Structure Property Relationships ◽  
Structure Activity ◽  
Camptothecin Analogs ◽  
Pharmacokinetic Properties ◽  
Quantitative Structure Activity Relationships

Camptothecin (CPT), obtained from Camptotheca acuminata (Nyssaceae), is a quinoline type of alkaloid. Apart from various traditional uses, it is mainly used as a potential cytotoxic agent acting against a variety of cancer cell lines. Though searches have been continued for last six decades, still it is a demanding task to design potent and cytotoxic CPTs. Different CPT analogs are synthesized to enhance the cytotoxic potential as well as to increase the pharmacokinetic properties of these analogs. Some of these analogs were proven to be clinically effective in different cancer cell lines. In this article, different CPT analogs have been highlighted extensively to get a detail insight about the structure-property relationships as well as different quantitative structure-activity relationships (QSARs) modeling of these analogs are also discussed. This study may be beneficial for designing newer CPT analogs in future.

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