scholarly journals FEA Based on 3D Micro-CT Images of Mesoporous Engineered Hydrogels

2015 ◽  
Vol 5 (6) ◽  
pp. 885-890
Author(s):  
L. Siad ◽  
J. Jing ◽  
J. Braux ◽  
M. Dubus ◽  
F. Velard ◽  
...  
Keyword(s):  
Computational Study ◽  
Compression Tests ◽  
Unconfined Compression ◽  
Fe Modelling ◽  
3D Images ◽  
Linear Elastic ◽  
Polymeric Biomaterials ◽  
Compressive Loads ◽  
Preliminary Study ◽  
Tomography Scan

The objective of this computational study was to propose a rapid procedure in obtaining an estimation of elastic moduli of solid phases of porous natural-polymeric biomaterials used for bone tissue engineering. This procedure was based on the comparison of experimental results to finite element (FE) responses of parallelepiped so-called representative volume elements (rev) of the material at hand. To address this issue a series of quasi-static unconfined compression tests were designed and performed on three prepared cylindrical biopolymer samples. Subsequently, a computed tomography scan was performed on fabricated specimens and two 3D images were reconstructed. Various parallelepiped revs of different sizes and located at distinct places within both constructs were isolated and then analyzed under unconfined compressive loads using FE modelling. In this preliminary study, for the sake of simplicity, the dried biopolymer solid is assumed to be linear elastic.

The Influence of Fiber Orientation on the Equilibrium Properties of Neutral and Charged Biphasic Tissues

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Thomas Nagel ◽  
Daniel J. Kelly
Keyword(s):  
Computational Study ◽  
Constitutive Models ◽  
Biological Tissues ◽  
Compression Tests ◽  
Unconfined Compression ◽  
Aligned Fibers ◽  
Compressive Loads ◽  
Vertically Aligned ◽  
Tissue Models ◽  
Biphasic Tissues

Constitutive models facilitate investigation into load bearing mechanisms of biological tissues and may aid attempts to engineer tissue replacements. In soft tissue models, a commonly made assumption is that collagen fibers can only bear tensile loads. Previous computational studies have demonstrated that radially aligned fibers stiffen a material in unconfined compression most by limiting lateral expansion while vertically aligned fibers buckle under the compressive loads. In this short communication, we show that in conjunction with swelling, these intuitive statements can be violated at small strains. Under such conditions, a tissue with fibers aligned parallel to the direction of load initially provides the greatest resistance to compression. The results are further put into the context of a Benninghoff architecture for articular cartilage. The predictions of this computational study demonstrate the effects of varying fiber orientations and an initial tare strain on the apparent material parameters obtained from unconfined compression tests of charged tissues.

A First Step towards a Tribological Approach to Investigate Cutting Tool Wear

2014 ◽  
Vol 611-612 ◽  
pp. 452-459 ◽  
Author(s):  
Giovenco Axel ◽  
Frédéric Valiorgue ◽  
Cédric Courbon ◽  
Joël Rech ◽  
Ugo Masciantonio
Keyword(s):  
Tool Wear ◽  
Cutting Tool ◽  
304L Stainless Steel ◽  
Fe Modelling ◽  
Wear Model ◽  
Cutting Tool Wear ◽  
The Will ◽  
Preliminary Study ◽  
The Impact ◽  
Macroscopic Parameters

The present work is motivated by the will to improve Finite Element (FE) Modelling of cutting tool wear. As a first step, the characterisation of wear mechanisms and identification of a wear model appear to be fundamental. The key idea of this work consists in using a dedicated tribometer, able to simulate relevant tribological conditions encountered in cutting (pressure, velocity). The tribometer can be used to estimate the evolution of wear versus time for various tribological conditions (pressure, velocity, temperature). Based on this design of experiments, it becomes possible to identify analytically a wear model. As a preliminary study this paper will be focused on the impact of sliding speed at the contact interface between 304L stainless steel and tungsten carbide (WC) coated with titanium nitride (TiN) pin. This experiment enables to observe a modification of wear phenomena between sliding speeds of 60 m/min and 180 m/min. Finally, the impact on macroscopic parameters has been observed.

Strength envelope of granular soil stabilized by multi-axial geogrid in large triaxial tests

2020 ◽  
Vol 57 (3) ◽  
pp. 448-452 ◽  
Author(s):  
A.S. Lees ◽  
J. Clausen
Keyword(s):  
Triaxial Compression ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Failure Envelope ◽  
Element Analysis ◽  
Linear Elastic ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic ◽  
Triaxial Compression Tests ◽  
Properties Of Soil

Conventional methods of characterizing the mechanical properties of soil and geogrid separately are not suited to multi-axial stabilizing geogrid that depends critically on the interaction between soil particles and geogrid. This has been overcome by testing the soil and geogrid product together as one composite material in large specimen triaxial compression tests and fitting a nonlinear failure envelope to the peak failure states. As such, the performance of stabilizing, multi-axial geogrid can be characterized in a measurable way. The failure envelope was adopted in a linear elastic – perfectly plastic constitutive model and implemented into finite element analysis, incorporating a linear variation of enhanced strength with distance from the geogrid plane. This was shown to produce reasonably accurate simulations of triaxial compression tests of both stabilized and nonstabilized specimens at all the confining stresses tested with one set of input parameters for the failure envelope and its variation with distance from the geogrid plane.

Microstructural changes in soft quick clay at failure

1970 ◽  
Vol 7 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Roland Pusch
Keyword(s):  
Shear Deformation ◽  
Shear Zone ◽  
Residual Strength ◽  
Rigid Bodies ◽  
Compression Tests ◽  
Unconfined Compression ◽  
Shear Forces ◽  
Microstructural Investigation ◽  
Shear Process ◽  
Quick Clay

A series of unconfined compression tests has been made on a marine, quick clay and small specimens were extracted for microstructural investigation. The natural microstructural pattern was characterized by a network of small aggregates connected by links of particles. The links broke down successively at increasing shear deformation and formed domain-like groups of particles. In the macroscopic shear zone the shear forces tended to orient and deform the aggregates.The aggregates behaved as rigid bodies to a certain stress level during the shear process. The concept of residual strength may correspond to the state where the majority of the links have been broken while the aggregates are still intact.

scholarly journals Multiscale modelling and homogenisation of fibre-reinforced hydrogels for tissue engineering

2018 ◽  
Vol 31 (1) ◽  
pp. 143-171 ◽  
Author(s):  
M. J. CHEN ◽  
L. S. KIMPTON ◽  
J. P. WHITELEY ◽  
M. CASTILHO ◽  
J. MALDA ◽  
...  
Keyword(s):  
Tissue Engineering ◽  
Applied Load ◽  
The Body ◽  
Unconfined Compression ◽  
Linear Elastic ◽  
Recent Approach ◽  
Poroelastic Material ◽  
3D Printed ◽  
Construct Dimensions

Tissue engineering aims to grow artificial tissues in vitro to replace those in the body that have been damaged through age, trauma or disease. A recent approach to engineer artificial cartilage involves seeding cells within a scaffold consisting of an interconnected 3D-printed lattice of polymer fibres combined with a cast or printed hydrogel, and subjecting the construct (cell-seeded scaffold) to an applied load in a bioreactor. A key question is to understand how the applied load is distributed throughout the construct. To address this, we employ homogenisation theory to derive equations governing the effective macroscale material properties of a periodic, elastic–poroelastic composite. We treat the fibres as a linear elastic material and the hydrogel as a poroelastic material, and exploit the disparate length scales (small inter-fibre spacing compared with construct dimensions) to derive macroscale equations governing the response of the composite to an applied load. This homogenised description reflects the orthotropic nature of the composite. To validate the model, solutions from finite element simulations of the macroscale, homogenised equations are compared to experimental data describing the unconfined compression of the fibre-reinforced hydrogels. The model is used to derive the bulk mechanical properties of a cylindrical construct of the composite material for a range of fibre spacings and to determine the local mechanical environment experienced by cells embedded within the construct.

scholarly journals ON THE ROLE OF HISTOMORPHOMETRIC (STEREOLOGICAL) MICROSTRUCTURE PARAMETERS IN THE PREDICTION OF VERTEBRAE COMPRESSION STRENGTH

2019 ◽  
Vol 38 (1) ◽  
pp. 63 ◽  
Author(s):  
Leszek Karol Wojnar ◽  
Aneta Gądek-Moszczak ◽  
Jacek Pietraszek
Keyword(s):  
Compression Strength ◽  
Correlation Coefficients ◽  
Diagnostic Techniques ◽  
Micro Ct ◽  
Compression Tests ◽  
Mineral Density ◽  
3D Images ◽  
Microstructure Parameters

The well-documented relation between bone mineral density (BMD) and bone compression strength constitutes the basis for osteoporosis diagnostics and the assessment of fracture risk. Simultaneously, this relation demonstrates a considerable scatter of results as bones of identical mineral density may have significantly different properties. The experimentally confirmed theorem that two materials or tissues of identical microstructure have identical properties leads to the evaluation of various quantitative stereological parameters (also referred to in biomedicine as histomorphology). These parameters, obtained from analysis of 2D or 3D images, have been used in numerous attempts to explain changes in bone strength. Although numerous correlation dependencies, often with high correlation coefficients, were evaluated, we do not know which parameters are worth evaluating, and there is no physical interpretation of these relations. An extended statistical analysis was accomplished on the basis of analysis of 3D images from 23 lumbar (L3) vertebrae scanned with micro-CT and the results of subsequent compression tests. A new parameter called SDF (structure destruction factor) was proposed in order to characterise the quality of 3D trabecular structures, and its significance was demonstrated. The final correlation function, which uses only three stereological parameters, made it possible to predict compression strength with considerable precision. The estimated values correlated very well with the apparent values (correlation coefficient r=0.96). Finally, the stereological parameters most suitable for characterisation of bone compression strength were chosen and a mechanism responsible for the changes in mechanical properties was proposed. The results obtained defined the necessary improvements in diagnostic techniques that would allow for more efficient quantitative microstructure evaluation and guidelines on how to improve treatment of patients with weakened bones.

Stabilization of clayey subgrade with waste pumice for road infrastructure

2015 ◽  
Vol 22 (5) ◽  
Author(s):  
Ömür Çimen ◽  
Mehmet Saltan ◽  
S. Nilay Keskin
Keyword(s):  
Mechanical Properties ◽  
Road Construction ◽  
High Plasticity ◽  
Test Results ◽  
Index Properties ◽  
Compression Tests ◽  
Unconfined Compression ◽  
Swelling Potential ◽  
Project Costs ◽  
High Plasticity Clay

AbstractHigh-plasticity clayey subgrade, which is unsuitable for road construction, may sometimes occur along highway routes. In such cases, engineers need to change the route of a highway project, resulting in an increase in road length and project costs. In this study, waste pumice was examined for stabilization of high-plasticity clayey subgrade, which is inappropriate for road construction. For this purpose, the physical and index properties of clay and pumice were determined. Then, the pumice was mixed with high plasticity clay at different ratios by weight. By performing standard Proctor compaction tests on the mixtures, the effects of adding pumice on compaction were also studied. Unconfined compression tests and California bearing ratio (CBR) tests were performed on all pumice-clay mixtures, and the test results and the CBR ratios were compared for each sample, respectively. The results showed that pumice stabilization improved the mechanical properties and reduced the swelling potential of high plasticity clayey subgrade.

scholarly journals The Effect of Polymer-Cement Stabilization on the Unconfined Compressive Strength of Liquefiable Soils

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Ali Ateş
Keyword(s):  
Compressive Strength ◽  
Compression Strength ◽  
Unconfined Compressive Strength ◽  
Soil Stabilization ◽  
Sandy Soils ◽  
Pulse Velocity ◽  
Unit Weight ◽  
Unconfined Compression Strength ◽  
Compression Tests ◽  
Unconfined Compression

Soil stabilization has been widely used as an alternative to substitute the lack of suitable material on site. The use of nontraditional chemical stabilizers in soil improvement is growing daily. In this study a laboratory experiment was conducted to evaluate the effects of waterborne polymer on unconfined compression strength and to study the effect of cement grout on pre-venting of liquefiable sandy soils. The laboratory tests were performed including grain size of sandy soil, unit weight, ultrasonic pulse velocity, and unconfined compressive strength test. The sand and various amounts of polymer (1%, 2%, 3%, and 4%) and cement (10%, 20%, 30%, and 40%) were mixed with all of them into dough using mechanical kneader in laboratory conditions. Grouting experiment is performed with a cylindrical mould of  mm. The samples were subjected to unconfined compression tests to determine their strength after 7 and 14 days of curing. The results of the tests indicated that the waterborne polymer significantly improved the unconfined compression strength of sandy soils which have susceptibility of liquefaction.

A Microstructure-Level Material Model for Simulating the Machining of Carbon Nanotube Reinforced Polymer Composites

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Ashutosh Dikshit ◽  
Johnson Samuel ◽  
Richard E. DeVor ◽  
Shiv G. Kapoor
Keyword(s):  
Carbon Nanotube ◽  
Weight Fraction ◽  
Material Model ◽  
Material Behavior ◽  
Compression Tests ◽  
Linear Elastic ◽  
Rate Dependent ◽  
Wide Range ◽  
Parametrization Scheme ◽  
Fraction Length

A continuum-based microstructure-level material model for simulation of polycarbonate carbon nanotube (CNT) composite machining has been developed wherein polycarbonate and CNT phases are modeled separately. A parametrization scheme is developed to characterize the microstructure of composites having different loadings of carbon nanotubes. The Mulliken and Boyce constitutive model [2006, “Mechanics of the Rate Dependent Elastic Plastic Deformation of Glassy Polymers from Low to High Strair Rates,” Int. J. Solids Struct., 43(5), pp. 1331–1356] for polycarbonate has been modified and implemented to capture thermal effects. The CNT phase is modeled as a linear elastic material. Dynamic mechanical analyzer tests are conducted on the polycarbonate phase to capture the changes in material behavior with temperature and strain rate. Compression tests are performed over a wide range of strain rates for model validation. The model predictions for yield stress are seen to be within 10% of the experimental results for all the materials tested. The model is used to study the effect of weight fraction, length, and orientation of CNTs on the mechanical behavior of the composites.

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