A Microstructural Model for the Anisotropic Drained Stiffness of Articular Cartilage

1990 ◽  
Vol 112 (4) ◽  
pp. 414-425 ◽  
Author(s):  
T. Farquhar ◽  
P. R. Dawson ◽  
P. A. Torzilli
Keyword(s):  
Articular Cartilage ◽  
Mechanical Response ◽  
Stress And Strain ◽  
Confined Compression ◽  
Mechanical Stiffness ◽  
Fibrous Network ◽  
Complete Treatment ◽  
Static Mechanical ◽  
Microstructural Model ◽  
Size Scales

A constitutive model for articular cartilage is developed to study directional load sharing within the soft biological tissue. Cartilage is idealized as a composite structure whose static mechanical response is dominated by distortion of a sparse fibrous network and by changes in fixed charge density. These histological features of living cartilage are represented in a microstructural analog of the tissue, linking the directionality of mechanical stiffness to the orientation of microstructure. The discretized ‘model tissue’ is used to define a stiffness tensor relating drained stress and strain over a regime of large deformation. The primary goal of this work was to develop a methodology permitting more complete treatment of anisotropy in the stiffness of cartilage. The results demonstrate that simple oriented microscopic behaviors can combine to produce complicated larger scale response. For the illustrative example of a homogeneous specimen subjected to confined compression, the model predicts a nonlinear anisotropic drained response, with inherent uncertainty at cellular size scales.

scholarly journals Level Set-Based Extended Finite Element Modeling of the Response of Fibrous Networks Under Hygroscopic Swelling

2020 ◽  
Vol 87 (10) ◽  
Author(s):  
P. Samantray ◽  
R. H. J. Peerlings ◽  
E. Bosco ◽  
M. G. D. Geers ◽  
T. J. Massart ◽  
...  
Keyword(s):  
Level Set ◽  
Degrees Of Freedom ◽  
Mechanical Response ◽  
Natural Fibers ◽  
Extended Finite Element ◽  
Level Set Function ◽  
Fibrous Network ◽  
Microstructural Model ◽  
Set Function ◽  
Heaviside Enrichment

Abstract Materials like paper, consisting of a network of natural fibers, exposed to variations in moisture, undergo changes in geometrical and mechanical properties. This behavior is particularly important for understanding the hygro-mechanical response of sheets of paper in applications like digital printing. A two-dimensional microstructural model of a fibrous network is therefore developed to upscale the hygro-expansion of individual fibers, through their interaction, to the resulting overall expansion of the network. The fibers are modeled with rectangular shapes and are assumed to be perfectly bonded where they overlap. For realistic networks, the number of bonds is large, and the network is geometrically so complex that discretizing it by conventional, geometry-conforming, finite elements is cumbersome. The combination of a level-set and XFEM formalism enables the use of regular, structured grids in order to model the complex microstructural geometry. In this approach, the fibers are described implicitly by a level-set function. In order to represent the fiber boundaries in the fibrous network, an XFEM discretization is used together with a Heaviside enrichment function. Numerical results demonstrate that the proposed approach successfully captures the hygro-expansive properties of the network with fewer degrees-of-freedom compared to classical FEM, preserving desired accuracy.

scholarly journals Diffusion-based degeneration of the collagen reinforcement in the pathologic human cornea

2021 ◽  
Vol 127 (1) ◽  
Author(s):  
Alessio Gizzi ◽  
Maria Laura De Bellis ◽  
Marcello Vasta ◽  
Anna Pandolfi
Keyword(s):  
Scalar Field ◽  
Mechanical Response ◽  
Mechanical Stability ◽  
Shape Change ◽  
Collagen Fibrils ◽  
Human Cornea ◽  
Collagen Structure ◽  
Cross Link ◽  
Mechanical Stiffness ◽  
Microstructural Model

AbstractWe describe a multiphysics model of the collagen structure of the cornea undergoing a progressive localized reduction of the stiffness, preluding to the development of ectasia and keratoconus. The architecture of the stromal collagen is assumed to follow the simplified two-family model proposed in Pandolfi et al. (A microstructural model of cross-link interaction between collagen fibrils in the human cornea. Philos Trans R Soc A 377:20180079, 2019), where the mechanical stiffness of the structure is supplied by transversal bonds within the fibrils of the same family (inter-crosslink bonds) and across the fibrils of the two families (intra-crosslink bonds). In Pandolfi et al. (A microstructural model of cross-link interaction between collagen fibrils in the human cornea. Philos Trans R Soc A 377:20180079, 2019), it was shown that the loss of the spherical shape due to the protrusion of a cone can be ascribed to the mechanical weakening of the intra-crosslink bonds in the central region of the collagen structure. In the present study, the reduction of bond stiffness is coupled to an evolutive pathologic phenomenon, modeled as a reaction–diffusion process of a normalized scalar field. We assume that the scalar field is a concentration-like measure of the degeneration of the chemical bonds stabilizing the structural collagen. We follow the evolution of the mechanical response of the system in terms of shape change, according to the propagation of the degeneration field, and identify the critical loss of mechanical stability resulting in the typical bulging of keratoconus corneas.

Study on Stress and Strain of Anchorage Using Finite Element Method

2013 ◽  
Vol 325-326 ◽  
pp. 1314-1317
Author(s):  
Cong Sheng Chen ◽  
Ping He ◽  
Cheng Yong Wang ◽  
Xue Hui Chen ◽  
Lei Huang ◽  
...  
Keyword(s):  
Finite Element ◽  
Strain Distribution ◽  
Maximum Stress ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Integrated Modeling ◽  
Stress And Strain ◽  
Steel Strand ◽  
Prestressed State ◽  
Stress And Strain Distribution

Three-dimensional integrated modeling method and the numerical simulation of elastoplastic finite element are adopted in the paper. The mechanical response of the five holes anchorage is analyzed in certain prestressed state. The stress and strain distribution information of the anchor ring, clip and steel strand is obtained respectively, and the structure safety is discussed by investigating on the maximum stress and strain.

Numerical Analysis of Branch Mechanical Response to Loading

2019 ◽  
Vol 45 (4) ◽  
Author(s):  
Barbora Vojáčková ◽  
Jan Tippner ◽  
Petr Horáček ◽  
Luděk Praus ◽  
Václav Sebera ◽  
...  
Keyword(s):  
Finite Element ◽  
Cross Sections ◽  
Mechanical Response ◽  
Mechanical Analysis ◽  
Beam Deflection ◽  
Design System ◽  
Elliptical Cross ◽  
Static Mechanical ◽  
The Difference ◽  
Tree Uprooting

Failure of a tree can be caused by a stem breakage, tree uprooting, or branch failure. While the pulling test is used for assessing the first two cases, there is no device-supported method to assess branch failure. A combination of the optical technique, pulling test, and deflection curve analysis could provide a device-supported tool for this kind of assessment. The aim of the work was to perform a structural analysis of branch response to static mechanical loading. The analyses were carried out by finite element simulations in ANSYS using beam tapered elements of elliptical cross-sections. The numerical analyses were verified by the pulling test combined with a sophisticated optical assessment of deflection evaluation. The Probabilistic Design System was used to find the parameters that influence branch mechanical response to loading considering the use of cantilever beam deflection for stability analysis. The difference in the branch’s deflection between the simulation and the experiment is 0.5% to 26%. The high variability may be explained by the variable modulus of the elasticity of branches. The finite element (FE) sensitivity analysis showed a higher significance of geometry parameters (diameter, length, tapering, elliptical cross-section) than material properties (elastic moduli). The anchorage rotation was found to be significant, implying that this parameter may affect the outcome in mechanical analysis of branch behavior. The branch anchorage can influence the deflection of the whole branch, which should be considered in stability assessment.

Oscillatory Compressional Behavior of Articular Cartilage and Its Associated Electromechanical Properties

1981 ◽  
Vol 103 (4) ◽  
pp. 280-292 ◽  
Author(s):  
R. C. Lee ◽  
E. H. Frank ◽  
A. J. Grodzinsky ◽  
D. K. Roylance
Keyword(s):  
Fluid Flow ◽  
Articular Cartilage ◽  
Molecular Mechanisms ◽  
Fluid Velocity ◽  
Streaming Potential ◽  
Usual Sense ◽  
Frequency Range ◽  
Confined Compression ◽  
Streaming Potentials ◽  
Compressive Stiffness

The compressive stiffness of articular cartilage was examined in oscillatory confined compression over a wide frequency range including high frequencies relevant to impact loading. Nonlinear behavior was found when the imposed sinusoidal compression amplitude exceeded a threshold value that depended on frequency. Linear behavior was attained only by suitable control of the compression amplitude. This was enabled by real time Fourier analysis of data which provided an accurate assessment of the extent of nonlinearity. For linear viscoelastic behavior, a stiffness could be defined in the usual sense. The dependence of the stiffness on ionic strength and proteoglycan content showed that electrostatic forces between matrix charge groups contribute significantly to cartilage’s compressive stiffness over the 0.001 to 20 Hz frequency range. Sinusoidal streaming potentials were also generated by oscillatory compression. A theory relating the streaming potential field to the fluid velocity field is derived and used to interpret the data. The observed magnitude of the streaming potential suggests that interstitial fluid flow is significant to cartilage behavior over the entire frequency range. The use of simultaneous streaming potential and stiffness data with an appropriate theory appears to be an important tool for assessing the relative contribution of fluid flow, intrinsic matrix viscoelasticity, or other molecular mechanisms to energy dissipation in cartilage. This method is applicable in general to hydrated, charged polymers.

Comparison of the equilibrium response of articular cartilage in unconfined compression, confined compression and indentation

2002 ◽  
Vol 35 (7) ◽  
pp. 903-909 ◽  
Author(s):  
R.K Korhonen ◽  
M.S Laasanen ◽  
J Töyräs ◽  
J Rieppo ◽  
J Hirvonen ◽  
...  
Keyword(s):  
Articular Cartilage ◽  
Unconfined Compression ◽  
Confined Compression ◽  
Equilibrium Response

scholarly journals Mechanical Characterization of Nanocomposite Joints Based on Biomedical Grade Polyethylene under Cyclical Loads

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2681
Author(s):  
Annamaria Visco ◽  
Cristina Scolaro ◽  
Antonino Quattrocchi ◽  
Roberto Montanini
Keyword(s):  
Titanium Dioxide ◽  
Mechanical Response ◽  
Mechanical Characterization ◽  
Laser Light ◽  
Mechanical Tests ◽  
Fatigue Tests ◽  
Weight Content ◽  
Percentage Weight ◽  
Static Mechanical

Polymeric joints, made of biomedical polyethylene (UHMWPE) nanocomposite sheets, were welded with a diode laser. Since polyethylene does not absorb laser light, nanocomposites were prepared containing different percentages by weight of titanium dioxide as it is a laser absorbent. The joints were first analyzed with static mechanical tests to establish the best percentage weight content of filler that had the best mechanical response. Then, the nanocomposites containing 1 wt% titanium dioxide were selected (white color) to be subjected to fatigue tests. The experimental results were also compared with those obtained on UMMWPE with a different laser light absorbent nano filler (carbon, with greater laser absorbing power, gray in color), already studied by our research team. The results showed that the two types of joints had an appreciable resistance to fatigue, depending on the various loads imposed. Therefore, they can be chosen in different applications of UHMWPE, depending on the stresses imposed during their use.

Design and Research on Aluminum-Plastic Trunk Lid

2012 ◽  
Vol 538-541 ◽  
pp. 833-840
Author(s):  
Duo Nian Yu ◽  
Li Yang Gu ◽  
Chong Yang Lu
Keyword(s):  
Design Method ◽  
The Body ◽  
Frame Structure ◽  
Light Weight ◽  
Mechanical Stiffness ◽  
Plastic Structure ◽  
Stiffness Properties ◽  
Body Design ◽  
Static Mechanical ◽  
Panel Thickness

Abstract: In this paper, the traditional trunk lid was analyzed using finite element method firstly, and then the basic mechanical properties of the lid were obtained, which were used as the topology optimization constrains of the trunk lid outer panel, then the aluminum alloy frame structure that could satisfy the static mechanical stiffness properties was designed; According to the requirement, the trunk lid inner panel was redesigned, the material properties determined in advance were given to the inner and outer panel respectively, after being assembled, the best panel thickness could be obtained by ways of size optimization. Compared to the analysis results, the new aluminum-plastic structure can meet the requirements in performance, and has significant effect on light-weight. This paper provides some reference for the development of the aluminum-plastic structure of the body design method.

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