PRISM :: Browsing by Author "Li, Leping"

Browsing by Author "Li, Leping"

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Open Access
An anatomically-accurate finite element knee model accounting for fluid pressure in articular cartilage
(2010) Gu, Ke; Li, Leping
Open Access
B-Spline Based 3D Model Reconstruction and Finite Element Analysis of Human Knee Joint
(2017) Zhu, Di; Li, Leping; Xue, Deyi; Johansen, Craig; Lu, Qingye
Knee joint is the largest diarthrodial joint in the human body, and the normal joint mechanics is essential for our daily life. Finite element analysis provides an efficient tool for studying knee joint mechanical behaviour under different conditions. Due to the complex shapes of the knee joint, it is important to obtain accurate models with realistic geometries prior to FE simulation. A semi-automatic 3D point cloud fitting procedure in MATLAB based on B-Splines that accounts for contact geometries and CAD compatibility was developed in this thesis. The reconstructed model was then used for nonlinear stress-relaxation simulations under ramp compressions, where pore pressure, contact pressure and reaction forces were investigated. The reconstruction procedure has successfully reduced overclosures at contact surfaces, promoted faster convergence and enhanced simulation performances. This study helps further build the bridge between 2D medical images and FE simulations.
Open Access
Effect of Defects, Inclusions and Inhomogeneities in Elastic Solids
(2019-12) Alhasadi, Mawafag F.; Federico, Salvatore; Epstein, M.; Li, Leping; Wan, Richard; Ru, Chongqing
This thesis focusses on the theory of materials with defects introduced by John D. Eshelby in the 50s and the 60s, which today we call Configurational Mechanics or, in his honour, Eshelbian Mechanics. The thesis consists of four interconnected parts. The first part is dedicated to the relation between two of Eshelby’s developments: the energy momentum tensor (or Eshelby stress tensor), describing the net force on a defect, and the Eshelby fourth-order tensor, which relates the strain in an inclusion in an otherwise homogeneous and isotropic matrix to the virtual strain (transformation strain) defining the geometrical misfit between inclusion and matrix, within the theory of small deformations. The second part of the research was prompted by the fact that, although the relation between Eshelby’s inclusion problem (Eshelby, 1951, 1975) and Noether’s theorem has been mentioned in literature, no explicit relation has ever been given, to the best of our knowledge. In a framework based on modern differential geometry, it is shown that the application of Noether’s theorem allows for straightforwardly obtaining the classical results by (Eshelby, 1951, 1975). The third part of the thesis aims at investigating the work of Eshelby (1951, 1975) on configurational forces and of Noll (1967) on material uniformity within a general framework including thermo-elasticity, volumetric growth inertial effects, in which the divergence of the Eshelby stress is called the Eshelby force. A differential identity is obtained for the modified Eshelby stress, which includes, as a particular case, the identity found by Epstein and Maugin (1990). Moreover, a differential identity is obtained for what is called the modified Eshelby power, representing the time counterpart of the Eshelby force. Then, a relation between the modified Eshelby force and the modified Eshelby power is derived in the dynamical case. Finally, based on the results obtained in the previous parts of the research, a large-deformation counterpart is proposed of the imagined procedure that Eshelby (1957) used to investigate the theory of inclusions in the case of infinitesimal deformations. A mixed multiplicative decomposition of the deformation gradient, in terms of the Bilby-Kröner-Lee and the Noll-Epstein-Maugin decompositions allows for obtaining the large-deformation fourth-order Eshelby tensor, a novel result.
Open Access
Electric Field Assisted Alignment of Nanotubes for Low-Pass and Band-Pass Filters
(2016) Li, Qiran; Kwok, Daniel; Li, Simon; Li, Leping; Yanushkevich, Yanushkevich
Because of their unique electrical properties, carbon nanotubes (CNTs), particularly the single-walled carbon nanotubes (SWCNTs), have shown potential applications in electronics. In this study, by controlling their alignments under varied electric fields, SWCNTs were used to prepare microelectrode devices, which were examined and show low-pass filtering harmonic responses. By analyzing the SWCNT-based devices (vs. bare-chip), equivalent circuit models were created to understand these devices and the mechanism of their filtering performance. After a series of simplification and optimization, a final model was obtained and a hypothesis was proposed to explain the relationships between the CNT structures and the corresponding electrical properties. The resulted model was verified about its predictability to the filtering performance of CNT-based devices. In addition, similar devices were fabricated with two types of Rosette nanotubes and were then analyzed regarding their electric properties, confirming its effectiveness of the methodology that was used for the CNT-based devices.
Open Access
Experimental Validation of Finite Element Predicted Bone Strain in the Human Metatarsal
(2017) Fung, Anita; Edwards, William Brent; Boyd, Steven Kyle; Schmidt, Tannin; Li, Leping; Wiley, James Preston
The objective of this study was to verify and validate a finite element modeling routine for the human metatarsal, which is a common location for stress fractures. Experimental strain measurements on 33 human cadaveric metatarsals subject to cantilever bending were compared with strain predictions from finite element (FE) models generated from computed tomography images. For the material property assignment of the FE models, a published density-elasticity relationship was compared with density-elasticity equations developed using optimization techniques. The correlations between the measured and predicted and predicted strains were very high (r2≥0.94) for all of the density-elasticity equations. However, the utilization of an optimized density-elasticity equation improved the accuracy of the finite element models, reducing the maximum error between measured and predicted strains by 10% to 20%. The finite element modeling routine could be used for investigating potential interventions to minimize metatarsal strains and the occurrence of metatarsal stress fractures.
Open Access
External and Internal Corrosion and Its Control of Natural Gas Pipelines
(2019-12) Qian, Shan; Cheng, Y. Frank; Li, Leping; Wang, Ruisheng; Oguocha, Ikechukwuka; Wong, Ron
Natural gas pipelines suffer from both external and internal corrosion during their service life, which may result in dramatic consequences. In this research, external corrosion of X52 pipeline steel under direct current (DC) interference was investigated in a simulated soil solution. Corrosion acceleration by DC was quantitatively determined as a function of DC current density. DC was found to shift the cathodic protection (CP) potential to positive and negative directions in the anodic and cathodic zones, respectively, on the pipelines, resulting in either corrosion enhancement or hydrogen evolution at the zones. The effect of DC on properties and performance of fusion bonded epoxy (FBE) coating applied on pipelines was studied. The presence of DC interference facilitates water permeation into the coating due to the altered molecular structure and decreased the coating resistance for corrosion protection. Furthermore, corrosion of X52 pipeline steel under dynamic DC interference was investigated. Dynamic DC further accelerates the steel corrosion compared to static DC at specific DC current densities. It is believed that the alternating current (AC) component included in the pulse DC contributes to the corrosion reaction. With increase in the DC pulse frequency, corrosion rate of the steel decreases. The wave form of the dynamic DC does not obviously affect the steel corrosion. Internal corrosion of X52 pipeline steel was investigated in CO2-containing thin layers of solution, simulating the actual corrosive environment generated in the interior of natural gas pipelines. A mechanistic model was developed to explain the internal corrosion of wet gas pipelines. With the decrease of the solution layer thickness, the corrosion rate of the steel reduces. An elevated temperature accelerates the corrosion reaction kinetics, and generates a compact and homogeneous FeCO3 film at the same time. The presence of acetic acid increases the steel corrosion, while the methanol reduces corrosion rate of the steel. For external corrosion control, a micro/nanostructured ZnO-alkylamine composite coating was developed by electrodeposition and anodization to possess multiple functions. The optimal coating film is superhydrophobic, with the water contact angle up to 158o. The coating possesses a good corrosion resistance and excellent self-cleaning performance and a strong anti-adhesion to pseudomonas aeruginosa bacteria. For internal corrosion control, the inhibition performance of imidazoline (IM) and sodium dodecylbenzenesulphonate (SDBS) inhibitors and their synergism on corrosion of X52 steel in CO2-saturated chloride solutions was investigated. The synergistic effect of the two inhibitors enhances the corrosion inhibition performance, compared to the inhibitors acting independently. The adsorption of both inhibitors on the steel is chemisorption, following the Temkin adsorption isotherm.
Open Access
Finite Element Study of the Healthy and Meniscectomized Knee Joints Considering Fibril-Reinforced Poromechanical Behaviour for Cartilages and Menisci
(2013-03-28) Kazemi Miraki, Mojtaba; Li, Leping
From an engineering standpoint, articular cartilage and meniscus are porous viscoelastic materials with water as their most prevalent component. However, fluid pressurization has been commonly ignored in the three-dimensional Finite Element (FE) models of the knee joint and the soft tissues have been usually assumed as single-phase elastic materials. These elastic models cannot capture the time-dependent behaviour of the joint and are limited to either the instantaneous or equilibrium response, depending on the modulus used. A patient-specific FE model describing the time-dependent response of the healthy and injured knee joints is still a challenge. The main objective of this research was to investigate the fluid-flow dependent creep/relaxation behaviours of the normal and meniscectomized knees using a patient-specific FE model of the knee joint. The model included distal femur, tibia, fibula, articular cartilages, menisci and four major ligaments: ACL, PCL, LCL and MCL. Cartilages and menisci were modelled as fluid-saturated solid matrices reinforced by a nonlinear collagen network. Both small and large deformations were considered in the simulations. The theory of quasi-linear viscoelasticity was used to describe the nonlinear behaviour of the collagen fibrils. Neo-Hookean hyperelasticity was considered for the non-fibrillar solid matrix of the tissues in large deformations. The constitutive models were numerically formulated in a co-rotational reference frame for large deformations and a user defined FORTRAN subroutine, UMAT, was developed to implement the material model in ABAQUS. The obtained results indicated the important role of fluid pressurization of cartilaginous tissues in the contact mechanics of the joint. Removal of the menisci not only changed the stresses in the cartilages, which was in agreement with the published studies, but also altered the distribution and the rate of dissipation of fluid pressure in the cartilages. While in the intact joint, the location of the maximum fluid pressure was dependent on the loading conditions, in the meniscectomized joint the location was predominantly determined by the site of meniscal resection. The results also indicated different load transfer mechanisms of the joint in creep and stress relaxation. In the creep loading, the stress in femoral cartilage decreased with time while the stress in the menisci increased. This resulted in a gradual transfer of the loading from the cartilage to the menisci. In stress relaxation, however, the stress level decreased with time in cartilages and menisci. Such phenomena cannot be captured using single-phase models of the joint.
Open Access
Finite Element-based Methods for Dent Assessment on Pipelines
(2023-12-19) zhao, jian; Cheng, Yufeng(Frank); Li, Leping; Tiamiyu, Ahmed Alade; Zhou, Qi; Chen, Zengtao
As a well-developed form for energy transportation over wide ranges and long distances, pipelines always encounter various threats in service. In recent years, with the strong demand of clean energy, hydrogen transport in existing pipelines induces new challenges to the pipelines. Dent is a common mechanical defect present on pipelines, compromising structural integrity and causing pipeline failures. To date, there have been limited methods available to assess dent, and a dent combined with other types of defects such as corrosion. In this work, novel methods and criteria were developed for assessment of pipeline dent, corrosion in dent and hydrogen distribution at the dent using finite element (FE) modeling. Denting and spring-back processes were modeled and plain dents were created on the pipeline. A new criterion based on ductile damage failure indicator analysis was proposed. Pressure-bearing capacity was assessed on corroded pipelines containing a dent, where the mutual interaction between corrosion and the dent were determined. In addition, a method was developed to assess the corrosion in dent by considering both mechanical and electrochemical forces. For dented pipelines repurposed for transporting hydrogen gas, a FE-based model was developed to determine the stress/strain and H atom concentrations at the dent, where denting, spring-back and cyclic loading processes were modeled. Furthermore, the hydrogen-induced crack initiation on the pipeline subject to denting process was investigated using the phase field method.
Open Access
Geometry Reconstruction and Finite Element Modelling of Porcine Knee Joint
(2017) Zheng, Xiaoyue; Li, Leping; Federico, Salvatore; Kwok, Daniel; He, Jianxun
Arthritis is a leading cause of disability in North America. It is believed to be associated with the abnormal contact mechanics of articular cartilage. Contact analyses are widely used to determine the mechanical interplays among the different tissues in the joint. Animal joints are often used to validate a computational model and understand human joint mechanics. The objectives of this research are to construct the geometry of the porcine stifle joint using a combined CT and automated indentation mapping method, and build a finite element model in ABAQUS to determine the joint mechanics. The porcine knee joint model were reconstructed using MATLAB and Rhinoceros. A knee compression was simulated with ABAQUS, which considered fluid pressure and flow in articular cartilages and menisci. The reaction predicted by the model generally agrees with the measurements from laboratory tests, which partially validates the modelling methodology.
Open Access
Ignition of Hydrogen Jets with Multistep Chemical Kinetics
(2016-01-14) Yang, Christine; Bauwens, Luc; Sudak, Les; Li, Leping; Jeje, Ayodeji Aderopo
The present report intends to deal with the spontaneous jet ignition, occurring just after the sudden outburst of hydrogen from a high-pressure reservoir into atmosphere. The propensity of hydrogen to ignite, is a complex problem, and little is known, in spite of numerous experiments and numerical analyses carried out. One possible scenario involves the effect of heat and mass diffusion at the contact surface, separating the cooled hydrogen from heated air, which may trigger chemistry and ultimately lead to ignition. A model with multistep kinetics for hydrogen-air combustion is examined here in the short time limit. A proper formulation has been developed by adding perturbation to the chemically frozen flow solution. A strategy for the numerical solution of the resulting linear problem involves splitting the problem into three subproblems. Results show two distinct regimes where early on, initiation is dominant, and at later times, chain-branching plays an important role.
Open Access
Impact of Knee Joint Loading on Site-Specific Cartilage Gene-Expression in a Porcine Model
(2016) Otoo, Baaba; Li, Leping; Herzog, Walter; Hart, David; Edwards, Brent
Cyclic mechanical loading of cartilage induces stresses and fluid flow which are thought to modulate chondrocyte metabolism. The uneven surface plus the heterogeneity of cartilage within a joint makes stress and fluid pressure distribution in the tissue non-uniform, and gene expression may vary at different sites as a function of load magnitude, frequency and time. In previous studies, cartilage explants were used for loading tests to investigate cartilage biological response to mechanical loading, which did not reflect well the loading conditions in a joint. In contrast, we used loading tests of intact knee joints, providing a more physiologically relevant mechanical environment. Gene expression levels of loaded samples were compared with that of corresponding control samples to establish variations. Variations in gene expression levels after mechanical loading provide an indication of the effect of local topography and structure of the cartilage on the metabolic activity of the tissue regulated by mechanical loading.
Open Access
Intercellular Gap Junction Communication in the Bovine Annulus Fibrosus
(2019-02-21) McWhae, Russell; Duncan, Neil A.; Matyas, John Robert; Sen, Arindom; Li, Leping; Salo, Paul T.
The intervertebral disc has a complex, anisotropic structure. The annulus fibrosus, the fibrous outer layer of the intervertebral disc, consists of fifteen to twenty-five concentric layers of collagen fibers at alternating orientations. Cells inside and between these lamellae are known to communicate with each other through gap junctions, protein channels that directly couple the membranes of adjacent cells and form interconnected networks that may be used to coordinate a response to mechanical stimuli. These fibroblastic cells fall into three distinct morphologies: spindle-shaped lamellar cells, round lamellar cells, and interlamellar cells. With confocal microscopy methods, gap-junctional intercellular signal propagation between groups of interconnected cells was examined. While the anisotropic microenvironment of the outer annulus was hypothesized to manifest in non-homogenous signal-propagation patterns, it was demonstrated that no clear directional biases or non-homogenous behavior existed among different cell morphologies and orientations; instead, intercellular signal propagation appears to be primarily proximity based.
Open Access
Modeling of the Water-based Heating System of the Mechanical Engineering Building at the University of Calgary
(2019-12) Ahmed, Saeed; Li, Simon; Li, Leping; Ramirez Serrano, Alejandro; Nezhad, Amir Sanati; Hu, Jinguang
In this research, the model of the water-based heating system of Mechanical Engineering Building (MEB) is developed. This project is conducted in collaboration with “Office of Sustainability” of University of Calgary (UofC), because one of their goals is to reduce the energy consumption of UofC’s buildings. The water-based heating system has one of the major share in total energy consumption of a building. It highlights the importance of building this model, which can help to understand some important aspects and variables (related to energy consumption) of the water-based heating system. The model has four major component models, namely boiler, Air Handling Unit (AHU), Reheat Coil (RHC) and radiator (RAD). A component model aggregately represents the similar type of equipment in MEB. For example, a single boiler model is used to represent two boilers of the water-based heating system of MEB. The component models of AHU and RHC are based on energy balance equations, and these are gray-box models. However, the models of boiler and RAD are black-box models, because some required data is not available for developing their gray-box models. The empirical data for developing component models is collected through Building Management System (BMS) software, with the help of Office of Sustainability. The model is developed in Simulink. An individual model for each component is developed and then parameters are estimated for each component model. The parameters of gray-box models are estimated in Simulink, whereas the coefficient parameters for black-box models are estimated in MS-Excel. The output of each component model is then compared with the measured data to ascertain the error. The integrated model of the water-based heating system is developed by connecting the component models. Being a pilot project, the worked helped all involved to understand the opportunities available and the difficulties present, to undertake a project related to UofC building heating system. The Simulink model developed can help the facility management of UofC to look into energy consumption of the water-based heating system of MEB.
Open Access
Modelling and Analysis of the Axial Vibration on BHA of Horizontal Drilling Rig
(2018-04-30) Xu, Jingxuan; Tu, Yiliu; Xue, Deyi; Li, Leping; Fapojuwo, Abraham O.
Horizontal drilling technology is a widely applied well drilling technology due to its capability of reducing drilling time and cost, and at same time increasing the production. In practice, oil and gas production companies employ rotary steerable system or positive displacement motor to steer the drill bit to follow a pre-planned well trajectory along a desired direction. Therefore, the efficiency and accuracy are the main concerns for the improvement of horizontal drilling technology and drill string vibration is the factor to influence these two major concerns. This thesis illustrates a dynamic mathematical model for the vibration of the bottom hole assembly (BHA) which is an important part of drill string. The mathematical model considers the friction between the wellbore and the BHA and the effect of drilling fluid. It investigates the major influencing factors on the vibration, such as weight on bit, friction coefficient, viscous damping coefficient, and the number of stabilizers. The dynamic mathematical model is validated by the finite element simulation and analysis. Moreover, it can monitor the deformation of BHA real time and help drillers adjusting the parameters when the well path deviates from the original planned trajectory.
Open Access
Novel Approach to Identify and Localize Chemical Leakages in Pipelines
(2016-02-08) Wei, Xiaomeng; Park, Simon; Ramirez-Serrano, Alejandro; Park, Simon; Ramirez-Serrano, Alejandro; Li, Leping; Wang, Xin
This study investigates a novel approach for identifying and localizing chemical leakages utilizing mesh-based electronic instruments and surface coating techniques. The proposed leak detection system includes one or more layers of flexible mesh electrodes formed by discrete conductive/nonconductive filaments. It is wrapped on top of the 3D structure needing to be monitored and coated with nano-composite based sensing material. The hydrocarbon sensing is performed by the chemiresistive properties of the sensing material coated on top of the filaments. During the monitoring, whenever the structure experiences changes in the hydrocarbon concentration level to which it is exposed, the sensing material will capture the changes and convert them to resistive changes. The conductive filaments in the mesh will then transmit the electrical signals gathered from the coating to the onsite electronic system. This electronic system is able to perform early stage data processing such as scanning, driving, calibrating and remote communication.
Open Access
Poromechanical Modeling of Porcine Knee Joint Considering Site-Dependent Material Properties of Articular Cartilage from Indentation Testing
(2020-06-01) Zare, Mojtaba; Li, Leping; Cheng, Yu; Edwards, William Brent
Articular cartilage mechanical properties can be ascribed to the variations of morphology and concentration of its constituents across the tissue. The knowledge of site-specific properties of articular cartilage of knee joints may be important for understanding the onset of cartilage degeneration in the knee. Few earlier studies have focused on the poromechanical response of knee joints with site-specific material properties across cartilage. Animal knee joints are often used to study the mechanical properties of soft tissues and validate a computational model of the knee joint and aim to translate the findings to human knee joint biomechanics. On that account, the objectives of this study were to explore the variations of cartilage mechanical properties across the tissue and evaluate the effect of site-specific mechanical properties of cartilage on the poromechanical response of a porcine knee joint model. Fresh porcine knee joints were used in the present study to extract cartilage properties and reconstruct a knee geometry using magnetic resonance imaging. The automated indentation testing with the Mach-1 tester was used to determine the site-dependent cartilage properties. A displacement input was applied to sampling points followed by a partial relaxation. The thickness mapping of the sampling points followed the indentation testing to collect all required data. The two-way ANOVA was performed on the measurement data and demonstrated the dependence of the cartilage thickness and reaction force on sampling regions. Further analyses of the indentation data showed that the variations of the recorded reaction forces were not solely due to the cartilage thickness. To reduce the effort of curve-fitting the material model parameters to various site-specific indentation data, the surface of articular cartilage was divided into 14 regions to obtain the region-dependent material properties. The non-fibrillar matrix and fibrillar network of femoral and tibial cartilages had various stiffnesses across the tissue as obtained from the fitting procedure. In the simulated knee joint, the force-compression relationship of the whole knee joint was determined by both the compression magnitude and the compression rate. By applying the region-dependent properties to finite element simulations of the porcine knee joint, the stress, fluid pressure, and contact pressure magnitudes and distributions of the cartilage were altered. The results indicated that the realistic implementation of region-dependent properties of tissues may be necessary for understanding the load distribution in the joint.
Open Access
Real-time Collision Detection Algorithm for Humanoid Robots
(2020-01-29) Moghaddasi, Shadi; Ramírez-Serrano, Alejandro; Westwick, David T.; Li, Leping
Humanoid robots (humanoids) are highly capable of assisting humans and working with them in cluttered and confined environments. However, they are not completely ready to work in close proximity with humans while not risking the safety of themselves and the objects and people around them. Current methods have not been fully successful in preparing humanoid for safe Human Robot Interaction (HRI) because they rely on expensive and fragile equipment, and erroneous techniques. This thesis presents a novel real-time methodology that enables the safe close proximity HRI for all types of humanoids (controlling systems, etc.). The proposed approach employs signals from robots’ motor joints and data from the computers running the robot to develop a collision detection algorithm. Using this algorithm, humanoids will be able to speedily identify impacted joints during a collision. Experimental results for the humanoid robot Taiko are presented to demonstrate the applicability of the proposed approach.
Open Access
Strain Rate Dependent Response and Fluid Load Support of the Knee Joint Under Compression
(2018-09-14) Rodriguez Marval, Marcel Leonardo; Li, Leping; Federico, Salvatore; Zhou, Qi; Cheng, Yufeng F.
The human knee joint is subjected to loading changes during daily activities. The investigation of the load response mechanisms within the knee contributes to the prevention, diagnosis and treatment of injury and disease of the joint. The load response of articular cartilage in the joint highly depends on the compression rate. This response has been extensively investigated in vitro with tissue discs, but not sufficiently examined in situ and in vivo within the intact joint. Computational simulation is a widely used tool to study this response. The development of imaging techniques has contributed to obtaining an accurate geometry of the knee joint, whose behaviour can then be simulated considering realistic contact conditions during knee compression. The role of the complex anatomy of the knee and its interplay between the various tissues needs to be considered in simulations and in vitro and in vivo studies to understand joint mechanics. This research is intended to deepen the understanding of the stress relaxation and creep response of the knee joint when the realistic human or animal geometry is considered. The objectives of this research are to (1) determine the compression rate-dependent response of the healthy and meniscectomized knee joints, (2) explore the role of fluid load support in healthy porcine knee joints subjected to compression and (3) evaluate the creep response of human knee joint in vivo using a combined imaging approach of MRI and dual fluoroscopy. Results from porcine joint tests revealed significant nonlinear compression-rate dependent load response and the influence of tissue hydration. A human subject test showed the feasibility of studying the creep response of the human joint in vivo, which may be used to validate a geometrically accurate model for computational simulations. This research will provide a better understanding of load share between the fluid pressure and tissue matrices within the knee joint, and how the load share changes with a compression rate that varies in daily activity.
Open Access
The Roles of the Normal Mechanical Properties of Articular Cartilage in the Contact Mechanics of the Human Knee Joint: a Finite Element Approach
(2013-11-14) Dabiri, Yaghoub; Li, Leping
In spite of numerous research devoted to the study of the mechanical behaviour of cartilage, few of them considered fluid pressure in an anatomically accurate knee joint model. Including the fluid phase as a cartilage constituent, this thesis investigated the mechanics of human knee joint. The main hypothesis of this thesis was that the depth-wise integrity of the structure of cartilage has an important role in its mechanical performance especially its fluid pressurization. The roles of depth-dependent properties, local degenerations and defects on the knee joint mechanics were modeled. Moreover, the effect of individual muscle forces on the knee joint mechanics was investigated. In one of our studies, four models including healthy and degenerated cartilage with local OA progressed from the superficial, to the middle and deep zones were compared. In another study, the effects of depth-wise progression of a local cartilage defect on the knee contact mechanics were investigated. A model with individual muscle forces was compared with a model without muscle forces to examine the effects of muscle forces. The normal cartilage produced higher surface fluid pressure under a given compression. The lack of structural integrity, as happened in local cartilage degeneration, resulted in reduced fluid pressure in the degenerated zone as well as at the cartilage-bone interface. Cartilage defects, on the other hand, had more complex effects on knee joint mechanics. While a local superficial defect reduced pressure in the remaining affected cartilage, a defect advanced to the middle zone increased fluid pressure. Regarding effects of muscle forces, the knee mechanics was noticeably affected when muscles were included. Contact pressure, for instance, was significantly increased in a model with muscle forces compared to a model without muscle forces. The results were in line with previous experimental and computational studies that reported the importance of the structural integrity and depth-dependent properties of cartilage. Integrating fluid pressure, complex three-dimensional geometry, depth-dependent properties, individual muscle forces, and a more realistic treatment of free surface fluid pressure, this project aimed to better understanding of human knee joint mechanics. Results may contribute to better understanding of osteoarthritis as well as the design of artificial cartilage.
Open Access
The Shielding Effect of Polyethylene Coating Disbondment on Permeability of Cahtodic Protection Current and the Resulting Pipeline Corrosion
(2018-08-17) Yin, Ke; Cheng, Y. Frank; Li, Leping; Xue, Deyi; Lu, Qingye
The shielding effect of polyethylene (PE) coating disbondment on cathodic protection (CP) permeability was investigated. Results demonstrated that CP became shielded by disbonded PE coating. The geometrical factors of coating holiday (i.e., holiday size) and coating disbondment (i.e., disbonding width and depth) played an essential role in CP permeability. When sulfate-reducing bacteria (SRB) were contained in the thin layer of solution trapped under the disbonded PE coating, the corrosion of the steel depended heavily on the thickness of the solution layer. There existed a critical solution layer thickness, i.e., 150 μm, where a maximum corrosion rate was reached. Pipeline corrosion in SRB-containing thin layers of solution trapped under disbonded coating was resulted from the synergism of microbiologically influenced corrosion (MIC) and the formation of corrosion product film on the steel surface.