Processing and electrical characterization of a unidirectional CFRP composite filled with double walled carbon nanotubes

Carbon nanotubes represent new emergent multifunctional materials that have potential applications for structural and electrically conductive composites. In the current paper we present a suitable technique for the integration of Double Walled Carbon Nanotubes (DWCNTs) in a unidirectional Carbon Fiber Reinforced Polymer (CFRP) with high volume content of carbon fiber. We showed that the electrical conductivity of the laminates versus temperature follows a non-linear variation which can be well described by the Fluctuation-Induced Tunneling Conduction (FITC) model. The parameters of this model for CFRP/ DWCNTs and CFRP without DWCNTs were determined using best fit curves of the experimental data. This study has shown that DWCNTs have strong influence in the conductivity through laminate thickness. However, there are no significant effects on the electrical conductivity measured in the other two principle directions of the composite laminate. Furthermore, it was found that electron conduction mechanism of carbon fibers is dominated by the FITC

Biomechanical assessment of composite versus metallic intramedullary nailing system in femoral shaft fractures: A finite element study

AbstractBackgroundIntramedullary nails are the primary choice for treating long bone fractures. However, complications following nail surgery including non-union, delayed union, and fracture of the bone or the implant still exist. Reducing nail stiffness while still maintaining sufficient stability seems to be the ideal solution to overcome the abovementioned complications.MethodsIn this study, a new hybrid concept for nails made of carbon fibers/flax/epoxy was developed in order to reduce stress shielding. The mechanical performance of this new implant in terms of fracture stability and load sharing was assessed using a comprehensive non-linear FE model. This model considers several mechanical factors in nine fracture configurations at immediately post-operative, and in the healed bone stages.ResultsPost-operative results showed that the hybrid composite nail increases the average normal force at the fracture site by 319.23N (P<0.05), and the mean stress in the vicinity of fracture by 2.11MPa (P<0.05) at 45% gait cycle, while only 0.33mm and 0.39mm (P<0.05) increases in the fracture opening and the fragments' shear movement were observed. The healed bone results revealed that implantation of the titanium nail caused 20.2% reduction in bone stiffness, while the composite nail lowered the stiffness by 11.8% as compared to an intact femur.InterpretationOur results suggest that the composite nail can provide a preferred mechanical environment for healing, particularly in transverse shaft fractures. This may help bioengineers better understand the biomechanics of fracture healing, and aid in the design of effective implants

Mesoscale modelling of tensile response and damage evolution in natural fibre reinforced laminates

A continuum damage mechanics based mesoscale model is developed within a thermodynamics framework to describe the in-plane tensile response in natural fibre composites. The standard Mesoscale Damage Theory (MDT) is modified to incorporate damage and inelasticity evolution in the fibre-direction, thereby capturing the unique nonlinear fibre-direction response evidenced in natural fibre composites (NFC). The multi-ply damage model is validated using tests on Flax/epoxy laminates and available data on Carbon/epoxy laminates. Model parameters are identified for Flax/epoxy by applying an optimisation algorithm that compares numerical predictions with experimental data. Predictions of mechanical response, stiffness degradation, and inelasticity correlate very well with experimental observations of Flax-laminates. This modified-MDT model offers a predictive, robust tool to aid the development of NFC engineering structures.This research is supported in part by Natural Sciences and Engineering Research Council of Canada e Discovery Grants program (NSERC-DG), funding reference RGPIN 2014-05838

Bone remodeling in a new biomimetic polymer-composite hip stem

Adaptive bone remodeling is an important factor that leads to bone resorption in the surroudning femoral bone and implant loosening. Taking into account this factor in the design of hip implants is of clinical importance, since it allows the prediction of the bone-density redistribution and enables the monitoring of bone adaptation after prosthetic implantation. In this paper adaptive bone remodeling around a new biomimetic polymer-composite based (CF/PA12) hip prosthesis is investigated in order to evaluate the amount of stress shielding and bone resorption. The design concept of this new prosthesis is based on a hollow sub-structure made of hydroxyapatite-coated, continuous carbon fiber (BF) reinforced polyamide 12 (PA12) composite with an internal soft polymer-based core. Strain energy density theory coupled with 3-D Finite Element models are used to predict bone desity redistributions in the femoral bone before and after total hip replacement using both polymer-composite and titanium stems. The result of numerical simulations of bone remodeling revealed that the CF-PA12 composite stem generates an excellent bone density pattern compared to the titanium-based stem, indicating the effectiveness of the composite stem to reduce bone resorption caused by stress shielding phenomenon. This may result in an extended lifetime of Total Hip Replacement (THR).Le remodelage osseux adaptatif est un ph\ue9nom\ue8ne important menant \ue0 une r\ue9sorption du tissu osseux dans lequel est implant\ue9e une tige f\ue9morale, ce qui en affecte la stabilit\ue9. La prise en compte de ce facteur dans la conception des proth\ue8ses de hanche rev\ueat une importance clinique particuli\ue8re en permettant de pr\ue9voir la redistribution de la densit\ue9 min\ue9rale osseuse et d\u2019\ue9valuer l\u2019adaptation osseuse cons\ue9cutive \ue0 la pose de la proth\ue8se. Le pr\ue9sent article traite de l\u2019\ue9valuation du remodelage adaptatif du tissu osseux entourant un nouveau mod\ue8le de proth\ue8se de hanche en polym\ue8re composite FC/PA12 biomim\ue9tique que nous avons effectu\ue9e dans le but de quantifier la r\ue9sorption osseuse par d\ue9viation des contraintes (ph\ue9nom\ue8ne de court-circuitage des contraintes) attribuable \ue0 la proth\ue8se. Recouverte d\u2019hydroxyapatite de calcium, la tige f\ue9morale \ue9tudi\ue9e se compose d\u2019une structure externe creuse monopi\ue8ce en polyamide 12 (PA12) renforc\ue9 de fibre de carbone (FC) dont la cavit\ue9 interne est remplie de polym\ue8re mou. L\u2019utilisation du crit\ue8re de l\u2019\ue9nergie de d\ue9formation minimale et de mod\ue8les 3D d\u2019\ue9l\ue9ments finis nous a permis de pr\ue9dire la distribution de la densit\ue9 min\ue9rale du tissu osseux f\ue9moral avant et apr\ue8s la pose d\u2019une proth\ue8se totale de hanche (PTH) comportant une tige f\ue9morale en polym\ue8re composite ou une tige en titane (Ti). Les r\ue9sultats des simulations num\ue9riques du remodelage osseux r\ue9v\ue8lent que la tige f\ue9morale en polym\ue8re composite FC/PA12 permet le maintien d\u2019une meilleure densit\ue9 min\ue9rale osseuse que la tige en titane, ce qui t\ue9moigne de l\u2019efficacit\ue9 de la tige en polym\ue8re composite \ue0 r\ue9duire la r\ue9sorption osseuse attribuable \ue0 la d\ue9viation des contraintes. Ce mod\ue8le de tige f\ue9morale pourrait donc prolonger la dur\ue9e de vie utile de la proth\ue8se totale de hanche.Peer reviewed: YesNRC publication: Ye

A biomechanical assessment of modular and monoblock revision hip implants using FE analysis and strain gage measurements

<p>Abstract</p> <p>Background</p> <p>The bone loss associated with revision surgery or pathology has been the impetus for developing modular revision total hip prostheses. Few studies have assessed these modular implants quantitatively from a mechanical standpoint.</p> <p>Methods</p> <p>Three-dimensional finite element (FE) models were developed to mimic a hip implant alone (Construct A) and a hip implant-femur configuration (Construct B). Bonded contact was assumed for all interfaces to simulate long-term bony ongrowth and stability. The hip implants modeled were a Modular stem having two interlocking parts (Zimmer Modular Revision Hip System, Zimmer, Warsaw, IN, USA) and a Monoblock stem made from a single piece of material (Stryker Restoration HA Hip System, Stryker, Mahwah, NJ, USA). Axial loads of 700 and 2000 N were applied to Construct A and 2000 N to Construct B models. Stiffness, strain, and stress were computed. Mechanical tests using axial loads were used for Construct A to validate the FE model. Strain gages were placed along the medial and lateral side of the hip implants at 8 locations to measure axial strain distribution.</p> <p>Results</p> <p>There was approximately a 3% average difference between FE and experimental strains for Construct A at all locations for the Modular implant and in the proximal region for the Monoblock implant. FE results for Construct B showed that both implants carried the majority (Modular, 76%; Monoblock, 66%) of the 2000 N load relative to the femur. FE analysis and experiments demonstrated that the Modular implant was 3 to 4.5 times mechanically stiffer than the Monoblock due primarily to geometric differences.</p> <p>Conclusions</p> <p>This study provides mechanical characteristics of revision hip implants at sub-clinical axial loads as an initial predictor of potential failure.</p

Biomechanical Measurement Error Can Be Caused by Fujifilm Thickness: A Theoretical, Experimental, and Computational Analysis

© 2017 Ahmed Sarwar et al. This is the first study to quantify the measurement error due to the physical thickness of Fujifilm for several material combinations relevant to orthopaedics. Theoretical and experimental analyses were conducted for cylinder-on-flat indentation over a series of forces (750 and 3000 N), cylinder diameters (0 to 80 mm), and material combinations (metal-on-metal, MOM; metal-on-polymer, MOP; metal-on-bone, MOB). For the scenario without Fujifilm, classic Hertzian theory predicted the true line-type contact width as WO={(8FDcyl)/(πLcyl)[(1-cyl2)/Ecyl+(1-flat2)/Eflat]}1/2, where F is compressive force, Dcyl is cylinder diameter, Lcyl is cylinder length, cyl and flat are cylinder and flat Poisson\u27s ratios, and Ecyl and Eflat are cylinder and flat elastic moduli. For the scenario with Fujifilm, experimental measurements resulted in contact widths of WF=0.1778×F0.2273×D0.2936 for MOM tests, WF=0.0449×F0.4664×D0.4201 for MOP tests, and WF=0.1647×F0.2397×D0.3394 for MOB tests, where F is compressive force and D is cylinder diameter. Fujifilm thickness error ratio WF/WO showed a nonlinear decrease versus cylinder diameter, whilst error graphs shifted down as force increased. Computational finite element analysis for several test cases agreed with theoretical and experimental data, respectively, to within 3.3% and 1.4%. Despite its wide use, Fujifilm\u27s measurement errors must be kept in mind when employed in orthopaedic biomechanics research

Biomechanical analysis using FEA and experiments of metal plate and bone strut repair of a femur midshaft segmental defect

© 2018 Jason Coquim et al. This investigation assessed the biomechanical performance of the metal plate and bone strut technique for fixing recalcitrant nonunions of femur midshaft segmental defects, which has not been systematically done before. A finite element (FE) model was developed and then validated by experiments with the femur in 15 deg of adduction at a subclinical hip force of 1 kN. Then, FE analysis was done with the femur in 15 deg of adduction at a hip force of 3 kN representing about 4 x body weight for a 75 kg person to examine clinically relevant cases, such as an intact femur plus 8 different combinations of a lateral metal plate of fixed length, a medial bone strut of varying length, and varying numbers and locations of screws to secure the plate and strut around a midshaft defect. Using the traditional “high stiffness” femur-implant construct criterion, the repair technique using both a lateral plate and a medial strut fixed with the maximum possible number of screws would be the most desirable since it had the highest stiffness (1948 N/mm); moreover, this produced a peak femur cortical Von Mises stress (92 MPa) which was below the ultimate tensile strength of cortical bone. Conversely, using the more modern “low stiffness” femur-implant construct criterion, the repair technique using only a lateral plate but no medial strut provided the lowest stiffness (606 N/mm), which could potentially permit more in-line interfragmentary motion (i.e., perpendicular to the fracture gap, but in the direction of the femur shaft long axis) to enhance callus formation for secondary-type fracture healing; however, this also generated a peak femur cortical Von Mises stress (171 MPa) which was above the ultimate tensile strength of cortical bone