Thermophysical properties and material modelling of acrylic bone cements used in vertebroplasty

The stabilization of osteoporotic vertebrae with acrylic bone cement, called vertebroplasty, is a common procedure in modern surgery. However, the thermomechanical-chemically coupled material behaviour of curing bone cements makes the application even for experienced surgeons difficult and can lead to potential complications like heat necrosis, leaking bone cement, embolisms and postoperative load shifting. In order to reduce these potential complications, to minimize the risks and to better understand the occurring effects, the thermophysical properties of a commercial acrylic bone cement were investigated in detail using differential scanning calorimetry, volumetric dilatometry and temperature controlled rheometry. More specifically, the reaction kinetics, the specific heat, the thermal conductivity, the thermal expansion, the chemical shrinkage as well as the mechanical behaviour was studied during the reaction process of the bone cement. Furthermore, the explored material behaviour is described by a customized material model that takes into account all observed effects. With the aid of this model the inhomogeneous chemical, thermal and mechanical states that appear during the application and curing of acrylic bone cements, can be studied by finite element treatment.     

添加磷酸氢钙对硅酸三钙骨水泥性能的影响

本文将磷酸氢钙(CaHPO₄·2H₂O,DCPD)添加到硅酸三钙(Ca₃SiO₅,C₃S)骨水泥中,采用X射线衍射(XRD),扫描电镜(SEM),万能力学测试机等手段对不同添加量的骨水泥进行表征,考察添加DCPD对硅酸三钙骨水泥性能的影响。实验表明,C₃S材料中添加10% DCPD有着优于单纯C₃S骨水泥的水化性能,骨水泥的初凝时间从92 min缩短到80 min;添加20%~30% DCPD能提高材料的短期力学强度,可以实现其短期抗压强度的优化;添加30%~40% DCPD的材料有着优良的生物活性与适中的可降解性能。结果表明,通过添加DCPD优化C₃S水泥的性能,对各种不同性能具有DCPD添加量的依赖性。通过进一步优化DCPD添加量,将可能获得优良的生物活性骨缺陷填充材料。     

Modification of acrylic bone cements by poly(ethylene glycol) with different molecular weight

The high polymerization temperature of acrylic bone cements can cause arthroplasty failure because of the thermal necrosis of surrounding bone tissue. To reduce this undesired effect we have developed novel acrylic bone cement composites containing a phase change material (PCM). As PCM poly(ethylene glycol) (PEG) of different molecular weight was applied and the effect of its incorporation on curing parameters, mechanical and morphological properties of acrylic bone cement was investigated. A significant decrease in maximum temperature from 65.8°C to 47.4°C and slight increase of setting time were observed. PEG introduction also contributed to the thermal stability of acrylic bone cement increase. SEM investigation of modified bone cement confirmed that the microstructure does not alter considerably because of PEG content. It was found that both PEG addition and incubation test contribute to an inconsiderable decrease in mechanical strength of bone cement. However, the mechanical strength increase can be caused by the fresh bone tissue incorporation into the pores appearing in bone cement. Copyright © 2016 John Wiley & Sons, Ltd.     

A method for more accurate FEA results on a medical device developed by 3D technologies

At present, 3‐dimensional models of all additive manufactured objects (AMOs) are accepted as a solid model for finite element analysis (FEA). FEA of AMOs may not reveal the real results because mechanical properties of default materials in CAD software and newly built AMOs are not equal to each other. This may produce problems especially for the end user due to unexpected failure or wear off. The aim of this study was to compare FEA results of an additive manufactured Ankle Foot Orthosis model under 2 different value sets, namely default material‐based mechanical properties and measured mechanical properties. In order to determine the real mechanical properties of the additive manufactured Ankle Foot Orthosis, 3‐dimensional printed test specimens with different infill densities were prepared and tested according to the recommended standards. Mechanical test results were then loaded in the CAD software and FEA was performed. This study illustrated that default mechanical properties of existing materials in CAD software produce misleading simulation results for AMOs, ie, real mechanical properties should be used to get more accurate results.     

The numerical simulation of the mechanical failure behavior of shear thickening fluid/fiber composites: A review

This study reveals the finite element modeling of mechanical failure behavior of shear thickening fluid (STF)/fiber composites under impact. Numerical analysis and finite element modeling of the rheological properties of non-Newtonian fluid, STF are introduced. This review summarizes the model coupling methods in finite element modeling and the mechanical failure behavior prediction models of STF/fiber composites under impact. Further, the influencing factors on the accuracy of mechanical failure simulation models are analyzed. Factors such as the friction between fibers, shear rate, filler particles in the fibers, hysteresis effect and the boundary conditions should be considered in simulating the shear thickening effect of the composites.     

Dimensional considerations on the mechanical properties of 3D printed polymer parts

Additive manufacturing offers a useful and accessible tool for prototyping and manufacturing small volume functional parts. Polylactic acid (PLA) and thermoplastic polyurethane (TPU) are amongst the most commonly used materials. Characterising 3D printed PLA and TPU is potentially important for both designing and finite element modelling of functional parts. This work explores the mechanical properties of additively manufactured PLA/TPU specimens with consideration to design parameters including size, and infill percentage. PLA/TPU specimens are 3D-printed in selected ISO standard geometries with 20%, 60%, 100% infill percentage. Tensile and compression test results suggest that traditional ISO testing standards might be insufficient in characterising 3D printed materials for finite element modelling or application purposes. Infill percentage in combination to design size, may significantly affect the mechanical performance of 3D printed parts. Dimensional variation may cause inhomogeneity in mechanical properties between large and small cross section areas of the same part. The effect was reduced in small cross section parts where reducing the nominal infill had less effect on the resulting specimens. The results suggest that for 3D printed functional parts with significant dimensional differences between sections, the material properties are not necessarily homogeneous. This consideration may be significant for designers using 3D printing for applications, which include mechanical loading.     

Analysis of Single-Walled Carbon Nanotubes Using a Chemical Bond Element Model

A three dimensional nano-scale finite element model (FEM), called the chemical bond element model, is proposed for the simulation of mechanical properties of single-walled carbon nanotubes (SWCNTs) based upon molecular mechanics method. Chemical bonds between carbon atoms are modeled by chemical bond elements. The constants of a sub-stiffness matrix are determined by using a linkage between molecular mechanics and continuum mechanics. In order to evaluate the correctness and performance of the proposed model, simulation was done to determine the influence of nanotube wall thickness, radius and length on the elastic modulus (Young's modulus and shear modulus) of SWCNTs. The simulation results show that the choice of wall thickness significantly affects the Young's modulus and shear modulus. The force field constants is also very important, because the elastic modulus is sensitive to force field constants and the elastic properties of SWCNT are related to the radii of the tubes. The contribution of length to elastic modulus is insignificant and can be ignored. In comparison with the Young's modulus and shear modulus reported in the literature, the presented results agree very well with the corresponding theoretical results and many experimental measurements. Furthermore, if the force constants are properly chosen, the present method could be conveniently used to predict the mechanical behavior of other single-walled nanotubes such as boron nitride nanotubes. The results demonstrate the value of the proposed model as a valuable tool in the study of mechanical behaviors of carbon nanotubes and in the analysis of nanotube-based equipments.     

Defect mode and crystal-electric-field effects on the thermal expansion and heat capacity of RB<Subscript>50</Subscript> boride

This study aimed to evaluate the suitability of using unfired and fired pumice as cement replacement materials as well as their effect on the thermal resistance of hardened ordinary Portland cement (OPC) pastes. Different OPC–pumice (unfired and fired) blends were prepared by partial replacement of OPC by 0, 10 and 20 of pumice (mass%). The effect of the addition of 1 and 5 % of active alumina on the mechanical properties and thermal resistance of different OPC–pumice (unfired) blends was investigated. The fire resistance test was done by exposing the hardened blended cement cubes to elevated temperatures of 200, 400, 600 and 800 °C for 3 h and allowed them to cool down to room temperature before testing for their mechanical properties. The phase composition and thermal analysis of some selected specimens were investigated by XRD, DSC and DTA/TG techniques. The obtained results indicated that replacing OPC by 10 and 20 % by pumice (unfired and fired) improved its thermal stability at different firing temperatures. The cement blend prepared by replacement of OPC with 10 % pumice showed the highest fire resistance. The addition of 1 and 5 % of alumina (A) to OPC–pumice blends causes a notable improve in their mechanical properties and thermal resistance.     

Study of the mechanical damping behavior of SBR-modified cement pastes by dynamic mechanical analyzer

Improvement in mechanical damping of SBR-modified cement pastes had been evaluated by dynamic mechanical analyzer. Specimens were fabricated and tested under 3-point flexure clamp at frequencies of 0.5–50 Hz or temperatures of ?30 to 70 °C. Significant improvement in damping was observed in cementitious-SBR composite specimens when SBR latex to cement ratio was 0.12, which is hypothesized to occur due to improvements in viscosity of cement paste. Furthermore, the SBR-modified cement pastes showed a decreased damping variation tendency with an increase of frequency. They also showed a peak damping variation tendency under the effect of the glass transition temperature. Based on the three element model, mechanical parameters are calculated by fitting the dynamic modulus of SBR-modified cement pastes.     

Creep loading response and complete loading–unloading investigation of industrial anti-vibration systems

This article presents engineering approaches to evaluate creep loading response and a complete loading–unloading procedure for rubber components used as anti-vibration applications. A damage function for creep loading and a rebound resilience function for mechanical unloading are introduced into hyperelastic models independently. Hence, a hyperelastic model can be extended for both creep and unloading evaluations. A typical rubber product and a dumbbell specimen were selected to validate the proposed approaches. It has been demonstrated that the predictions offered by the new models are consistent with the experimental data. In addition, a loading procedure using the same final value, with and without involving unloading, prior to a creep test can produce different results. The proposed approach can capture this phenomenon which was observed in the literature. The proposed approach can also be easily incorporated into commercial finite element software (e.g., Abaqus). It is demonstrated that the proposed method may be used for anti-vibration products at an appropriate design stage.     

Electrostatic correlations and fluctuations for ion binding to a finite length polyelectrolyte

A statistical mechanical model is presented which explicitly accounts for the fluctuations, the electrostatic, and the excluded volume correlations for ions bound to a polyelectrolyte such as DNA. The method can be employed to treat a wide range of ionic conditions including multivalent ions. The microscopic framework of the theory permits the use of realistic finite length and grooved structural model for the polyelectrolyte and modeling of the finite size of the bound ions. Test against Monte Carlo simulations suggests that the theory can give accurate predictions for the ion distribution and the thermodynamic properties. For multivalent ions, the theory makes improved predictions as compared with the mean-field approach. Moreover, for long polyelectrolyte and dilute salt concentration, the theory predicts ion binding properties that agree with the counterion condensation theory.     

原位沉析法制备可吸收壳聚糖/羟基磷灰石棒材

利用原位沉析法制备出一种以壳聚糖 (Chitosan ,CS)为基体 ,羟基磷灰石 (Hydroxyapatite,HA)为填料的新颖的复合材料 ,系统研究了HA含量对复合材料的力学性能和吸水率的影响 .CS HA的弯曲强度为 6 7 8(MPa) ,弯曲模量为 3 3(GPa) ,剪切强度为 2 1 2 (MPa) ,压缩强度为 4 7 8(MPa) ,均比人的自然骨高 2～ 3倍 ,基本满足了作为骨折内固定材料的力学性能的要求 .HA加入到CS使CS HA复合材料的吸水率下降 ,有助于延缓其力学强度在湿态环境下的衰减     

In situ latex synthesis of magnetic polymer nanocomposites for application in magnetorheological materials

A new magnetic polymer nanocomposite based on Fe₃O₄ nanoparticles and nature rubber was prepared by the in situ latex method. This process was fast, versatile, reliable, safe, environmentally friendly, and inexpensive. The magnetorheological effect and mechanical properties of magnetic polymer nanocomposites were investigated in detail. The tensile strength of magnetic polymer nanocomposites without other reinforcing fillers was about 14.6 MPa. At the same time, the relative and absolute magnetorheological effect was about 365.0% and 3.64 MPa, respectively, which were almost 10 times with respect to other magnetic polymer nanocomposites based on nature rubber. Furthermore, the relationships between microstructure and mechanical behavior of magnetic polymer nanocomposites were simulated and discussed by the numerical treatment of a new theoretical model associated with finite element analysis for explaining the micro‐mechanism of magnetic polymer nanocomposites with high performance. The work did not only provide a universal route for the rational design and preparation of magnetic polymer nanocomposites with simultaneously high magnetic sensitivity and mechanical properties for various applications but also propose a new method to improve dispersion of magnetic particles in nature rubber for various applications.     

Finite element simulation for yield stress of hard poly(vinyl chloride)/acrylonitrile-butadiene-styrene blends at different crosshead speeds

Hard poly(vinyl chloride)(PVC)/acrylonitrile-butadiene-sryrene(ABS) blends were prepared using injection-molding and influence of crosshead speed on mechanical properties was examined.Based on morphology parameters obtained from transmission electron microscopy photography and the material parameters from true stress-strain curves of neat PVC and ABS,yield stresses of the blends at different crosshead speeds were simulated employing a two-dimensional nine-particle model based on the finite element analysis(FEA).The FEA results were compared with the experimental yielding stress and the good agreement validated the simulation approach.The FEA approach allowed establishing a yielding criterion related to local yielding of the interstitial matrix between ABS particles.     

Influence of the molding angle on tensile properties of FDM parts with orthogonal layering

Fused deposition molding (FDM) is one of the most widely used three‐dimensional (3D) printing technologies. This paper explores the influence of the forming angle on the tensile properties of FDM specimens. Orthogonal layering details were studied through experiments, theory, and finite element simulations. The stiffness and strength of the specimens were analyzed using the classical laminated plate theory and the Tsai–Wu failure criterion. The experimental process was simulated using finite element simulations. Results show that it is feasible to predict the stiffness and strength of FDM specimens using classical laminated plate theory and the Tsai–Wu failure criterion. A molding angle of 45° leads to specimens with maximized tensile properties. Numerical simulations show that changing the molding angle changes the internal stress and deformation fields inside samples, leading to FDM samples with different mechanical properties due to the orthogonal layers at different molding angles.     

A mesoscale study of thermal expansion behaviors of epoxy resin and carbon fiber/epoxy unidirectional composites based on periodic temperature and displacement boundary conditions

The thermal expansion behaviors of neat epoxy resin and carbon fiber/epoxy unidirectional (UD) composites were experimentally and numerically studied in this paper. The dynamic mechanical analysis (DMA), thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and thermal conductivity measurement were used to measure the thermo-mechanical properties of epoxy resin at different temperatures. The dilatometer was used to measure the thermal strains and linear CTEs of neat epoxy resin and UD composites. In addition, a mesoscale finite element model based on the periodic temperature and displacement boundary conditions was presented to analyze the thermal expansion behaviors of UD composites. The resin-voids representative volume element (RVE) was used to calculate the thermo-mechanical properties of several kinds of resin-voids mixed matrix. From the results it can be found that the glass transition temperature of epoxy resin, porosity and fiber orientation angle have significant effects on the thermal expansion behaviors of UD composites. The mesoscale finite element analyses (FEA) have obvious advantages than various existing analysis models by comparing their predictive results. The distributions of thermal displacement, thermal stress and thermal strain were extracted between the carbon fiber, resin-voids mixed matrix and their interface, and also between the front and back surfaces of the loading direction, to further investigate thermal expansion structure effects of UD composites. This paper revealed that the mesoscale FEA based on periodic temperature and displacement boundary conditions can be also used for thermal expansion researches of other complex structure composites.     

Effect of the mechanical activation of nepheline concentrate on its binding properties in mixed cements

Binding properties of a Portland cement-nepheline-water formulation were studied in relation to its nepheline content by using a preliminary mechanical activation. A thermal analysis was used to estimate the hydration rate of cement phases in the system under study. The accelerating role of nepheline in hardening of mechanically activated Portland cement-nepheline formulations was revealed and found to be more pronounced in early stages. The gain in the strength of the cement stone was analyzed in relation to the formulation composition and hardening duration.     

Investigation on mechanical properties, durability and micro-structural development of steel slag blended cements

To improve the properties of steel slag blended cements, a chemical activator was added into blended cements, the mechanical properties and durability of steel slag blended cements were investigated. The results show that steel slag in blended cement pastes presents low hydraulic activity and makes practically no contribution to strength development. After the addition of chemical activator, the mechanical properties and durability of ternary blended cements are increased significantly. The hydration process and micro-structural development of blended cement was investigated by isothermal calorimeter and scanning electric microscope, respectively. Steel slag started hydration in the first 3?days in the presence of chemical activator, steel slag and granulate blast furnace slag reacted with Ca(OH)₂ to form a dense microstructure as curing proceeded. Therefore, both early and late compressive strengths of steel slag blended cement with 35% cement clinker and 30% steel slag can be comparable with those of Portland cement.