Indirect tension test of epoxy asphalt mixtureusing microstructural finite-element model

A finite-element model of the thermosetting epoxy asphalt mixture（EAM） microstructure is developed to simulate the indirect tension test（IDT）.Image techniques are used to capture the EAM microstructure which is divided into two phases：aggregates and mastic.A viscoelastic constitutive relationship,which is obtained from the results of a creep test,is used to represent the mastic phase at intermittent temperatures.Model simulation results of the stiffness modulus in IDT compare favorably with experimental data.Different loading directions and velocities are employed in order to account for their influence on the modulus and the localized stress of the microstructure model.It is pointed out that the modulus is not consistent when the loading direction changes since the heterogeneous distribution of the mixture internal structure,and the loading velocity affects the localized stress as a result of the viscoelasticity of the mastic.The study results can provide a theoretical basis for the finite-element method,which can be extended to the numerical simulations of asphalt mixture micromechanical behavior.

Perfectly matched layer-absorbing boundary condition for finite-element time-domain modeling of elastic wave equations

The perfectly matched layer （PML） is a highly efficient absorbing boundary condition used for the numerical modeling of seismic wave equation. The article focuses on the application of this technique to finite-element time-domain numerical modeling of elastic wave equation. However, the finite-element time-domain scheme is based on the second- order wave equation in displacement formulation. Thus, the first-order PML in velocity-stress formulation cannot be directly applied to this scheme. In this article, we derive the finite- element matrix equations of second-order PML in displacement formulation, and accomplish the implementation of PML in finite-element time-domain modeling of elastic wave equation. The PML has an approximate zero reflection coefficients for bulk and surface waves in the finite-element modeling of P-SV and SH wave propagation in the 2D homogeneous elastic media. The numerical experiments using a two-layer model with irregular topography validate the efficiency of PML in the modeling of seismic wave propagation in geological models with complex structures and heterogeneous media.

Three-dimensional magnetotellurics modeling using edgebased finite-element unstructured meshes

Three-dimensional forward modeling magnetotellurics （MT） problems. We present a is a challenge for geometrically complex new edge-based finite-element algorithm using an unstructured mesh for accurately and efficiently simulating 3D MT responses. The electric field curl-curl equation in the frequency domain was used to deduce the H （curl） variation weak form of the MT forward problem, the Galerkin rule was used to derive a linear finite-element equation on the linear-edge tetrahedroid space, and, finally, a BI-CGSTAB solver was used to estimate the unknown electric fields. A local mesh refinement technique in the neighbor of the measuring MT stations was used to greatly improve the accuracies of the numerical solutions. Four synthetic models validated the powerful performance of our algorithms. We believe that our method will effectively contribute to processing more complex MT studies.

Three-dimensional land FD-CSEM forward modeling using edge finite-element method

A modeling tool for simulating three-dimensional land frequency-domain controlled-source electromagnetic surveys,based on a finite-element discretization of the Helmholtz equation for the electric fields,has been developed.The main difference between our modeling method and those previous works is edge finite-element approach applied to solving the three-dimensional land frequency-domain electromagnetic responses generated by horizontal electric dipole source.Firstly,the edge finite-element equation is formulated through the Galerkin method based on Helmholtz equation of the electric fields.Secondly,in order to check the validity of the modeling code,the numerical results are compared with the analytical solutions for a homogeneous half-space model.Finally,other three models are simulated with three-dimensional electromagnetic responses.The results indicate that the method can be applied for solving three-dimensional electromagnetic responses.The algorithm has been demonstrated,which can be effective to modeling the complex geo-electrical structures.This efficient algorithm will help to study the distribution laws of3-D land frequency-domain controlled-source electromagnetic responses and to setup basis for research of three-dimensional inversion.

Finite-element 3D modeling of stress patterns around a dipping fault

Stresses in a block around a dipping fracture simulating a damage zone of a fault are reconstructed by finite-element modeling. A fracture corresponding to a fault of different lengths, with its plane dipping at different angles, is assumed to follow a lithological interface and to experience either compression or shear. The stress associated with the destruction shows an asymmetrical pattern with different distances from the highest stress sites to the fault plane in the hanging and foot walls. As the dip angle decreases,the high-stress zone becomes wider in the hanging wall but its width changes negligibly in the foot wall.The length of the simulated fault and the deformation type affect only the magnitude of maximum stress,which remains asymmetrical relative to the fault plane. The Lh/Lfratio, where Lhand Lfare the widths of high-stress zones in the hanging and foot walls of the fault, respectively, is inversely proportional to the fault plane dip. The arithmetic mean of this ratio over different fault lengths in fractures subject to compression changes from 0.29 at a dip of 80°to 1.67 at 30°. In the case of shift displacement, ratios are increasing to 1.2 and 2.94, respectively.Usually they consider vertical fault planes and symmetry in a damage zone of faults. Following that assumption may cause errors in reconstructions of stress and fault patterns in areas of complex structural setting. According geological data, we know the structures are different and asymmetric in hanging and foot walls of fault. Thus, it is important to quantify zones of that asymmetry. The modeling results have to be taken into account in studies of natural faults, especially for practical applications in seismic risk mapping, engineering geology, hydrogeology, and tectonics.

Finite-element modeling and simulations of the intra-body communication used for biomedical monitoring

The finite-element modeling and simulations of the intra-body communication （IBC） were investigated to provide a theoretical basis for biomedical monitoring. A finite-element model for the whole human body was developed to simulate the IBC. The simulation of galvanic coupling IBC and electrostatic coupling IBC were implemented along with different signal transmission paths, and their attenuations were calculated. Our study showed that the position near the signal electrode had higher potential than other positions in the two types of IBC, while the potential generally decreased along the axis of the body parts. Both signal attenuations of the two types IBC increased with increasing signal transmission distance, and the electrostatic coupling IBC had comparatively higher receiving potential than the galvanic coupling IBC. The results indicated that the proposed modeling method could be used for the research of biomedical monitoring based on IBC technology.

FINITE-ELEMENT MODELLING OF SOIL-GEOGRID INTERACTION DEALING WITH THE PULLOUT BEHAVIOUR OF GEOGRIDS

To predict the behavior of geogrids embedded in sand under pullout loading conditions, the two dimensional plane-stress finite element model was presented. The interactions between soil and geogrid were simulated as non-linear springs, and the stiffness of the springs was determined from simple tests in the specially designed pullout box. The predicted behavior of the geogrid under pullout load agrees well with the observed data including the load-displacement properties, the displacement distribution along the longitudinal direction and the mobilization of the frictional and bearing resistance. (Edited author abstract) 8 Refs.

MODELING OF CONTROLLED THERMO-MECHANICAL PROCESSING OF TUBES FOR ENHANCED MANUFACTURING AND PERFORMANCE

An integrated mathematical model to simulate seamless tube rolling processes has been developed at The Timken Company. The model is capable of simulating the thermal, deformation and microstructure evolution in the piercing, elongating and reducing/sizing and the austenite decomposition in the mill annealing and cooling operations. Finite difference schemes are employed to model cooling, reducing/sizing and stretch reducing, and finite-element schemes are employed to simulate piercing and elongating. The model predicts the thermal history, deformation, rolling load, torque, recrystallization and grain growth in hot tube rolling, austenite decomposition in cooling or annealing, and the final structure-properties. In this paper mathematical models which are employed to describe the thermal, deformation and microstructure evolution along with the modeling results are presented. The developed 'tube rolling mill in the computer' provides a powerful tool for engineers for product and process development, process control, process optimization and quality control.

Numerical investigation of dual-porosity model with transient transfer function based on discrete-fracture model

Based on the characteristics of fractures in naturally fractured reservoir and a discrete-fracture model, a fracture network numerical well test model is developed. Bottom hole pressure response curves and the pressure field are obtained by solving the model equations with the finite-element method. By analyzing bottom hole pressure curves and the fluid flow in the pressure field, seven flow stages can be recognized on the curves. An upscaling method is developed to compare with the dual-porosity model （DPM）. The comparisons results show that the DPM overestimates the inter-porosity coefficient ）, and the storage factor w. The analysis results show that fracture conductivity plays a leading role in the fluid flow. Matrix permeability influences the beginning time of flow from the matrix to fractures. Fractures density is another important parameter controlling the flow. The fracture linear flow is hidden under the large fracture density. The pressure propagation is slower in the direction of larger fracture density.

Dynamic Finite Element Modeling and Simulation of Soft Robots

Soft robots have become important members of the robot community with many potential applications owing to their unique flexibility and security embedded at the material level.An increasing number of researchers are interested in their designing,manufacturing,modeling,and control.However,the dynamic simulation of soft robots is difficult owing to their infinite degrees of freedom and nonlinear characteristics that are associated with soft materials and flexible geometric structures.In this study,a novel multi-flexible body dynamic modeling and simulation technique is introduced for soft robots.Various actuators for soft robots are modeled in a virtual environment,including soft cable-driven,spring actuation,and pneumatic driving.A pneumatic driving simulation was demonstrated by the bending modules with different materials.A cable-driven soft robot arm prototype and a cylindrical soft module actuated by shape memory alley springs inspired by an octopus were manufactured and used to validate the simulation model,and the experimental results demonstrated adequate accuracy.The proposed technique can be widely applied for the modeling and dynamic simulation of other soft robots,including hybrid actuated robots and rigid-flexible coupling robots.This study also provides a fundamental framework for simulating soft mobile robots and soft manipulators in contact with the environment.

Endodontic management of a fused left maxillary second molar and two paramolars using cone beam computed tomography: A case report

BACKGROUND Fused teeth usually involve several complications,such as the development of caries in the groove between fused crowns,tooth impaction,diastemas,aesthetic and periodontal problems,and pulpal pathosis,due to the complex anatomical structure of fused teeth.A thorough diagnosis is paramount to forming an accurate treatment plan and obtaining a favourable prognosis.With the advent of cone-beam computed tomography(CBCT),accurate 3-dimensional images of teeth and their surrounding dentoalveolar structures can now be readily obtained,and the technology can accurately provide a minimally invasive approach to acquire detailed diagnostic information.Therefore,we utilize CBCT data herein to generate a digital model for the infected region in a patient,and this model enables us to better plan the management of his case.CASE SUMMARY This report details the diagnosis and endodontic treatment of a rare case involving a fused maxillary second molar and two paramolars with apical periodontitis.The patient experienced pain upon biting and cold sensitivity in the area of the maxillary left molar.No caries or other defects were identified in these teeth,and a normal response to a pulp electric viability test was observed.With the aid of CBCT and digital model technology,we initially suspected that the infection originated from the isthmus between the maxillary second molar and two paramolars.Therefore,we only treated the isthmus by an endodontic approach and did not destroy the original tooth structure;furthermore,the vital pulp was retained,and good treatment outcomes were observed at the 24-month follow-up.CONCLUSION This finding may provide new insights and perspectives on the diagnosis and treatment of fused teeth.

Dentoalveolar changes following maxillary distraction osteogenesis

The purpose of this study was to compare the dentoalveolar changes produced when using two different intraoperative surgical procedures for maxillary distraction osteogenesis. Eight patients were assigned into two groups according to the surgical procedure: down-fracture (DF, n = 6) vs non-down-fracture (NDF, n = 2). Lateral cephalograms and 3-D models before and after maxillary distraction were analyzed. The Mann-Whitney U test was used to compare the differences in the amounts of advancement and dento-alveolar changes between the DF and NDF groups. The significance level was established at 0.05. Although a significantly greater amount of maxillary movement was observed in the DF group (10.0 mm ± 2.2) than in the NDF group (5.9 mm ± 2.3), significantly greater arch length (8.7 mm ± 5.2) and arch width changes (6.0 mm ± 1.0) were observed in the NDF group than in the DF group, (arch lengths 3.0 mm ± 1.1 and arch width changes 3.2 mm ± 2.0). A significantly greater amount of dental anchorage loss was observed in the NDF group. The use of the NDF procedure resulted in greater amounts of dental anchorage loss than resulted from the DF procedures when tooth-borne devices were used during maxillary distraction osteogenesis. The type of surgical procedure might play an important role in the amount and direction of the dental changes.

Behavior and modeling of tessellated shear walls in a structural frame system

This paper studies the behavior of a reinforced concrete(RC)structural frame employing a tessellated structuralarchitectural(TeSA)shear wall as the lateral-load resisting element.TeSA walls are made of interlocking modules(tiles)that provide easier repairability and replaceability.A nonlinearfinite element model of a TeSA wall with tiles interlocking in one direction(1-D interlocking)is validated using test data.An RC frame from a building is modeled with a 1-D interlocking TeSA shear wall.The effects of varying rigidity of the wall-frame connections(rigid,hinged,slotted)on the lateral strength of the system and the axial load demands of the gravity-load resisting systems are evaluated.Finally,the effect of connection details on the damage of the TeSA wall is also studied.The study shows that the lateral strength of the system is the highest with a rigid connection between the wall and the system,followed by the system with hinged connections.Slotted connections,which provided no vertical coupling between the wall and the frame result in the lowest lateral strength.TeSA wall experienced“slight damage”up to a drift ratio of 2%.The system with rigid connections between the wall and the frame experienced the most damage,followed by system with hinged and slotted connections.

数字化技术在上颌骨缺损赝复体修复中的应用

上颌骨缺损是口腔颌面部中最常见的缺损,可能造成患者生理及心理障碍。传统颌骨缺损修复制作流程复杂、技术敏感性高。随着数字化技术在口腔领域的发展及应用,上颌骨缺损的修复治疗已展现出显著优势。本文简要介绍了上颌骨缺损赝复体修复的治疗过程,并从上颌骨缺损三维数据获取、数字化设计及数字化制造这3个方面对数字化技术在赝复体修复中的应用做一综述。

上颌尖牙转矩结合颊廊对微笑美影响的研究

目的:评价不同上颌尖牙转矩与不同大小的颊廊两两结合后对微笑美的影响。方法:一张成年女性口周微笑相,经过三维数字化模型和图像处理软件拟合,获得49张微笑照片(颊廊调整从0%至30%,间隔5%,尖牙转矩调整从-18°~12°,间隔5°),每张照片赋予相应编号(1~49),打乱照片的顺序将其放在同一相册中,指导60名口腔专业人士和60名非专业人士利用视觉模拟量表对照片的美观程度进行打分。结果用一般线性模型,Kruskal-Wallis检验,Mann-Whitney U检验等统计学方法,P<0.05为差异有统计学意义。结果:(1)尖牙转矩与颊廊的交互作用无统计学意义(P>0.05);(2)当转矩不变时,改变颊廊对微笑美学的影响有统计学意义(P<0.05),当颊廊为10%~20%时,得分之间差异具有统计学意义(P<0.05),颊廊为15%时,得分最高(P<0.05);(3)当颊廊不变时,绝大多数情况下改变尖牙转矩对微笑美的影响无统计学意义(P<0.05)。结论:大多数情况下上颌尖牙转矩与颊廊两两结合后并未发现对微笑美有加强或消减的作用,对美观的影响主要取决于颊廊,可接受的范围为10%~20%,且15%时微笑相最佳。

A novel phenomenological model using a sine function for finite-element simulation of large-strain hot deformation

In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without reaching an obvious peak stress; in other situations, the flow stress decreases after reaching peak stress and then attains a steady value. A new phenomenological model,described by a sine-function equation, is proposed to define the relationship between flow stress and deformation parameters. A series of isothermal compressions for a carbon steel were carried out, as a case study, to obtain basic experimental data.Parameters of the new model were sequentially determined. The predicted results of the proposed model were compared with actual measured data. Good accuracy was found in the standard statistical parameters of correlation coefficient, root mean square error, and average absolute relative error with the values of 0.935, 7.137 MPa and 4.352%, respectively. Discussion of applications of different models in finite-element simulation demonstrated the benefit of the new model. When comparing the simulation results of three different deformation patterns with large strain, the new model showed 10%–20% lower predicted forming load than the original Arrhenius equation, and better applicability and reliability than modified Arrhenius equations.

上颌后牙区、上颌窦、颧骨及颧骨种植体的三维有限元模型建立

目的:探讨上颌骨后牙区、上颌窦、颧骨及颧骨种植体的三维有限元建模方法。方法:采用螺旋CT扫描正常成人颅颌骨,利用3D-Doctor软件进行数据采集,数据导入ABAQUS软件中建立三维有限元模型,并模拟建立颧骨种植体模型。结果:建立的三维有限元模型几何相似性好,在操作平台上可随意观察。结论:采用CT扫描技术及ABAQUS建模技术可以建立切实可行的上颌骨后牙区、上颌窦、颧骨及颧骨种植体的生物力学模型。

冲顶式上颌窦提升植骨牙种植动物模型的建立

【目的】建立冲顶式上颌窦提升植骨牙种植的动物模型,以供上颌窦提升植骨牙种植的深入研究。【方法】拔除16只狗双侧上颌第一、第二磨牙,行冲顶式上颌窦提升,提升高度为2mm、4mm,一侧植骨,一侧不植骨,分别于术后3周、6周、12周、24周处死动物各4只,标本都经大体观察、放射检查及组织学检查。【结果】移植骨愈合良好,种植体牢固,窦底黏膜完整。上颌窦提升2mm时,种植体顶端可见骨质存在;提升4mm时,只见窦黏膜,不见新骨。上颌窦提升同期植骨并植入种植体,可见种植体顶端有新骨形成,覆盖种植体。【结论】狗有理想的上颌窦提升解剖条件,窦底提升术时可将窦底黏膜提升并保持完整,移植骨能形成新骨与牙种植体形成骨性结合,可作为研究上颌窦提升植骨同期牙种植动物模型。

可摘局部义齿上颌赝复体设计及其生物力学评价

对单侧上颌缺损的腭部封闭式和阻塞式赝复体进行几何仿真,并对这两种重建方法分别进行卡环和附着体固位方式设计,并对重建的生物力学效果进行了对比研究。模拟加载肌肉约束和力边界条件,分析四种不同上颌赝复体的应力分布,综合考虑义齿、基托、牙面板、阻塞器、卡环和附着体结构等强度问题,以及余留牙和赝复体的应力大小和分布趋势。根据应力结果,优化设计,为赝复体的临床成功作出生物力学的评价。分析结果表明:整个赝复体修复上颌结构各部分应力都在强度允许范围内,余留天然牙和牙槽骨上应力分布合理,赝复体有效传导力。阻塞器式赝复体材料属性与牙槽骨比较接近或略低于骨,填充了缺损侧上颌空腔,增大了与上颌的接触面积,使应力有效传导,在结构上较上腭封闭赝复体更为合理。四种赝复体天然牙应力和位移值比较表明,附着体固位阻塞器赝复体避免了天然牙应力集中,对义齿赝复体的固位和动力支持都非常有利。

3D-Nurbs曲面建模法建立上颌前牙段及其牙周组织的有限元模型

目的:建立上颌前牙段及其牙周组织的高质量三维有限元模型。方法:应用薄层CT技术扫描得到的牙齿及牙周组织截面影像的DICOM数据,结合逆向工程软件Geomagic及CAD生成上颌前牙段及其牙周组织的iges曲面模型,利用Hypermesh划分网格并检查单元的质量,生成可分析的三维有限元实体模型。结果和结论:建立了上颌前牙段及其牙周组织(包括牙周膜、牙槽骨)的高质量三维有限元模型,包括640 396个单元,117 889个节点。这种新的建模方法简单易行,适合口腔牙体牙周等复杂组织的建模;所建模型相似性高,可供研究分析在各种不同正畸矫治力系统作用下,上颌前牙段单个牙齿或节段牙齿的生物力学规律。