基于实体模型的牙颌组织三维有限元建模问题探讨

通过常用牙颌组织三维有限元建模方法的简述与比较 ,提出了自己的基于DICOM数据的高精度建模方法 ,该方法保留了实体模型的几何信息 ,可保证良好的几何相似性 ;建模速度快 ;不损坏实物模型。适用于临床医疗的实际需要 ,为有限元方法在口腔医学的应用提供了一条颇具成效的思路。并给出了相应的应用实例     

基于条件生成对抗网络的缺失牙体功能性咬合面形态设计方法

针对牙齿修复体设计中未考虑牙齿磨耗形态分布以及标准牙难以表达天然牙形态多样性的问题,提出基于颌位空间约束以及牙齿磨耗面引导的缺失牙体功能性咬合面形态设计方法.利用启发式搜索算法半自动提取牙齿磨耗面,并采用自适应视距的正交投影法计算出牙冠及其磨耗面在正视方向上的深度图像.通过对缺失牙齿功能性咬合面特征分级表达,采用基于颌...     

基于NURBS曲面技术和CT图像的三维实体重建

以某实际牙体CT图像为例,应用边界提取函数和非递归形式的迷宫算法等手段完成CT图像边缘提取和坐标记录,然后采用基于NURBS曲面技术的三维实体模型重建方法,建立了完整的牙齿三维实体模型.本文方法不仅可用于其他生物组织的三维建模,而且更可为机械零部件的逆向工程设计提供参考.     

牙颌模型的三维激光测量及模型重建

牙颌模型的数据测量是进行口腔修复CAD/CAM的基础。本文采用自制三维激光测量仪对牙颌表面数据进行三维测量,获得了单颗后磨牙缺失的牙颌模型多片三维点云数据。将各片数据在反求软件Surfacer平台上通过三点定位法进行数据拼合,准确地表示出缺失牙上下颌的咬合关系,重建牙颌的实体模型。     

基于颌位空间约束的缺损牙体曲面统计重建算法

重建符合牙齿咬合接触关系的缺损牙体曲面是全冠、嵌体、贴面等多类修复体造型过程中均需要解决的关键问题。针对规模有限的标准模板牙冠难以表达牙齿自然形态多样性的不足,提出了基于颌位空间约束的缺损牙齿曲面统计重建算法。采用广义普氏分析构建样本牙冠曲面之间的对应关系,在主要特征近似对齐的基础上计算平均牙冠;结合样本牙冠与平均牙冠对应点间的欧氏距离,建立可以表达样本牙冠与平均牙冠形态区别的差异矩阵,利用主成分分析方法求解影响平均牙冠形态的主要特征矢量,在此基础上建立基于参数表达的统计牙冠模型;根据缺损牙体的残留区域形态及其颌位接触关系采集局部约束特征点,以此反求统计模型的形变参数,构建基于颌位空间约束的统计牙冠,实现缺损牙体曲面的形态重建。下颌第一磨牙的重建试验表明,所建立的统计牙冠不仅具有足够的解剖形态特征,而且能与缺损牙体的残留形态以及邻牙、对颌牙相适应,具有良好的颌位接触关系,后期设计不需要复杂的调颌检测。     

机械制图课改中三维模型库的开发和研究

针对机械制图课程教学中普遍存在的教学模型及挂图数量不足、教学难度大等问题,简述了使用SolidWorks软件建立三维实体模型的过程以及机械制图虚拟模型库的设计流程、内容组成、网络发布等。实践证明,该模型库的设计是成功的,不仅弥补了实物模型库的不足,而且具有更多优势。     

泥浆泵模块化设计方法研究

介绍了模块化设计方法的概念和意义,并结合模块化设计理念提出了一种泥浆泵模块化设计方法。依据产品功能和属性分析将泥浆泵规划为9大模块、16种标准化模块接口、不同规格的模块骨架和模块实体及10余种泥浆泵机型。根据模块化设计要求创建了泥浆泵3D模型库,搭建了基于Rulestream的泥浆泵模块化配置管理系统,最终形成了基于NX+TC+RS的泥浆泵模块化设计平台。     

基于HAJIF系统的汽车部件模型库设计与实现

随着计算机技术的不断发展,汽车设计与制造行业越来越重视通用化、标准化的要求.精细的标准化需求带来的是汽车零部件的不断细分与统一.本文基于XML与OpenGL设计并实现了汽车部件模型库,该模型库的建立可以集成前人丰富的有限元建模经验以及宝贵的几何造型数据,对众多汽车零部件模型库进行统一化管理和私人化存储,在一定程度上提高...     

基于SolidWorks的机械制图虚拟模型库的建立

着重介绍了使用Solid Works2010软件建立三维实体模型的过程,简述了机械制图虚拟模型库的设计流程、内容组成及分类,并引出建立该库对于中职机械制图教学的意义。     

氧化锆全瓷和EMAX铸瓷的高嵌体及邻颌部分嵌体在后牙不同釉质存留面积下的粘接强度分析

目的 分析氧化锆全瓷和EMAX铸瓷的高嵌体及邻颌部分嵌体在后牙不同釉质存留面积下的粘接强度。方法 本研究选取治疗时间为2021年7月至2022年7月的120例后牙缺损患者为研究对象,通过电脑随机分配方式将患者分为研究组(氧化锆全瓷)和对照组(EMAX铸瓷),每组60例。收集患者后牙粘结强度指标。结果 研究组修复体完整性、牙龈健康状况低于对照组(P<0.05),研究组邻牙间隙大于对照组(P<0.05);在后牙不同釉质存留面积下,对照组和研究组在颌侧、舌侧、咬合面的粘结强度比较,差异无统计学意义(P>0.05)。结论 氧化锆全瓷和EMAX铸瓷在后牙不同釉质存留面积下的粘接强度无明显差异。可根据患者的具体情况选择合适的修复材料。     

周期性复合材料微结构的多目标拓扑优化设计

基于多尺度均匀化方法,以组分材料用量为约束,以等效弹性模量矩阵主对角线上分量的加权组合最大为目标,建立周期性复合材料微结构的多目标优化设计模型。利用优化准则法控制设计目标与材料分布,以敏度过滤技术抑制棋盘格效应,实现微结构的构型优化。研究比较微结构网格粗细、材料组分比对不同目标元素优化结果的影响。通过典型算例验证优化模型和优化算法的有效性。     

The biomechanics of a validated finite element model of stress shielding in a novel hybrid total knee replacement

This study proposes a novel hybrid total knee replacement (TKR) design to improve stress transfer to bone in the distal femur and, thereby, reduce stress shielding and consequent bone loss. Three-dimensional finite element (FE) models were developed for a standard and a hybrid TKR and validated experimentally. The Duracon knee system (Stryker Canada) was the standard TKR used for the FE models and for the experimental tests. The FE hybrid device was identical to the standard TKR, except that it had an interposing layer of carbon fibre-reinforced polyamide 12 lining the back of the metallic femoral component. A series of experimental surface strain measurements were then taken to validate the FE model of the standard TKR at 3000 N of axial compression and at 0 degreeof knee flexion. Comparison of surface strain values from FE analysis with experiments demonstrated good agreement, yielding a high Pearson correlation coefficient of R(2)= 0.94. Under a 3000N axial load and knee flexion angles simulating full stance (0O degree, heel strike (200 degrees, and toe off (600 degrees during normal walking gait, the FE model showed considerable changes in maximum Von Mises stress in the region most susceptible to stress shielding (i.e. the anterior region, just behind the flange of the femoral implant). Specifically, going from a standard to a hybrid TKR caused an increase in maximum stress of 87.4 per cent (O0 degree from 0.15 to 0.28 MPa), 68.3 per cent (200 degrees from 1.02 to 1.71 MPa), and 12.6 per cent (600 degrees from 2.96 to 3.33 MPa). This can potentially decrease stress shielding and subsequent bone loss and knee implant loosening. This is the first report to propose and biomechanically to assess a novel hybrid TKR design that uses a layer of carbon fibrereinforced polyamide 12 to reduce stress shielding.     

Development and experimental validation of a three-dimensional finite element model of the human scapula

A new modelling approach, using a combination of shell and solid elements, has been adopted to develop a realistic three-dimensional finite element (FE) model of the human scapula. Shell elements were used to represent a part of the compact bone layer (i.e. the outer cortical layer) and the very thin and rather flat part of the scapula--infraspinous fossa and supraspinous fossa respectively. Solid elements were used to model the remaining part of the compact bone and the trabecular bone. The FE model results in proper element shapes without distortion. The geometry, material properties and thickness were taken from quantitative computed tomography (CT) data. A thorough experimental set-up for strain gauge measurement on a fresh bone serves as a reference to assess the accuracy of FE predictions. A fresh cadaveric scapula with 18 strain gauges fixed at various locations and orientations was loaded in a mechanical testing machine and supported at three locations by linkage mechanisms interconnected by ball joints. This new experimental set-up was developed to impose bending and deflection of the scapula in all directions unambiguously, in response to applied loads at various locations. The measured strains (experimental) were compared to numerical (FE) strains, corresponding to several load cases, to validate the proposed FE modelling approach. Linear regression analysis was used to assess the accuracy of the results. The percentage error in the regression slope varies between 9 and 23 per cent. It appears, as a whole, that the two variables (measured and calculated strains) strongly depend on each other with a confidence level of more than 95 per cent. Considering the complicated testing procedure on a fresh sample of scapula, the high correlation coefficients (0.89-0.97), the low standard errors (29-105 micro epsilon) and percentage errors in the regression slope, as compared to other studies, strongly suggest that the strains calculated by the FE model can be used as a valid predictor of the actual measured strain. The model is therefore an alternative to a rigorous three-dimensional model based on solid elements only, which might often be too expensive in terms of computing time.     

A three-dimensional finite element model from computed tomography data: a semi-automated method

Three-dimensional finite element analysis is one of the best ways to assess stress and strain distributions in complex bone structures. However, accuracy in the results may be achieved only when accurate input information is given. A semi-automated method to generate a finite element (FE) model using data retrieved from computed tomography (CT) was developed. Due to its complex and irregular shape, the glenoid part of a left embalmed scapula bone was chosen as working material. CT data were retrieved using a standard clinical CT scanner (Siemens Somatom Plus 2, Siemens AG, Germany). This was done to produce a method that could later be utilized to generate a patient-specific FE model. Different methods of converting Hounsfield unit (HU) values to apparent densities and subsequently to Young's moduli were tested. All the models obtained were loaded using three-dimensional loading conditions taken from literature, corresponding to an arm abduction of 90 degrees. Additional models with different amounts of elements were generated to verify convergence. Direct comparison between the models showed that the best method to convert HU values directly to apparent densities was to use different equations for cancellous and cortical bone. In this study, a reliable method of determining both geometrical data and bone properties from patient CT scans for the semi-automated generation of an FE model is presented.     

Finite element prediction of endosteal and periosteal bone remodelling in the turkey ulna: effect of remodelling signal and dead-zone definition

Bone remodelling is the adaptation of bone mass in response to localized changes in loading conditions. The nature of the mechanical signal governing remodelling, however, remains the subject of continued investigation. The aims of this study were to use an iterative finite element (FE) bone remodelling technique to explore the effect of different remodelling signals in the prediction of bone remodelling behaviour. A finite element model of the turkey ulna, following that of Brown et al., was analysed using the ABAQUS package. The model was validated against the static predictions of the Brown et al. study. A bone remodelling technique, based on swelling algorithms given by Taylor and Clift, was then applied to predict the dramatic change in loading conditions imposed. The resulting changes in FE mid-shaft bone geometry were compared with the remodelling observed experimentally and showed good agreement. The tensile principal stress was found to be the best remodelling signal under the imposed conditions. Localized sensitivities in the remodelling patterns were found, however, and the definition of the dead zone was modified as a result. Remodelling with the new dead-zone definition showed that both the tensile principal stress and the tensile principal strain produced the remodelling patterns that agreed most closely with experiment.     

电动汽车车身的回传射线矩阵刚度链分析方法

基于LifeDrive纯电动汽车模块化结构形式,通过拓扑优化得到一款纯电动汽车车架结构;建立了基于梁单元的车架结构回传射线矩阵计算模型;由模型得到车架梁单元尺寸以及车身与车架之间的多个耦合力,以更合理的刚度链方法优化了车身简化模型的主断面参数;利用有限元方法计算了车身与车架的承载度。结果证明设计的车架与车身结构满足目标承载度和刚度性能的要求,该方法为非承载式电动汽车车身及车架的概念设计提供了参考。     

Effect of interface conditions between ultrahigh molecular weight polyethylene and polymethyl methacrylate bone cement on the mechanical behaviour of total shoulder arthroplasty

The aim of this study was to investigate the effect of the interface condition between polymethyl methacrylate (PMMA) bone cement and the ultrahigh molecular weight (UHMWPE) glenoid component on cement stresses and glenoid component tilting in a finite element (FE) model. The background of this research is that most FE models assume bonding between the PMMA bone cement and the UHMWPE component, although it is very doubtful that this bonding is present. An FE model of a cemented glenoid component was developed and a joint compression force and subluxation force of 725 and 350 N respectively were applied. The maximal principal stresses in the cement layer ranged between 21.30 and 32.18 MPa. Glenoid component tilting ranged between 0.943 degrees and 0.513 degrees. It was found that the interface condition has a large effect on the maximal principal stresses and glenoid component tilting. Whether adhesion between the UHMWPE component and PMMA bone cement occurs is unknown beforehand and, as a result, design validation using the FE technique should be carried out both by using contact elements in combination with a coefficient of friction as well as by a full bonding at this interface.     

Experimental based finite element simulation of cold isostatic pressing of metal powders

The present work addresses the various ingredients required for reliable finite element simulations of cold isostatic pressing (CIP) of metal powders. A plastic constitutive model for finite deformation is presented and implemented into an explicit finite element (FE) code. The FE implementation is verified so that numerical errors (both temporal and spatial errors) are kept under control. Thereafter, uniaxial die compaction experiments are performed required for determining the material parameters in the constitutive model. Subsequently they are applied for the simulation of a “complex” CIP process. The experimental observations of the complex CIP process were used to validate the overall method by comparing the FE results (final dimensions and average relative density) to the experimental observations. The numerical results (final dimensions and relative density) are in good agreement with the experimental observations.     

空压机系统冲击动力特性有限元分析

构造船用空气压缩机系统各零、部件及整机的实体模型,建立系统的冲击动力分析有限元模型。应用I DEAS软 件计算了空压机系统的固有特性、约束模态和冲击动态响应,给出各自由度方向加速度冲击载荷作用时系统的振动响应 及动态应力,为确定船用空压机的抗冲击能力及减振装置的合理设计提供了理论依据。     

Effects of acetabular resurfacing component material and fixation on the strain distribution in the pelvis

A 3D finite element (FE) model of an implanted pelvis was developed as part of a project investigating an all-polymer hip resurfacing design. The model was used to compare this novel design with a metal-on-metal design in current use and a metal-on-polymer design typical of early resurfacing implants. The model included forces representing the actions of 22 muscles as well as variable cancellous bone stiffness and variable cortical shell thickness. The hip joint reaction force was applied via contact modelled between the femoral and acetabular components of the resurfacing prosthesis. Five load cases representing time points through the gait cycle were analysed. The effect of varying fixation conditions was also investigated. The highest cancellous bone strain levels were found at mid-stance, not heel-strike. Remote from the acetabulum there was little effect of prosthesis material and fixation upon the von Mises stresses and maximum principal strains. Implant material appeared to have little effect upon cancellous bone strain failure with both bended and unbonded bone-implant interfaces. The unbonded implants increased stresses in the subchondral bone at the centre of the acetabulum and increased cancellous bone loading, resembling behaviour obtained previously for the intact acetabulum.