Influence of abutment material on the stress of implant-supported all-ceramic single crown

In order to investigate the influence of abutment material on the stress of implant-supported all-ceramic single crown, a 3D finite element model of implant-supported mandibular first premolar was computed by COSMOS/M 2.85 software. Alumina, zirconia, and titanium were used as abutment materials respectively. Vertical 600 N and horizontal 225 N load was applied on the occlusal surface. The results show that the stress distribution of implant-supported single crown was similar for different abutment materials. Maximum stresses within the crown were higher when titanium abutment was used. Maximum stress of titanium abutment was lower than that of ceramic abutment. Within the screw and fixture, maximum stresses had no difference under vertical loading but higher as titanium abutment was used under horizontal loading. There was no difference of maximum stress within the bone when different abutment materials were used. The present findings indicate that the abutment material had no influence on the stress distribution of implant-supported all-ceramic single crown but maximum stress when the titanium abutment was lower than that of ceramic abutment.     

Comparison of stress distribution of platform-switched and non-platform switched abutment for implant supported single crown

The influence of platform-switched abutment on stress distribution within the surrounding bone,fixture,abutment,and screw under various loading conditions were studied.Two 3-D finite element models representative of an implant-supported metal crown for the mandibular first molar and its surrounding bone were computed.Model A simulated the implant with non-platform-switched abutment and model B was for platform-switched abutment.A load of 100 N was applied vertically and obliquely at the center fossa,the tip of the buccal cusp and the distal fossa,respectively.The results show that the distribution of Von Mises stress in the two models is similar.When platform-switched abutment is used,the maximum Von Mises stress within the surrounding bone is lower;however,this value is higher within the fixture and screw.     

花山拱坝右坝肩溶洞对坝体及坝肩的影响分析

为评价花山拱坝右坝肩溶洞对坝体及坝肩的影响,采用三维有限元方法,对不同工况不同方案下坝体和坝肩岩体应力变形进行计算分析,并利用超载法分析了不同方案下的坝肩稳定状况.结果表明:溶洞的存在对坝体的应力变形及坝肩的整体稳定性影响较小,对坝肩岩体应力变形的影响也仅限于溶洞附近区域;溶洞回填处理后,其附近的变形得到有效控制.综合来看,溶洞的存在对整个工程影响较小,经过回填处理后,整个工程的安全性是有保障的.     

附着体式固定义齿倾斜基牙修复前后应力分布的 各向异性三维有限元分析

失牙后未能及时修复将造成邻牙向缺隙侧倾斜,从而牙体缺隙侧应力集中,牙槽骨破坏。采用常规的修复方法难以获得好的修复效果或将对基牙造成更大的损伤,采用各向异性的数据建立修复前后具有可对比性的三维有限元模型,研究采用附着体修复方法,在修复前后不同受载情况下,得到了修复前后基牙的应力分布数据,结果表明：倾斜基牙单独承受牙牙时,基牙近中牙槽骨应力较高。附着体式固定义齿修复后,在承担牙力时,倾斜基牙的应力分布能明显得到改善。本研究为临床修复倾斜基牙提出了新的修复方法,并为采用附着体修复倾斜基牙提供了生物力学依据。     

连退炉导向辊热凸度对辊形及带钢应力分布的影响

为了更有效地控制连退炉内导向辊热凸度和改善带钢的跑偏及瓢曲变形,以单锥度辊为研究对象,运用MARC有限元软件,定量计算了在加热段和快冷段不同导向辊温差时的导向辊热凸度及其对导向辊辊形和带钢应力分布的影响.研究发现：导向辊热凸度随导向辊温差增大呈直线上升的趋势.在加热段,随着导向辊温差的增大,导向辊产生热凸度后的形状分别为双锥度辊、单锥度辊和“M”型辊,带钢张应力和带钢最大应力分布随着导向辊温差的增大而改变;在快冷段,导向辊产生热凸度后变为双锥度辊,导向辊热凸度会影响带钢张应力值和最大应力值,但不影响其分布.     

Formation and evolution of gas flow channels in the abutment pressure area

The permeability of coal ahead of the working face obviously changes dues to changes in abutment pressure. The formation and evolution of gas flow channels within the abutment pressure area was studied by analyzing the fracture extension mechanism and fracture development in different zones of the abutment pressure area. Fracture and damage mechanics theory is used to understand the observations. The following two techniques were used to understand the evolution of gas flow channels: field observation of the characteristic fractures at different positions relative to the working face and fluorescence micrographs of prepared coal samples. Bending tensile fractures develop along an approximately vertical direction that forms a microscopic network of channels in areas of stress concentration. The abutment pressure affects the local stress and, hence, the local gas conduction. The fractures induced by large deformation and plastic flow form macroscopically networked channels in the reduced stress area. Closer to the working face the gas flow channels evolve from microscopic to macroscopic and from isolated to network. Gas permeability continuously increases during this time. This is corroborated by field observations of the displacement of top coal and the gas flow from gas extraction drillings.     

在水平荷载下整体式桥台桥梁受力分析

目的为找出在升温温差和降温温差下桥台桩柱内实测应力的分布和变化规律,分析水平荷载作用下整体式桥台桥梁的受力性能．方法以富裕工业园跨线桥为工程背景,以试验桥的左侧桥台作为试验对象,采用计算精度高的P-y曲线法对整体式桥台桥梁在制动力作用下的受力进行分析．结果通过与试验桥桥台桩柱内应力试验实测值的对比分析所得出P—y曲线法计算桩土相互作用的精度高于“m”法．试验桥的单侧桥台在制动力作用下的受力与在均匀温差作用下的受力具有相似性．结论采用P-y曲线法分析在水平荷载下整体式桥台桥梁的受力特性具有较高的可行性．     

Effect of roller shapes on strip buckling in a continuous annealing furnace

The effect of roller shapes on strip buckling in a continuous annealing furnace was focused on. The tensile stress distribution, the transverse compressive stress, and the critical buckling stress of the strip were studied by the finite element method (FEM) when the flat roller, crown roller, single taper roller, and double taper roller were used, respectively. Simulation results show that strip buckling is most likely to occur with the crown roller, then the double taper roller, and finally the single tape...     

两种不同固位体设计的可摘局部义齿对牙槽骨的应力研究

用三维光弹性应力分析方法，对Ｔｈｏｍｐｓｏｎ半精密附着体固位与ＲＰＩ卡环固位下颌双侧游离端可摘局部义齿在牙槽骨内的应力分布进行了研究。同时，比较了两种不同固位方法的牙槽骨内的应力分布规律。获得了基牙根尖应力。     

路桥过渡段台背路堤差异沉降的模拟分析

针对高等级公路路桥过渡段易出现桥头跳车病害的现状,结合河南省济焦新高速公路工程实体,采用4种不同的搭板和填筑方式分析它们对减少路桥过渡段桥头跳车的效果。应用快速拉格朗日有限差分计算程序FLAC软件,对桥台台背路堤填土变形及力学特性进行数值模拟分析。结果表明:不同的搭板方式和填筑材料均影响桥台台背处路堤差异沉降大小和沉降速率;在4种搭板方式中,二次搭板 填筑砾石方式对降低台背路堤差异沉降的效果最好。     

工作面支承压力分布的研究

为了研究采场支承压力,运用FLAC3D软件建立工作面开采数值模拟模型,研究了工作面前支承压力分布形态及应力峰值的位置,通过与理论计算、现场实测的结果相比较,得出数值模拟、理论分析、现场实测的结果是基本一致的,提出了采场前支承压力的计算方法,对井下工作面超前支护距离设计具有借鉴意义。     

三单位全瓷固定桥破坏机理及过程的数值模拟

针对全瓷桥修复体在临床易发生崩瓷、折裂破坏以及其破坏过程和机理仍不十分明确等问题,采用真实破裂过程分析RFPA 2D系统,模拟了静载荷条件下三单位氧化锆全瓷桥底冠的破坏过程,分析了其破坏机理.应力指纹图和主应力分布图显示全瓷桥的破坏模式属于拉破坏且裂纹最初萌生于全瓷桥连接体下部.对比数值模拟的破坏模式和已有的试验结果,发现二者破坏模式十分吻合.RFPA 2D 能够全程逐步自动追踪全瓷固定桥折裂全过程,该项研究可作为试验研究、临床观察研究、全瓷固定桥抗折裂破坏能力研究的一种重要补充手段.     

溃坝水流三维湍流的试验与数值分析

采用假定溃口形状,选取临界漫顶及坝体完全淹没2组不同流量,进行定床物理模型试验,测量了溃口内部水流的垂线流速分布.采用CFD软件FLUENT对2组三维溃坝水流进行全流场湍流数值模拟,其结果与试验值吻合较好,同时较为精细地捕捉到了坝前水位稳定后溃坝水流三维流场、湍动能和壁面剪切应力.结果表明:高强度壁面剪切应力可能为坝体侵蚀主要因素,在坝顶及溃口与坝面的连接处壁面剪切应力及湍动能出现极大值,强湍动能将使得侵蚀的泥沙迅速扩散到水体当中,随着水流的运动向下游输移.三维流动的存在,使得泥沙向下游输运的过程中先向溃口内部集中,到达下游河道后再逐渐扩散到整个河道中.小流量情况下,这一趋势不太明显,随着漫顶流量的增大这一趋势明显增强.以上水力条件可能为溃口迅速展宽、降低的主要因素.     

基于非线性有限元的高拱坝坝肩稳定性分析-研究生论坛

处于复杂地质条件下的拱坝,坝肩岩体稳定性问题是其发生事故的重要原因之一。某水电站拱坝右坝肩发育有靠近坝体的蚀变集中带及沿该集中带的多条断层,左坝肩在坝肩槽不同高程有多条断层出露,地形地质复杂。为了正确合理地研究其坝肩岩体的稳定特性,根据水电站坝址区地形地质条件,充分考虑拱坝左右坝肩的主要断层及蚀变带等不利地质构造,建立三维有限元模型,模拟拱坝及坝区岩体在正常运行及温降工况下的应力场,采用点安全系数法分析坝肩岩体在加固和未加固的情况下的稳定性,并运用综合强度储备法评价坝肩的极限承载能力。研究结果表明,坝肩岩体点安全系数均处于合理范围内且相对较高,综合安全系数相对较大,说明坝基加固措施合理有效,坝肩具有较强的承载能力。     

Comparative Evaluation of the Implant Made of Yttrium-partially Stabilized Zirconia and Pure Titanium on Stress Distribution by Anisotropic Finite Element Method

1Introduction Implantplacementindentistry[1]andorthopedics[2]isapredicabletreatmentmodality.Thematerialsforden talimplantsandjointsaremetalandpolyethylene.These materialshavebeenusedfordecades;however,thein creasingproblemssuchasthewearofthepolyethylene,t…     

Xive种植系统在修复牙列缺损的临床应用

探讨Xive种植体修复牙列缺损的临床应用效果。85例牙列缺损患者,采用Xive种植系统进行延期或即刻种植、一期埋入加二期暴露的两次手术方式,共植入215颗种植体。其中54例患者的117颗行单冠修复,16例的42颗行联冠修复,15例的56颗行固定桥修复,全部采用粘结固定;临床随诊观察一至四年,215颗种植体中,仅有2颗于种植体延期种植术后4周脱落,考虑系Ⅱ型糖尿病血糖没能有效控制发生感染所致,其余功能行使均良好至今;种植体的成功率为99.07%,患者满意度为95.29%。临床结果证明,在严格控制适应证、合理设计术式及合并采用骨增量技术的基础上,使用Xive种植系统修复牙列缺损可获得令人满意的修复效果。     

Test studies of gas flow in rock and coal surrounding a mined coal seam

An analysis of the variation rule of abutment pressure at the mining working face in a single coal seam and the mechanical behavior of surrounding rock during stoping is presented. Consideration of the elastic and plastic deformation zones that develop during the mining process allowed the determination of a relationship between horizontal stress and vertical stress. Based on this, a confined pressure unloading test was conducted by the use of the “gas-containing coal thermo-fluid-solid coupling 3-axis servo seepage” experimental apparatus. Thus, gas flow patterns in the elastic and plastic zones were derived from an experimental point of view. Darcy’s law and the Klinkenberg effect were used to derive a gas flow equation for the elastic and plastic stress fields. The study of gas flow phenomena at the working face during coal mining is of great importance for the study of gas migration and enrichment patterns.     

Analysis of ARMPS2010 database with La Model and an updated abutment angle equation

The Analysis of Retreat Mining Pillar Stability(ARMPS) program was developed by the National Institute for Occupational Safety and Health(NIOSH) to help the United States coal mining industry to design safe retreat room-and-pillar panels. ARMPS calculates the magnitude of the in-situ and mining-induced loads by using geometrical computations and empirical rules. In particular, the program uses the ‘‘abutment angle" concept in calculating the magnitude of the abutment load on pillars adjacent to a gob. In this paper, stress measurements from United States and Australian mines with different overburden geologies with varying hard rock percentages were back analyzed. The results of the analyses indicated that for depths less than 200 m, the ARMPS empirical derivation of a 21° abutment angle was supported by the case histories; however, at depths greater than 200 m, the abutment angle was found to be significantly less than 21°. In this paper, a new equation employing the panel width to overburden depth ratio is constructed for the calculation of accurate abutment angles for deeper mining cases. The new abutment angle equation was tested using both ARMPS2010 and La Model for the entire case history database of ARMPS2010. The new abutment angle equation to estimate the magnitude of the mining-induced loads used together with the La Model program was found to give good classification accuracies compared to ARMPS2010 for deep cover cases.     

综放回采巷道围岩力学特征实测研究

通过对综放面回采巷道围岩的深部位移、表面位移、应力分布以及支架荷载的实测分析，得出综放面回采巷道围岩力学特征分布规律．研究表明，临近工作面巷道围岩处于支承压力降低区，支架荷载下降，但支架和围岩变形最剧烈，表明巷道围岩处于岩石峰后的力学状态．围岩变形主要发生支承压力影响区，合理的巷道支护应能控制采动影响剧烈阶段的围岩变形，顺槽支护设计理念应从载荷控制向变形控制转变．     

承压式溢流井淤积实验研究

为研究承压式溢流井的淤积规律,通过模型实验实测了井底面速度分布,并据此计算出相应的床面切应力。根据相似准则进行泥沙沉积实验,得到不同工况下的泥沙沉积分布。结果显示,溢流井内流场在恒定流工况时由一对大致对称的椭圆形涡流组成,而且涡流周围区域的紊动能及切应力均较大,其冲刷力亦较强,泥沙难以沉积下来。涡流中心和四周角落区域的切应力及冲刷力较小,有大量泥沙沉积。分析比较泥沙沉积位置与切应力分布,即可估计出模型沙的临界切应力值为0.05～0.07N/m2。