Finite Element Analysis and Experiment Research on Surface Residual Stress of Ceramics Grinding

The theoretical model of residual stress of ceramics grinding has been established applying thermal elastoplastic mechanics theory. While grinding at the course of grinding wheel moved along workpiece surface the distributing regulation of residual stress can be simplified into thermal elastioplastic mechanical issue, under the action of the both moving centralized force and heat source. Calculating and evaluating of surface residual stress using current procedure of finite element analysis which has been reformed is successful. Comparing with X-ray diffraction experiment method, satisfactory precision has been acquired. The results of experiment show the changing regularity of residual stresses after grinding Al 2O 3 using diamond wheel, on condition that alter grinding parameters. The values of residual compress stress are taken place changing at key certain critical point on their figure as follow: When grinding depth a p is lower than 50 μm, the residual compress stresses are increased with grinding depth increasing, on the contrary as a p>50 μm. At V w<8 m/min, the residual compress stresses increased rapidly with feed speed of workpiece increasing, on the contrary at V w>8 m/min.When V s<25 m/s the residual stress increased with wheel speed increasing and keep stable in value at V s>25 m/s.According to grinding mechanism the cause of residual stress transform has been explained.

FINITE ELEMENT COMPUTER MODEL OF MICROWAVE HEATED CERAMICS

At present,the concerned papers appeared in special magazines about discussing or introducing finite element method for calculating temperature distribution in ceramic body during microwave sintering, are not a good many, but it seems that finite element method is more convenient than finite difference method in dealing with special or complex geometry of ceramic body. In this paper, we describe a 3D finite element model simulating the heating pattern of ceramic microwave sintering in TE(10N) single-mode rectangular cavity in which the microwave energy deposition pattern in the samples can be expressed as an analysis function of space, and present a series of transient temperature distributions and heating rates of ceramic cylinders and cuboids tender variable thermal conductivities, dieletric loss factors,power consumer-levels, etc. These digital solutions may provide a better understanding of eliminating thermal runaway and improving temperature homogeneity.

Finite Element Analysis of the Contact Mechanics of Ceramic-on-Ceramic Hip Resurfacing Prostheses

Ceramics are good alternative to metal as bearing couple materials because of their better wear resistance. A Finite Element(FE) study was performed to investigate the contact mechanics and stress distribution of Ceramic-on-Ceramic (COC) hip resurfacingprostheses. It was focused in particular on a parametric study to examine the effects of radial clearance, loading,alumina coating on the implants, bone quality, and fixation of cup-bone interface. It was found that a reduction in the radialclearance had the most significant effect on the predicted contact pressure distribution among all of the parameters considered inthis study. It was determined that there was a significant influence of non-metallic materials, such as the bone underneath thebearing components, on the predicted contact mechanics. Stress shielding within the bone tissue was found to be a major concernwhen regarding the use of ceramic as an alternative to metallic resurfacing prostheses. Therefore, using alumina implantswith a metal backing was found to be the best design for ceramic resurfacing prostheses in this study. The loading, bone quality,and acetabular cup fixation conditions were found to have only minor effects on the predicted contact pressure distribution alongthe bearing surfaces.

ANALYSIS OF ELECTRIC BOUNDARY CONDITION EFFECTS ON CRACK PROPAGATION IN PIEZOELECTRIC CERAMICS

There are three types of cracks: impermeable crack, permeable crack and conducting crack, with different electric boundary conditions on faces of cracks in piezoelectric ceramics, which poses difficulties in the analysis of piezoelectric fracture problems. In this paper, in contrast to our previous FEM formulation, the numerical analysis is based on the use of exact electric boundary conditions at the crack faces, thus the common assumption of electric impermeability in the FEM analysis is avoided. The crack behavior and elasto-electric fields near a crack tip in a PZT-5 piezoelectric ceramic under mechanical, electrical and coupled mechanical- electrical loads with different electric boundary conditions on crack faces are investigated. It is found that the dielectric medium between the crack faces will reduce the singularity of stress and electric displacement. Furthermore, when the permittivity of the dielectric medium in the crack gap is of the same order as that of the piezoelectric ceramic, the crack becomes a conducting crack, the applied electric field has no effect on the crack propagation.

Element Analysis of Ceramic Coatings under Spherical Indentation with Metallic Interlayer: PartⅡRing Crack

Spherical indentation of ceramic coatings with metallic interlayer was performed by means of axisymmetric finite element analysis （FEA）. Two typical ceramic coatings with relatively high and low elastic modulus deposited on aluminum alloy and carbon steel were considered. The fracture mechanics of the ceramic coatings mechanisms due to occurrence of surface ring cracks extending traverse the coating thickness under spherical indentation are investigated within the framework of linear fracture mechanics. The J-integral associated to such cracks was computed. The evolution of J-integral vs the crack length and the indentation depth was studied. The effects of the interlayer, the coating and the substrate on the J-integral evolution were discussed. The results show that a suitable metallic interlayer can improve the fracture resistance of the coating systems under the same indentation conditions through reducing the J-integral.

Finite Element Analysis of Ceramic Coatings under Spherical Indentation with Metallic Interlayer: PartⅠUncracked Coatings

Spherical indentation of ceramic coatings with metallic interlayer was performed by means of axisymmetric finite element analysis （FEA）. Two typical ceramic coatings with relatively high and low elastic modulus deposited on aluminum alloy and carbon steel were considered. Various combinations of indenter radius-coating thickness ratios and interlayer thickness-coating thickness ratios were used in the modeling. The effects of the interlayer, the coating and the substrate on the indentation behavior, such as the radial stress distribution along the coating surface as well as the coating interface, and the plastic deformation zone evolution in the substrate were investigated in connection with the above mentioned ratios. The coating cracking dominant modes were also discussed within the context of the peak tensile stresses on the coating surface and on the coating interface.

Three-dimensional analysis of elastic stress distribution of indented ceramic surface by finite element method

The three-dimensional stress distributions in the area surrounding indentation pattern for three different materials, Al2O3, Si3N4 and SiC were analyzed by finite element method(FEM). Those theoretical results were also compared with the experimental ones by Rockwell hardness test. The effect of loading stress on the plastic deformation in specimens, surface was investigated on the assumption of shear strain energy theory by Huber-Mises when the materials were indented. The distributions of nomal stress, shear stress, and Mises stress were analysed with variations of loading conditions. It is clear that the analytical results for the stress distributions, the crack length and its density of probability are in good agreement with the experimental results.

Relationship Between Electric Properties and Temperature of ZrB_2-SiC Composite Ceramic Heating Element

ZrB2 -SiC composite ceramic has been successfully introduced as heating element in super high temperature .field. This paper further investigated the microstructure of ZrB2 - SiC composite ceramic heating element and the relationship between electric properties and temperature. SEM photos show that the heating element consists of SiC grains and ZrBz grains smaller than 10 μm. The voltage and current gradually increase and the furnace tempera- ture rises lineally with heating time prolonging. The electric resistance increases linearly with the temperature rising. The service temperatltre of the heating element can reach 1 800 ℃ and 2 150 ℃ in air and argon at- mosphere, respectively.

Computational Modeling of Dual-Phase Ceramics with Finsler-Geometric Phase Field Mechanics

A theory invoking concepts from differential geometry of generalized Finsler space in conjunction with diffuse interface modeling is described and implemented in finite element(FE)simulations of dual-phase polycrystalline ceramic microstructures.Order parameters accounting for fracture and other structural transformations,notably partial dislocation slip,twinning,or phase changes,are dimensionless entries of an internal state vector of generalized pseudo-Finsler space.Ceramics investigated in computations are a boron carbide-titanium diboride(B4C-TiB2)composite and a diamond-silicon carbide(C-SiC)composite.Deformation mechanisms-in addition to elasticity and cleavage fracture in grains of any phase-include restricted dislocation glide(TiB2 phase),deformation twinning(B4C and-SiC phases),and stress-induced amorphization(B4C phase).The metric tensor of generalized Finsler space is scaled conformally according to dilatation induced by cavitation or other fracture modes and densification induced by phase changes.Simulations of pure shear consider various morphologies and lattice orientations.Effects of microstructure on overall strength of each composite are reported.In B4C-TiB2,minor improvements in shear strength and ductility are observed with an increase in the second phase from 10 to 18%by volume,suggesting that residual stresses or larger-scale crack inhibition may be responsible for toughness gains reported experimentally.In diamond-SiC,a composite consisting of diamond crystals encapsulated in a nano-crystalline SiC matrix shows improved strength and ductility relative to a two-phase composite with isolated bulk SiC grains.

Failure pattern in ceramic metallic target under ballistic impact

The ballistic resistance and failure pattern of a bi-layer alumina 99.5%-aluminium alloy 1100-H12 target against steel 4340 ogival nosed projectile has been explored in the present experimental cum numerical study.In the experimental investigation,damage induced in the ceramic layer has been quantified in terms of number of cracks developed and failure zone dimensions.The resultant damage in the backing layer has been studied with variation in the bulge and perforation hole in the backing layer with the varying incidence velocity.The discussion of the experimental results has been further followed by three dimensional finite element computations using ABAQUS/Explicit finite code to investigate the behaviour of different types of bi-layer targets under multi-hit projectile impact.The JH-2 constitutive model has been used to reproduce the behaviour of alumina 99.5%and JC constitutive model has been used for steel 4340 and aluminium alloy 1100-H12.The total energy dissipation has been noted to be of lesser magnitude in case of sub-sequential impact in comparison to simultaneous impact of two projectiles.The distance between the impact points of two projectiles also effected the ballistic resistance of bi-layer target.The ballistic resistance of single tile ceramic front layer and four tile ceramic of equivalent area found to be dependent upon the boundary conditions provided to the target.

上颌第一磨牙基牙不同聚合度对Inceram-Z全瓷冠应力分布影响的三维有限元研究

目的:探讨上颌第一磨牙基牙不同聚合度对全瓷冠和牙本质应力分布的影响。方法:通过有限元方法建立三组基牙不同聚合度的有限元模型,并对模型垂直施加600N的作用力。结果:随着基牙聚合度的减小,全瓷冠的应力值呈下降趋势,同时牙本质的应力值呈上升趋势,所有应力峰值均小于材料本身的抗压强度。结论:基牙不同聚合度对全瓷冠及牙本质的应力分布是有影响的,本实验为全瓷修复体的优化设计提供实验和理论依据。

多裂隙缺陷陶瓷轴承破坏机理研究

针对氮化硅陶瓷轴承的多裂隙缺陷会影响其力学性能及使用寿命的问题,提出了一种结合离散元(DEM)仿真和FISH语言程序的方法研究轴承缺陷。首先,采用DEM对轴承进行建模,通过力学校准实验测定相关力学性能参数,并通过试错法进行细观参数的标定,采用FISH语言程序建立氮化硅陶瓷轴承简化模型,并在模型中预制不同倾角和数量的平行裂隙缺陷;然后,通过模拟和数值计算,研究了裂纹在不同倾角和数量裂隙缺陷下的演化规律,同时结合裂纹周围的速度矢量场,分析了裂纹扩展的复杂性。实验结果揭示了受压下多裂隙缺陷的陶瓷材料损伤破坏机制,可为陶瓷轴承加工工艺、故障诊断、力学性能及使用寿命等研究提供理论指导。

ANALYSIS OF DAMAGE NEAR A CONDUCTING CRACK IN A PIEZOELECTRIC CERAMIC

The finite element formulation for analyzing static damage near a conducting crack in a thin piezoelectric plate is established from the virtual work principle of piezoelectricity.The damage fields under various mechanical and electrical loads are calculated carefully by using an effective iterative procedure.The numerical results show that all the damage fields around a crack tip are fan-shaped and the electric field applied has great influence on the mechanical damage, which is related to the piezoelectric properties.

Study on solder joint reliability of ceramic ball grid array component based on design of experiment method

Four process parameters, pad diameter, stencil thickness, ball diameter and stand-off were chosen as four control factors. By using an L25 （5^6 ） orthogonal array the ceramic ball grid array （ CBGA ） solder joints which have 25 different combinations of process parameters were designed. The numerical models of all the 25 CBGA solder joints were developed using the Sugrace Evolver. Utilizing the sugrace coordinate exported from the 25 CBGA solder joints numerical models, the finite element analysis models were set up and the nonlinear finite element analysis of the CBGA solder joints under thermal cycles were pegrormed by ANSYS. The thermal fatigue life of CBGA solder joint was calculated using Coffin-Manson equation. Based on the calculated thermal fatigue life results, the range analysis and the variance analysis were pegrormed. The results show that the fatigue life of CBGA solder joint is affected by the pad diameter, the stencil thickness, the ball diameter and the stand-off in a descending order, the best combination of process parameters results in the longest fatigue life is 0.07 mm stand-off, 0.125 mm stencil thickness of, 0.85 mm ball diameter and 0. 89 mm pad diameter. With 95% confidence the pad diameter has a significant effect on the reliability of CBGA solder joints whereas the stand-off, the stencil thickness and the ball diameter have little effect on the reliability of CBGA solder joints.

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.

SLA打印制备融合TPMS氧化铝陶瓷支架结构优化设计研究

三周期最小表面(TPMS)结构具有优异的力学性能与生物医学性能,设计制造合适的TPMS骨支架结构能为骨修复、骨替代、骨愈合的临床治疗提供可能。本文基于人体骨组织结构参数分别设计了以P、G、D三种类型为主的TPMS支架及其不同融合系数K值影响下的融合TPMS支架,采用紫外立体光刻技术(SLA)打印制备了陶瓷生坯,通过脱脂与烧结后处理获得了成型氧化铝陶瓷支架,并对支架模型与成型陶瓷试样分别进行了有限元仿真与实验测试。结果表明:1)陶瓷支架具有相对光滑的表面与较高的成型精度,其整体形态与设计模型基本一致,侧面比顶面稍显粗糙。2)与单类型结构相比,融合TPMS结构支架表现出较好的抗压强度与应力分布。其中,当融合系数K=4时,P与G结构融合支架支架的力学性能最优,抗压强度为71.72 MPa,最大应力与平均应力分别为141.90和13.214 MPa;3)融合结构的渗透性均弱于单类型结构,且不同融合系数K值的结构支架渗透性也不同,结合数值模拟与实验数据,当融合系数K=1、2时,P与G结构、P与D结构融合支架渗透性表现较好。综上,当融合系数K=1时,P与G结构融合支架同时具备较优的力学性能和渗透性,适合作为人体骨支架结构类型。

高压陶瓷电容特性及在配网柱上开关的应用研究

电压传感器是深度融合型柱上开关的关键器件,其自身直接承受电压载荷,是深度融合柱上开关产品开发成败的关键。以无机物介质为载体的高压陶瓷电容器,具有体积小、容量大、寿命长的特点,尤其契合深度融合型固封极柱的结构特点和应用场景。文中首先分析了陶瓷电容器件特性,再结合深度融合柱上开关产品的具体应用场景,开发了基于高压陶瓷电容器的一二次融合柱上开关产品;相关研究表明,高压陶瓷电容器在配网领域应用具有相当潜力。

装配式陶瓷薄板单元组件系统施工技术

针对广东省珠海市横琴口岸通关大厅空间跨度大、层高高、墙面开口数量多、工期紧的难题,对项目整体视觉效果及总工期进行分析,决定采用装配式施工方法,根据支撑点的距离,设计为钢质竖向主龙骨、铝合金装配式挂件系统,面材采用陶瓷薄板。通过装配式施工技术,并运用BIM深化设计及测算单块陶瓷薄板的大小尺寸,并与龙骨通过转接件勾搭式连接,墙面采用单元装配式安装系统。最终证明装配式施工方法既可减少施工作业面,又可提高工作效率,降低安全隐患且与其他专业交叉施工互不影响,具有较大的推广价值。