Modeling Technology in Finite Element Analysis of Electrostatic Proximity Fuze Problem

In order to analyze the electrostatic field concerned with electrostatic proximity fuze problem using the available finite analysis software package, the technology to model the problem with a scale reduction object and boundary was presented. The boundary is determined by the maximum distance the sensor can detect. The object model is obtained by multiplying the terms in Poisson's equation with a scale reduction factor and the real value can be reconstructed with the same reverse process after software calculation. Using the finite element analysis program, the simulation value is close to the theoretical value with a little error. The boundary determination and scale reduction method is suitable to modeling the irregular electrostatic field around air targets, such as airplane, missile and so on, which is based on commonly used personal computer (PC). The technology reduces the calculation and storage cost greatly.

Finite element failure analysis of continuous prestressed concrete box girders

In order to analyze the load carrying capacity of prestressed concrete box girders, failure behaviors of in-situ deteriorated continuous prestressed concrete box girders under loading are experimentally observed and a finite failure analysis method for predicting behaviors of box girders is developed. A degenerated solid shell element is used to simulate box girders and material nonlinearity is considered. Since pre-stressed concrete box girders usually have a large number of curve prestressed tendons, a type of combined element is presented to simulate the prestressed tendons of box girders, and then the number of elements can be significantly reduced. The analytical results are compared with full-scale failure test results. The comparison shows that the presented method can be effectively applied to the failure analysis of in-situ continuous prestressed concrete box girders, and it also shows that the studied old bridge still has enough load carrying capacity.

Integrity and Failure Analysis of Cement Sheath Subjected to Coalbed Methane Fracturing

Perforation and fracturing are typically associated with the development of coalbed methane wells.As the cement sheath is prone to failure during this process,in this work,the effects of the casing pressure,elastic modulus of the cement,elastic modulus of the formation,and casing eccentricity on the resulting stresses are analyzed in the frame of a finite element method.Subsequently,sensitivity response curves of the cement sheath stress are plotted by normalizing all factors.The results show that the maximum circumferential stress and Mises stress of the cement sheath increase with the casing internal pressure,elastic modulus of the cement and casing eccentricity.As the elastic modulus of the formation increases,the maximum circumferential stress of the cement sheath decreases,and its maximum Mises stress increases slightly.The cement sheath undergoes tensile failure during coalbed methane fracturing.The stress sensitivity of the cement sheath to the influential parameters is in the following order:casing internal pressure>elastic modulus of cement sheath>casing eccentricity>elastic modulus of formation.

Ply-by-Ply Failure Analysis of Laminates under Dynamic Loading

Ply-by-ply failure analysis of symmetric and anti-symmetric laminates under uniform sinusoidal transverse dynamic loading is performed for a specified duration.The study investigates the first ply failure load,followed by the detection of successive ply failures and their failure modes using various failure theories.Some of the well-established failure theories,mostly used by the researchers,are considered for the failure prediction in laminates.The finite element computational model based on higher order shear deformation displacement field is used for the failure analysis and the complete methodology is computer coded using FORTRAN.The ply-discount stiffness reduction scheme is employed to modify the material properties of the failed lamina.The failure theories used in the analysis are compared according to their ability to predict failure load,failed ply,failure mode and progression of failure.The failure analysis is performed for both the cross-ply and angle-ply laminates with all edges simply supported and clamped.The significance of fibre orientation and stacking sequence in terms of the strength of a laminate and failure progression is also highlighted.

Interference of the Cloud to Capacitance Proximity Fuze

Based on the study of the characteristics of the cloud, firstly the interference mechanism of the capacitance proximity fuze passing through the cloud has been studied. Analysis shows that the medium property of the cloud only, has little effect on the capacitance proximity fuze. Secondly, the adherence interference of the cloud to capacitance proximity fuze has been studied for the first time in this paper. Then finite element analysis (FEA) method has been used to simulate the adherence interference of the cloud. Simulation result shows that the cloud adherence effect interferes the output of the capacitance fuze greatly. At last, experiments have been made for the study of the cloud interference.

Numerical Calculation of Artillery-Fuze System Dynamic Characteristics

A numerical calculation method based on the finite element analysis of dynamic characteristics of artillery-fuze system is discussed in detail. Pretension element is used to mesh the couple structure between artillery and fuze to analyze the change of dynamic characteristics of artillery-fuze system when pre-tightening force varies between artillery and fuze. Numerical calculation of the finite element analysis and actual hammering test of a artillery-fuze system are carried out with the same input to verify the accuracy of numerical calculation. The results show that the finite element model of artillery-fuze system is credible and the calculation accuracy is perfect.

Finite element analysis of stress distribution and burst failure of SiC_f/Ti-6Al-4V composite ring

A three-dimensional cyclic symmetry finite element model of titanium-matrix composites（TMCs） ring was developed to investigate the stress distribution and burst failure. The effects of fiber volume fractions, reinforced areas, thermal residual stresses and two different temperatures on stress distribution were studied. The burst speed was obtained through analyzing the hoop tensile stresses under a series of rotating speeds. The results indicate that at the two different temperatures, the influences of fiber volume fractions and reinforced areas on stress level and distribution are different. Some proposals are provided for the structure design of the TMCs ring. With regard to thermal residual stresses, a larger reinforced area is an advisable choice for design of the ring at higher temperature.

NONLINEAR FINITE ELEMENT ANALYSIS OF CONCRETE OFFSHORE PLATFORMS

Taking account of the progressive cracking and crushing of the concrete, the full-range nonlinear analysis has been made for a R.C. Structure, from loading to cracking until crushing for some elements. The diagrams showing the distribution of the stresses and the horizontal displacements and the pictures showing the cracking and crushing of the concrete are given. This paper also gives the comparison between the results of nonlinear analysis and linear analysis.

Damage smear method for rock failure process analysis

Damage smear method(DSM)is adopted to study trans-scale progressive rock failure process,based on statistical meso-damage model and finite element solver.The statistical approach is utilized to reflect the mesoscopic rock heterogeneity.The constitutive law of representative volume element(RVE)is established according to continuum damage mechanics in which double-damage criterion is considered.The damage evolution and accumulation of RVEs are used to reveal the macroscopic rock failure characteristics.Each single RVE will be represented by one unique element.The initiation,propagation and coalescence of meso-to macro-cracks are captured by smearing failed elements.The above ideas are formulated into the framework of the DSM and programed into self-developed rock failure process analysis(RFPA)software.Two laboratory-scale examples are conducted and the well-known engineering-scale tests,i.e.Atomic Energy of Canada Limited’s(AECL’s)Underground Research Laboratory(URL)tests,are used for verification.It shows that the simulation results match with other experimental results and field observations.

Experimental and finite element analysis for fracture of coating layer of galvannealed steel sheet

Mechanical properties of galvannealed (GA) steel sheet used for automotive exposed panel and predicted failure phenomenon of its coating layer were evaluated using finite element method. V-bending test was performed to understand better the fracture of coating layer of GA steel sheet during plastic deformation. Yield strength of the coating layer was calculated by using a relative difference between hardness of coating layer measured from the nano-indentation test and that of substrate. To measure shearing strength at the interface between substrate and coating layer, shearing test with two specimens attached by an adhesive was carried out. Using the mechanical properties measured, a series of finite element analyses coupled with a failure model was performed. Results reveal that the fracture of coating layer occurs in an irregular manner at the region where compressive deformation is dominant. Meanwhile, a series of vertical cracks perpendicular to material surface are observed at the tensile stressed-region. It is found that 0.26-0.28 of local equivalent plastic strain exists at the coating and substrate at the beginning of failure. The fracture of coating layer depends on ductility of the coating layer considerably as well.

APPLICATION OF STOCHASTIC FINITE ELEMENT METHOD TO STRENGTH AND STABILITY ANALYSIS OF EARTH DAMS

This paper applies the stochastic finite element method to analyse the statistics of stresses in earth dams and assess the safety and reliability of the dams. Formulations of the stochastic finite element method are briefly reviewed and the procedure for assessing dam's strength and stability is described. As an example, a detailed analysis for an actual dam Nululin dam is performed. A practical method for studying built-dams based on the prototype observation data is described.

Finite Element Analysis of Graphite/Epoxy Composite Pressure Vessel

Shell structure is widely used in industrial applications, such as in machinery, aerospace, ship and building fields, as well as containers of pressurized chemicals or liquefied natural gas. Graphite/epoxy composites has advantages of light weight, high strength, corrosion resistance, low expansion, low shrin kage and are often used in the form of composite pressure vessel for various engineering applications. In this study, the stress distributions of composite pressure vessel were analyzed. The finite element code ANSYS was used in analysis, in which the eight-node element SHELL 281 was adopted. The internal pressure 20 MPa, as in container of compressed natural gas, was applied inside the symmetrical cross-ply graphite/epoxy composite pressure vessel. The finite element model was established with suitable mesh size and boundary conditions. The stress distributions are discussed for the composite pressure vessel, especially for the inner two layers at the junction of semis pherical part. The Tsai-Hill criterion was used to assess the failure of composite pressure vessel.

玛多7.4级地震野马滩大桥桥台纵桥向破坏机理分析

针对2021年青海玛多7.4级地震中野马滩大桥的桥台震害,开展基于Pushover分析的桥台纵桥向破坏机理研究。提出土-桩-桥台精细化有限元模拟方法,以及基于地勘资料的模型土体参数确定实用方法,建模方法和加载模式要点为:(1)适用于土-桥台相互作用的分布式p-y弹簧修正模型;(2)可识别背墙弯曲、剪切或弯-剪多种破坏模式的背墙非线性梁柱单元-墙底非线性剪切单元串联模型;(3)土-搭板和土-翼墙摩擦弹簧;(4)基于分布式间隙单元的可捕捉地震中主梁与背墙接触位置变化的Pushover加载模式,从而实现了桥台纵桥向地震损伤破坏全过程模拟。结果表明:野马滩桥台在水平地震作用下,背墙底截面先发生屈服,随后背墙剪力达到抗剪能力峰值,桥台整体水平承载力开始退化,直至背墙底完全剪断,而桩基础并不发生明显损伤。总体而言,桥台破坏模式为背墙弯-剪破坏,数值分析结果与桥台实际震害相符。

高压管汇由壬翼形螺母的失效原因

页岩气压裂施工中,某高压管汇由壬翼形螺母在服役期间发生断裂,从失效由壬翼形螺母断口位置取样,进行宏观、微观观察,断口能谱分析,硬度测试及金相检验等,并利用ABAQUS软件对由壬翼形螺母进行力学分析,揭示其失效机理。结果表明:螺母内径存在多点疲劳源,断口中央有明显贝纹线且被红褐色(Fe_(2)O_(3))、黄绿色(FeCl_(2))腐蚀产物覆盖;微观断口表面存在球状氧化物,能谱分析表明其含有一定量的Ca、Si元素,螺母原材料中存在较多C类和D类非金属氧化物;硬度和金相组织均达到工艺要求;有限元分析所得产生应力集中的部位与实际断裂位置一致,即靠近母由壬螺纹顶端处,且最大应力为910 MPa,超出材料屈服强度。故由壬翼形螺母失效机理为腐蚀疲劳断裂。最后,提出了相应的改进措施。

钢桁架在冲击荷载作用下的动态响应研究

圆钢管桁架在土木工程和海洋工程领域应用较多,除了承受竖向荷载外,还易遭受冲击偶然荷载作用。以偏心质量下抵抗冲击荷载的钢桁架为研究对象,利用LS-DYNA软件建立了节点冲击有限元模型。从破坏特征、冲击响应和耗能能力等方面研究了其抗冲击能力,对冲击次数、冲击速度和钢材屈服强度进行了参数分析,最后基于有限元模拟结果,提出了主管凹陷变形与转角之间的表达式。结果表明:经历多次摆锤冲击后,主管发生严重的凹陷变形,刚度显著降低;冲击速度达到3.0 m·s^(-1)时,冲击力峰值提高了84.8%,冲击区域支管节点发生挤压弯曲破坏,主管凹陷变形是主要的耗能机制。有限元模拟结果可为提高实际钢桁架的抗冲击性能提供参考。

型钢混凝土T形截面剪力墙基于性能的变形限值研究

为更好地评估T形截面型钢混凝土(steel reinforced concrete,SRC)剪力墙变形性能,采用ABAQUS有限元软件对按照规范设计的324个T形截面SRC剪力墙构件的破坏形态和变形性能进行研究,根据收集的试验数据分析构件的破坏形态,提出T形截面SRC剪力墙的破坏形态划分准则;以构件的各材料应变极限值为准则来判别构件的性能状态,考虑轴压比、剪跨比、弯剪比、腹板暗柱配钢率、暗柱纵筋配筋率及箍筋暗柱特征值对构件变形性能的影响。对不同性能状态变形限值和参数进行线性回归分析,得到不同破坏类型下各性能状态位移角限值计算式;按规范ASCE 41修正各性能状态变形限值的失效概率,得到具有15%、20%、35%失效概率保证的各性能状态变形限值取值表。研究表明:剪跨比、轴压比对构件各性能状态位移角限值影响较大,暗柱腹板配钢率、纵筋配筋率及箍筋特征值对构件位移角限值影响相对较小,但能提高其延性。按规范ASCE 41修正后的位移角限值取值较为合理且有一定的安全储备。为T形截面SRC剪力墙基于性能的抗震设计与性能评估提供参考。

环氧树脂混凝土装配式桁架下弦K型节点力学试验及有限元分析

通过静力试验研究了环氧树脂混凝土装配式桁架下弦K型节点的破坏形态、承载能力和节点板的应力与应变分布情况,并进行了有限元模拟分析。结果表明:环氧树脂混凝土下弦K型节点在下弦杆靠近节点板的两侧出现5条竖直裂缝,最终节点板左侧下弦杆处的竖直裂缝前后贯通,弦杆发生拉弯破坏,节点的极限承载力为421.5 kN;有限元模拟结果与试验结果吻合较好,验证了有限元模拟的可靠性。

基于有限元和DIC测试对FRP部分约束混凝土柱应变响应及数值模型研究

纤维增强聚合物(FRP)部分约束混凝土应用可以提高混凝土的承载力和经济价值。然而,FRP部分约束混凝土在垂直方向上不均匀应变响应还不够深入,应力-应变模型不够准确。本文通过应变片和数字图像相关(DIC)记录对FRP部分约束混凝土进行了轴向压缩试验,并利用ABAQUS有限元建立了包括0/1,1/4,1/3,1/2,2/3,3/4和1/1约束面积比的部分约束混凝土。试验结果表明:DIC和应变片结果分别反应了垂直和水平方向的应变规律,即试件在应变硬化或应变软化响应下均发生了明显的应变局部化;有限元结果能捕捉到试件表面约束力与x,y和z三轴的应变关系,得到了不同约束面积比的FRP部分约束混凝土柱的应力-应变关系,所提出的应力-应变模型能有较高的预测效果。

正交异性钢-钢纤维混凝土组合桥面板疲劳极限状态研究

为了解正交异性钢-钢纤维混凝土(Steel Fiber Reinforced Concrete,SFRC)组合桥面板的疲劳性能及失效机理,以川南城际铁路临港长江大桥为背景,设计、制作正交异性钢-SFRC组合桥面板足尺模型进行疲劳试验,采用ANSYS软件建立试件有限元模型,研究关键细节的疲劳应力和开裂等情况。基于有限元模型,分析不同设计参数(钢顶板厚度、栓钉布置、SFRC抗拉强度及层厚)下组合桥面板疲劳极限状态的失效模式,并提出了主要控制参数取值建议。结果表明:200万次疲劳加载后足尺模型的实测最大裂缝宽度为0.136 mm,出现在SFRC层上缘,钢结构未开裂,组合桥面板疲劳性能良好;组合桥面板疲劳极限状态主要由SFRC层开裂控制,钢顶板厚度、栓钉布置对组合桥面板疲劳性能的影响较小,SFRC抗拉强度和层厚对组合桥面板疲劳性能影响较大,为主要控制参数;在常规正交异性钢桥面板上铺设薄层(厚度不超过50 mm)SFRC时,SFRC抗拉强度不应小于5 MPa,在常规正交异性钢桥面板上铺设普通SFRC(钢纤维体积含量不高于1%,抗拉强度不高于3 MPa)时,SFRC层厚不宜低于100 mm。

高速卷板机涂布辊轴失效分析及优化设计

为解决涂布辊轴在高速旋转时阶梯轴连接处断裂的问题,对涂布辊轴进行了可靠性分析,通过理论计算和有限元仿真分析可知,连接处轴截面直径为110 mm的最大切应力为304.3~417.4 MPa,属于危险载荷。并且该处在4 000 N压力作用下,应力集中处与最大切应力处相同,两者相互叠加使得涂布辊轴在此处发生断裂。基于上述结果进行了尺寸优化分析,并提出了一种渐变型涂布辊轴结构,分析结果表明,其所受应力均在使用要求范围内。