Finite element analysis of creep fracture initiation in a model superalloy material

Detailed finite element analyses were performed for a single edge-cracked specimen geometry under both plane stress and plane strain constraint for a superalloy material that obeys a power-law creep relationship. The objectives of these analyses were to elucidate the stationary creep crack-tip fields and to provide guidance for the experimental measurement of crack-tip deformations. New results demonstrate that, for both plane stress and plane strain, the angular variations in the creep strain fields do not agree with HRR-type predictions, although the radial variations are in agreement with HRR-type creep strain field predictions in a zone very near the crack tip. Thus, the use of experimental measurement of surface displacement and/or strain data for the location of HRR-type fields may not be possible, unless modifications to the existing HRR-type theory are made. It is also noted that the size of the stress-based HRR-dominance zone is only a fraction of the creep zone size in plane stress, and is very small (especially along =0°) compared to the creep zone size in plane strain. Furthermore, the dominance of the singular strain fields are at least two orders of magnitude smaller than the corresponding stress dominance zones. As such, unless the microstructural features of the material are smaller than the dimensions of the dominance zones, the basis for using stress or strain-based fracture parameters derived from the HRR-type fields for prediction of creep fracture initiation is unclear.     

A finite element algorithm to study creep cracks based on the creep hardening surface

This work addresses finite element (FE) modelling of creep cracks under reversed and cyclic loads in steels. A constitutive model based on the creep hardening surface developed by Murakami and Ohno has been selected for this purpose. This model is particularly accurate for describing creep under reversed and cyclic loads and requires no additional material constants. An FE algorithm for this model has been derived and implemented into a research code FVP. The algorithm is verified by comparing the numerical predictions with closed form solutions for simple geometries and loading configurations. FE predictions are compared with experimental data for a stationary crack in a compact tension specimen. The stress and strain fields in the vicinity of a crack under a sustained load are compared with those for the intermediate unloading case. Several integral fracture parameters are investigated as to their appropriateness for describing creep cracks under reversed and cyclic loads.     

Determination of creep parameters from indentation creep experiments: a parametric finite element study for single phase materials

Abstract

This paper explores the possibilities of determining creep parameters for a simple Norton law material from indentation creep testing. Using creep finite element analysis the creep indentation test technique is analysed in terms of indentation rates at constant loads. Emphasis is placed on the evolving stress distribution in front of the indenter during indentation creep. Moreover the role of indenter geometry, size effects and of macroscopic constraints is explicitly considered. A simple procedure is proposed to translate indentation creep results into constitutive creep equations for cases where the dimensions of the tested material are significantly larger than the indenter. The influence of macroscopic constraints becomes important when the size of the indenter is of the same order of magnitude as the size of the testing material. As a striking example for size effects and for macroscopic constraints the indentation creep process in a thin film is analyzed. The results contribute to a better mechanical understanding of indentation creep testing.     

基于SolidWorks Simulation的受力弯管有限元分析

针对大口径热量表检测装置检测DN50 mm、DN65 mm、DN80 mm的热量表时,在入水口弯管处出现管道局部翘起现象,采用solidworks实现受力弯管的三维建模,在simulation有限元仿真环境下,对不同结构的受力弯管进行变形位移、应力、应变分析,为弯管的设计研究、安装调试提供参考。     

Finite element analysis of the effects of comers on residual stresses in protective oxide scales

Finite element simulations are used to examine residual thermal stresses and strains in corner regions of protective Al₂O₃ scales on Fe₃Al specimens, both during cooling from oxide formation temperatures and during subsequent thermal cycling. The effects of a corner's radius of curvature and oxide thickness, as well as the impact of aluminide plasticity, are considered. Localized plasticity is found to have a major influence on net deformation and on the magnitude and location of maximum stress. As the ratio of corner curvature to oxide thickness (r_s/t) is reduced, stresses within the oxide corner shift from highly compressive to tensile and the location of the maximum principal stress moves from the substrate to the oxide scale. Based on these stress distributions prior to the development of any flaws, key implications about the tendencies for damage are addressed. The stress evolution during cooling and thermal cycling is presented; these results demonstrate the effects of temperature-dependent material properties. For the material behavior assumed in this study, thermal cycling does not cause significant stress relaxation.     

移动式低温LNG贮罐强度的有限元分析

为实现移动式低温LNG贮罐的优化设计与安全运行,以高真空多层绝热结构LNG贮罐为研究对象,在分析其结构与承载特点的基础上,针对实际使用中经历的启动、制动、颠簸等多种工况,采用有限元方法分析了该类贮罐总体及局部的应力强度分布。结果表明:多种工况下,内容器内壁靠近滑动端支承的部位应力强度均最高,特别是遭遇羁绊颠簸时,其最大应力强度达到323.5MPa,比静态操作提高了62.5%,因此在LNG贮罐内、外容器上设置合适厚度与间距的加强圈对降低局部应力强度很有必要。同时水平加速度在-0.5g-1.0g区间交变时的疲劳分析与评定表明,LNG贮罐当前结构满足疲劳强度的要求,但最大交变应力强度点均出现在靠近固定支承的加强圈的边缘,说明结构不连续等对贮罐膜应力状态的破坏是导致疲劳失效的主因,故移动式LNG贮罐应尽量采用圆滑过渡结构。     

Finite element analysis and parametric study of steel-concrete composite beams

A finite element model is presented to predict the stresses and deformations in steel-concrete composite beams. The model takes into account the effect of cracking and tension-stiffening in the tensed concrete, and of longitudinal slip between the steel beam and the concrete slab due to the ‘partial interaction’ of theconnectors. Some comparisons with experimental data available in literature are reported to validate the efficiency of the proposed model. Finally, a parametric study was done to investigate the effects of the geometric and mechanical variables as boundary conditions and the slip modulus of the connectors.     

Analysis of non-localized creep induced strains and stresses in notches

A method for the estimation of time-dependent strains and stresses induced in notches has been developed. The aim of the method is to generate a solution for the creep strain and stress at the notch root based on the linear-elastic stress state, the constitutive law, and the material creep model. The proposed solution is an extension of Neuber’s total strain energy density rule for the case of time-independent deformation. The method was derived for both localized and non-localized creep in a notched body. Predictions were compared with finite element data and good agreement was obtained for various geometrical and material configurations in plane stress conditions.     

Quantification of stress redistribution due to mismatch in creep properties in welded branch pipes

This paper reports steady‐state stress distributions within the weld metal in a welded branch component, via detailed three‐dimensional elastic‐creep finite element analyses. The creep exponent and constants for the base and weld metal are systematically varied to simulate under‐matching, even‐matching and over‐matching conditions in creep. Various loading conditions are also considered to see the effect of the loading mode. It is found that the mismatch effect in creep on steady‐state stresses within the weld metal can be uniquely quantified by the mismatch factor, defined as a function of creep exponent and constant. Ratios of section‐averaged (effective and maximum principal) stresses for the mismatched case to those for the even‐matched case are linearly dependent on the mismatch factor.     

Finite element analysis of stiffened laminated plates under transverse loading

A finite element model is developed to study the behavior of stiffened laminated plates under transverse loadings. Transverse shear flexibility is incorporated in both beam and plate displacement fields. A laminated plate element with 45 degrees of freedom is used in conjunction with a laminated beam element having 12 degrees of freedom for the bending analysis of eccentrically-stiffened laminated plates. The validity of the formulation is demonstrated by comparing with the available solutions in the literature. The numerical results are presented for eccentrically-stiffened layered plates having various boundary conditions and with stiffeners varying in number.     

卷对卷纳米压印脱模过程的有限元模拟

本文提出卷对卷纳米压印脱模的两种形式并分析了脱模过程中的阻力.选取垂直于光栅形微结构的截面作为研究对象,忽略脱模过程中旋转角度的影响,将模板上微结构当作竖直平移脱离胶层的方式来处理,利用ANSYS有限元软件模拟了卷对卷脱模过程中不同位置的变形和等效应力分布.结果显示脱模过程中出现两处应力集中,且应力集中处的最大应力在脱模刚发生时出现波动,随后逐渐增大.     

脉冲管制冷机中板弹簧的有限元分析

利用ANSYS有限元分析软件对外径为120 mm的板弹簧进行了应力和轴向刚度分析,得出了弹簧的厚度、涡旋角、涡旋槽个数以及涡旋槽宽度这些几何参数与其应力分布特性和轴向刚度性能的关系.首次提出了一个刚度应力比的概念,用刚度应力比值的大小来评价板弹簧性能的好坏,并将其作为板弹簧的设计依据.     

低温绝热气瓶的有限元热分析与试验研究

通过有限元方法对充满低温液体的气瓶进行传热分析,与试验的结果相结合,分析气瓶的颈管、支撑结构和绝热结构的漏热量并对产品结构进行优化设计,来保证达到优良的绝热性能.     

Influence of initial ovality on creep life of P92 pipe bends subjected to in-plane bending

Initial ovality is an inevitable problem in the process of pipe bends manufacturing which results in the stress redistribution of the pipe bends working at high temperature. In order to study the influence of ovality on creep life of pipe bends, full-size creep experiment of P92 pipe bend subjected to in-plane bending has been conducted. The creep strains and outside diameters of dangerous positions have been measured. The microstructures of three different positions of the pipe bend were compared through SEM and the results showed the number and size of the carbide precipitation were the largest at the flank of the pipe bend, which indicated that the creep damage developed fastest at the flank. The modified Kachanov–Robatnov constitutive equations were used to stimulate the creep of P92 pipe bends with FEA software. The representative stress, damage and multiaxiality distributions of the pipe bends have been discussed. The FEA results were consistent with the experimental results and the influence of initial ovality on creep life of P92 pipe bends were analyzed. The results showed that creep life of pipe bends reduced by the increase of ovality and their relationship coincided with the parabolic law.     

大马力拖拉机驱动桥有限元分析及试验研究

驱动桥作为拖拉机的传动和承载部件,受力较大且使用频繁,通过对桥壳模型的有限元分析,可以验证设计的安全性并可以通过分析结果来改进设计。首先采用Pro/E对拖拉机驱动桥壳、转向节、半轴进行三维建模并导入Hypermesh中进行有限元分析的前处理工作,然后将导出的文件输入ANSYS中进行有限元分析。最后通过桥壳的刚度试验和疲劳试验验证了此驱动桥的安全性,并给出了改进意见。     

磷酸二氢钾(KDP)晶体纳米压痕过程的有限元分析

为了求得KDP晶体的应力-应变曲线以及材料的屈服应力,基于圣维南定理和实验得到的材料性能参数建立了KDP晶体的压痕过程仿真模型,利用ABAQUS有限元分析软件对KDP晶体压痕过程进行了有限元仿真,得到了KDP晶体的载荷-位移曲线和加/卸载过程中的等效应力变化规律.仿真结果表明:加载过程中最大应力集中在压头尖角处,卸载后最大应力分布在压头棱边所留下的压痕处,KDP晶体材料的屈服应力为120MPa.     

Finite element analysis and experimental research on notched strengthening effect of P92 steel

Abstract

The notched strengthening effect during creep of P92 steel has been studied by finite element analysis and experimental research. It was found that there was a transforming tendency from ductile to brittle at the root of the notch and the extent of the transforming intensified with the increment of the nominal stress. It was the transforming tendency that increased the value of creep life enhancement factor. With the help of finite element software, Kachanov–Rabotnov creep damage constitutive model was embedded into the interface program and the notched specimens creep was simulated. The result has shown the Kachanov–Rabotnov model can be used to simulate the notched strengthening effect of P92 steel accurately when the material constant α?=?0·73.     

液化天然气铁路罐车罐体的有限元分析

依据TB/T1335—1996《铁道车辆强度设计及试验鉴定规范》及70 t级铁路货车的强度考核要求,采用ANSYS有限元方法对中国北车集团所设计的、拥有自主知识产权的中国首个液化天然气铁路罐车罐体进行静强度计算。计算结果表明,罐体高应力区主要集中在水平拉杆组件和玻璃钢支撑位置。其中,玻璃钢支撑位置内罐加强圈最大应力879 MPa,外补强板最大应力460 MPa,均超出材料的许用应力。对超出许用应力部分进行结构改进,对加强圈添加翼板,外补强板添加14 mm厚筋板。改进结构后,内罐加强圈厚度为16 mm时,加强圈结构最大应力246 MPa;外补强板筋板间隔角度为30°时,外补强板及筋板结构的最大应力为276 MPa。改进后的罐体结构满足强度考核要求。     

Finite element analysis and the stress correspondence paradigm

The underlying mechanics of the finite element method as applied to structural analysis is explored in paradigmatic terms. It is shown that the stress correspondence paradigm has the most explanatory power and that it can be axiomatized from a very basic principle, the Hu-Washizu theorem, which is a variation of the least action principle. Numerical experiments are presented to show that the predictions based on analytical quantification from the stress correspondence paradigm are verifiable.