Parametric study on single shot peening by dimensional analysis method incorporated with finite element method

Shot peening is a widely used surface treatment method by generating compressive residual stress near the surface of metallic materials to increase fatigue life and re- sistance to corrosion fatigue, cracking, etc. Compressive re- sidual stress and dent profile are important factors to eval- uate the effectiveness of shot peening process. In this pa- per, the influence of dimensionless parameters on maximum compressive residual stress and maximum depth of the dent were investigated. Firstly, dimensionless relations of pro- cessing parameters that affect the maximum compressive residual stress and the maximum depth of the dent were de- duced by dimensional analysis method. Secondly, the in- fluence of each dimensionless parameter on dimensionless variables was investigated by the finite element method. Fur- thermore, related empirical formulas were given for each di- mensionless parameter based on the simulation results. Fi- nally, comparison was made and good agreement was found between the simulation results and the empirical formula, which shows that a useful approach is provided in this pa- per for analyzing the influence of each individual parameter.

Three-dimensional forward modeling for magnetotelluric sounding by finite element method

A finite element algorithm combined with divergence condition was presented for computing three-dimensional(3D) magnetotelluric forward modeling. The finite element equation of three-dimensional magnetotelluric forward modeling was derived from Maxwell's equations using general variation principle. The divergence condition was added forcedly to the electric field boundary value problem, which made the solution correct. The system of equation of the finite element algorithm was a large sparse, banded, symmetric, ill-conditioned, non-Hermitian complex matrix equation, which can be solved using the Bi-CGSTAB method. In order to prove correctness of the three-dimensional magnetotelluric forward algorithm, the computed results and analytic results of one-dimensional geo-electrical model were compared. In addition, the three-dimensional magnetotelluric forward algorithm is given a further evaluation by computing COMMEMI model. The forward modeling results show that the algorithm is very efficient, and it has a lot of advantages, such as the high precision, the canonical process of solving problem, meeting the internal boundary condition automatically and adapting to all kinds of distribution of multi-substances.

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.

Alternating Direction Finite Volume Element Methods for Three-Dimensional Parabolic Equations

This paper presents alternating direction finite volume element methods for three-dimensional parabolic partial differential equations and gives four computational schemes, one is analogous to Douglas finite difference scheme with second-order splitting error, the other two schemes have third-order splitting error, and the last one is an extended LOD scheme. The L2 norm and H1 semi-norm error estimates are obtained for the first scheme and second one, respectively. Finally, two numerical examples are provided to illustrate the efficiency and accuracy of the methods.

Three-Dimensional Thermo-Elastic-Plastic Finite Element Method Modeling for Predicting Weld-Induced Residual Stresses and Distortions in Steel Stiffened-Plate Structures

The objective of the present paper is to develop nonlinear finite element method models for predicting the weld-induced initial deflection and residual stress of plating in steel stiffened-plate structures. For this purpose, three-dimensional thermo-elastic-plastic finite element method computations are performed with varying plate thickness and weld bead length (leg length) in welded plate panels, the latter being associated with weld heat input. The finite element models are verified by a comparison with experimental database which was obtained by the authors in separate studies with full scale measurements. It is concluded that the nonlinear finite element method models developed in the present paper are very accurate in terms of predicting the weld-induced initial imperfections of steel stiffened plate structures. Details of the numerical computations together with test database are documented.

Validation and application of three-dimensional discontinuous deformation analysis with tetrahedron finite element meshed block

In the last decade, three dimensional discontin- uous deformation analyses （3D DDA） has attracted more and more attention of researchers and geotechnical engineers worldwide. The original DDA formulation utilizes a linear displacement function to describe the block movement and deformation, which would cause block expansion under rigid body rotation and thus limit its capability to model block de- formation. In this paper, 3D DDA is coupled with tetrahe- dron finite elements to tackle these two problems. Tetrahe- dron is the simplest in the 3D domain and makes it easy to implement automatic discretization, even for complex topol- ogy shape. Furthermore, element faces will remain planar and element edges will remain straight after deformation for tetrahedron finite elements and polyhedral contact detection schemes can be used directly. The matrices of equilibrium equations for this coupled method are given in detail and an effective contact searching algorithm is suggested. Valida- tion is conducted by comparing the results of the proposed coupled method with that of physical model tests using one of the most common failure modes, i.e., wedge failure. Most of the failure modes predicted by the coupled method agree with the physical model results except for 4 cases out of the total 65 cases. Finally, a complex rockslide example demon- strates the robustness and versatility of the coupled method.

An Efficient Multiple-Dimensional Finite Element Solution for Water Flow in Variably Saturated Soils

Multiple-dimensional water flow in variably saturated soils plays an important role in ecological systems such as irrigation and water uptake by plant roots; its quantitative description is usually based on the Richards＇ equation. Because of the nonlinearity of the Richards＇ equation and the complexity of natural soils, most practical simulations rely on numerical solutions with the nonlinearity solved by iterations. The commonly used iterations for solving the nonlinearity are Picard and Newton methods with the former converging at first-order rate and the later at second-order rate. A recent theoretical analysis by the authors, however, revealed that for solving the diffusive flow, the classical Picard method is actually a chord-Newton method, converging at a rate faster than first order; its linear convergence rate is due to the treatment of the gravity term. To improve computational efficiency, a similar chord-Newton method as for solving the diffusive term was proposed to solve the gravity term. Testing examples for one-dimensional flow showed significant improvement. The core of this method is to produce a diagonally dominant matrix in the linear system so as to improve the iteration-toiteration stability and hence the convergence. In this paper, we develop a similar method for multiple-dimensional flow and compare its performance with the classical Picard and Newton methods for water flow in soils characterised by a wide range of van Genuchten parameters.

Analysis of the Influence of Parafunctional Loads on the Bone-Prosthesis System: A Non-Linear Finite Element Analysis

The present study evaluates the effects of occlusal loading on an implant-supported dental implant with external hexagon dental implant-abutment systems, using the finite element method analysis. Tensile analyses were performed to simulate different axial and obliquous masticatory loads. The influence of the variations in the contouring conditions of the interfaces was analyzed to weigh the osseointegration with linear and non-linear cases, by means of a parametric design. The geometry selected to place the prostheses was a jaw section, considering the properties of the set of cortical and trabecular bones. The results show that for non-linear contour conditions, the stress presents smaller value distributions and signals a different place in the screw-implant interface as the factor of the greater weight in this study. The location indicated that von Mises stress concentrations are not exclusive to the contact regions studied, moving to an area that is not in direct contact with the non-linear contact interfaces. In addition, the direction of load with an angle of 15 degrees presented the highest values of von Mises stress.

Finite Element Modelling of Steel Beams with Web Openings

Height limitations are not uncommon in multi-storey buildings due to economic requirements and esthetical considerations. Substantial spaces are normally required to enable the passage of large pipes and ducts beneath steel beams leading to uneconomic floor heights. The most adopted solution for this issue is the use of steel beam web openings to provide the required space for services. These openings could lead to a significant decrease of the beam load carrying capacity depending on the adopted openings shape, size and location. These aspects motivated the present study based on FE simulations calibrated against numerical and test results. The results accuracy enabled a comprehensive parametric analysis of beams with web openings to be made focused on the profile size, web opening location, among others. The study also investigated the efficiency of longitudinal stiffeners welded at the opening region and benefits of using an adequate edge concordance radius in beams with rectangular and square openings. The obtained results showed the need of using welded longitudinal stiffeners in order to increase the beams ultimate load carrying capacity. This adoption can double or even triple the ultimate load of beams with rectangular and square opening heights equal to 0.75 H, respectively.

Algebraic Calculation Method of One-Dimensional Steady Compressible Gas Flow

This paper describes a new method of calculation of one-dimensional steady compressible gas flows in channels with possible heat and mass exchange through perforated sidewalls. The channel is divided into small elements of a finite size for which mass, energy and momentum conservation laws are written in the integral form, assuming linear distribution of the parameters along the length. As a result, the calculation is reduced to finding the roots of a quadratic algebraic equation, thus providing an alternative to numerical methods based on differential equations. The advantage of this method is its high tolerance to coarse discretization of the calculation area as well as its good applicability for transonic flow calculations.

Finite Element Simulation of the Polymeric Liquid Flow in Coat-hanger Die

A three - dimenslonal finite element model is developed to deal with the polymeric liquid flow in coat - hanger die. This model is used to predict the flow behavior of the 2％ CMC/watsr solution in the coat - hanger die with linearly taper manifolds and its validity is experimentally verified quantitatively and qualitatively by using Laser Doppler Velocimetry and Particle Image Velocimetry respectively.

Three dimensional tectonic stress field in North China

According to the latest data of geological structure, geophysics, in-situ stress measurement and focal mechanism,3-D tectonic stress field model in North China is built and 3-D tectonic stress field pattern of North China aresimulated by finite element method. Then the overall characteristics and regional specific feature of North Chinaare studied. Finally, the influences of the valid dynamic boundary conditions of North China Block, active faultsand the inhomogeneity of crustal medium on tectonic stress field of North China are investigated.

Influence of Residual Stress on the Dimensional Instability of 7075 Aluminum Cone-Shaped Shells

This paper dealt with the influence of residual stress on the dimensional instability of 7075 aluminum cone-shaped shells. Finite element method was introduced to calculate residual stress distributions in 7075 aluminum cone-shaped shells during conventional heat treatment (CHT) and deep cryogenic treatment (DCT). An example was given to demonstrate effects of deep cryogenic treatment (DCT) and conventional heat treatment (CHT) on dimensional instability. It is concluded that initial residual stresses have detrimental influence on the dimensional instability of 7075 aluminum cone-shaped shells.

严寒地区拱坝溢流表孔三维有限元数值模拟分析

溢流表孔作为拱坝重要的泄水建筑物,对大坝安全运行具有重要的作用。以某拱坝溢流表孔为例,该表孔地处高纬度严寒地区、结构复杂且地震烈度高,通过三维有限元法对表孔在不同工况下的静、动力应力进行计算分析,根据计算结果,对表孔结构进行配筋设计,确定受拉钢筋的布置方式及配筋量,使表孔结构钢筋布置满足承载力及正常使用要求。研究结果可为类似工程配筋设计提供参考依据。

牙周辅助加速成骨正畸增加牙槽骨量前后正畸牙移动的生物力学特征

背景:人们对正畸治疗的需求日益增加,牙周辅助加速成骨正畸技术可以使以往受限于菲薄牙槽骨三维形态的正畸牙移动有了更多的可能。目的:利用三维有限元分析法对牙周辅助加速成骨正畸手术增加牙槽骨量前、后正畸牙移动的生物力学进行探究。方法:选择1例需正畸前进行牙周辅助加速成骨正畸手术以增加下颌前牙区唇侧骨量的患者,根据其术前及术后6个月的锥形束CT数据构建术前及术后三维有限元分析模型,结合患者临床隐形矫治中正畸牙的移动过程,2个模型均分别模拟33牙远中移动0.25 mm、舌向移动0.25 mm、压低移动0.10 mm,利用ANSYS workbench 2020软件分析在无托槽隐形矫治器的作用下33牙牙体、牙周膜、周围牙槽骨的应力分布及初始位移趋势。结果与结论:①牙体应力:在相同的正畸牙移动方式下,术前33牙牙体的最大Von-Mises应力与整体应力均大于术后,手术前后的最大等效应力分布区域相近、Von-Mises应力整体分布趋势接近;②牙周膜应力:在相同的正畸牙移动方式下,术前33牙牙周膜的最大Von-Mises应力与整体应力均大于术后,手术前后的最大等效应力分布区域相近、Von-Mises应力整体分布趋势接近;③牙槽骨应力:在相同的正畸牙移动方式下,术前33牙周围牙槽骨的最大Von-Mises应力值大于术后,手术前后的等效应力分布表现为由牙槽嵴顶处向根方逐步减小;④初始位移:在相同的正畸牙移动方式下,术前33牙6个观测点在主要位移方向上的初始位移量均小于术后,并且呈现出位移量由牙尖向根尖点逐步减小的趋势;⑤结果显示:牙周辅助加速成骨正畸手术增加牙槽骨量前后,正畸牙移动的生物力学特征存在差异,在隐形矫治器的作用下,术后牙体、牙周膜、周围牙槽骨的等效应力较术前小,术后正畸牙的初始位移较术前大,这提示牙周辅助加速成骨正畸手术可以通过增加牙槽骨厚度解除菲薄牙槽骨对正畸牙移动的限制,有效改善牙根、牙周膜、牙槽骨的受力,避免了菲薄牙槽骨区正畸牙受力移动时产生应力集中从而引起并发症的状况,同时提高了牙齿的移动效率。

高铁荷载下路堤和路堑段地面振动特性现场测试与数值分析

对巴黎-布鲁塞尔高速铁路地面振动开展现场测试,对比分析了高铁运行引起的路堤和路堑段地面振动特性以及传播衰减规律。基于2.5维有限元法基本原理,推导并建立了高铁荷载下路堤和路堑段2.5维有限元动力计算模型,详细讨论了路堤和路堑设计参数对地面振动特性的影响。结果表明:距轨道较近处的地面振动幅值主要受列车轴重影响,而距轨道较远处则由中间车相邻转向架轮对的叠加效应主导。高铁运行引起的路堤和路堑段地面振动随与轨道距离增加而减小,中高频成分振动的衰减速率显著大于其他频段。路堤和路堑段地面振动1阶主频主要由列车荷载的基频f_1主导,随车速提高逐渐向高频方向移动。路堤和路堑对地面振动的衰减规律有重要影响,路堤段地面振动随与轨道间距的衰减过程可分为两个阶段,而路堑段地面振动衰减过程则可分为三个阶段,且振动在堑顶处有较为明显的局部放大现象。当与路堤段轨道间距≥19.0 m(路堑段≥23.0 m)后,地面振动Z振级VL_Z均小于80.0 dB。同时,高铁荷载下地面振动随路堤高度或路堑深度的增加而减小,当超过某一限值时,继续增加路堤高度或路堑深度难以有效减小地面振动。路堤段地面振动随路堤弹性模量的增大而减小。此外,在确保稳定性的前提下,较陡的路堑边坡更有利于减小高铁运行引起的地面振动。

基于逆有限元法的三维壁板结构变形场重构

过约束状态下的结构内部转角不连续,会导致结构变形场难以准确重构。该文以飞行器进气道典型三维壁板结构为对象,开展超静定状态下结构变形场重构方法研究。将子区域划分与逆有限元法相结合,实现了基于实测应变数据的超静定结构全场变形重构。对静载工况下三维壁板结构开展变形场重构数值仿真研究,验证算法的可行性和重构精度;进一步开展了试验研究,实现了变载荷工况下基于实测应变的三维壁板结构全场变形重构,并利用实测位移数据验证重构变形场的精度。试验结果表明:位移测点处的重构位移值与实测位移值的相对误差在10%左右,结合子区域划分和逆有限元法的变形重构算法可以准确重构出过约束工况下三维壁板结构的全场变形。

建立基于浸入边界有限元法的三维静脉瓣流固耦合数值模型

目的 探究静脉内血液与瓣膜之间的流固耦合动态过程和保证血液单向回流的生理机制。方法 基于浸入边界有限元法,结合人体下肢静脉医学图像及牛大隐静脉的解剖结构和尺寸,采用超弹性本构模型描述静脉瓣膜在生理条件下不可压缩、非线性和超弹性力学响应,构建静脉血管和静脉瓣膜的三维数值模型。结果 研究结果可视化地展示静脉动态运输血液的过程以及静脉瓣膜防止反流的功能机制,再现静脉内瓣膜运动和血液流动的周期性特点,讨论和量化了整个心动周期内的重要生理数据,包括静脉内血液的压力、流速和流量以及静脉瓣膜的开口面积、静脉瓣膜表面的应力和应变分布等。结论 三维流固耦合模型可数值再现静脉内生理动态过程,为进一步揭示静脉疾病相关机制提供重要的参考和指导意义。