Comparative study between crack closure model and Willenborg model for fatigue prediction under overload effects

A comparative study is performed between a crack closure model and the Willenborg model, which can calculate the fatigue crack growth rate under the overload effects. The modified virtual crack annealing (VCA) model is briefly reviewed, which is based on the equivalent plastic zone concept. In this method, the retardation phenomenon is explained by the crack closure level variation, which is derived from the interactions between forward and reverse plastic zones ahead of the crack tip. As a comparison, the Forman equation in conjunction with the Willenborg model is also reviewed. The retardation phenomenon is described by directly modifying the stress intensity factor. It is known that the large plastic zone created by the overload can decelerate the fatigue crack growth rate until the crack grows beyond this region. A relationship between the plastic zone and the modified stress intensity factor is developed, which is a mathematical fitting equation instead of physical-based formulation. The experimental data in aluminum alloys are used to val-idate these two models. Overall, good agreement is observed between the model predictions and the testing data. It is noted that the approach based on modified VCA model can give more accurate prediction curves than the Willenborg model.     

基于改进型近场动力学方法的复合材料单向板变形与破坏分析

针对复合材料单向板的变形与破坏问题,采用经典的键型近场动力学(Peridynamics,PD)理论进行建模分析,利用基体键与纤维键描述单向板宏观各向异性,同时在基体键中引入反映长程力尺寸效应的核函数修正项改进近场动力学本构模型,构建相应的准静态数值求解体系。使用传统PD模型与改进型PD模型对单轴拉伸单向板变形进行定量计算,二者所得计算结果较理论解相对误差分别为3.5%和1.7%,表明改进型PD模型具有更高的定量计算精度。开展含不同角度中心裂纹单向板单轴拉伸破坏试验与数值模拟,二者所得单向板最终破坏形式与破坏特点均吻合,表明当前模型与方法能够有效处理单向板的破坏问题。最后对纤维角度为0°单向板的拉伸破坏过程展开模拟分析,结果表明单向板在前期主要出现基体开裂,当裂纹扩展至夹持区域后,结构出现纤维断裂,最终形成贯穿整个结构的断面导致单向板发生破坏。     

Interactive database of cosmic ray anisotropy (DB-A10)

The worldwide neutron monitor network is a unique tool for obtaining with high accuracy the information on density variations, energy spectrum and anisotropy of comic rays at the Earth, outside its atmosphere and magnetosphere. These hourly averaged parameters were obtained over the whole period of cosmic ray monitoring by the ground level neutron monitor network (from 1957 till present) and are collected within the MySQL database. The Internet-project has developed for free access and supplying of cosmic ray density and anisotropy data in different formats.     

注塑件相似度计算方法

提出一种标准化的塑件相似度计算方法,塑件相似度由规范化的属性距离加权求和构成,并引入灵敏度系数对相似度、区分度进行调整。各权值按塑件各属性项对目标量的影响程度进行分配。所提出的算法可用于基于实例推理的注塑模设计中相似塑件的搜索与匹配。     

应用广义阶梯函数解圆板的塑性极限分析问题

在文献「１」的基础上，进一步应用广义阶梯函数对承受边缘弯矩，局部均布荷载和线性分布荷载的简支圆板进行塑性极限分析，给出了简支圆板在Ｔｒｅｓｃａ屈服条件下，边缘弯矩，局部均布荷载和线性分布荷载所满足的关系式。     

Coupled FEM Analyses on Electro-mechanical Problem of Electrostrictive Plate with Elliptical Hole

A detailed theoretical construction of general coupled 3D FEM analyses of anisotropic dielectrics is first presented by considering the electric body force and body couple moment. A 3D electrostrictive element is subsequently defined in ABAQUS user subroutine UEL and the post-processing of finite element method （FEM） results is realized by UVARM and dummy element method. Then the developed technique is used to solve the electro-elastic field of an isotropic electrostrictive plate with an elliptical hole subjected to electrical load. By comparing the coupled and uncoupled numerical results, the traditional uncoupled analytical method can cause a large error when the applied electric field or the electrostrictive performance of the dielectric is high, and thus the present coupled analysis is especially necessary.     

高强度碳纤维增强复合材料层合板的钻削制孔过程及其缺陷形成分析

单向层合结构的高强度碳纤维增强树脂基复合材料已逐渐发展成为航空承力结构件的主要材料,相关的切削加工需求也越来越多。由于显著的各向异性,单向层合结构的碳纤维复合材料易在切削加工中形成缺陷,难切削加工性明显。针对T800级高强度CFRP单向层合材料开展直角自由切削试验,研究其在切削过程中的切削力和切削热随纤维方向角的变化产生的各向异性行为。针对制孔刀具三尖钻和八面钻开展CFRP层合板的钻削制孔试验,研究了三尖钻和八面钻的具体钻削过程中切削力、扭矩和切削温度的变化规律及其对钻削缺陷形成的影响。此外,对钻削制孔形成的孔壁加工表面进行分析,得到了典型孔壁缺陷的形貌照片并分析其形成原因。     

某结构件的非线性弹塑性分析计算

使用有限元软件MSC/Nastran,对某结构件进行了非线性弹塑性计算,分析对比了结构应力以及残余应力与材料屈服极限之间的关系,计算结果与试验值基本吻合,说明使用该软件进行工程结构非线性弹塑性计算是准确的。     

2198铝锂合金后续热处理制度及对织构影响的研究

通过力学性能和组织观察研究了2198新型铝锂合金的后续固溶时效热处理制度,并通过XRD衍射仪对原始板材和热处理之后的板材进行织构测算。对比分析表明：2198铝锂合金最佳固溶制度选为500℃×1 h小时,最佳时效制度定为175℃×20小时。经过重新固溶时效后,材料组织形貌、力学性能基本保持不变而延伸率变化小于3%。原始板材织构主要存在着较强的{-110}〈-1-12〉组分以及{001}〈0-10〉,{-3311}〈-1-10〉和{-5512}〈3-95〉组分,但经过重新固溶时效之后,主要织构变为{-110}〈-1-12〉,{-3313}〈-1-10〉和{-112}〈1-11〉组分,呈明显弱化趋势。从而改善此合金趋于各向同性条件下的抗疲劳性能与耐蚀性能。     

各向异性Kelvin开孔泡沫模型的弹性性能

在弹性小变形情况下,基于构造的各向异性Kelvin模型对开孔泡沫材料的变形进行了分析。综合考虑了胞体中斜支柱的轴向、弯曲和剪切变形以及水平支柱的轴向变形的影响,利用最小势能原理得到了材料的弹性性能与各向异性比及相对密度的关系。研究结果表明,各向异性比越大,沿胞体伸长方向的相对弹性模量和泊松比越大,而在垂直于胞体伸长方向上的相应值反而越小;两个方向上的相对弹性模量均随相对密度增加而增大,泊松比的变化趋势则正好相反。本文预测结果较好地符合了实验数据的变化趋势,且与已有的G-K模型比较接近,证明了该模型的有效性。