基于内聚力模型的颗粒增强耐火材料界面脱粘力学性能研究

采用基于内聚力模型的Surface-based cohesive法对耐火材料界面相的力学行为进行模拟,仿真再现了耐火材料界面脱粘的整个过程。研究了受载形式、颗粒相形状以及分布方式对界面力学性能的影响。结果表明,界面脱粘可以分为界面承载、界面损伤和损伤扩展三个阶段。圆形颗粒情况下,界面损伤最先出现在垂直加载方向的界面两端附近,受拉时界面脱粘过程较快,且最大应力值大于受压状态;椭圆形颗粒情况下,界面损伤最先出现在长轴端部附近,脱粘所需时间稍长于圆形颗粒,且=45°倾斜的椭圆形颗粒界面上应力最小。     

聚醚醚酮的室温单轴棘轮行为

在室温下对聚醚醚酮(PEEK)进行一系列非对称应力控制的单轴循环棘轮变形试验,研究了应力水平、加载历史、应力速率和峰值应力保持时间对PEEK棘轮行为的影响规律。结果表明：PEEK在非对称应力循环加载下产生了明显的棘轮行为,棘轮应变包含可恢复的黏弹性应变和不可恢复的黏塑性应变;棘轮应变和棘轮应变速率均随着应力水平的增加而增大;PEEK的棘轮行为具有明显的加载历史效应,高平均应力的加载历史会抑制后续低平均应力循环过程中棘轮变形的发生,低平均应力的加载历史对后续高平均应力循环过程中的棘轮变形影响不大;PEEK的棘轮行为具有明显的时间相关特性,应力速率越低、峰值应力保持时间越长,棘轮应变越大。     

含韧性界面相的颗粒增强复合材料的损伤研究

基于增量损伤理论,提出一个可描述颗粒增强复合材料渐进式脱粘损伤、基体塑性变形及颗粒尺寸效应的本构模型。采用双夹杂模型将韧性界面相嵌入到增量损伤理论模型,用界面分离的能量平衡式来描述颗粒增强复合材料的渐进式脱粘损伤。该模型可研究颗粒尺寸效应和界面性能对复合材料应力-应变关系的影响,并可解释界面相对复合材料力学性能的颗粒尺寸效应的影响。     

铀表面铝镀层热应力的有限元分析

对铀表面磁控溅射沉积铝镀层的热应力进行了热弹塑性有限元分析。结果表明：镀层内的热应力较大,达到铝的屈服强度,镀层界面两侧存在明显应力梯度,试样侧边存在由于边缘效应引起的应力分布不均匀性,至侧边约4倍镀层厚度处,应力分布不均匀性逐渐消失;沉积温度升高,界面塑性应变明显增大,镀层弹性模量和泊松比对镀层界面热应力和塑性应变的影响较小,而屈服强度的影响较大,减薄镀层厚度有利于改善镀层界面的热应力和塑性应变。     

粘着与速度对滑动摩擦变形影响的研究

研究了在不同剪切强度和滑动速度参数下,两粗糙面间滑动过程中对等效塑性应变、y向和x向变形的影响。随着界面剪切强度增加,等效塑性应变的分布由良好对称转变成沿接触界面与滑动反方向扩大。在滑动中,界面剪切强度和滑动速度都影响y向和x向变形。随着滑动速度的减小,粗糙表面的变形越大黏着效应越明显。     

碳纳米管增强聚合物复合材料的界面脱黏及应力分布

碳纳米管和复合材料基体间的界面力学行为是影响复合材料宏观力学性能的重要因素,为此本文利用有限单元法对单壁碳纳米管增强聚合物复合材料的界面脱黏、切应力分布及拔出载荷进行了数值模拟。建立了一个轴对称三圆柱壳模型,引入ABAQUS中的Cohesive单元模拟了单壁碳纳米管和聚合物基体之间的界面层,分析了单壁碳纳米管的长细比、界面强度以及热残余应力等因素对碳纳米管与聚合物基体间的界面切应力以及拔出载荷的影响。模拟结果表明：当单壁碳纳米管的长度变化为50~100 nm、与基体之间的界面强度为50~100 MPa、环境温度变化为100℃ 时,碳纳米管的长细比、界面强度以及由于热失配所引起的残余应力对单壁碳纳米管与聚合物基体间的界面切应力以及拔出载荷有着显著的影响。     

增强体颗粒失效对SiCp/Al复合材料屈服强度的影响

采用Eshelby等效夹杂理论,分析SiCp/Al复合材料受载时作用在SiC颗粒上的应力.假设SiC颗粒失效符合Weibull统计分布,在综合考虑复合材料各种强化机制的基础上,引入颗粒失效对材料屈服强度的影响,建立SiCp/Al复合材料的屈服强度模型.结果表明,该模型预测的屈服强度与相应的实验结果吻合较好.同时模型显示在屈服状态下,颗粒直径较小时,复合材料的颗粒失效以界面脱粘为主,而随着粒度的增大,颗粒的断裂分数迅速增大,颗粒失效则转变为由颗粒断裂和界面脱粘共同控制.     

颗粒填充复合材料细观力学行为的数值分析

通过三相材料中基体应力分布的分析计算,结合损伤萌生的力学条件,对颗粒填充复合材料的强化效应和增韧效应进行力学分析.计算结果表明,当聚合物受力变形时,刚性无机粒子的存在产生应力集中效应,引发其周围的基体屈服,这种基体的屈服将吸收大量变形功,从而达到增韧效果.文中通过界面的厚度以及界面相材料的刚度对颗粒填充复合材料的力学行为进行分析,对于较薄的界面层,外载作用下基体容易产生脱粘开裂,随着界面厚度的增加,界面屈服的趋势优于基体的脱粘开裂.因此,采用柔性界面层包覆刚性粒子进行填充改性是实现材料强韧化的有效途径.     

橡胶纯剪试件变形与断裂的有限元分析

用非线性有限元法分析橡胶纯剪试件变形与理想纯剪变形之间的差异.结果表明试件中心接近纯剪,但是靠近自由边界的区域应力比较复杂,受自由边界影响的区域随应变的增加而减小,试件的宽高比越大变形越接近理想纯剪变形.对橡胶纯剪试件存在中心裂纹和边缘裂纹时的撕裂能进行计算,断裂形成大裂纹时撕裂能与裂纹尺寸无关,有限元解与以前的结果吻合较好;对于小裂纹,撕裂能与裂纹尺寸成线性关系.同时分析不同材料模型对橡胶纯剪试件变形和断裂的影响.分析表明,不同应变能函数的材料模型模拟的结果略有不同.     

分级淬火热处理双相钢在拉伸变形时的应变分配

采用亚微米级分辨率的数字图像相关(DIC)方法,探究了分级淬火得到的马氏体体积分数分别为33.8%和58.3%双相钢在不同拉伸变形量下的应变分配规律。结果表明:两种双相钢在不同变形量下的微观应变分配规律相似,应变分布都很不均匀,且变形量较大时应变分布不均匀性更为显著;在马氏体体积分数较小的双相钢中,应变在铁素体和马氏体间分配的不均匀性更显著;微区内存在应变集中的变形带,变形带主要分布在铁素体上,在块状马氏体间的较窄铁素体区域出现的概率比较大;在马氏体上或相界面处也有少量应变集中的变形带,马氏体体积分数较小时沿相界面扩展的变形带数量较多;马氏体体积分数较大时变形带穿过马氏体的概率更大。     

Elastic-plastic analysis of the stress and strain distributions in asymmetric rolling

Asymmetric plane strain plate rolling is analysed numerically by using an elastic-viscoplastic finite-element method. The asymmetric conditions are here due to different interface friction conditions of the two rolls. Two sets of different interface friction conditions are used. The influence of the degree of reduction on the curvature of the rolled plate and the corresponding distributions of the stress and strain are examined. For the rolling parameters considered, the curvature of the plate is found to be towards the roll with highest friction. The largest curvature is obtained for the biggest difference in interface friction conditions. The curvature shows a change from increasing to decreasing curvature with increasing reduction followed by a change in the distribution of the strain.     

Investigation of the coupled distribution of initial and machining-induced residual stress on the surface of thin-walled parts

Residual stress on the machined surface and the subsurface is known to influence the distortion of thin-walled parts. Therefore, it is essential to predict the distribution of surface residual stress accurately. In this paper, the coupled distribution law of initial residual stress and machining-induced residual stress is investigated. Firstly, a model with initial residual stress is established and incorporated into thermal mechanical coupled finite element model of 2-D cutting. Then, a tensile fixture is designed to impose initial stress into a thin-walled part of Al-6061, and cutting experiments are carried out. The residual stress distribution is measured by X-ray diffraction/electropolishing method. The results of experiments and simulation show that in the plastic deformation zone, the initial residual stress has no significant influence on the distribution of the machining-induced residual stress. In the elastic deformation zone, the stress that linear grows along depth from zero to initial residual stress is superimposed on machining-induced residual stress. The mathematical model of stress coupling distribution on the surface of thin-walled parts is established by numerical method. Finally, it is found that the effect of coupled stress distribution on distortion is more significant with the decrease of thickness (from 3 to 0.5 mm) of the thin-walled parts.     

Determination of subsurface plastic strain in machining using an embossed grid

A technique is described for embossing an orthogonal array of lines (grid) on prepared metal surfaces. Workpieces of oxygen-free high conductivity copper and 18% nickel maraging steel were machined orthogonally under dry unlubricated conditions and the plastic strain distribution in the surface region was determined from the distortion of the array. It is shown that appreciable plastic strain can be produced, the distribution of which is complex. It is suggested that such strains may be important in machining because they can affect the residual stress distribution which, in turn, can have a controlling influence on the behavior of components in service with respect to their resistance to fatigue, creep and stress corrosion cracking.     

FINITE ELEMENT ANALYSIS ABOUT STRESS AND STRAIN OF SURFACE PEELING IN Cu-Fe-P SHEET

The microstructure of surface peeling in finish rolled Cu-0.1Fe-0.03P sheet is analyzed by scanning electron microscope and energy dispersive spectroscope. Fe-rich areas of different contents are observed in the matrix. The stress distributions and strain characteristics at the interface between Cu matrix and Fe particle are studied by elastic-plastic finite element plane strain model. Larger Fe particles and higher deforming extent of finish rolling are attributed to the intense stress gradient and significant non-homogeneity equivalent strain at the interface and accelerate surface peeling of Cu-0.1Fe-0.03P lead frame sheet.     

Investigations on welding residual stress and distortion in a cylinder assembly by means of a 3D finite element method and experiments

In the present work, both experimental and numerical simulation methods are used to investigate the characteristics of welding distortion and residual stress distribution. A 3D thermo-mechanical Finite Element Analysis (FEA) method is used to predict the welding distortion and residual stress of cylinder-shaped multi-pass layer weldments. Each weld pass is performed using a quarter-circle balanced welding procedure. To investigate the influence of deposition sequence and welding heat input on the welding distortion and residual stress, a continuous welding procedure is also calculated. The corresponding FEA models considered a moving heat source, the deposition sequence, and temperature-dependent thermal and mechanical properties. The results predicted by 3D FEA model are generally in good agreement with the measurements. Finally, the numerical and experimental results suggest that both deposition sequence and heat input affect welding distortion and residual stress distribution. Furthermore, the 3D thermal-mechanical FEA method can predict cylinder-type welding distortion.     

对薄壁圆筒单道环形焊缝所引起的残余应力和变形计算方法的改进

本文叙述了薄壁圆筒单道环形焊缝所引起的残余应力和变形的新的计算方法。这种方法采用正态分布载荷假设代替均匀分布载荷假设[1],得到了更符合实际测量值的计算结果。特别是环向应力的计算结果消除了由于均布载荷假设所引起的应力值的突变。     

梯度结构对氧化铝陶瓷涂层抗冲击载荷性能的影响

梯度结构陶瓷涂层以其优异的抗热震性表现出巨大的工程应用前景。为推动梯度陶瓷涂层在机械零件表面强化上的应用,采用“三明治”式梯度结构形式,建立镍基氧化铝梯度陶瓷涂层在冲击载荷作用下有限元模型,分析冲击载荷作用下涂层的力学性能,以及梯度层的结构形式、厚度及层数等参数对涂层的力学性能影响。结果表明：较无梯度结构陶瓷涂层相比,梯度结构能有效减缓涂层与基体结合面上的应力突变,涂层内部最大Mises应力明显降低,合理的梯度结构能改善涂层内部Mises应力分布,改变应力分布特征,减缓表面陶瓷涂层的冲击应力,从而防止陶瓷涂层在冲击载荷作用下脱落。最后对制备层状结构梯度陶瓷涂层时,如何进行梯度层结构设计进行了探讨,并提出了采用0.25次方幂指数梯度结构,得出10层中间层就可有效减缓冲击载何、降低Mises应力突变的结论。     

铝合金板淬火应力与框形零件变形的数值分析

在ABAQUS软件中模拟了2A12铝合金的淬火过程,进行了实际板材淬火和钻孔法应力测量试验,仿真所得板材表面应力值与实际测量结果误差约为10.1％～16.5％,且都具有对称分布的特点,说明通过淬火仿真获得的板材内应力分布与实际淬火相吻合.基于仿真的应力分布进行加工仿真,研究了单框零件相对板厚位置对加工变形的影响,提出了由板材加工框形零件的加工变形控制策略.     

考虑颗粒分布影响的液-固二相流体润滑研究

对多颗粒分布的液-固二相流体润滑进行了研究。对有颗粒存在时的润滑区域进行划分,建立了多颗粒状态下的雷诺方程,引进颗粒的速度、大小、位置,颗粒间的距离等参数,在给定油膜承载力的情况下运用有限元法对有限长滑块进行了数值求解。结果表明:颗粒的存在使颗粒附近的压力分布有了明显的变化;油膜承载力越大,颗粒对压力分布、最小油膜厚度的影响越明显;颗粒处于运动状态或静止状态对压力分布和最小油膜厚度的影响趋势是一致的,但运动颗粒的影响程度较小些;颗粒间的距离、颗粒半径、颗粒数目对压力分布也有比较大的影响。     

压气机叶片流固耦合的强度和振动研究

为了研究流固耦合场对叶片强度与振动参数的影响,采用流体动力学和有限元方法,对压气机叶片进行了单向流固耦合分析。通过软件之间的接口,实现压力场数据的传递,并对加载气动力后的计算模型进行强度分析和模态分析,得到压气机大小叶片的应力应变云图以及固有频率和相应的模态振型,计算比较了离心力、气动力对应力和固有频率的影响。计算结果表明,流固耦合对叶片的结构强度和模态振型影响较小。通过频率分析,找出了叶片的共振频率,从而为叶片的优化提供依据。