钻孔法测量残余应力过程中钻孔附加应变的研究（Ⅱ）

本文应用弹塑性理论研究了被测试样的屈服强度、应力场对钻孔法测量残余应力过程中钻孔附加应变的影响,使用简化的理论模型推导了低速旋转钻头钻孔产生附加应变的一般表达式.结果表明钻孔引入的附加应变与被测试样的原始残余应力状态有关,随应力水平增加而增大,在压应力减小到某一临界值σ时,钻孔附加应变为零。在 Ly12铝合金上的实验测量结果与理论结果一致。     

钻孔法测量残余应力过程中钻孔附加应变

本文叙述了钻孔法测量残余应力过程中的附加应变.研究应力水平对附加应变的影响是在单向应力条件下进行的,结果表明,钻孔条件、材料状态以及残余应力达到一定值时,附加应变为零.     

钻孔法和光栅应变花测试复合材料的残余应力

残余应力对材料、结构的疲劳强度和使用寿命等性能的影响早已为人们所熟知,由于它的大小、方向和分布随制造加工或处理方法不同而有很大的随机性,国内外对它的研究很重视。对于各向异性的复合材料,随着加上生产制造过程及工艺参数的不同,其中的残余应力的大小、方向等就更加复杂。从国内外对残余应力的研究中,可以看出大多数都着重于实验研究。本文应用钻孔法和云纹干涉技术的成果,针对残余应力测试中的特点,尤其是在利用钻孔法和云纹干涉技术测试残余应力时存在的问题,在目前绝大多数云纹干涉技术所使用的正交光栅的基础上,提出并研制出一种三个方向的光栅,即在原来 0°、90°两个方向光栅上,再加上一个 45°方向的光栅,在进行云纹干涉测试时,一次加载时就可以同时测试出三个独立的位移场:u场、v场和s场,利用这三个位移场就可以得到相应的三个应变:ε0、ε90和ε45,进而可以计算得到相应的应力。     

耐磨胶粘涂层固化残余应力的测试分析

将多根电阻丝平行于界面预埋在耐磨涂层中不同深度处，通过半桥电路测定了相应深度处涂层的固化残余应力。结果表明，紧接界面处耐磨胶粘涂层的残余应力最高，自界面开始处外约０．５ｍｍ层厚范围内的残余应力逐渐减小，可见涂层的固化残余应力主要来自底材表面对其固化收缩的阻碍效应。用适量的橡胶增韧是减小耐磨胶粘涂层固化残余应力的可行途径。     

固化温度对碳纤维/环氧基体界面行为影响的分析

对界面粘结性能及热残余应力影响下的单纤维复合材料的界面行为进行了分析。采用界面的弹性-软化内聚力模型,用解析法对单纤维复合材料由固化引起的热残余应力、以及单纤维碎断过程纤维的轴向应力分布进行了模拟,得到了碳纤维/环氧树脂在常温和高温固化两种情况的界面粘结性能。结果表明：与常温固化相比,高温固化后,界面的剪切强度增幅不大,界面的断裂韧性显著增加;高温固化后形成的界面,使界面的软化提前、界面的脱粘延迟;高温固化产生的纤维轴向和界面径向热残余应力对界面的软化均有延迟作用;界面径向热残余应力还对界面的脱粘有延迟作用。     

钻孔偏心对松弛应变和残余应力的影响

用盲孔释放法测残余应力的基本理论导出在任意钻孔偏心下应变释放系数 A、B 的精确公式.同时通过用偏心公式和不偏心公式计算得到的残余应力值的比较,说明钻孔偏心量对残余应力值影响很大.     

三维粘弹性复合材料层合板固化残余应力研究

应用改进的有限元算法,综合考虑了碳纤维复合材料固化过程中树脂的化学收缩、应力松弛、材料的热收缩,建立了一个基于三维线性粘弹性的积分模型对复合材料层合板热压罐成型工艺过程中产生的残余应力进行了研究。结果表明:本文提出的方法能够完整地模拟树脂的固化过程并计算层合板的固化残余应力;对于文中的正交对称层合板而言,热收缩是影响残余应力大小的主要因素;固化完成后,0°铺层内的中面中心区域层间残余应力值接近于0,边缘区域会迅速增加,容易发生分层破坏;任意点处,轴向应力比其他两个方向的应力高出1~2个数量级;残余应力值沿厚度方向有较大变化;树脂的应力松弛行为会在一定程度上降低残余应力。     

Z-pin复合材料细观模型固化残余应力研究

针对植入Z-pin后碳纤维增强复合材料的微观结构，通过施加Z-pin周期性边界约束条件，建立了Z-pin复合材料单层板单胞细观模型．考虑固化过程中树脂体积收缩、弹性模量随固化度变化和纤维因Z-pin进入偏转因素，运用有限单元法计算了单胞结构在固化成型工艺过程中树脂和纤维应力发展和分布，并研究了Z-pin直径和分布密度对单层板面内残余应力的影响．结果表明：凝胶点之前，树脂模量和残余应力很小，凝胶点之后，树脂模量和残余应力增加较快；残余应力分布与纤维偏转有关；Z-pin直径和分布密度增加会使固化残余应力增大．     

侧限条件下路基压实黏土的水平残余应力试验分析

路基填土是一种松散的土体材料,经压实才能体现出良好的力学性质。路基填土被压实后,土体中会产生较大的水平残余应力。掌握路基压实黏土水平残余应力的主要特征是进一步研究路基结构工程性质的关键。为此,本文研制了一套在侧限条件下测试压实黏土水平残余应力的试验装置,进行了高液限黏土在不同压实度和含水率条件下的水平残余应力变化规律试验分析。试验表明:在相同含水率条件下,压实黏土水平残余应力随压实度的提高呈折线形增大;在同一压实度下,压实黏土的水平残余应力随含水率的升高近似呈线性减小趋势;对比分析可知,压实度对压实黏土水平残余应力的影响程度明显大于含水率。     

钻孔偏心下的应变释放系数及残余应力

用钻孔应变释放法测残余应力的基本理论导出在任意钻孔偏心下应变释放系数[A],[B]的精确公式.揭示了各传统近似方法(丝栅中心应变法、纵向线积分平均应变法及有效面积上积分平均应变法)的应变释放系数随r_м/а的变化规律。并采用数值逼近法求解了钻孔偏心时的应变释放系数及残余应力.结果表明,偏心对残余应力影响很大。     

反应堆贯穿件J形焊缝残余应力研究1）

焊接残余应力是引起应力腐蚀开裂的主要原因,准确地掌握残余应力的分布是对结构完整性评定的关键.为了探明反应堆压力容器顶盖控制棒驱动机构（control rod drive mechanism,CRDM）贯穿件J形焊缝残余应力的分布,本研究加工两个CRDM贯穿件实验模拟件,采用盲孔法测试两个J形接头的焊接残余应力.通过实验探明了CRDM贯穿件焊缝残余应力的分布规律,为反应堆压力容器结构完整性的研究提供必要参考.     

Path dependency in hybrid structures with simultaneous ductile and brittle connections and materials

This article considers a steel–stud–concrete hybrid structure with a Fibre Reinforced Polymer plate adhesively-bonded to the steel member. Owing to the combination of ductile and brittle materials and connections present, the failure behavior of such a structure can be influenced by residual stresses, which in turn depend on the plasticity-inducing load paths previously experienced by the structure. Plasticity of only the stud connections generates a different residual stress pattern from plasticity of only the steel member, and an understanding of the mechanics of residual stress generation in each case is fundamental to the development of a framework of ideas on path dependency in such structures. Measurements of deformation do not necessarily permit faithful reconstruction of residual stress profiles, as these measurements typically give total (elastic plus plastic) deformations from the times that the measurements start, while the residual stresses are related to the elastic components of deformation from the times that the structural components were manufactured. Numerical work is thus needed to determine residual stresses. To that end, a verified finite element program is here used to investigate residual stress patterns in the above hybrid structure due to plasticity of either the studs or the steel member. For yield of the steel, the effects on the residual stresses of initial self-equilibrating stresses in the steel member are investigated. Crucial to the success of the analyses are curvilinear or multi-linear loading/unloading constitutive relationships not only for the materials, but also for the connections. The residual stress profiles from the steel yield and stud yield analyses are examined and compared, and ideas for extension of the work are suggested.     

工艺过程对固体氧化物燃料电池材料力学性能的影响

固体氧化物燃料电池在生产过程中采用不同的加工手段,加工过程会产生一定的损伤,同时材料烧结过程产生比较大的残余应力,这些因素都会影响电池的使用寿命和完整性.本文通过实验测试,研究了不同加工过程对材料性能的影响,其中包括直接冲剪,激光切割以及切割后研磨等方法,并测试了这些加工手段对应的试件的强度.结果显示,直接冲剪法造成性能的分散性比较大,激光切割的性能较好,而研磨加工法对材料的性能影响最小;受残余应力或各层有效应力的作用,单层阳极材料的强度要高于双层电池结构材料的强度;利用弯曲法测试了半电池结构中的残余应力和不同薄膜对应的厚度残余应力,测试的结果和热弹性力学计算结果进行了对比.由于在高温时阳极材料有应力松弛现象,计算得出的残余应力高于实验测试结果.     

硅基底多层薄膜结构材料残余应力的微拉曼测试与分析

针对MEMS器件制备中两种典型的硅基底多层薄膜结构的残余应力问题,本文提出了利用微拉曼光谱技术测量其残余应力的方法,分析并给出了硅基底多层薄膜结构中的残余应力分布规律。实验结果表明,在硅基底和薄膜内存在较大的工艺残余应力,残余应力在基底内靠近薄膜两侧部分呈非线性变化,在基底内主要呈线性变化,并引起基底整体翘曲。基于实验结果分析,提出了硅基底多层薄膜结构的分层结构模型。本文工作表明微拉曼光谱技术是测量与研究硅基底多层薄膜结构残余应力的一种有力手段。     

Evaluation of Residual Stresses Induced by Robotized Hammer Peening by the Contour Method

Welded components suffer from high tensile residual stresses close to the weld beads. These stresses seem to be the origin of premature cracking which could result in a catastrophic rupture during operation and a reduction of the lifespan of these components. In this context, the Hydro-Québec’s Research Institute (IREQ) developed a technique of residual stresses relaxation by robotized hammer peening which makes it possible to release stresses close to surface and preserve the mechanical and dimensional properties of manufactured components. Robotized hammer peening was used to induce compressive residual stresses on initially stress free samples of austenitic stainless steel 304L. Hammer peening layers from one to nine were performed and the resulting residual stresses were evaluated thanks to the contour technique. Complete 2D residual stress fields on samples cross sections were obtained. The ability of hammer peening to relax residual stresses within welded plates was then quantified on austenitic stainless steel 304L plates welded with a 308 steel and hammer peened. These tests show the efficiency of hammer peening as a method to relax tensile residual stresses and induce compressive ones to a depth of a few millimetres. Process parameters were optimized such as the number of hammer peening layers to be applied to reduce processing time and maximization of the intensity and spatial distribution of the compressive residual stresses.     

喷丸镍基合金材料微区残余应力的切槽法测量研究

本文结合聚焦离子束-电子束(Focused ion beam-electron beam,简称FIB-EB)双束系统和真空镀膜工艺,进行微区散斑的制备工艺研究,并将所发展的微散斑制备工艺应用于喷丸镍基合金材料表面制斑,进而结合切槽法进行残余应力高温释放规律的测量研究。在FIB-EB双束系统下记录切槽前后制斑微区的图像,利用数字图像相关法计算切槽后的位移,结合InglisMuskhelishvili理论公式可计算得到残余应力。文中研究了不同温度及保温时间对残余应力释放的影响规律。结果表明,残余应力随保温时间的增长释放速度逐渐减小,最后残余应力趋于稳定值。同时,温度越高,残余应力释放越彻底,800℃下近乎完全释放。该工艺具有适用性好,效率高等优点,可望在材料微区变形测量中得到进一步应用。     

磁电复合材料中拓扑磁结构的力学调控

磁性斯格明子是在一些铁磁材料中存在的一种重要拓扑磁结构,由于其具有独特的磁-电-力-热多场耦合特性,在未来新型自旋电子器件中有着广泛的应用前景。然而,磁性斯格明子一般需要在外加磁场下才能稳定存在,极大地限制了其在自旋电子器件中的实际应用。本文基于实空间下磁电材料的相场模拟,发现铁电和铁磁复合薄膜中铁电斯格明子可以通过界面变形来稳定铁磁斯格明子。由于力电耦合效应,铁电层中铁电斯格明子的非均匀分布极化在界面产生周期性的非均匀界面变形。界面变形通过力磁耦合效应,使铁磁层中的磁性斯格明子在没有外加磁场的条件下能够稳定存在。本文的研究结果表明,基于磁电复合材料中的力-电-磁耦合效应,通过优化设计复合材料中不同组元的结构,可以实现拓扑磁结构的力学调控,从而为设计基于拓扑磁结构的新型自旋电子器件提供了新思路。     

Experimental Evaluation of Residual Stresses in Pipes Manufactured by UOE and ERW Processes

Pipes are basic elements used in the construction of pipelines for the long-distance transportation of oil and gas and their derivatives. They can be manufactured by cold forming processes such as UOE and ERW, both widely used in the oil and gas industry. These processes produce high levels of non-uniform plastic deformation, which introduce a new state of residual stress into the material. In some cases, these stresses combine with mechanical stresses generated by external loads leading to service failures, interrupting the transmission line and increasing the risk of accidents. Therefore, determining in advance the residual stress distribution in pipes is an important task which involves the evaluation of the structural integrity. Six pipe samples obtained by the UOE and ERW processes were measured and evaluated using a portable optical device that combines radial in-plane digital speckle pattern interferometer (DSPI) with the incremental hole-drilling technique to measure residual stresses. The experimental results indicate a distinct residual stress distribution for each manufacturing process, while the measured residual stress distributions in the longitudinal and circumferential directions were similar at all measurement locations along an individual pipe.     

压力容器斜接管区域应力状态的实验研究

压力容器接管区域应力场的获得是压力容器强度分析和结构设计的基础。本文采用实验研究的方法,对压力容器斜接管区域的应力状态进行分析研究。根据实验研究的目的,按照工程设计标准设计、制造了一台大型带有两个斜接管压力容器的实验模型,进行了实验方案设计,采用电测法进行了容器斜接管区域的应力测试,在实验数据科学、合理处理的基础上,获得了容器斜接管区域的应力状态和分布规律。实验研究结果表明,容器斜接管锐角侧、钝角侧和相贯线最低点都存在着较大的局部应力,且锐角侧的局部应力数值最大,但是相贯线上的局部应力影响范围较小。     

Two Dimensions Residual Stresses Analysis Through Incremental Groove Machining Combined with Electronic Speckle Pattern Interferometry

In this study a new residual stress determination method in two directions simultaneously is presented. This method is based on stresses relaxation in a groove that is machined incrementally. The residual stresses relaxation occurs simultaneously from both the depth and the length of the groove. Thus, measuring the surface strain field generated by the relaxation enables to determine the stress gradient both along the depth and the length of the groove. To measure the surface strain in a direction perpendicular to the groove, a digital speckle pattern interferometer is used. This method is suitable when the residual stress field in the structure varies in the depth as well as along the surface of the part, like for example in a welded structure. The method is tested here on an aluminium plate in which a central band has been shot peened.