中子衍射测量残余应力研究进展

中子衍射技术是一种测量材料或工程部件内部的三维应力状态的方法。综述了近年来中子衍射在宏观部件焊接、热加工与热处理过程中残余应力测量的应用,在探究材料微观变形机理方面的应用,在金属基复合材料与多相合金中各相微观应变测量的应用,以及与其他残余应力测量技术对比等方面的研究情况,并展望了中子衍射测量技术的应用前景。     

晶体材料内部残余应力衍射法无损检测的研究进展

目前能够准确、无损地测试材料内部残余应力的手段主要是中子衍射和同步辐射,但这两种测试手段需要核反应堆或高能同步辐射源,投资巨大,只为少数发达国家的少数实验室所拥有,难以应用到实际生产中。短波长X射线衍射仪通过钨靶-K_α特征射线(波长约0.02 nm)以及独特的谱接收方式,达到或接近同步辐射及中子衍射对晶体材料内部晶格应变的无损定点测试,为内部残余应力无损检测的广泛应用开辟了一条新的渠道。介绍了中子衍射和同步辐射对残余应力测试的国内外研究现状,重点展示了短波长X射线衍射仪用于内部应力测试的结果,并就三种测试方法特点进行了对比分析。     

X射线衍射法测试轧板表面残余应力

从试验角度讨论采用X射线衍射法测试轧板表面残余应力时遇到的一些问题。用X射线衍射法测试织构材料的表面残余应力时会出现2θ-sin2ψ震荡现象,但是测得的应力数据与加工工艺仍保持对应,反映出不同工艺对板材表面残余应力的影响。考虑到在较大的ψ角范围内缩小各衍射峰强度差异,对于面心立方钢铁材料宜选用(311)晶面测试。增加测试的ψ角站数也有助于得到好的应力测试效果。     

用X射线衍射法测定振动时效后水电站钢岔管中的残余应力

介绍了采用振动时效技术消减水电站钢岔管焊接残余应力,以及用X射线衍射法进行焊接残余应力测试来对振动时效效果进行定量评价。并举例说明X射线衍射测试焊接残余应力的应用情况。     

角度分散法中子衍射应力测试技术的应用

由于中子具有较高的穿透能力,利用中子衍射容易获得块状试样内部特定位置的三维点阵面间距,从而实现应变/应力分布的较准确评价。首先介绍了各种应力测试技术的研究现状以及角度分散法中子衍射应力测试技术的基本原理;然后结合冲压成型试样的强度评价、复层钢板拉伸变形后的残余应变评价以及负荷条件下钢筋混凝土中钢筋的应力分布等中子衍射典型试验研究,说明角度分散法中子衍射应力测试技术在国外已广泛应用于工程结构件与材料内部应力的定量研究;最后展望了角度分散法中子衍射应力测试技术在国内的研究前景。     

能量色散法在铁单晶应力测量中的应用

为了更精确地进行材料内部的应力测量,尝试了用能量色散法进行应力测量的模拟研究。模拟计算的结果分析表明：能量色散法进行应力测量的分辨率（3．9×10^-4）优于传统的应力测量方法的分辨率（101）,并且在波长选定的情况下,狭缝的宽度与试样厚度是影响结果的主要因素。     

Determination of Remnant Residual Stresses in Fracture Toughness Specimens Extracted From Large Components

Abstract: Material fracture toughness data are required to undertake fitness‐for‐service assessments of engineering components containing cracks. Calculations of crack driving force in the component are compared with material fracture toughness values to assess the likelihood of subsequent failure. Experimental measurements of fracture toughness are usually made on small specimens extracted from a larger ‘parent’ component following strict experimental guidelines, formulated to ensure measured toughness values in the fracture specimens are appropriate for use in the full‐size component. Implicit in this procedure is the assumption that the extracted fracture specimens contain no residual stresses, with any residual stresses in the full‐size component being accounted for in the crack driving force calculation. This paper considers a recent conjecture within the structural integrity community that the extracted fracture specimens may themselves contain a residual stress field which may influence measurements of fracture toughness. This could potentially lead to a degree of ‘double accounting’, i.e. the effect of residual stresses may be included in both the material toughness and the crack driving force. This, in turn, could lead to unnecessary conservatism in safety assessments. To explore this conjecture, the results of numerical modelling and neutron diffraction measurements of residual stresses in fracture specimens extracted from two different welded parent components are presented. One of the components is significantly larger than the extracted specimens, with the other being marginally larger than the extracted specimens. Results confirm the intuitive expectation that the residual stresses in specimens extracted from much larger components are negligible, whereas if the dimensions of the extracted specimens are comparable with the larger component then significant residual stresses may remain.     

高强度钢丝残余应力的研究进展

回顾了近年来以珠光体钢丝为代表的高强度钢丝残余应力的数值模拟及其相关试验研究进展,主要介绍常规X射线衍射、中子衍射及同步辐射X射线衍射技术在钢丝残余应力分析中的应用,对残余应力的来源、测量原理及其结果进行了讨论;简述了残余应力对钢丝性能,如拉伸、应力松驰和环境促进断裂性能等指标的影响,同时对通过改变残余应力分布实现钢丝性能优化的主要工艺进行了介绍.     

Experimental Investigation Into the Fatigue of Welded Stiffened 350WT Steel Plates Using Neutron Diffraction Method

Abstract: The propagation of fatigue cracks under constant amplitude cyclic loading was studied in welded stiffened steel plates. The residual stresses in the stiffened plates were measured using the neutron diffraction strain‐scanning technique. The neutron diffraction measurements indicated that, in general, the residual stresses were tensile near the welded stiffeners and compressive between the stiffeners and ahead of the starter notch tips. Fatigue testing indicated that the fatigue crack growth rates of the stiffened plates were, in general, lower than that of a corresponding unstiffened plate, especially near the notch tips, where compressive residual stresses existed. An analytical method, using Green's function, was developed to predict the fatigue crack growth rates. Reasonable accuracy was obtained.     

In Situ Monitoring of Thermally Cycled Metal Matrix Composites by Neutron Diffraction and Laser Extensometry

A novel stroboscopic neutron diffraction data collection system has beendeveloped. In combination with scanning laser extensometry this has beenused to investigate the thermal cycling behaviour of SiC short fibrereinforced Al matrix composites. Three-dimensional unit cell finite elementmodels have been produced, incorporating matrix deformation both by creepand plasticity. Comparison of the experimental results with modelpredictions has allowed conclusions to be drawn about the deformationprocesses which dominate at different parts of the thermal cycle.     

欧美最新X射线衍射残余应力测定标准介绍

对最新的欧盟X射线衍射残余应力测定标准EN15305-2008,从测试原理、材料特性、仪器的选择、限制条件及处理方法等方面进行了详细的介绍。指出在进行X射线残余应力测定时特别需要注意以下几个方面：EN153052008和美国X射线残余应力测定标准ASTME915—2010均明确要求采用不假定剪切应力为零的完整应力方程和椭圆拟合方法,否则会出现系统误差;用于拟合的sin^2φ值在正负妒方向上最少需要测试7个,建议测试9个以上;测定钛合金材料残余应力时建议使用铜靶X射线管,如使用其他靶材则需考虑X射线穿透深度不同带来的与标准方法的差异;应选择高能量分辨率、不易产生X射线辐射饱和的探测器;无应力铁粉残余应力测定的精度要求为正常±6．9MPa,最大±14MPa。     

Residual Stress Evolution in Repair Welds

Abstract: The aim of this paper is to study the influence of the repair procedure on the evolution of residual stress distribution in butt welds. C-Mn steel coupon plates of 11 mm thickness were prepared, subjected to stress relief heat treatment and welded with two beads, using the gas metal arc welding process. After the deposition of two weld beads, two successive repair welds were made on the middle length of the second bead. Longitudinal and transverse residual stresses were measured in the vicinity of the weld, after deposition of the two weld beads and after each repair weld. Residual stress evaluation was conducted using an X-ray diffraction method. The repair welds caused a decrease in magnitude of the initial longitudinal residual welding stresses, and an increase of the transverse residual stress magnitude, in tension at points within the repair length, and in compression at points outside the repair length.     

搅拌摩擦焊接件内部残余应力无损测试研究进展

搅拌摩擦焊是近年来发展的一种新型焊接技术,目前国内主要着力于搅拌摩擦焊工艺及应用方面的研究,但由于测试方法和相关设备的限制,关于搅拌摩擦焊接件内部残余应力的研究几乎是空白,而国外利用其先进的中子衍射和高能同步辐射装置已经开展了较多搅拌摩擦焊接件内部残余应力的无损测试。综述了近10余年来国外搅拌摩擦焊接件内部残余应力测试的研究进展,讨论了影响残余应力测试结果的各种因素;最后介绍了国内用短波长X射线衍射仪测试材料内部残余应力的探索,对未来准确、高效、经济而无损地测试搅拌摩擦焊接件内部残余应力的研究方向进行了展望。     

全因子试验设计在X射线衍射法测试高应力标样残余应力值中的应用

针对X射线法测试残余应力值的主要参数——准直器直径、曝光时间和β角数量,依据6σ的DMAIC流程和全因子试验设计,研究了标准高应力试样残余应力值的测试方法。结果表明:上述参数对探测器X光子接收数量、衍射峰强度和峰背比的大小有较大影响。为提高测试精确度和重复性,在满足检测效率的前提下,可选择较小的准直器直径、较长的曝光时间和较大的β角数量进行残余应力测试。对于标准高应力试样,选择2mm准直管、3s曝光时间和11个β角参数测定的残余应力值与标准值最为接近。     

Effect of Temperature on the Residual Stresses in an Integral Structure with a Crack‐Retarding Patch

Abstract: The application of bonded ‘straps’ has been proposed for extending the fatigue life of aircraft structures, particularly for integral structures with low inherent crack‐retarding capability. A potential disadvantage in the use of bonded crack retarders is the difference between the coefficients of thermal expansion between the strap and substrate materials, which causes residual stresses when the temperature deviates from the curing or assembly temperature. The evolution of these stresses in flight is important to take into account to accurately assess the fatigue crack growth behaviour of the structure. In this work, the residual strains in an aluminium compact‐tension sample adhesively reinforced with a titanium strap have been measured with neutron diffraction and modelled with a finite element approach at room temperature and at ?50 °C. It was found that a linear elastic approach could accurately be used to predict the residual stresses. The residual stresses were found to be about twice as large at ?50 °C as at room temperature.     

Neutron and Synchrotron X-ray Strain Scanning

Abstract: Neutron and synchrotron X-ray strain scanning provide the opportunity for mapping residual strain distributions within polycrystalline materials non-destructively. The neutron method is now reasonably mature, industrial standards for measurement are being defined and new dedicated neutron strain scanners are being built at ISIS in the UK and at the ILL, France, as well as in the United States. Synchrotron strain scanning on the other hand is relatively new and is much less well developed but, with penetrations typically hundreds of times greater than most laboratory X-rays and intensities millions of times greater, it can provide maps of near- and sub-surface strain of unparalleled detail and strain resolution. The capabilities and complementarity of the two methods are reviewed and contrasted in this paper through a series of case studies.     

新型储氢材料的中子衍射研究

利用高灵敏度中子粉末衍射对新型储氢材料Li2NH,LiNH2,Li4BN3H10和BH3NH3的晶体结构进行了研究.通过对中子衍射数据的拟合分析得到了材料的晶格参数,原子占位和键长等数据.研究发现测量的氢原子占位结果与X-光衍射测量的结果有明显差别.结果表明储氢材料的氧释放温度与材料中的N-H或B-H键的键长成对应关系.通过将不同的储氢材料,例如LiBH4和LiNH2,进行复合改变材料中N-H和B-H氢键的强度,可以合成新的材料,有望达到储氢的目标.     

J75不锈钢淬火应力的X射线衍射分析

利用铬靶X射线在侧倾结合固定ψ法基础上对J75不锈钢的（311）面进行了淬火应力测量,得到了不同淬火温度下J75合金试样中心点的残余应力值和近表面微应变效应。结果表明：试样表面残余压应力值在-400～-650MPa,最大值出现在淬火温度为700℃左右;淬火使衍射峰半高宽由1．25°增加至1．4°以上,显著增加了J75合金的位错等缺陷。受淬火瞬时热应力分布影响,越靠近试样表面衍射峰的宽化越严重。